[D] Spinophorosaurus nigerensis [sG] [T]
Describer
Remes, Ortega, Fierro, Joger, Kosma, Ferrer , Ide & Maga 2009
Time
?Jurassic Middle Bajocian Bathonian
Classification
Saurischia Sauropodomorpha Sauropoda
Diet
Herbivore
Fossilsite
Argiles de l\\\'Irhazer, Irhazer Group, Rural Community of Aderbissinat, Thirozerine Dept., Agadez Region, Niger
Info
Abstract
Background
The early evolution of sauropod dinosaurs is poorly understood because of a highly incomplete fossil record.New discoveries of Early and Middle Jurassic sauropods have a great potential to lead to a better understanding of early sauropod evolution and to reevaluate the patterns of sauropod diversification.
Principal Findings
A new sauropod from the Middle Jurassic of Niger, Spinophorosaurus nigerensis n. gen. et sp., is the most complete basal sauropod currently known. The taxon shares many anatomical characters with Middle Jurassic East Asian sauropods, while it is strongly dissimilar to Lower and Middle Jurassic South American and Indian forms. A possible explanation for this pattern is a separation of Laurasian and South Gondwanan Middle Jurassic sauropod faunas by geographic barriers. Integration of phylogenetic analyses and paleogeographic data reveals congruence between early sauropod evolution and hypotheses about Jurassic paleoclimate and phytogeography.
Conclusions
Spinophorosaurus demonstrates that many putatively derived characters of Middle Jurassic East Asian sauropods are plesiomorphic for eusauropods, while South Gondwanan eusauropods may represent a specialized line. The anatomy of Spinophorosaurus indicates that key innovations in Jurassic sauropod evolution might have taken place in North Africa, an area close to the equator with summer-wet climate at that time. Jurassic climatic zones and phytogeography possibly controlled early sauropod diversification.
Holotype
Specimen numbers GCP-CV-4229 (provisionally housed at the Museo Paleontolo´gico de Elche, Spain; collection abbreviation GCP stands for Grupo Cultural Paleontolo´gico de Elche) and NMB-1699-R (provisionally housed at the Staatliches Naturhistorisches Museum Braunschweig, Germany, collection abbreviation NMB), a braincase, postorbital, squamosal, quadrate, pterygoid, surangular, and a nearly complete postcranial skeleton of a single individual, lacking the sternum, antebrachium, manus, and pes. In future, the specimens will be managed by the Muse´e National d’Histoire Naturelle, Niamey, Niger.
Paratype
Specimen number NMB-1698-R, a partial skull and incomplete postcranial skeleton. Additional elements not preserved in the holotype individual include the premaxilla,maxilla, lacrimal, dentary, angular (most of these fragmentary), a complete set of right dorsal ribs, the humerus, and an isolated pedal phalanx. The identical morphology of the overlapping elements (postorbital, squamosal, pterygoid, surangular, teeth, axial skeleton, scapula) and the proximity of both skeletons in the same stratigraphical level (see below) justify their referral to the same species.
Etymology
The genus name refers to the presence of spikebearing osteoderms, Latin spina, spike, Greek phoro, to bear, and sauros, lizard. The species epithet refers to the Republic of Niger, the provenance of this taxon.
Locality and horizon
The fossils were recovered in an area north of the Rural Community of Aderbissinat (Thirozerine Dept.,Agadez Region, Republic of Niger). GPS coordinates may be provided on request; the locality data are archived in the Museo Paleontologico de Elche, Spain and in the Staatliches Naturhistorisches Museum Braunschweig, Germany. The site is located about 30 km to the north and stratigraphically below the outcrops of the Tegama Group in the classic ‘‘Falaise de Tiguidit’’. Both partial skeletons were found in a massive to finely laminated red siltstone containing some carbonate in its matrix. The siltstone layer is several meters thick and yielded the sauropod remains in its upper half. The holotype and paratype were found in the same level of this layer, about 15 meters laterally apart from each other.
In this area, layers are subhorizontal and bear some minor faults. At the top of the unit (about one meter above the level of the skeletons), paleosoils and carbonate deposits are common. Lithostratigraphic characteristics of the area, with units of red clay showing interbedded sand beds (yielding traces of subaerial exposure and some dinosaur footprints), allow the localization of the site at the base of the Irhazer Group (‘‘Argiles de l’Irhazer’’ below the Tiourare´n Formation). The Irhazer Group has traditionally been considered Jurassic to ‘‘Neocomian’’ in age. Subsequently, a Lower Cretaceous age for the Tiourarén Formation has been proposed, carrying important evolutionary and biogeographic implications. Recently, the pre-Aptian and post-Triassic age of the Tiourarén Formation has been critically discussed, leading to the conclusion that the represented fauna fits more parsimoniously in a late Middle Jurassic to early Late Jurassic scene.
The stratigraphical and phylogenetic position of Spinophorosaurus is consistent with an even earlier age, presumably Middle Jurassic (Bajocian-Bathonian). However, since it is currently not possible to date the strata of the Irhazer Group directly, it cannot be excluded that the Argiles de l’Irhazer are even older (Lower Jurassic). The lower age limit is given only by the Teloua sandstones of the underlying Agadez Group, which contain Chirotherium trace fossils and are therefore regarded as Upper Triassic.
Diagnosis
A basal sauropod diagnosed by the following combination of characters (autapomorphies are marked by *): A small pineal foramen that opens dorsally between the contralateral frontals, not parietals*; laterally oriented basal tubera*; spatulate teeth with large, spaced denticles in the apical region, with a higher number of denticles mesially; cranial cervical vertebrae with accessory cranial processes on the prezygapophyses; cervical vertebrae with U-shaped recess between centrum and interpostzygapophyseal lamina (tpol) in lateral view*; triangular caudal process on caudal cervical diapophyses; enlarged cervical epipophyses, having the form of caudally directed, triangular processes; spinodiapophyseal laminae (spdl) restricted to sacral vertebrae; strong rugosities on neural spines extending over the proximal and middle caudal vertebrae; apex of proximal and middle caudal neural spines saddle-shaped*; distal chevrons transformed into overlapping rod-like horizontal elements whose cranial and caudal projections contact at the level of the middle part of the vertebral centra*; kidney-shaped coracoid*; coracoid with large biceps tubercle and furrow on its ventromedial edge; short, robust pubis with an ischial ridge that extends down to the pubic foot; femur shaft with large foramen on its caudal side, lateral to the fourth trochanter*; possession of spike-bearing osteoderms, probably placed in the distal tail region.
Remes, Ortega, Fierro, Joger, Kosma, Ferrer , Ide & Maga 2009
Time
?Jurassic Middle Bajocian Bathonian
Classification
Saurischia Sauropodomorpha Sauropoda
Diet
Herbivore
Fossilsite
Argiles de l\\\'Irhazer, Irhazer Group, Rural Community of Aderbissinat, Thirozerine Dept., Agadez Region, Niger
Info
Abstract
Background
The early evolution of sauropod dinosaurs is poorly understood because of a highly incomplete fossil record.New discoveries of Early and Middle Jurassic sauropods have a great potential to lead to a better understanding of early sauropod evolution and to reevaluate the patterns of sauropod diversification.
Principal Findings
A new sauropod from the Middle Jurassic of Niger, Spinophorosaurus nigerensis n. gen. et sp., is the most complete basal sauropod currently known. The taxon shares many anatomical characters with Middle Jurassic East Asian sauropods, while it is strongly dissimilar to Lower and Middle Jurassic South American and Indian forms. A possible explanation for this pattern is a separation of Laurasian and South Gondwanan Middle Jurassic sauropod faunas by geographic barriers. Integration of phylogenetic analyses and paleogeographic data reveals congruence between early sauropod evolution and hypotheses about Jurassic paleoclimate and phytogeography.
Conclusions
Spinophorosaurus demonstrates that many putatively derived characters of Middle Jurassic East Asian sauropods are plesiomorphic for eusauropods, while South Gondwanan eusauropods may represent a specialized line. The anatomy of Spinophorosaurus indicates that key innovations in Jurassic sauropod evolution might have taken place in North Africa, an area close to the equator with summer-wet climate at that time. Jurassic climatic zones and phytogeography possibly controlled early sauropod diversification.
Holotype
Specimen numbers GCP-CV-4229 (provisionally housed at the Museo Paleontolo´gico de Elche, Spain; collection abbreviation GCP stands for Grupo Cultural Paleontolo´gico de Elche) and NMB-1699-R (provisionally housed at the Staatliches Naturhistorisches Museum Braunschweig, Germany, collection abbreviation NMB), a braincase, postorbital, squamosal, quadrate, pterygoid, surangular, and a nearly complete postcranial skeleton of a single individual, lacking the sternum, antebrachium, manus, and pes. In future, the specimens will be managed by the Muse´e National d’Histoire Naturelle, Niamey, Niger.
Paratype
Specimen number NMB-1698-R, a partial skull and incomplete postcranial skeleton. Additional elements not preserved in the holotype individual include the premaxilla,maxilla, lacrimal, dentary, angular (most of these fragmentary), a complete set of right dorsal ribs, the humerus, and an isolated pedal phalanx. The identical morphology of the overlapping elements (postorbital, squamosal, pterygoid, surangular, teeth, axial skeleton, scapula) and the proximity of both skeletons in the same stratigraphical level (see below) justify their referral to the same species.
Etymology
The genus name refers to the presence of spikebearing osteoderms, Latin spina, spike, Greek phoro, to bear, and sauros, lizard. The species epithet refers to the Republic of Niger, the provenance of this taxon.
Locality and horizon
The fossils were recovered in an area north of the Rural Community of Aderbissinat (Thirozerine Dept.,Agadez Region, Republic of Niger). GPS coordinates may be provided on request; the locality data are archived in the Museo Paleontologico de Elche, Spain and in the Staatliches Naturhistorisches Museum Braunschweig, Germany. The site is located about 30 km to the north and stratigraphically below the outcrops of the Tegama Group in the classic ‘‘Falaise de Tiguidit’’. Both partial skeletons were found in a massive to finely laminated red siltstone containing some carbonate in its matrix. The siltstone layer is several meters thick and yielded the sauropod remains in its upper half. The holotype and paratype were found in the same level of this layer, about 15 meters laterally apart from each other.
In this area, layers are subhorizontal and bear some minor faults. At the top of the unit (about one meter above the level of the skeletons), paleosoils and carbonate deposits are common. Lithostratigraphic characteristics of the area, with units of red clay showing interbedded sand beds (yielding traces of subaerial exposure and some dinosaur footprints), allow the localization of the site at the base of the Irhazer Group (‘‘Argiles de l’Irhazer’’ below the Tiourare´n Formation). The Irhazer Group has traditionally been considered Jurassic to ‘‘Neocomian’’ in age. Subsequently, a Lower Cretaceous age for the Tiourarén Formation has been proposed, carrying important evolutionary and biogeographic implications. Recently, the pre-Aptian and post-Triassic age of the Tiourarén Formation has been critically discussed, leading to the conclusion that the represented fauna fits more parsimoniously in a late Middle Jurassic to early Late Jurassic scene.
The stratigraphical and phylogenetic position of Spinophorosaurus is consistent with an even earlier age, presumably Middle Jurassic (Bajocian-Bathonian). However, since it is currently not possible to date the strata of the Irhazer Group directly, it cannot be excluded that the Argiles de l’Irhazer are even older (Lower Jurassic). The lower age limit is given only by the Teloua sandstones of the underlying Agadez Group, which contain Chirotherium trace fossils and are therefore regarded as Upper Triassic.
Diagnosis
A basal sauropod diagnosed by the following combination of characters (autapomorphies are marked by *): A small pineal foramen that opens dorsally between the contralateral frontals, not parietals*; laterally oriented basal tubera*; spatulate teeth with large, spaced denticles in the apical region, with a higher number of denticles mesially; cranial cervical vertebrae with accessory cranial processes on the prezygapophyses; cervical vertebrae with U-shaped recess between centrum and interpostzygapophyseal lamina (tpol) in lateral view*; triangular caudal process on caudal cervical diapophyses; enlarged cervical epipophyses, having the form of caudally directed, triangular processes; spinodiapophyseal laminae (spdl) restricted to sacral vertebrae; strong rugosities on neural spines extending over the proximal and middle caudal vertebrae; apex of proximal and middle caudal neural spines saddle-shaped*; distal chevrons transformed into overlapping rod-like horizontal elements whose cranial and caudal projections contact at the level of the middle part of the vertebral centra*; kidney-shaped coracoid*; coracoid with large biceps tubercle and furrow on its ventromedial edge; short, robust pubis with an ischial ridge that extends down to the pubic foot; femur shaft with large foramen on its caudal side, lateral to the fourth trochanter*; possession of spike-bearing osteoderms, probably placed in the distal tail region.