Lessons learned about the base of the Reptilia – part 3

Earlier here and here we learned about cranial traits that distinguished pre-reptiles from reptiles and the new Lepidosauromorpha from the new Archosauromorpha. Here we’ll look at the post-crania starting with character # 130 from the large reptile tree.

130 – Cervical centra: In pre-reptiles and the new Lepidosauromorpha: height = length. In the new Archosauromorpha: height < length.

135 – Cervical ribs robust: In pre-reptiles and others. In Lepidosauromorphs (but not Cephalerpeton) they are average in size and descending.

143 – Presacrals: fewer than 26 in Gephyrostegus + the Lepidosauromorphs. 26 to 30 in Utegenia to Coelostegus but more than 30 in Brouffia + Westlothiana.

159 – T-shaped interclavicle in Lepidosauromorpha and higher Archosauromorpha (but this is not a sharp divide with the posterior stem lengthening and the shield shrinking in a series of taxa

161 – Scapula and coracoid fused: Gephyrostegus watsoni to Casineria and basal Lepidosauromorpha

165 – Scapula/scapulocoracoid robust – Lepidosauromorpha, but not Cephalerpeton

167 – Olecranon not present – Utegenia to Westlothiana, but not Lepidosauromorpha

169 – Humerus torsion > 30 degrees – Reptilia

172 – Radius + ulna greater than three times their combined width: only Cephalerpeton

173 – Manus subequal to pes – Lepidosauromorpha

174 – Metacarpals 1-3 aligned: Gephryostegus + Reptilia

175 – Longest metacarpal: 3 and 4 in pre-reptiles and basal Archosauromorpha. 4 is the longest in Lepidosauromorpha and Synapsida.

187 – Pelvic plates fused plesiomorphically. Separated in Gephyrostegus watsoniThuringothyris (basal Lepidosauromorpha?) Brouffia and Casineria. Does this mean these taxa are immature? Maybe. Or maybe this is a transition trait based on size (neotony?).

188 – Pubis orientation – Anterior in pre-reptiles and the new Archosauromorpha. Medial in the new Lepidosauromorpha.

208 – Metatarsal 1 vs. 3 – Smaller than half in Silvanerpeton, Gephyrostegus bohemicus and Paleothyris, all separated from each other, so by convergence

210 – Metatarsals 2-4 shorter than half the tibia –  new Lepidosauromorpha (but not Labidosaurus)

211 – Four is the widest metatarsal in Silvanerpeton to Captorhinidae and Archosauromorpha (but not Paleothyris and Synapsida by convergence)

215 – Metacarpals 1-3 aligned – the Reptilia, but not Synapsida

218 – Pedal 4.1 is 3x longer than wide – At least Paleothyris and Hylonomus

Merry Christmas, everyone!

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