[D] Jibeinia luahera [~/~]
Describer
Hou, 2000
Time
Cretaceous Early Barremian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Unnamed Clade
Fossilsite
Yixian Formation, at the Dongtuyao brick factory near the village of Senjitu, Fengning Co. Hebei Province, China.
Info
Nearly complete skeleton.
Jibeinia luanhera was collected from the same geological formation, and not far from the locality of Vescornis. Unfortunately, the holotype of Jibeinia luanhera (the only specimen known) is lost (L. Hou, personal communication, 2001). Furthermore, the casts of the holotype are of low quality and the available illustrations of Jibeinia luanhera add no information. The description of Jibeinia luanhera includes certain morphological characteristics that radically differ from the condition in Vescornis. For example, Jibeinia luanhera was found to have more maxillary teeth, no keel on the sternum, digit III in the manus with three phalanges, and astragalus and calcaneum unfused to the tibia. If correctly described, these characteristics unambiguously shows that Jibeinia luanhera is of a different taxon from Vescornis.
However, the lack of the holotype of Jibeinia luanhera precludes an evaluation of these observations. Given the similar geological circumstances for the findings, their almost identical size, and the many shared morphological characteristics, it is clearly possible that a future reexamination of the holotype Jibeinia luanhera (if found) may result in the synonymization of this taxon and Vescornis. Zhang, Ericson and Zhou (2004)
Jibeinia luanhera from the Late Jurassic of Hebei Province and its comparison to Confuciusornis. After large collections were made from the Early Cretaceous of Liaoning, at the beginning of summer 1993, Mr. Pai Li, an engineer from the Hebei Provincial Office of Geology, received word of a Mesozoic bird specimen at Fengning Co.. Together with Lianhai Hou and Zhonghe Zhou, an investigation was thereby conducted. Upon the day of arrival at the village of Linjituxiang, a relatively complete avian specimen was presented to the group by one of the local farmers. The next day the fossil locality at the Dongtuyao brick factory was evaluated, where the mudstones of the Yixian Fm. were identified interbedded between limestones. Co-occurring paleontological data include plants and fish taxa including Lycoptera, Yanosteus longidorsalis, and Peipiaosteus, indicating that the stratigraphic position should be slightly higher than the sediments that produce Confuciusornis. The specimen from this locality is more derived than Confuciusornis but more primitive than the Early Cretaceous Sinornis and Cathayornis and thereby represents an intermediate form and significant evolutionary link.
Etymology
Jibeinia luanhera is produced from Fengning Co. which is located in Northern Hebei Province and is known by the appellation the Jibei Region. The Chinese character Ji represents one of the nine geographical divisions of ancient China which embraces parts of Manchuria, Jilin, Shanxi, and part of Henan Province. Bei is Chinese for north. Species etymology is derived from the Luanhe River.
Diagnosis
The maxilla contains numerous acute but unserrated teeth, the sternum is large and broad, the xiphoid process (medial column) is long, lateral processes are not well developed, carpals are unfused but are in tight association, digit III is reduced, cervical centra are extremely concave, distal pubes are fused but not expanded, proximal metatarsals are incompletely fused, distal metatarsals are completely independent, and MtII is shorter than MtIII and MtIV.
Locality and age
The specimen is derived from the gray Late Jurassic interbedded mudstones of the Yixian Fm. at the Dongtuyao brick factory near the village of Senjitu, Fengning Co., Hebei Province. [The Dinosauria 2004 :Yixian Fm, Liaoning, China]
Description
The specimen approaches Cathayornis in size, consisting of a relatively complete skeleton with an incomplete skull. The postcrania are exposed dorsally and ventrally and the cranium is only exposed ventrally, but this allows a clear description of the mandible. Posterior to the frontals the cranium is missing. The postcrania are predominantly represented only by impressions. Ilium and ischium are obscure due to compressional distortion. The nasal process of the premaxilla is slender and long, there are one to four teeth present on the rostrum, and only a portion of the maxilla bearing dentition is visible because the rest is obscured by the mandible. Six widely spaced teeth are visible and alveoli for replacement dentition are absent. Dental morphology is nearly completely consistent with the London specimen of Archaeopteryx, noted by Martin (1991), in which he describes a constricted neck between the lengthy tooth crown and expansive tooth root. But on Jibeinia the apex of the crown is longer, more acute, and is posteriorly curved. This dental morphology differs from theropods and more closely resembles that of the Crocodylia.
The mandible is relatively well preserved with the left ramus being basically complete. In lateral perspective the mandible is slightly dorsally curved with an arched ventral margin, the dentary is relatively dorsoventrally slender and is relatively long. The posterior elements have been subjected to compressional distortion and thus only the articular is recognized as being extremely well developed with its terminus dorsally oblique. A well developed dentition is present in tight association anteriorly, but posteriorly it resembles that of the maxilla by becoming widely spaced. The individual teeth are relatively large and morphologically resemble those of the maxilla. The longest tooth in the series is 10 mm. Only the anterior portion of the frontal and parietal’s interior lamina are preserved. There is a short vomer inlaid between two expansive palatines but posterior to it, the morphology and placement of the pterygoids are vague.
The cervical series is short, with only six amphicoelous centra visible. The anterior centra are small but gradually enlarge posteriorly. Lateral pleurocoels are present and neural spines are relatively low and broad. Lengths of the robust cervical ribs are unclear. Dorsal vertebral count is also vague because the majority is obscured, but five amphicoelous anterior lumbars are visible with centra morphologically similar to, but larger than the cervicals, a ventral keel is absent, several rib heads are still in articulation on the left side, and intervertebral plates are present between the centra. There are a minimum of eight sacral vertebra based upon diapophyseal count; the diapophyses are relatively short, and centra are not fused. The caudal vertebrae are fused but not completely, and approximately 10-12 vacuities perforate the diapophyses. Thus the caudals are basically fused to form a conical pygostyle. Neural spines are also fused to form an undulating dorsal ridge. The most anterior caudals are anteroposteriorly compressed and transversely expanded, ventrally there are distinct processes, and diapophyses are particularly elongated.
The coracoid is the best preserved element in the pectoral girdle. Terminal articulations of the furcula are missing, and only the right scapula is present. The coracoid is not elongated, its proximal end is extremely thin with a small rounded head dorsally while distally its contact with the scapula is extremely broad and thick, and as such its has a general morphology of an acutely robust triangular plate. The scapula is an elongated and thickened element and its proximal end overlies the coracoid. The scapular crest is extremely elongated and laterally projected. The clavicle branches are laterally compressed and relatively broad; their proximal ends are acute processes, but do not completely form a well developed articulation with the coracoids. The sternum is the largest element on the skeleton with a multifaceted morphology. Its transverse breadth is 18 mm which barely exceeds its 17 mm anteroposterior length, a character shared with Archaeopteryx bavarica. Morphologically it is more similar to that of Cathayornis, but differs in having an extremely short lateral process and a xiphoid process which is the longest on the element. On each side of the posterior xiphoid process there is a small medially hooked projection.
Ventrally on the sternum a carina is absent, although the ventral surface is relatively convex, particularly approaching both sides of the midline. It is also convex at the midpoint of the midline, which may represent an incipient carina. There are also relatively distinct, regular ventrolateral grooves which may represent attachment points facilitating pectoral musculature. Rib morphology is simple: bicapitate, slender, and long. Several ribs are still articulated to the thoracic and lumbar centra. Gastral ribs are rare but conspicuous. It is quite evident that rib morphology closely resembles that of Chaoyangia from the Early Cretaceous Lofotang Fm., only more primitive. Although the left forelimb is basically missing, the right forelimb is completely preserved. Termini of the relatively robust humerus are present but the shaft is represented by a distinct impression. The proximal end is medially curved with a small but distinct head that is associated with a medial and lateral tuberosity. All three processes project distinctly from the proximal surface.
Although the deltoid process is not well developed, it still projects laterally. A small depression distal to the medial tuberosity may represent an incipient pneumatocoel. The distal humerus is simple in morphology with a slight lateral expansion. Genuine medial and lateral condyles are not yet formed, and as such the distal end is represented by a slightly depressed planar surface. The ulna is predominantly represented by a depression in the matrix. Its shaft is straight, the proximal end is slightly curved but not expanded, an olecranon process is absent, and the distal end is laterally expanded with a concave terminus. The radius is more slender than the ulna and is extremely straight; its proximal end is not expanded for contact with the ulna, its distal end is laterally expanded to form a cone that approaches the distal end of the ulna, and its terminus is a small rounded facet that surpasses the distal end of the ulna. There are still two independent carpals which differ from the condition of the Early Cretaceous birds. These elements overlap slightly with the one on the ulnar side being relatively large but the one on the radial side being relatively small. The three metacarpals are unfused, resembling the condition of Confuciusornis and Archaeopteryx. McI is short and in close association with the carpals. McII is the largest in the series. McIII expands from its midshaft to its distal end and its breadth is equivalent to McII, a condition resembling Confuciusornis but differing from Archaeopteryx. Digit I is elongated and greatly surpasses the lengths of McII and McIII, implying a strong flight stroke.
The independent first digit gradually becomes reduced although its phalanx and ungual are more well developed than in the Early Cretaceous Sinornis or Cathayornis, and thus represents a transitional phase in the evolution of flight. Digit II resembles Confuciusornis by being the most robust in the series and being composed of two phalanges, the distal of which is relatively small. The size of the ungual is equivalent to that on digit I but has more curvature. The impression of digit III also resembles Confuciusornis and Archaeopteryx by being composed of three phalanges and an ungual, but it differs in its most distal phalanx being the shortest, the digit is independent, and has been shifted medially. The pelvic girdle and sacrum have been subjected to compressional distortion, prohibiting a description of the ilium. As such it is only recognized in the right hindlimb region as being a robust element. Only the left side of the ischium is visible, indicating that it is relatively short with a slender slightly curved distal end. The pubis is the longest element in the pelvic girdle with fused and unexpanded termini. These three pelvic elements are unfused, the ischium and pubis are posteriorly oblique, and appear relatively primitive.
The hindlimb is the best preserved element on the specimen with the elements being basically complete. The femur is relatively thin, straight, and weak, with a small head that lacks a neck, still preserving the morphology of its reptilian ancestors, and resembling the condition in Confuciusornis and Archaeopteryx. Distal condyles are not well developed and the terminus is gently concave.
The tibiotarsus is long but not robust. Its proximal end is slightly inflated with a rather planar facet, and lacks medial and lateral articular surfaces in addition to a cnemial crest. Its distal end is also slightly expanded but a trochlea between the medial and lateral condyles is absent and there is only a very slight concave facet. There are at least three independent tarsals retained represented by the astragalus, calcaneum, and centrale. The tarsometatarsus is the shortest element on the hindlimb. Among the metatarsals, MtV has been lost, MtII, III, and IV are not completely fused, MtIII is the longest, MtII is shorter than its two counterparts, and as in the general avian condition, MtIV is the shortest in the sequence and in opposition. The length of the digit I ungual exceeds its phalanx, while the length of the digit II ungual is only slightly shorter than its two associated phalanges. The ungual on digit III is slightly small, and digit IV is the shortest in the sequence.
Jibeinia measurements (mm).
Approximate cranial length 26.0
Preserved length of nasal process of premaxilla 8.0
External nares length 4.0
Mandible length 20.0
Scapula length 20.0
Scapula breadth 1.5
Coracoid length 11.5
Coracoid distal breadth 7.2
Furcula branch length 10.5
Sternum length 17.0
Sternum breadth 18.0
Humerus length 23.3
Humerus proximal breadth 6.0
Humerus distal breadth 4. 0
Ulna length 24.0
Radius length 24.2
MtI length 2.0
Manus digit I length 4.0
Manus digit I ungual length 2.5
MtII length 9.3
First phalanx of manus digit II length 6.0
Second phalanx of manus digit II length 3.7
Digit II ungual length 2.1
First phalanx of manus digit III length 3.2
Second phalanx of manus digit III length 1.1
Femur length 22.2
Distal femur breadth 2.5
Proximal femur breadth 3.0
Tibiotarsus length 28.0
Tibiotarsus proximal breadth 3.5
Tibiotarsus distal breadth 3.2
Tarsometatarsus length 16.3
Tarsometatarsus proximal breadth 3.0
Tarsometatarsus distal breadth 3.2
Pes digit I ungual length 7.5
Pes digit II ungual length 13.0
Pes digit III ungual length 18.0
Pes digit IV ungual length 14.0
Comparison
The general morphology of this Late Jurassic bird is more derived than both Confuciusornis or Archaeopteryx and it possesses characters attributed to extant taxa, particularly in the absence of an elongated tail. However, it should still be retained in the sub-class Sauriurae containing Confuciusornis and Archaeopteryx based upon the presence of a dentition, unfused metacarpals, three independent manus digits, the presence of gastral ribs, and the primitive morphology of the hindlimb. As previously stated, this taxon is a transitional form lying between the Late Jurassic and later Early Cretaceous taxa as further documented below. The posterior skull of Jibeinia is not preserved although its basic morphology is discernable through an impression in the matrix, indicating that it is relatively short with a relatively large cranium, thus being more well developed than in both Confuciusornis and Archaeopteryx. The posterior portion of the Jibeinia mandible is obliquely inclined posteroventrally, which also differs distinctly from the relatively linear ventral mandible on the other two genera.
The skull compares more closely to the Early Cretaceous Cathayornis and Sinornis; however, as indicated in the description above, the dental morphology is more consistent with that of Archaeopteryx, although there are some slight distinctions. On the Berlin specimen, the Archaeopteryx dentition is relativelyobust with the apices posteriorly curved, whereas in the Eichstatt specimen the dentition is slender and long (Howgate, 1984) although in general morphology they are consistent by the presence of a constricted neck between the tooth root and crown. The Jibeinia dentition is slightly more acute and there are two pairs of teeth on the premaxilla, in contrast to Archaeopteryx which has three pairs. Dentition on the maxilla and mandible of Archaeopteryx is relatively abundant and has been studied by numerous workers (Martin and Stewart, 1977, 1980; Martin, 1991; Dames, 1888; Petronievics, 1925; Wellnhofer, 1974; Ostrom, 1976; Brodkorb,1971). After their study of the London specimen, Martin et al. (1980) suggested that the dentition of Archaeopteryx resembled that of the Crocodylia. On none of the specimens is there evidence of lateral tooth replacement.
In Jibeinia and Archaeopteryx specimens, tooth replacement occurs from beneath the tooth. Although there is no actual documentation of a Crocodylian mode of tooth replacement in the available specimens, a medial cavity of the root for facilitating replacement dentition is quite distinct on both genera (Fig. 40a). The dentition of Jibeinia is comparable to those of the Early Cretaceous taxa in its morphology but the dental battery is increased. The Cathayornis dentition is clearly in a phase of reduction, with the mandible only possessing two teeth, whereas the maxilla is edentulous and the premaxilla bears four small teeth. The dentitions of Ichthyornis and Hesperornis, however, are comparable. Because a vast majority of Early Cretaceous specimens is only preserved as impressions in the matrix and the Early Cretaceous specimens from Spain and Russia lack cranial material, further comparisons cannot be conducted.
Plesiomorphic characters of the Jibeinia forelimb include a humerus that is simple in morphology and lacks a pneumatocoel; carpals, tarsals, and phalanges are all unfused; MtI is present; and digit III is still composed of three phalanges, which are all characters consistent with Archaeopteryx and Confuciusornis. Distinct from these two genera, however, are the relatively distinct medial and lateral tuberosities of the proximal humerus, the length of the digit I ungual is equivalent to MtII and MtIII, digits are tightly associated, and unguals have been reduced. These characters represent a development toward functional flight, are more derived than the morphology of Archaeopteryx or Confuciusornis, and there is a trend toward fusion of the carpals and phalanges in preparation for independent aerial locomotion. However, Jibeinia is more primitive than Sinornis, Cathayornis, and the specimens from Spain, as the latter have incipient pneumatocoels; McI has become lost; fusion of Mc2 and Mc3 has begun; and only two phalanges remain on digit III. The Early Cretaceous flight mechanism is relatively dexterous, powerful, and much more advanced toward the functionality of modern forms. The pectoral girdle is more derived than on Confuciusornis and Archaeopteryx, most noticeably expressed in the modification of the coracoid, in which its proximal end has become thin or modified for a more dexterous articulation, whereas on the former two genera the coracoid is a short and broadened plate with its proximal end unreduced or more closely preserving the basic morphology of their reptilian ancestors. Because the origin of flight lies in the propulsive mechanism of the pectoral musculature, the morphology of the avian sternum directly influences the functional strength associated with the flight stroke, thus the evolutionary phase of the sternum reflects the functional ability for flight. The Jibeinia sternum is much more derived than the older genera, although its breadth still exceeds its length but its configuration is relatively complex. On the two former genera the sternum is small and shaped as a short transversely broadened plate. This is a primary reason some workers believe there is an inability for flight in Archaeopteryx. However, it is important here to note that on the Archaeopteryx specimens at hand, it is only the Archaeopteryx bavarica specimen that preserves a sternum. The Confuciusornis sternum is still simple in morphology, lacking a xiphoid or posterolateral processes. Compared to Early Cretaceous genera, the pectoral girdle of Jibeinia is distinctly primitive and cumbersome. The Cathayornis coracoid is not only elongated and compressed, the proximal end maintains an articular surface for the scapula and humerus, the scapula is basically thin, narrow, and scimitar-shaped, while the sternum maintains two elongated posterolateral processes, a shorter xiphoid process, and anteriorly there appears an incipient carina. However, on both Jibeinia and the Early Cretaceous forms the general morphology of the sternum is broad and circular, unlike that on the much younger Ichthyornis in which there is a well developed sternum with a carina.
The hindlimb of Jibeinia is in a transitional phase between the Late Jurassic and Early Cretaceous forms, as noted in the unfused proximal metatarsals. However, initial proximal fusion of the metatarsals is inconsistent between Archaeopteryx, Confuciusornis, and the Early Cretaceous taxa, and thus this character is autapomorphic on Jibeinia and slightly resembles the derived condition on the domestic chicken Gallus. During ontogeny of the Gallus tarsometatarsus, preliminary fusion occurs distally prior to gradual proximal fusion. Based upon this, one may speculate that Jibeinia was the direct ancestor to extant Aves. It must also be noted that the second metatarsal on Jibeinia is the shortest, which also differs from all known Mesozoic taxa. The discussion conducted above illustrates the transitional phase between the Jurassic and Cretaceous that Jibeinia represents and provides genuine evidence for the continuity of biotic evolution. Concurrently, this specimen confirms evolutionary phases developing from primitive to derived states. The significance of the discovery of this specimen is self evident, as it indicates a relatively continuous systematic development in the early evolution of Aves. Jibeinia represents one of two specimens produced from the Yixian Fm. of Hebei Province. The second specimen is produced from a higher stratigraphic level and is morphologically more derived. It is quite evident that although Jibeinia and Confuciusornis are both produced from the Yixian Fm., the latter is more primitive and the former displays more autapomorphic characters, but not to the extent of possessing a derived sternum with a distinct carina as noted on Liaoningornis. Morphologically, Jibeinia approaches taxa from the Early Cretaceous Jiufotang Fm. including Sinornis and Cathayornis but it is still more primitive and as such, as a transitional taxon, represents geologic evidence further substantiating evolutionary theory.
Although the cranium of Jibeinia is incomplete, characters documented include the relatively short rostrum, nasal process of the premaxilla is not as well developed, and the premaxilla is not as fused as on Cathayornis. Confuciusornis, however, is also relatively derived in its edentulous premaxilla. Thus, it is significant that within early avian evolution, the presence or absence of a dentition does not necessarily represent a primitive or derived character state but only a distinction in inherited genetic coding. This is further illustrated in a comparison of Cathayornis to the Late Cretaceous Ichthyornis and Hesperornis which are several tens of millions of years younger but bear a much more complete dentition. The dental morphology of Jibeinia thus resembles that on Archaeopteryx, Cathayornis, Hesperornis, Ichthyornis, and other birds with a dentition.
After Aves diverged from the Reptilia, its first major modification lay in the forelimb. The discovery of Archaeopteryx not only stimulated workers to consider the origin of Aves but the origin of flight itself, resulting in multidisciplinary research which produced various contradictory hypotheses that persist into the present. In general, there are four groups in the animal kingdom with the capability of flight: The most prominent group is also the most abundant and is represented by the insects, which rely predominantly on keratinous membrane for this function. The other three groups are vertebrates including Aves, the Chiroptera, and the extinct Pterosauria, each bearing individual flight mechanisms. Although the pterosaurs and bats rely on dermal membrane, though flight mechanisms are mutually exclusive. The fossil record of pterosaurs predates that for Aves with the first documentation of the group from the Early Jurassic as opposed to the Late Jurassic record of Aves. Consequently, in the Early and Middle Mesozoic the vertebrates with flight capability were dominated by the Reptilia, mirroring the predominance of reptiles in terrestrial habitats.
In the Early and Middle Jurassic the Pterosauria were extensively distributed as carnivores. Currently, there are no specimens of birds that predate the Late Jurassic and thus the question arises as to whether this is related to the domination of the Pterosauria which perhaps represented the natural enemies of early birds and thus kept avian population to an absolute minimum through predation. Flight mechanism of the pterosaurs relied completely on the extremely extended fourth digit and thus conjecture interprets wing folding to be an impossibility. Padian (1983) determined the wing membrane of pterosaurs to be composed predominantly of supporting fibers. In contrast, the wing membrane of the Chiroptera is composed of elastic fibers which are supported between the hallux and the other digits, and thus all the phalanges are elongated allowing flexibility of the wing membrane to conform to the configuration of the digits, representing the most derived condition. But as in the pterosaurs, there is functional limitation to this design, as opposed to that of Aves which is represented by a complex of overlapping integumentary structures, and which represents the most efficient mechanism for flight currently found in vertebrates. In recent years, in addition to the discovery of reptiles such as Megalancosaurus, with limb elements sharing characters with Aves (Feduccia, 1993), there are additional reptilian specimens such as the small pseudosuchian, Longisquama, from the Early Triassic of the former Soviet Union (Sharov, 1970) that appears to share a common ancestor with Aves in its possession of elongated scale-like structures on its torso. Others question its relationship to both Aves or even the Reptilia (Olshevsky, 1991). Currently, there are two major hypotheses regarding the origin of flight. The theory of an arboreal genesis, or from gliding, was earliest proposed by Marsh (1880, 1881) with modern analogues represented by flying squirrels, flying reptiles, and the Malaysian “flying frog” Rhacophorus.
Under this scenario, the earliest avian members leaped between trees as precocious feathered forms with underdeveloped forelimbs. After a long period of natural selection in which the distance between arboreal habitats increased, gliding was elevated to a higher degree resulting in continuous modification to the forelimb, particularly in the development of feathers upon digit II and the ulna. This theory is still quite popular and receives support from a multitude of workers. The second theory as proposed by Bock (1984, 1986), states that avian ancestors were ground dwelling reptiles that underwent an extensive period of natural selection to become functionally bipedal as primitive tenacious ground dwelling birds with the capacity for tree climbing. Terrestrial and arboreal saltation gradually extended in distance and thus resulted in early stages of gliding combined with gradual gliding between differential tree heights and slowly developing the initial power stroke which ultimately strengthened the functional bility for flight. This theory requires numerous modifications upon well-known avian taxa prior to a final extended phase of completion. It also implies an intermediate ancestral reptilian form which had an independent ability to inhabit the atmospheric realm through gradual transition phases.
The current most primitive specimens, represented by Archaeopteryx and Confuciusornis, provide strong support for this theory in their presence of forelimb digits and recurved claws for grasping in arboreal realms. This is particularly noticeable in the mobility of the digit I and III unguals in Confuciusornis. Concurrently, the pes of Confuciusornis, with its pollex in opposition to the other three digits, insures the ability for stable perching. The second theory relating to the origin of flight has gained prominent support rapidly (Balda et al., 1985). It was initially proposed by Williston (1879), who recognized that within the process of cursoriality, the forelimbs of the bipedal dinosaurs would be used for assistance in stability and would gradually transform into a feathered wing. He hypothesized that in the Triassic, avian ancestors probably maintained elongated lateral digits to increase functional cursoriality accompanied by the gradual expansion of scales into feathers. Nopcsa (1907) concurred and further asserted that the origin of Aves lay in rapid bipedal reptiles with elongated tails.
Therefore, the primitive avian forelimb (proto-wing) would have been an apparatus for assisting propulsion and strengthening the motivating force of the hindlimb. Within the past ten years, support for this theory has been gaining, particularly among those such as Balda et al. (1985) who reevaluated the skeleton of Archaeopteryx and elucidated the plausibility of the theory by clarifying that the hindlimb of Archaeopteryx is extremely well developed with an elongated tibia and a femur and tarsometatarsus length index slightly larger than two to one. This is consistent with extremely rapid cursoriality. Secondly, the hallux ungual is not elongated, the other digit unguals are not strongly recurved or acute, and flexor processes are small, which are characters that approach extant ground dwelling birds in the order Galliformes.
In the large quantity of Confuciusornis specimens, the general condition of the pes unguals are not as large or recurved as the manus unguals, although a relatively large and recurved pes ungual is present. Thus the hindlimb of this taxon primarily functioned for the grasping of arboreal branches or trunks. The significance of the opposable hallux on the first birds reflects the ability for the rapid departure from the terrestrial surface, which was beneficial toward the development of the forelimb wing in addition to perching in arboreal habitats. The enhancement of digits I and III on the Confuciusornis forelimb facilitated ability to grasp branches or trunks upon gliding or flying through arboreal habitats.
Compared to extant members of Aves, the wing morphology of Archaeopteryx and Confuciusornis do not represent actual legitimate wings despite the presence of flight feathers. This is due to the presence of diverged metacarpals, three unmodified digits, the presence of well developed ungual phalanges, principle forelimb elements being simple in morphology and lacking pneumatocoels, in addition to sharing numerous forelimb characters with several reptiles. The forelimb of Jibeinia, however, is much more derived. Although the humerus is simple in morphology, it maintains a sinuous curvature, and the differential degree of robusticity between the radius and ulna is increased. Furthermore, McI is reduced and MtII and III have become more closely associated, initiating fusion at their termini. Digits have also begun to facilitate preliminary stages of flight with digit II being more well developed, feathered, elongated, and robust, while digits I and III have become reduced. Unguals have become smaller with that on digit III trending toward becoming lost. Jibeinia certainly had the ability to fly, although its wing is still noticeably primitive compared to the Early Cretaceous forms which have undergone even more substantial modifications including characters such as the loss of McI, complete proximal fusion of McII and III, retention of only two phalanges on digit III, humerus with a pneumatocoel, and sternum with a low carina, providing a more substantial ability for flight. In contrast, the sternum of Jibeinia is broad in morphology and lacks a carina. The hindlimb of Jibeinia lies in a transition phase between Confuciusornis and Early Cretaceous taxa with its most conspicuous character being the unfused proximal metatarsals, which differs from the fused condition on Confuciusornis and the Early Cretaceous forms, and is consistent with extant taxa. Perhaps then, Jibeinia is the direct ancestor to several extant taxa, although this hypothesis is a subject for a different and more detailed study.
Source: Polyglot Paleontologist
Comment by Michel Mortimer
Etymology
\\\"from the Luanhera(?) river in Northern Hebei\\\", \\\"Yibei\\\" means northern Hebei Province and luanhera is from a river name that originated in Fengning, the regio of it\\\'s discovery.
Holotype
(IVPP collection) (~115 mm) partial skull, lower jaw, (22 mm), five cervical vertebrae (~2.4 mm), four dorsal vertebrae (~2.9 m), dorsal ribs, sacrum, six caudal vertebrae, pygostyle (13 mm), scapula, coracoids, furcula, sternum, sternal ribs?, humerus (23.3 mm), radius (24.2 mm), ulna (24 mm), metacarpal I (2 mm), phalanx I-1 (4 mm), manual ungual I (2.5 mm), metacarpal II (9.3 mm), phalanx II-1 (6 mm), phalanx II-2 (3.7 mm), manual ungual II (2.1 mm), metacarpal III (8.3 mm), phalanx III-1 (1.5 mm), phalanx III-2 (2.9 mm), manual ungual III (1 mm), partial ilium, pubis (21 mm), partial ischium?, femora (22.2 mm), tibiae (28 mm), distal tarsal, tarsometatarsus (16.3 mm), pes, feather impressions
Diagnosis
Two non-ungual phalanges in manual digit III.
Description
If we scale from the femoral length of Confuciusornis, Jibeinia would measure about 115 mm long, not counting tail feathers, which is about half the size of Confuciusornis. Jibeinia was originally used as the label on a figure of a skeleton described as the Jibei bird in Hou (1997). This counted as a nomen nudum. It was later (2000) featured in the Picture Book of Chinese fossil birds in a way which would make it an official taxon.
The skull is poorly preserved, with the dorsal section missing and everything crushed. The beak is pointed and the upper jaw has a roughly straight lower margin. There are at least five teeth in the upper jaw. The dentary is narrow with at least six teeth. The teeth lack serrations and have expanded roots. What may be the articular region of the lower jaw viewed ventrally shows strong medial and lateral processes.
Five or six short cervical vertebrae and four dorsal vertebrae are preserved. No details are visible. There are many dorsal ribs preserved and smaller elements that could be uncinate processes or sternal ribs. No gastralia are present. At least six, possibly seven, sacral vertebrae are present with sutures still visible between the centra. There appear to be six free caudal vertebrae and a pygostyle extending the length of about eight centra. The free caudal vertebrae all have transverse processes and the pygostyle viewed ventrally tapers to a sharp point.
The scapula is narrow and has a triangular anteriorly projecting acromion process. The distal end appears sharp, but this could be due to breakage. The coracoid is very large and strut-like with a greatly expanded distal end that broadly contacts the sternum anterolaterally. The furcula is very narrow and quite possibly V-shaped, it\\\'s certainly not as U-shaped as confuciusornithids or Archaeopteryx. It has an interclavicular angle of 60-70 degrees or so. The middle section is represented by a dotted line in the figure, which could represent the impression of the bone or hypothetical guesswork. The dotted line shows a very sharp V-shape without a hypocleidium. The sternum is nicely preserved and no keel is indicated. The anterior is convex, with the coracoids attaching more laterally than Confuciusornis. The lateral processes consist of a long narrow posterolaterally pointing process and a small triangular posteriorly pointing process behind it. There is a long narrow midline posterior process as well.
The humerus has a much lower deltopectoral crest than confuciusornithids and a prominent posteriorly projecting internal tuberosity. The distal end is not as expanded as confuciusornithids either. The radius is slender (~40% of ulnar width) and longer than the humerus by 4% and the ulna is bowed. The manus is distinctive. The metacarpals are unfused, metacarpal I is 21% of metacarpal II in length and metacarpal III is 90%. Metacarpal III is slightly thinner than metacarpal II and bowed laterally. There are two non-ungual phalanges on digits II and III. The proximal phalanx on II is longest, while the distal phalanx on III is longest. There are three unguals, all of which are reduced. Manual ungual III is smallest, while ungual I is slightly larger than ungual II.
The ilium is poorly prserved and it\\\'s structure can not be determined. The pubis is slender and bowed cranially. It lacks an obturator notch and has a symphysis over the distal 28%. The pubic foot is small, triangular and only projects posteriorly. What may be the plate-like remains of an ischium is present, but is too poorly preserved for comment.
The femur has a declined head and tibial condyle that projects further distally than the fibular condyle. The tibia is 126% of femoral length and has a fibular crest. No fibula is preserved. At least one distal tarsal is preserved. The metatarsus is non-arctometatarsalian and proximally fused. Metatarsal II is shortest, while metatarsal IV is slightly shorter than metatarsal III. Metatarsal IV is not noticeably thinner than the others. The first digit is retroverted and metatarsal I is placed almost at the distal end of metatarsal II. On the left pes, pedal ungual II is subequal to ungual III, while on the right it is 30% larger. There is no heel on phalanx II-2 however and the flexor tubercle on ungual II is not enlarged, so I doubt the digit was hyperextendable. Compared to Confuciusornis, the hallux is longer (~66% of digit III, opposed to ~50%) and digit IV is shorter, being closer to digit II in length.
There are feathers preserved, including primaries and secondaries. Also, the photocopy quality is bad, but there appears to be a pair of long narrow tail feathers as in confuciusornithids.
Realtionships
This is obviously a member of th Pygostylia based on the pygostyle and long strut-like coracoid. It lacks the confuciusornithid synapomorphies of toothlessness, deltopectoral crest of humerus prominent and subquadrangular and manual ungual II much smaller than other manual unguals. The only character shared with confuciusornithids is the presence of long, paired tail feathers that may be indicated in the photograph. Jibeinia seems more derived than confuciusornithids based on the following characters: strong medial and lateral processes of articular, interclavicular angle much less than 90 degrees, manual digit I shorter than metacarpal II, reduced manual unguals, manual phalanx II-1 longer than II-2 and only two phalanges in manual digit III.
Unfortunately, assignment to the Enantiornithines is uncertain due to the lack of information on Asian species. Only Spanish and Argentinian species have been subjected to cladistic analyses and many \\\"enantiornithine\\\" characters aren\\\'t present in some Chinese species (eg. laterally convex coracoid, reduced metatarsal IV). In addition, some enantiornithines (Iberomesornis, Cathayornis caudatus) seem much more basal than others (Neuquenornis, Concornis). A detailed analysis of known enantiornithines is desperately needed, but is not within the scope of this description. Jibeinia will however briefly be compared to enantiornithines.
The jaws are toothed as in Cathayornis, Cusprostrisornis, Eoenantiornis, Largirostrornis, Liaoxiornis, Sinornis and the Spanish nestling, unlike Boluochia and Gobipteryx. Boluochia, Cathayornis yandica, Eoenantiornis, Iberomesornis, Jibeinia, Largirostrornis, Liaoxiornis and Sinornis have a pygostyle, while Cathayornis caudatus, Longchengornis do not. The coracoid of Jibeinia is slightly convex laterally. Concornis, Enantiornis, Eoalulavis, Neuquenornis, the Spanish hatchling and an unnamed French form (Buffetaut, 1998) also have laterally convex coracoids, considered a enantiornithine synapomorphy, while Cathayornis caudatus, Cuspirostrisornis, Iberomesornis and a Mongolian species (Dong, 1993) lack this feature. Jibeinia\\\'s furcula has a larger interclavicular angle than Concornis, Eoalulavis, Iberomesornis, Neuquenornis and Sinornis. The metacarpals of Cathayornis, Concornis, Eoalulavis, Largirostrornis, Neuquenornis and a Lecho specimen (Walker, 1981) are fused, while Jibeinia, Otogornis, Sinornis and a Mongolian species are unfused. In Cathayornis, Concornis, Eoalulavis, Longchengornis, Neuquenornis, Sinornis, the Spanish hatchling and a Lecho specimen, the third metacarpal is longer than the second, which is an enantiornithine synapomorphy Jibeinia lacks. Cathayornis, Concornis, Eoenantiornis and Sinornis only have one phalanx on the third manual digit, which is less than Jibeinia. Boluochia, Cusprostrisornis, Jibeinia and Sinornis have a pubic foot, while Cathayornis, Largirostrornis(?) and Longchengornis(?) lack one. The fourth metatarsal is noticeably thinner than the others in Avisaurus, Boluochia, Concornis, Cuspirostrisornis, Lectavis, Neuquenornis, Soroavisaurus and Yungavolucris, but not in Cathayornis caudatus, Iberomesornis, Largirostrisornis and Sinornis.
So based on the above information, Jibeinia is more basal than ornithothoracines based on the presence of more than one phalanx on manual digit III and a large interclavicular angle. It is excluded from the Enantiornithes based on metacarpal II being longer than metacarpal III. In addition, Jibeinia lacks synapomorphies within the enantiornithines when they can be determined. I propose that Jibeinia be placed as a pygostylian more derived than confuciusornithids and more basal than ornithothoracines. This interpretation is open to change as Hou\\\'s description is translated and further details are revealed.
Hou, 2000
Time
Cretaceous Early Barremian
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Unnamed Clade
Fossilsite
Yixian Formation, at the Dongtuyao brick factory near the village of Senjitu, Fengning Co. Hebei Province, China.
Info
Nearly complete skeleton.
Jibeinia luanhera was collected from the same geological formation, and not far from the locality of Vescornis. Unfortunately, the holotype of Jibeinia luanhera (the only specimen known) is lost (L. Hou, personal communication, 2001). Furthermore, the casts of the holotype are of low quality and the available illustrations of Jibeinia luanhera add no information. The description of Jibeinia luanhera includes certain morphological characteristics that radically differ from the condition in Vescornis. For example, Jibeinia luanhera was found to have more maxillary teeth, no keel on the sternum, digit III in the manus with three phalanges, and astragalus and calcaneum unfused to the tibia. If correctly described, these characteristics unambiguously shows that Jibeinia luanhera is of a different taxon from Vescornis.
However, the lack of the holotype of Jibeinia luanhera precludes an evaluation of these observations. Given the similar geological circumstances for the findings, their almost identical size, and the many shared morphological characteristics, it is clearly possible that a future reexamination of the holotype Jibeinia luanhera (if found) may result in the synonymization of this taxon and Vescornis. Zhang, Ericson and Zhou (2004)
Jibeinia luanhera from the Late Jurassic of Hebei Province and its comparison to Confuciusornis. After large collections were made from the Early Cretaceous of Liaoning, at the beginning of summer 1993, Mr. Pai Li, an engineer from the Hebei Provincial Office of Geology, received word of a Mesozoic bird specimen at Fengning Co.. Together with Lianhai Hou and Zhonghe Zhou, an investigation was thereby conducted. Upon the day of arrival at the village of Linjituxiang, a relatively complete avian specimen was presented to the group by one of the local farmers. The next day the fossil locality at the Dongtuyao brick factory was evaluated, where the mudstones of the Yixian Fm. were identified interbedded between limestones. Co-occurring paleontological data include plants and fish taxa including Lycoptera, Yanosteus longidorsalis, and Peipiaosteus, indicating that the stratigraphic position should be slightly higher than the sediments that produce Confuciusornis. The specimen from this locality is more derived than Confuciusornis but more primitive than the Early Cretaceous Sinornis and Cathayornis and thereby represents an intermediate form and significant evolutionary link.
Etymology
Jibeinia luanhera is produced from Fengning Co. which is located in Northern Hebei Province and is known by the appellation the Jibei Region. The Chinese character Ji represents one of the nine geographical divisions of ancient China which embraces parts of Manchuria, Jilin, Shanxi, and part of Henan Province. Bei is Chinese for north. Species etymology is derived from the Luanhe River.
Diagnosis
The maxilla contains numerous acute but unserrated teeth, the sternum is large and broad, the xiphoid process (medial column) is long, lateral processes are not well developed, carpals are unfused but are in tight association, digit III is reduced, cervical centra are extremely concave, distal pubes are fused but not expanded, proximal metatarsals are incompletely fused, distal metatarsals are completely independent, and MtII is shorter than MtIII and MtIV.
Locality and age
The specimen is derived from the gray Late Jurassic interbedded mudstones of the Yixian Fm. at the Dongtuyao brick factory near the village of Senjitu, Fengning Co., Hebei Province. [The Dinosauria 2004 :Yixian Fm, Liaoning, China]
Description
The specimen approaches Cathayornis in size, consisting of a relatively complete skeleton with an incomplete skull. The postcrania are exposed dorsally and ventrally and the cranium is only exposed ventrally, but this allows a clear description of the mandible. Posterior to the frontals the cranium is missing. The postcrania are predominantly represented only by impressions. Ilium and ischium are obscure due to compressional distortion. The nasal process of the premaxilla is slender and long, there are one to four teeth present on the rostrum, and only a portion of the maxilla bearing dentition is visible because the rest is obscured by the mandible. Six widely spaced teeth are visible and alveoli for replacement dentition are absent. Dental morphology is nearly completely consistent with the London specimen of Archaeopteryx, noted by Martin (1991), in which he describes a constricted neck between the lengthy tooth crown and expansive tooth root. But on Jibeinia the apex of the crown is longer, more acute, and is posteriorly curved. This dental morphology differs from theropods and more closely resembles that of the Crocodylia.
The mandible is relatively well preserved with the left ramus being basically complete. In lateral perspective the mandible is slightly dorsally curved with an arched ventral margin, the dentary is relatively dorsoventrally slender and is relatively long. The posterior elements have been subjected to compressional distortion and thus only the articular is recognized as being extremely well developed with its terminus dorsally oblique. A well developed dentition is present in tight association anteriorly, but posteriorly it resembles that of the maxilla by becoming widely spaced. The individual teeth are relatively large and morphologically resemble those of the maxilla. The longest tooth in the series is 10 mm. Only the anterior portion of the frontal and parietal’s interior lamina are preserved. There is a short vomer inlaid between two expansive palatines but posterior to it, the morphology and placement of the pterygoids are vague.
The cervical series is short, with only six amphicoelous centra visible. The anterior centra are small but gradually enlarge posteriorly. Lateral pleurocoels are present and neural spines are relatively low and broad. Lengths of the robust cervical ribs are unclear. Dorsal vertebral count is also vague because the majority is obscured, but five amphicoelous anterior lumbars are visible with centra morphologically similar to, but larger than the cervicals, a ventral keel is absent, several rib heads are still in articulation on the left side, and intervertebral plates are present between the centra. There are a minimum of eight sacral vertebra based upon diapophyseal count; the diapophyses are relatively short, and centra are not fused. The caudal vertebrae are fused but not completely, and approximately 10-12 vacuities perforate the diapophyses. Thus the caudals are basically fused to form a conical pygostyle. Neural spines are also fused to form an undulating dorsal ridge. The most anterior caudals are anteroposteriorly compressed and transversely expanded, ventrally there are distinct processes, and diapophyses are particularly elongated.
The coracoid is the best preserved element in the pectoral girdle. Terminal articulations of the furcula are missing, and only the right scapula is present. The coracoid is not elongated, its proximal end is extremely thin with a small rounded head dorsally while distally its contact with the scapula is extremely broad and thick, and as such its has a general morphology of an acutely robust triangular plate. The scapula is an elongated and thickened element and its proximal end overlies the coracoid. The scapular crest is extremely elongated and laterally projected. The clavicle branches are laterally compressed and relatively broad; their proximal ends are acute processes, but do not completely form a well developed articulation with the coracoids. The sternum is the largest element on the skeleton with a multifaceted morphology. Its transverse breadth is 18 mm which barely exceeds its 17 mm anteroposterior length, a character shared with Archaeopteryx bavarica. Morphologically it is more similar to that of Cathayornis, but differs in having an extremely short lateral process and a xiphoid process which is the longest on the element. On each side of the posterior xiphoid process there is a small medially hooked projection.
Ventrally on the sternum a carina is absent, although the ventral surface is relatively convex, particularly approaching both sides of the midline. It is also convex at the midpoint of the midline, which may represent an incipient carina. There are also relatively distinct, regular ventrolateral grooves which may represent attachment points facilitating pectoral musculature. Rib morphology is simple: bicapitate, slender, and long. Several ribs are still articulated to the thoracic and lumbar centra. Gastral ribs are rare but conspicuous. It is quite evident that rib morphology closely resembles that of Chaoyangia from the Early Cretaceous Lofotang Fm., only more primitive. Although the left forelimb is basically missing, the right forelimb is completely preserved. Termini of the relatively robust humerus are present but the shaft is represented by a distinct impression. The proximal end is medially curved with a small but distinct head that is associated with a medial and lateral tuberosity. All three processes project distinctly from the proximal surface.
Although the deltoid process is not well developed, it still projects laterally. A small depression distal to the medial tuberosity may represent an incipient pneumatocoel. The distal humerus is simple in morphology with a slight lateral expansion. Genuine medial and lateral condyles are not yet formed, and as such the distal end is represented by a slightly depressed planar surface. The ulna is predominantly represented by a depression in the matrix. Its shaft is straight, the proximal end is slightly curved but not expanded, an olecranon process is absent, and the distal end is laterally expanded with a concave terminus. The radius is more slender than the ulna and is extremely straight; its proximal end is not expanded for contact with the ulna, its distal end is laterally expanded to form a cone that approaches the distal end of the ulna, and its terminus is a small rounded facet that surpasses the distal end of the ulna. There are still two independent carpals which differ from the condition of the Early Cretaceous birds. These elements overlap slightly with the one on the ulnar side being relatively large but the one on the radial side being relatively small. The three metacarpals are unfused, resembling the condition of Confuciusornis and Archaeopteryx. McI is short and in close association with the carpals. McII is the largest in the series. McIII expands from its midshaft to its distal end and its breadth is equivalent to McII, a condition resembling Confuciusornis but differing from Archaeopteryx. Digit I is elongated and greatly surpasses the lengths of McII and McIII, implying a strong flight stroke.
The independent first digit gradually becomes reduced although its phalanx and ungual are more well developed than in the Early Cretaceous Sinornis or Cathayornis, and thus represents a transitional phase in the evolution of flight. Digit II resembles Confuciusornis by being the most robust in the series and being composed of two phalanges, the distal of which is relatively small. The size of the ungual is equivalent to that on digit I but has more curvature. The impression of digit III also resembles Confuciusornis and Archaeopteryx by being composed of three phalanges and an ungual, but it differs in its most distal phalanx being the shortest, the digit is independent, and has been shifted medially. The pelvic girdle and sacrum have been subjected to compressional distortion, prohibiting a description of the ilium. As such it is only recognized in the right hindlimb region as being a robust element. Only the left side of the ischium is visible, indicating that it is relatively short with a slender slightly curved distal end. The pubis is the longest element in the pelvic girdle with fused and unexpanded termini. These three pelvic elements are unfused, the ischium and pubis are posteriorly oblique, and appear relatively primitive.
The hindlimb is the best preserved element on the specimen with the elements being basically complete. The femur is relatively thin, straight, and weak, with a small head that lacks a neck, still preserving the morphology of its reptilian ancestors, and resembling the condition in Confuciusornis and Archaeopteryx. Distal condyles are not well developed and the terminus is gently concave.
The tibiotarsus is long but not robust. Its proximal end is slightly inflated with a rather planar facet, and lacks medial and lateral articular surfaces in addition to a cnemial crest. Its distal end is also slightly expanded but a trochlea between the medial and lateral condyles is absent and there is only a very slight concave facet. There are at least three independent tarsals retained represented by the astragalus, calcaneum, and centrale. The tarsometatarsus is the shortest element on the hindlimb. Among the metatarsals, MtV has been lost, MtII, III, and IV are not completely fused, MtIII is the longest, MtII is shorter than its two counterparts, and as in the general avian condition, MtIV is the shortest in the sequence and in opposition. The length of the digit I ungual exceeds its phalanx, while the length of the digit II ungual is only slightly shorter than its two associated phalanges. The ungual on digit III is slightly small, and digit IV is the shortest in the sequence.
Jibeinia measurements (mm).
Approximate cranial length 26.0
Preserved length of nasal process of premaxilla 8.0
External nares length 4.0
Mandible length 20.0
Scapula length 20.0
Scapula breadth 1.5
Coracoid length 11.5
Coracoid distal breadth 7.2
Furcula branch length 10.5
Sternum length 17.0
Sternum breadth 18.0
Humerus length 23.3
Humerus proximal breadth 6.0
Humerus distal breadth 4. 0
Ulna length 24.0
Radius length 24.2
MtI length 2.0
Manus digit I length 4.0
Manus digit I ungual length 2.5
MtII length 9.3
First phalanx of manus digit II length 6.0
Second phalanx of manus digit II length 3.7
Digit II ungual length 2.1
First phalanx of manus digit III length 3.2
Second phalanx of manus digit III length 1.1
Femur length 22.2
Distal femur breadth 2.5
Proximal femur breadth 3.0
Tibiotarsus length 28.0
Tibiotarsus proximal breadth 3.5
Tibiotarsus distal breadth 3.2
Tarsometatarsus length 16.3
Tarsometatarsus proximal breadth 3.0
Tarsometatarsus distal breadth 3.2
Pes digit I ungual length 7.5
Pes digit II ungual length 13.0
Pes digit III ungual length 18.0
Pes digit IV ungual length 14.0
Comparison
The general morphology of this Late Jurassic bird is more derived than both Confuciusornis or Archaeopteryx and it possesses characters attributed to extant taxa, particularly in the absence of an elongated tail. However, it should still be retained in the sub-class Sauriurae containing Confuciusornis and Archaeopteryx based upon the presence of a dentition, unfused metacarpals, three independent manus digits, the presence of gastral ribs, and the primitive morphology of the hindlimb. As previously stated, this taxon is a transitional form lying between the Late Jurassic and later Early Cretaceous taxa as further documented below. The posterior skull of Jibeinia is not preserved although its basic morphology is discernable through an impression in the matrix, indicating that it is relatively short with a relatively large cranium, thus being more well developed than in both Confuciusornis and Archaeopteryx. The posterior portion of the Jibeinia mandible is obliquely inclined posteroventrally, which also differs distinctly from the relatively linear ventral mandible on the other two genera.
The skull compares more closely to the Early Cretaceous Cathayornis and Sinornis; however, as indicated in the description above, the dental morphology is more consistent with that of Archaeopteryx, although there are some slight distinctions. On the Berlin specimen, the Archaeopteryx dentition is relativelyobust with the apices posteriorly curved, whereas in the Eichstatt specimen the dentition is slender and long (Howgate, 1984) although in general morphology they are consistent by the presence of a constricted neck between the tooth root and crown. The Jibeinia dentition is slightly more acute and there are two pairs of teeth on the premaxilla, in contrast to Archaeopteryx which has three pairs. Dentition on the maxilla and mandible of Archaeopteryx is relatively abundant and has been studied by numerous workers (Martin and Stewart, 1977, 1980; Martin, 1991; Dames, 1888; Petronievics, 1925; Wellnhofer, 1974; Ostrom, 1976; Brodkorb,1971). After their study of the London specimen, Martin et al. (1980) suggested that the dentition of Archaeopteryx resembled that of the Crocodylia. On none of the specimens is there evidence of lateral tooth replacement.
In Jibeinia and Archaeopteryx specimens, tooth replacement occurs from beneath the tooth. Although there is no actual documentation of a Crocodylian mode of tooth replacement in the available specimens, a medial cavity of the root for facilitating replacement dentition is quite distinct on both genera (Fig. 40a). The dentition of Jibeinia is comparable to those of the Early Cretaceous taxa in its morphology but the dental battery is increased. The Cathayornis dentition is clearly in a phase of reduction, with the mandible only possessing two teeth, whereas the maxilla is edentulous and the premaxilla bears four small teeth. The dentitions of Ichthyornis and Hesperornis, however, are comparable. Because a vast majority of Early Cretaceous specimens is only preserved as impressions in the matrix and the Early Cretaceous specimens from Spain and Russia lack cranial material, further comparisons cannot be conducted.
Plesiomorphic characters of the Jibeinia forelimb include a humerus that is simple in morphology and lacks a pneumatocoel; carpals, tarsals, and phalanges are all unfused; MtI is present; and digit III is still composed of three phalanges, which are all characters consistent with Archaeopteryx and Confuciusornis. Distinct from these two genera, however, are the relatively distinct medial and lateral tuberosities of the proximal humerus, the length of the digit I ungual is equivalent to MtII and MtIII, digits are tightly associated, and unguals have been reduced. These characters represent a development toward functional flight, are more derived than the morphology of Archaeopteryx or Confuciusornis, and there is a trend toward fusion of the carpals and phalanges in preparation for independent aerial locomotion. However, Jibeinia is more primitive than Sinornis, Cathayornis, and the specimens from Spain, as the latter have incipient pneumatocoels; McI has become lost; fusion of Mc2 and Mc3 has begun; and only two phalanges remain on digit III. The Early Cretaceous flight mechanism is relatively dexterous, powerful, and much more advanced toward the functionality of modern forms. The pectoral girdle is more derived than on Confuciusornis and Archaeopteryx, most noticeably expressed in the modification of the coracoid, in which its proximal end has become thin or modified for a more dexterous articulation, whereas on the former two genera the coracoid is a short and broadened plate with its proximal end unreduced or more closely preserving the basic morphology of their reptilian ancestors. Because the origin of flight lies in the propulsive mechanism of the pectoral musculature, the morphology of the avian sternum directly influences the functional strength associated with the flight stroke, thus the evolutionary phase of the sternum reflects the functional ability for flight. The Jibeinia sternum is much more derived than the older genera, although its breadth still exceeds its length but its configuration is relatively complex. On the two former genera the sternum is small and shaped as a short transversely broadened plate. This is a primary reason some workers believe there is an inability for flight in Archaeopteryx. However, it is important here to note that on the Archaeopteryx specimens at hand, it is only the Archaeopteryx bavarica specimen that preserves a sternum. The Confuciusornis sternum is still simple in morphology, lacking a xiphoid or posterolateral processes. Compared to Early Cretaceous genera, the pectoral girdle of Jibeinia is distinctly primitive and cumbersome. The Cathayornis coracoid is not only elongated and compressed, the proximal end maintains an articular surface for the scapula and humerus, the scapula is basically thin, narrow, and scimitar-shaped, while the sternum maintains two elongated posterolateral processes, a shorter xiphoid process, and anteriorly there appears an incipient carina. However, on both Jibeinia and the Early Cretaceous forms the general morphology of the sternum is broad and circular, unlike that on the much younger Ichthyornis in which there is a well developed sternum with a carina.
The hindlimb of Jibeinia is in a transitional phase between the Late Jurassic and Early Cretaceous forms, as noted in the unfused proximal metatarsals. However, initial proximal fusion of the metatarsals is inconsistent between Archaeopteryx, Confuciusornis, and the Early Cretaceous taxa, and thus this character is autapomorphic on Jibeinia and slightly resembles the derived condition on the domestic chicken Gallus. During ontogeny of the Gallus tarsometatarsus, preliminary fusion occurs distally prior to gradual proximal fusion. Based upon this, one may speculate that Jibeinia was the direct ancestor to extant Aves. It must also be noted that the second metatarsal on Jibeinia is the shortest, which also differs from all known Mesozoic taxa. The discussion conducted above illustrates the transitional phase between the Jurassic and Cretaceous that Jibeinia represents and provides genuine evidence for the continuity of biotic evolution. Concurrently, this specimen confirms evolutionary phases developing from primitive to derived states. The significance of the discovery of this specimen is self evident, as it indicates a relatively continuous systematic development in the early evolution of Aves. Jibeinia represents one of two specimens produced from the Yixian Fm. of Hebei Province. The second specimen is produced from a higher stratigraphic level and is morphologically more derived. It is quite evident that although Jibeinia and Confuciusornis are both produced from the Yixian Fm., the latter is more primitive and the former displays more autapomorphic characters, but not to the extent of possessing a derived sternum with a distinct carina as noted on Liaoningornis. Morphologically, Jibeinia approaches taxa from the Early Cretaceous Jiufotang Fm. including Sinornis and Cathayornis but it is still more primitive and as such, as a transitional taxon, represents geologic evidence further substantiating evolutionary theory.
Although the cranium of Jibeinia is incomplete, characters documented include the relatively short rostrum, nasal process of the premaxilla is not as well developed, and the premaxilla is not as fused as on Cathayornis. Confuciusornis, however, is also relatively derived in its edentulous premaxilla. Thus, it is significant that within early avian evolution, the presence or absence of a dentition does not necessarily represent a primitive or derived character state but only a distinction in inherited genetic coding. This is further illustrated in a comparison of Cathayornis to the Late Cretaceous Ichthyornis and Hesperornis which are several tens of millions of years younger but bear a much more complete dentition. The dental morphology of Jibeinia thus resembles that on Archaeopteryx, Cathayornis, Hesperornis, Ichthyornis, and other birds with a dentition.
After Aves diverged from the Reptilia, its first major modification lay in the forelimb. The discovery of Archaeopteryx not only stimulated workers to consider the origin of Aves but the origin of flight itself, resulting in multidisciplinary research which produced various contradictory hypotheses that persist into the present. In general, there are four groups in the animal kingdom with the capability of flight: The most prominent group is also the most abundant and is represented by the insects, which rely predominantly on keratinous membrane for this function. The other three groups are vertebrates including Aves, the Chiroptera, and the extinct Pterosauria, each bearing individual flight mechanisms. Although the pterosaurs and bats rely on dermal membrane, though flight mechanisms are mutually exclusive. The fossil record of pterosaurs predates that for Aves with the first documentation of the group from the Early Jurassic as opposed to the Late Jurassic record of Aves. Consequently, in the Early and Middle Mesozoic the vertebrates with flight capability were dominated by the Reptilia, mirroring the predominance of reptiles in terrestrial habitats.
In the Early and Middle Jurassic the Pterosauria were extensively distributed as carnivores. Currently, there are no specimens of birds that predate the Late Jurassic and thus the question arises as to whether this is related to the domination of the Pterosauria which perhaps represented the natural enemies of early birds and thus kept avian population to an absolute minimum through predation. Flight mechanism of the pterosaurs relied completely on the extremely extended fourth digit and thus conjecture interprets wing folding to be an impossibility. Padian (1983) determined the wing membrane of pterosaurs to be composed predominantly of supporting fibers. In contrast, the wing membrane of the Chiroptera is composed of elastic fibers which are supported between the hallux and the other digits, and thus all the phalanges are elongated allowing flexibility of the wing membrane to conform to the configuration of the digits, representing the most derived condition. But as in the pterosaurs, there is functional limitation to this design, as opposed to that of Aves which is represented by a complex of overlapping integumentary structures, and which represents the most efficient mechanism for flight currently found in vertebrates. In recent years, in addition to the discovery of reptiles such as Megalancosaurus, with limb elements sharing characters with Aves (Feduccia, 1993), there are additional reptilian specimens such as the small pseudosuchian, Longisquama, from the Early Triassic of the former Soviet Union (Sharov, 1970) that appears to share a common ancestor with Aves in its possession of elongated scale-like structures on its torso. Others question its relationship to both Aves or even the Reptilia (Olshevsky, 1991). Currently, there are two major hypotheses regarding the origin of flight. The theory of an arboreal genesis, or from gliding, was earliest proposed by Marsh (1880, 1881) with modern analogues represented by flying squirrels, flying reptiles, and the Malaysian “flying frog” Rhacophorus.
Under this scenario, the earliest avian members leaped between trees as precocious feathered forms with underdeveloped forelimbs. After a long period of natural selection in which the distance between arboreal habitats increased, gliding was elevated to a higher degree resulting in continuous modification to the forelimb, particularly in the development of feathers upon digit II and the ulna. This theory is still quite popular and receives support from a multitude of workers. The second theory as proposed by Bock (1984, 1986), states that avian ancestors were ground dwelling reptiles that underwent an extensive period of natural selection to become functionally bipedal as primitive tenacious ground dwelling birds with the capacity for tree climbing. Terrestrial and arboreal saltation gradually extended in distance and thus resulted in early stages of gliding combined with gradual gliding between differential tree heights and slowly developing the initial power stroke which ultimately strengthened the functional bility for flight. This theory requires numerous modifications upon well-known avian taxa prior to a final extended phase of completion. It also implies an intermediate ancestral reptilian form which had an independent ability to inhabit the atmospheric realm through gradual transition phases.
The current most primitive specimens, represented by Archaeopteryx and Confuciusornis, provide strong support for this theory in their presence of forelimb digits and recurved claws for grasping in arboreal realms. This is particularly noticeable in the mobility of the digit I and III unguals in Confuciusornis. Concurrently, the pes of Confuciusornis, with its pollex in opposition to the other three digits, insures the ability for stable perching. The second theory relating to the origin of flight has gained prominent support rapidly (Balda et al., 1985). It was initially proposed by Williston (1879), who recognized that within the process of cursoriality, the forelimbs of the bipedal dinosaurs would be used for assistance in stability and would gradually transform into a feathered wing. He hypothesized that in the Triassic, avian ancestors probably maintained elongated lateral digits to increase functional cursoriality accompanied by the gradual expansion of scales into feathers. Nopcsa (1907) concurred and further asserted that the origin of Aves lay in rapid bipedal reptiles with elongated tails.
Therefore, the primitive avian forelimb (proto-wing) would have been an apparatus for assisting propulsion and strengthening the motivating force of the hindlimb. Within the past ten years, support for this theory has been gaining, particularly among those such as Balda et al. (1985) who reevaluated the skeleton of Archaeopteryx and elucidated the plausibility of the theory by clarifying that the hindlimb of Archaeopteryx is extremely well developed with an elongated tibia and a femur and tarsometatarsus length index slightly larger than two to one. This is consistent with extremely rapid cursoriality. Secondly, the hallux ungual is not elongated, the other digit unguals are not strongly recurved or acute, and flexor processes are small, which are characters that approach extant ground dwelling birds in the order Galliformes.
In the large quantity of Confuciusornis specimens, the general condition of the pes unguals are not as large or recurved as the manus unguals, although a relatively large and recurved pes ungual is present. Thus the hindlimb of this taxon primarily functioned for the grasping of arboreal branches or trunks. The significance of the opposable hallux on the first birds reflects the ability for the rapid departure from the terrestrial surface, which was beneficial toward the development of the forelimb wing in addition to perching in arboreal habitats. The enhancement of digits I and III on the Confuciusornis forelimb facilitated ability to grasp branches or trunks upon gliding or flying through arboreal habitats.
Compared to extant members of Aves, the wing morphology of Archaeopteryx and Confuciusornis do not represent actual legitimate wings despite the presence of flight feathers. This is due to the presence of diverged metacarpals, three unmodified digits, the presence of well developed ungual phalanges, principle forelimb elements being simple in morphology and lacking pneumatocoels, in addition to sharing numerous forelimb characters with several reptiles. The forelimb of Jibeinia, however, is much more derived. Although the humerus is simple in morphology, it maintains a sinuous curvature, and the differential degree of robusticity between the radius and ulna is increased. Furthermore, McI is reduced and MtII and III have become more closely associated, initiating fusion at their termini. Digits have also begun to facilitate preliminary stages of flight with digit II being more well developed, feathered, elongated, and robust, while digits I and III have become reduced. Unguals have become smaller with that on digit III trending toward becoming lost. Jibeinia certainly had the ability to fly, although its wing is still noticeably primitive compared to the Early Cretaceous forms which have undergone even more substantial modifications including characters such as the loss of McI, complete proximal fusion of McII and III, retention of only two phalanges on digit III, humerus with a pneumatocoel, and sternum with a low carina, providing a more substantial ability for flight. In contrast, the sternum of Jibeinia is broad in morphology and lacks a carina. The hindlimb of Jibeinia lies in a transition phase between Confuciusornis and Early Cretaceous taxa with its most conspicuous character being the unfused proximal metatarsals, which differs from the fused condition on Confuciusornis and the Early Cretaceous forms, and is consistent with extant taxa. Perhaps then, Jibeinia is the direct ancestor to several extant taxa, although this hypothesis is a subject for a different and more detailed study.
Source: Polyglot Paleontologist
Comment by Michel Mortimer
Etymology
\\\"from the Luanhera(?) river in Northern Hebei\\\", \\\"Yibei\\\" means northern Hebei Province and luanhera is from a river name that originated in Fengning, the regio of it\\\'s discovery.
Holotype
(IVPP collection) (~115 mm) partial skull, lower jaw, (22 mm), five cervical vertebrae (~2.4 mm), four dorsal vertebrae (~2.9 m), dorsal ribs, sacrum, six caudal vertebrae, pygostyle (13 mm), scapula, coracoids, furcula, sternum, sternal ribs?, humerus (23.3 mm), radius (24.2 mm), ulna (24 mm), metacarpal I (2 mm), phalanx I-1 (4 mm), manual ungual I (2.5 mm), metacarpal II (9.3 mm), phalanx II-1 (6 mm), phalanx II-2 (3.7 mm), manual ungual II (2.1 mm), metacarpal III (8.3 mm), phalanx III-1 (1.5 mm), phalanx III-2 (2.9 mm), manual ungual III (1 mm), partial ilium, pubis (21 mm), partial ischium?, femora (22.2 mm), tibiae (28 mm), distal tarsal, tarsometatarsus (16.3 mm), pes, feather impressions
Diagnosis
Two non-ungual phalanges in manual digit III.
Description
If we scale from the femoral length of Confuciusornis, Jibeinia would measure about 115 mm long, not counting tail feathers, which is about half the size of Confuciusornis. Jibeinia was originally used as the label on a figure of a skeleton described as the Jibei bird in Hou (1997). This counted as a nomen nudum. It was later (2000) featured in the Picture Book of Chinese fossil birds in a way which would make it an official taxon.
The skull is poorly preserved, with the dorsal section missing and everything crushed. The beak is pointed and the upper jaw has a roughly straight lower margin. There are at least five teeth in the upper jaw. The dentary is narrow with at least six teeth. The teeth lack serrations and have expanded roots. What may be the articular region of the lower jaw viewed ventrally shows strong medial and lateral processes.
Five or six short cervical vertebrae and four dorsal vertebrae are preserved. No details are visible. There are many dorsal ribs preserved and smaller elements that could be uncinate processes or sternal ribs. No gastralia are present. At least six, possibly seven, sacral vertebrae are present with sutures still visible between the centra. There appear to be six free caudal vertebrae and a pygostyle extending the length of about eight centra. The free caudal vertebrae all have transverse processes and the pygostyle viewed ventrally tapers to a sharp point.
The scapula is narrow and has a triangular anteriorly projecting acromion process. The distal end appears sharp, but this could be due to breakage. The coracoid is very large and strut-like with a greatly expanded distal end that broadly contacts the sternum anterolaterally. The furcula is very narrow and quite possibly V-shaped, it\\\'s certainly not as U-shaped as confuciusornithids or Archaeopteryx. It has an interclavicular angle of 60-70 degrees or so. The middle section is represented by a dotted line in the figure, which could represent the impression of the bone or hypothetical guesswork. The dotted line shows a very sharp V-shape without a hypocleidium. The sternum is nicely preserved and no keel is indicated. The anterior is convex, with the coracoids attaching more laterally than Confuciusornis. The lateral processes consist of a long narrow posterolaterally pointing process and a small triangular posteriorly pointing process behind it. There is a long narrow midline posterior process as well.
The humerus has a much lower deltopectoral crest than confuciusornithids and a prominent posteriorly projecting internal tuberosity. The distal end is not as expanded as confuciusornithids either. The radius is slender (~40% of ulnar width) and longer than the humerus by 4% and the ulna is bowed. The manus is distinctive. The metacarpals are unfused, metacarpal I is 21% of metacarpal II in length and metacarpal III is 90%. Metacarpal III is slightly thinner than metacarpal II and bowed laterally. There are two non-ungual phalanges on digits II and III. The proximal phalanx on II is longest, while the distal phalanx on III is longest. There are three unguals, all of which are reduced. Manual ungual III is smallest, while ungual I is slightly larger than ungual II.
The ilium is poorly prserved and it\\\'s structure can not be determined. The pubis is slender and bowed cranially. It lacks an obturator notch and has a symphysis over the distal 28%. The pubic foot is small, triangular and only projects posteriorly. What may be the plate-like remains of an ischium is present, but is too poorly preserved for comment.
The femur has a declined head and tibial condyle that projects further distally than the fibular condyle. The tibia is 126% of femoral length and has a fibular crest. No fibula is preserved. At least one distal tarsal is preserved. The metatarsus is non-arctometatarsalian and proximally fused. Metatarsal II is shortest, while metatarsal IV is slightly shorter than metatarsal III. Metatarsal IV is not noticeably thinner than the others. The first digit is retroverted and metatarsal I is placed almost at the distal end of metatarsal II. On the left pes, pedal ungual II is subequal to ungual III, while on the right it is 30% larger. There is no heel on phalanx II-2 however and the flexor tubercle on ungual II is not enlarged, so I doubt the digit was hyperextendable. Compared to Confuciusornis, the hallux is longer (~66% of digit III, opposed to ~50%) and digit IV is shorter, being closer to digit II in length.
There are feathers preserved, including primaries and secondaries. Also, the photocopy quality is bad, but there appears to be a pair of long narrow tail feathers as in confuciusornithids.
Realtionships
This is obviously a member of th Pygostylia based on the pygostyle and long strut-like coracoid. It lacks the confuciusornithid synapomorphies of toothlessness, deltopectoral crest of humerus prominent and subquadrangular and manual ungual II much smaller than other manual unguals. The only character shared with confuciusornithids is the presence of long, paired tail feathers that may be indicated in the photograph. Jibeinia seems more derived than confuciusornithids based on the following characters: strong medial and lateral processes of articular, interclavicular angle much less than 90 degrees, manual digit I shorter than metacarpal II, reduced manual unguals, manual phalanx II-1 longer than II-2 and only two phalanges in manual digit III.
Unfortunately, assignment to the Enantiornithines is uncertain due to the lack of information on Asian species. Only Spanish and Argentinian species have been subjected to cladistic analyses and many \\\"enantiornithine\\\" characters aren\\\'t present in some Chinese species (eg. laterally convex coracoid, reduced metatarsal IV). In addition, some enantiornithines (Iberomesornis, Cathayornis caudatus) seem much more basal than others (Neuquenornis, Concornis). A detailed analysis of known enantiornithines is desperately needed, but is not within the scope of this description. Jibeinia will however briefly be compared to enantiornithines.
The jaws are toothed as in Cathayornis, Cusprostrisornis, Eoenantiornis, Largirostrornis, Liaoxiornis, Sinornis and the Spanish nestling, unlike Boluochia and Gobipteryx. Boluochia, Cathayornis yandica, Eoenantiornis, Iberomesornis, Jibeinia, Largirostrornis, Liaoxiornis and Sinornis have a pygostyle, while Cathayornis caudatus, Longchengornis do not. The coracoid of Jibeinia is slightly convex laterally. Concornis, Enantiornis, Eoalulavis, Neuquenornis, the Spanish hatchling and an unnamed French form (Buffetaut, 1998) also have laterally convex coracoids, considered a enantiornithine synapomorphy, while Cathayornis caudatus, Cuspirostrisornis, Iberomesornis and a Mongolian species (Dong, 1993) lack this feature. Jibeinia\\\'s furcula has a larger interclavicular angle than Concornis, Eoalulavis, Iberomesornis, Neuquenornis and Sinornis. The metacarpals of Cathayornis, Concornis, Eoalulavis, Largirostrornis, Neuquenornis and a Lecho specimen (Walker, 1981) are fused, while Jibeinia, Otogornis, Sinornis and a Mongolian species are unfused. In Cathayornis, Concornis, Eoalulavis, Longchengornis, Neuquenornis, Sinornis, the Spanish hatchling and a Lecho specimen, the third metacarpal is longer than the second, which is an enantiornithine synapomorphy Jibeinia lacks. Cathayornis, Concornis, Eoenantiornis and Sinornis only have one phalanx on the third manual digit, which is less than Jibeinia. Boluochia, Cusprostrisornis, Jibeinia and Sinornis have a pubic foot, while Cathayornis, Largirostrornis(?) and Longchengornis(?) lack one. The fourth metatarsal is noticeably thinner than the others in Avisaurus, Boluochia, Concornis, Cuspirostrisornis, Lectavis, Neuquenornis, Soroavisaurus and Yungavolucris, but not in Cathayornis caudatus, Iberomesornis, Largirostrisornis and Sinornis.
So based on the above information, Jibeinia is more basal than ornithothoracines based on the presence of more than one phalanx on manual digit III and a large interclavicular angle. It is excluded from the Enantiornithes based on metacarpal II being longer than metacarpal III. In addition, Jibeinia lacks synapomorphies within the enantiornithines when they can be determined. I propose that Jibeinia be placed as a pygostylian more derived than confuciusornithids and more basal than ornithothoracines. This interpretation is open to change as Hou\\\'s description is translated and further details are revealed.