[D] Cathayornis yandica [~/~]
Describer
Zhou, Jin & Chang, 1992
Time
Cretaceous Early
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Ornithothoraces Enantiornithes
Fossilsite
Jiufotang Formation, Liaoning, China
Length
(25.4 mm = 1 inch): 96 mm long (top of skull to tip of toes) 52 mm across at wings; Matrix: 100 mm by 141 mm
Info
Cathayornis yandica ~/~ (Zhou, Jin & Chang, 1992) > Cathayornis caudatus ~/~ (Hou, 1997)
Partial skeleton.
Ammended diagnosis
A small genus, skull is small with a minimum amount of fusion, rostrum is relatively long and low, foramen magnum is positioned ventrally, and a relatively full dentition is present on premaxilla and dentary. Scapula is straight and slender with an oblique acromion process. Coracoid has an expansive contact with the sternum, and proximal end becomes narrow. Ventral surface of the sternum is projected, carina is low, and lateral processes are well developed with termini that are expanded as oblique triangles. Humerus and ulna are equivalent in length, humeral head is small or undeveloped, medial and lateral tuberosities are distinct, and there is a small pneumatocoel. Ulna is robust, slightly curved, and possesses a small olecranon process. Radius is slender with an expanded proximal end. Proximal carpals are fused and there is a carpal trochlea. Reduced unguals are present on the first and second digits. Pelvic girdle is unfused. Fibula is long, conical, and is not fused with the tibiotarsus. Pes talons are not extremely curved. Pygostyle is present.
Cathayornis yandica Zhou, Jin and Zhang, 1992 The morphology and paleoecology of Cathayornis is relatively well understood (Zhou et al., 1992; Zhou, 1995), as the majority of specimens excavated from Boluochi, Chaoyang Co, Liaoning Province, belong to this genus. It is recognized as a small taxon with little individual variation and resembles the extant Passeriformes, a family which is adapted to a variety of habitats and displays a large range of morphological variation. The summary below reiterates the work of Zhou in addition to supplementing this work by more recent reevaluation.
Specimen
A nearly complete skeleton lacking tarsometatarsus and pes is incomplete.
Specimen 9169A and B (positive and negative) is housed at the Institute of Vertebrate Paleontology and Paleoanthropology.
Ammended species diagnosis
A small species within the genus with a transverse groove between the frontal and parietal. A minumum of three teeth are present on the dentary. Sternum possesses a manubrium. Tarsometatarsus is longer than half the length of the tibiotarsus. Caudal vertebrae are shortened, and are not fused with the pygostyle.
Locality and stratigraphic position
Light gray mudstones of the Early Cretaceous Jiufotang Fm., at the village of Boluochi, Chaoyang Co., Liaoning Province.
Summary
Among the known Early Cretaceous Aves, Cathayornis represents a small genus that is well preserved, particularly in the cranium, forelimb, and sternum. Many hind limb haracters are still uncertain as the tarsometatarsus is not preserved, although several phalanges and pes unguals are present, allowing interpretation of some adaptive characteristics. The skull is preserved in lateral perspective, it is relatively long and low with basically unfused cranial elements. The premaxilla is not elongated, does not form a hooked beak, and possesses a minimum of four short and conical teeth that have a slight constriction at their base, resembling Archaeopteryx and Jibeinia.
The nasal process of the premaxilla is slender and long, causing the rostral region to be relatively elongated. External nares are large elongated ellipses and constitute the most conspicuous character of the skull, being a result of the low and planar anterior rostrum, although this bill is still not as pronounced as on the Anseriformes. The maxilla is nearly triangular with a minimum of four teeth. Frontals are elongated, transversely expanded, and constitute the vast majority of the cranium.
The position of the foramen magnum is one of the significant characters in determining the evolutionary level of the avian condition. The preservation of the cervical vertebrae in relation to the skull indicates that the Cathayornis foramen magnum is neither posteriorly located nor has it migrated to become completely ventral as in extant taxa. Zhou et al. (1992) stated that “the foramen magnum probably occupies a posteroventral position on the skull.” Therefore, it occupies a phase between Jibeinia and later avian taxa. The anterior mandible is slender and posteriorly broad, the ventral margin is straight, but a precise tooth count is obscured by compressional distortion, although at least three teeth are visible.
The cervical series of Cathayornis is relatively long, with perhaps over 8-10 centra. The specimen is preserved with the neck and cranium dorsally retracted and thus cervical articulation is considered relatively flexible.
However, detailed observation indicates that the centra are still not heterocoelous or saddle-shaped, but are procoelous, retaining the morphology of its reptilian ancestors. The dorsal vertebrae are not fused, further indicating its primitive condition. There are a minimum of eight fused sacral centra; the diapophyses on the posterior two centra are fused but retain fenestra. Posterior to the sacrals and anterior to the pygostyle are several flexible caudal centra, the precise count of which is unclear. The pygostyle is not well developed and is relatively elongated with an acute terminus, being a little more derived than on Jibeinia or Sinornis.
The term “wing” is applied for the first time in the description of Cathayornis, which is significant in two respects. The forelimb of this genus has entered into the fundamental morphology of the true avian wing: the humerus bears a pneumatocoel, the proximal carpometacarpus is fused, and a carpal trochlea is present (Zhou, 1992). This indicates increased mobility between the carpometacarpus and radius to supplement primary flight, such that not only is original dorsal-ventral mobility possible, but an extensive range of forelimb excursion is now possible, approaching that of extant Aves. Secondly, the forelimb morphology has developed into the fundamental model of a wing: the articular relationship between the distal humerus and the proximal ulna has become more complex because the ulna has a small olecranon process and the humerus has a shallow opposing sulcus to facilitate it.
Thus, the Cathayornis forelimb can execute the function of a true wing despite the presence of vestigial talons on the digits. The humerus of Cathayornis is more derived than those of Jibeinia and other older taxa, as expressed by the presence of a pneumatocoel despite its small size, a relatively large deltoid process, and the relatively well developed distal medial and lateral condyles. Therefore, the determination of a shallow olecranon fossa as described by Zhou (1992) is hereby regarded as credible. However, he also noted the presence of an ectepicondylar process which, in this text, cannot be corroborated.
The ulna is robust with a slightly curved proximal end, a short olecranon process associated with a cotyle, and relatively distinct distal medial and lateral condyles but which are not noticeably laterally expanded. The transverse diameter of the ulna is twice that of the radius. The radius has an extremely straight shaft with a relatively well developed capital tuberosity, a laterally expanded and compressed distal end, and a tendinal groove that is present at the medial side of the distal expansion. Two independent carpals are present. The ulnare is nearly saddle-shaped and the radiale is relatively small and irregular in morphology. The remaining carpals have become reduced and fused with McII and McIII to form the carpometacarpus. Although in Cathayornis this element is fused, it is still primitive because only a well developed carpal trochlea represents an apomorphy.
On all the primitive fossil birds to date, this is the first documentation of a fused carpometacarpus. On Jibeinia and Sinornis the carpals and metacarpals are unfused and thus are not recognized as a legitimate carpometacarpus. Phylogenetically, this character is extremely significant toward Cathayornis. In addition, the digits in this genus have been highly modified: digit II retains only two phalanges with an ungual, and digit III retains only a single phalanx, consistent with extant taxa. However the presence of two small unguals is distinct from extant forms and the digit II second phalanx has yet to become laterally compressed. The sternum morphology is the most characteristic feature of the genus.
Sanz and Buscalioni (1992) described an Early Cretaceous specimen from the Las Hoyas region of Spain that they named Concornis lacustris. It is regrettable that cranial material is not present, although the postcrania are relatively well represented. This genus shares numerous characters with Cathayornis including a fundamentally similar characteristic V-shaped furcula, an elongated furcular process, and clavicle branches that are straight and robust.
The coracoid and sternum articulation is exceptionally broadened, the terminus is very slightly anteriorly concave, the proximal end is thin but the coracoid head is slightly broadened for articulation with the humerus. The sterna of each genus are similar, resembling a top or gyroscope. The anterior surface is acute and the posterior face is broadened. Both sterna have a low carina and elongated lateral processes that expand to terminate as a boot, and the posterior processes are also relatively long. However, the two are noticeably distinct in that the shafts of the Cathayornis lateral processes are extremely thin, whereas those of Concornis are relatively robust. The termini of the Cathayornis posterior processes are acute but on the latter are extremely robust and do not become reduced or thinned.
On Cathayornis the medial process of the sternum is short and blunt but on the Spanish form it is relatively long. Furthermore, anterior to the lateral process on Concornis, is a short process (process craniolateralis), but Cathayornis lacks this feature and its posterior process is shorter than its posterolateral process, whereas these counterparts on Concornis are nearly equivalent in length. Concornis therefore appears to be more derived. Only a portion of the Cathayornis tarsometatarsus is preserved on the hindlimb but the femur and tibiotarsus are extremely well preserved despite being shifted in position. The femur resembles that of Sinornis.
It is relatively long and robust, its head is large and distinctly projected, the shaft is slightly curved, and the distal medial and lateral condyles are well developed, with the lateral condyle being relatively large. The tibiotarsus is slightly longer than the femur, there is an expanded portion proximomedially, and the articular surface is slightly expanded and concave. At the distal end the condyles are not as distinctly laterally projected as on the femur.
Only a portion of the tarsometatarsus is present and a majority of the digits are not preserved with only several slender phalanges and three unguals represented. The curvature of the unguals is unlike the strong arc seen in Jibeinia, Sinornis, or Boluochia and instead is more gently curved. By applying curvature parameters to determine habitat adaptation as conducted by Feduccia (1993), Cathayornis then falls out of the range of being a small perching form. Unfortunately, the tibiotarsus of this small form is not very diagnostic and complete digit measurements are not available for analysis. From the portion preserved, however, it is recognized that the three metatarsi are unfused, the phalanges represented are relatively long, and the talons do not display intense curvature.
Thus this small form may be an Early Cretaceous analogue adapted to a shrub habitat. It may also have been adapted to riparian habitats based upon its relatively low skull with a rather planar and elongated bill, perhaps subsisting on small fish and foliage. Following a consistent increase in the adaptation to its environment, it perhaps evolved toward wading or more aquatic behavior. If this interpretation is accurate, then Cathayornis, together with Gansus, represent the most primitive morphology adapted to this type of avian behavior. The latter genus, although also an Early Cretaceous form, occurs stratigraphically higher. Obviously, this behavioral interpretation is based primarily upon cranial morphology and talon curvature and is presented as a preliminary hypothesis. Remaining skeletal morphology of this genus has yet to become modified enough for determining adaptation to a riparian environment.
But measurements of the forelimbs of wading and swimming birds, as well as those of Jibeinia and Sinornis, are compared, and show that the metacarpal and digit length are distinctly shorter than the humerus and radius/ulna length. These parameters in Cathayornis are basically consistent (humerus length 17 mm, ulna length 27 mm, radius length 26 mm, carpometacarpus and digit length approximately 26 mm) and are extremely close to indices of extant wading and natatorial taxa, representing sufficient supplemental evidence to support the interpretation of adaptation to riparian habitats. The evolutionary level of Cathayornis has already been provided in the discussion of the forelimb. Within the framework of the continuity of avian evolution, Cathayornis is regarded as concrete evidence for the continuity of the Confuciusornis-Jibeinia-Sinornis lineage.
Source: Polyglot Paleontologist
Zhou, Jin & Chang, 1992
Time
Cretaceous Early
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Ornithothoraces Enantiornithes
Fossilsite
Jiufotang Formation, Liaoning, China
Length
(25.4 mm = 1 inch): 96 mm long (top of skull to tip of toes) 52 mm across at wings; Matrix: 100 mm by 141 mm
Info
Cathayornis yandica ~/~ (Zhou, Jin & Chang, 1992) > Cathayornis caudatus ~/~ (Hou, 1997)
Partial skeleton.
Ammended diagnosis
A small genus, skull is small with a minimum amount of fusion, rostrum is relatively long and low, foramen magnum is positioned ventrally, and a relatively full dentition is present on premaxilla and dentary. Scapula is straight and slender with an oblique acromion process. Coracoid has an expansive contact with the sternum, and proximal end becomes narrow. Ventral surface of the sternum is projected, carina is low, and lateral processes are well developed with termini that are expanded as oblique triangles. Humerus and ulna are equivalent in length, humeral head is small or undeveloped, medial and lateral tuberosities are distinct, and there is a small pneumatocoel. Ulna is robust, slightly curved, and possesses a small olecranon process. Radius is slender with an expanded proximal end. Proximal carpals are fused and there is a carpal trochlea. Reduced unguals are present on the first and second digits. Pelvic girdle is unfused. Fibula is long, conical, and is not fused with the tibiotarsus. Pes talons are not extremely curved. Pygostyle is present.
Cathayornis yandica Zhou, Jin and Zhang, 1992 The morphology and paleoecology of Cathayornis is relatively well understood (Zhou et al., 1992; Zhou, 1995), as the majority of specimens excavated from Boluochi, Chaoyang Co, Liaoning Province, belong to this genus. It is recognized as a small taxon with little individual variation and resembles the extant Passeriformes, a family which is adapted to a variety of habitats and displays a large range of morphological variation. The summary below reiterates the work of Zhou in addition to supplementing this work by more recent reevaluation.
Specimen
A nearly complete skeleton lacking tarsometatarsus and pes is incomplete.
Specimen 9169A and B (positive and negative) is housed at the Institute of Vertebrate Paleontology and Paleoanthropology.
Ammended species diagnosis
A small species within the genus with a transverse groove between the frontal and parietal. A minumum of three teeth are present on the dentary. Sternum possesses a manubrium. Tarsometatarsus is longer than half the length of the tibiotarsus. Caudal vertebrae are shortened, and are not fused with the pygostyle.
Locality and stratigraphic position
Light gray mudstones of the Early Cretaceous Jiufotang Fm., at the village of Boluochi, Chaoyang Co., Liaoning Province.
Summary
Among the known Early Cretaceous Aves, Cathayornis represents a small genus that is well preserved, particularly in the cranium, forelimb, and sternum. Many hind limb haracters are still uncertain as the tarsometatarsus is not preserved, although several phalanges and pes unguals are present, allowing interpretation of some adaptive characteristics. The skull is preserved in lateral perspective, it is relatively long and low with basically unfused cranial elements. The premaxilla is not elongated, does not form a hooked beak, and possesses a minimum of four short and conical teeth that have a slight constriction at their base, resembling Archaeopteryx and Jibeinia.
The nasal process of the premaxilla is slender and long, causing the rostral region to be relatively elongated. External nares are large elongated ellipses and constitute the most conspicuous character of the skull, being a result of the low and planar anterior rostrum, although this bill is still not as pronounced as on the Anseriformes. The maxilla is nearly triangular with a minimum of four teeth. Frontals are elongated, transversely expanded, and constitute the vast majority of the cranium.
The position of the foramen magnum is one of the significant characters in determining the evolutionary level of the avian condition. The preservation of the cervical vertebrae in relation to the skull indicates that the Cathayornis foramen magnum is neither posteriorly located nor has it migrated to become completely ventral as in extant taxa. Zhou et al. (1992) stated that “the foramen magnum probably occupies a posteroventral position on the skull.” Therefore, it occupies a phase between Jibeinia and later avian taxa. The anterior mandible is slender and posteriorly broad, the ventral margin is straight, but a precise tooth count is obscured by compressional distortion, although at least three teeth are visible.
The cervical series of Cathayornis is relatively long, with perhaps over 8-10 centra. The specimen is preserved with the neck and cranium dorsally retracted and thus cervical articulation is considered relatively flexible.
However, detailed observation indicates that the centra are still not heterocoelous or saddle-shaped, but are procoelous, retaining the morphology of its reptilian ancestors. The dorsal vertebrae are not fused, further indicating its primitive condition. There are a minimum of eight fused sacral centra; the diapophyses on the posterior two centra are fused but retain fenestra. Posterior to the sacrals and anterior to the pygostyle are several flexible caudal centra, the precise count of which is unclear. The pygostyle is not well developed and is relatively elongated with an acute terminus, being a little more derived than on Jibeinia or Sinornis.
The term “wing” is applied for the first time in the description of Cathayornis, which is significant in two respects. The forelimb of this genus has entered into the fundamental morphology of the true avian wing: the humerus bears a pneumatocoel, the proximal carpometacarpus is fused, and a carpal trochlea is present (Zhou, 1992). This indicates increased mobility between the carpometacarpus and radius to supplement primary flight, such that not only is original dorsal-ventral mobility possible, but an extensive range of forelimb excursion is now possible, approaching that of extant Aves. Secondly, the forelimb morphology has developed into the fundamental model of a wing: the articular relationship between the distal humerus and the proximal ulna has become more complex because the ulna has a small olecranon process and the humerus has a shallow opposing sulcus to facilitate it.
Thus, the Cathayornis forelimb can execute the function of a true wing despite the presence of vestigial talons on the digits. The humerus of Cathayornis is more derived than those of Jibeinia and other older taxa, as expressed by the presence of a pneumatocoel despite its small size, a relatively large deltoid process, and the relatively well developed distal medial and lateral condyles. Therefore, the determination of a shallow olecranon fossa as described by Zhou (1992) is hereby regarded as credible. However, he also noted the presence of an ectepicondylar process which, in this text, cannot be corroborated.
The ulna is robust with a slightly curved proximal end, a short olecranon process associated with a cotyle, and relatively distinct distal medial and lateral condyles but which are not noticeably laterally expanded. The transverse diameter of the ulna is twice that of the radius. The radius has an extremely straight shaft with a relatively well developed capital tuberosity, a laterally expanded and compressed distal end, and a tendinal groove that is present at the medial side of the distal expansion. Two independent carpals are present. The ulnare is nearly saddle-shaped and the radiale is relatively small and irregular in morphology. The remaining carpals have become reduced and fused with McII and McIII to form the carpometacarpus. Although in Cathayornis this element is fused, it is still primitive because only a well developed carpal trochlea represents an apomorphy.
On all the primitive fossil birds to date, this is the first documentation of a fused carpometacarpus. On Jibeinia and Sinornis the carpals and metacarpals are unfused and thus are not recognized as a legitimate carpometacarpus. Phylogenetically, this character is extremely significant toward Cathayornis. In addition, the digits in this genus have been highly modified: digit II retains only two phalanges with an ungual, and digit III retains only a single phalanx, consistent with extant taxa. However the presence of two small unguals is distinct from extant forms and the digit II second phalanx has yet to become laterally compressed. The sternum morphology is the most characteristic feature of the genus.
Sanz and Buscalioni (1992) described an Early Cretaceous specimen from the Las Hoyas region of Spain that they named Concornis lacustris. It is regrettable that cranial material is not present, although the postcrania are relatively well represented. This genus shares numerous characters with Cathayornis including a fundamentally similar characteristic V-shaped furcula, an elongated furcular process, and clavicle branches that are straight and robust.
The coracoid and sternum articulation is exceptionally broadened, the terminus is very slightly anteriorly concave, the proximal end is thin but the coracoid head is slightly broadened for articulation with the humerus. The sterna of each genus are similar, resembling a top or gyroscope. The anterior surface is acute and the posterior face is broadened. Both sterna have a low carina and elongated lateral processes that expand to terminate as a boot, and the posterior processes are also relatively long. However, the two are noticeably distinct in that the shafts of the Cathayornis lateral processes are extremely thin, whereas those of Concornis are relatively robust. The termini of the Cathayornis posterior processes are acute but on the latter are extremely robust and do not become reduced or thinned.
On Cathayornis the medial process of the sternum is short and blunt but on the Spanish form it is relatively long. Furthermore, anterior to the lateral process on Concornis, is a short process (process craniolateralis), but Cathayornis lacks this feature and its posterior process is shorter than its posterolateral process, whereas these counterparts on Concornis are nearly equivalent in length. Concornis therefore appears to be more derived. Only a portion of the Cathayornis tarsometatarsus is preserved on the hindlimb but the femur and tibiotarsus are extremely well preserved despite being shifted in position. The femur resembles that of Sinornis.
It is relatively long and robust, its head is large and distinctly projected, the shaft is slightly curved, and the distal medial and lateral condyles are well developed, with the lateral condyle being relatively large. The tibiotarsus is slightly longer than the femur, there is an expanded portion proximomedially, and the articular surface is slightly expanded and concave. At the distal end the condyles are not as distinctly laterally projected as on the femur.
Only a portion of the tarsometatarsus is present and a majority of the digits are not preserved with only several slender phalanges and three unguals represented. The curvature of the unguals is unlike the strong arc seen in Jibeinia, Sinornis, or Boluochia and instead is more gently curved. By applying curvature parameters to determine habitat adaptation as conducted by Feduccia (1993), Cathayornis then falls out of the range of being a small perching form. Unfortunately, the tibiotarsus of this small form is not very diagnostic and complete digit measurements are not available for analysis. From the portion preserved, however, it is recognized that the three metatarsi are unfused, the phalanges represented are relatively long, and the talons do not display intense curvature.
Thus this small form may be an Early Cretaceous analogue adapted to a shrub habitat. It may also have been adapted to riparian habitats based upon its relatively low skull with a rather planar and elongated bill, perhaps subsisting on small fish and foliage. Following a consistent increase in the adaptation to its environment, it perhaps evolved toward wading or more aquatic behavior. If this interpretation is accurate, then Cathayornis, together with Gansus, represent the most primitive morphology adapted to this type of avian behavior. The latter genus, although also an Early Cretaceous form, occurs stratigraphically higher. Obviously, this behavioral interpretation is based primarily upon cranial morphology and talon curvature and is presented as a preliminary hypothesis. Remaining skeletal morphology of this genus has yet to become modified enough for determining adaptation to a riparian environment.
But measurements of the forelimbs of wading and swimming birds, as well as those of Jibeinia and Sinornis, are compared, and show that the metacarpal and digit length are distinctly shorter than the humerus and radius/ulna length. These parameters in Cathayornis are basically consistent (humerus length 17 mm, ulna length 27 mm, radius length 26 mm, carpometacarpus and digit length approximately 26 mm) and are extremely close to indices of extant wading and natatorial taxa, representing sufficient supplemental evidence to support the interpretation of adaptation to riparian habitats. The evolutionary level of Cathayornis has already been provided in the discussion of the forelimb. Within the framework of the continuity of avian evolution, Cathayornis is regarded as concrete evidence for the continuity of the Confuciusornis-Jibeinia-Sinornis lineage.
Source: Polyglot Paleontologist