Earlier here and elsewhere we looked at the origin of the Amniota. Today we’ll take a look at the cladogram (Fig. 1) and some of the taxa no one expected to see on this side of the anamniote/amniote transition series.
As before, the Amniota is divided at its base into the new Lepidosauromorpha (taxa closer to lepidosaurs) and the new Archosauromorpha (closer to archosaurs).
Eldeceeon rolfei – (Smithson 1994, ~27 cm in total length, Early Carboniferous (Viséan) ~335 mya), is from the same formation that yielded Silvanerpeton and Westlothiana. Eldeceeon is known from two dissimilar specimens that nest together. They have a smaller skull and slightly shorter limbs with smaller girdles while retaining a deep ventral pelvis.
Gephyrostegus watsoni – (Brough and Brough 1967) was originally named Diplovertebron punctatum (Watson 1926, Fig. 5), but reassigned to Gephyostegus bohemicus by Carroll (1970) despite the size difference. Carroll thought G. watsoni was a juvenile. Klembara et al. (2014) agreed. The high arched neural spines, small intercentra, and the extreme lean of the posterior skull mark this small basal amniote/gephyrostegid distinct from all others. Egg shapes were found nearby along with insects. The embryo shown is hypothetical.
Solenodonsaurus janenschi – (Broili 1924) Early Permian ~13 cm skull length was considered the sister to all other amniotes by all prior workers, but here Solenodonsaurus nests as a basal archosauromorph, basal to chroniosuchids.
Chroniosuchids – (Tverdokhlebova 1972) Early Permian ~7 cm skull length, were considered aberrant pre-reptiles by all prior workers, but here they nest within the Archosauromorpha. Note the convergent appearance of an antorbital fenestra.
Westlothiana – (Smithson & Rolfe 1990) lived ~338 mya, earlier than any other known reptile. This reconstruction has longer anterior dorsal ribs and shorter posterior dorsal ribs than originally reconstructed. A longer torso is a different solution to egg containment.
Brouffia orientalis – (Carroll and Baird 1972) Westphalian, Late Carboniferous, (CGH IIIB 21 c. 587) and counterpart (MP451), specimen 1 of Brough and Brough (1967) was considered very small Gephyrostegus with two sacrals and an intertemporal. Carroll (1970) considered it not congeneric. Carroll and Baird (1972) considered it a primtiive reptile with a single sacral and no intertemporal. The missing skull of the sister taxon Casineria (Fig. 8) probably looks like this one.
We’ll look at basal Lepidosauromorpha tomorrow.
Broili F von 1924. Ein Cotylosaurier aus der oberkarbonischen Gaskohle von Nürschan in Böhmen. Sitzungsberichte der Mathematisch-Naturwissenschaftlichen Abteilung der Bayerischen Akademie der Wissenschaften zu München 1924: 3-11.
Brough MC and Brough J 1967. Studies on early tetrapods. III. The genus Gephyrostegus. Philosophical Transactions of the Royal Society B252: 147-165.
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–1
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Carroll RL 1970. The ancestry of reptiles. Philosophical Transactions of the Royal Society B257: 267-308.
Clack JA and Klembara J 2009. An articulated specimen of Chroniosaurus dongusensis and the morphology and relationships of the chroniosuchids. Special Papers in Palaeontology, 81: 15–42.
Danto M, Witzmann F and Müller J 2012. Redescription and phylogenetic relationships of Solenodonsaurus janenschi Broili, 1924, from the Late Carboniferous of Nyrany, Czech Republic. Fossil Record 15 (2) 2012, 45–59.
Klembara J, Clack J, and Cernansky A 2010. The anatomy of palate of Chroniosaurus dongusensis (Chroniosuchia, Chroniosuchidae) from the Upper Permian of Russia. Palaeontology 53: 1147-1153.
Klembara J, Clack J, Milner AR and Ruta M 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Laurin M and Reisz 1999. A new study of Solenodonsaurus janenschi, and a reconsideration of amniote origins and stegocephalian evolution. Canadian Journal of Earth Sciences 36:1239-1255.
Paton RL Smithson TR and Clack JA 1999. An amniote-like skeleton from the Early Carboniferous of Scotland. Nature 398: 508-513.
Schoch RR, Voig S and Buchwitz M 2010. A chroniosuchid from the Triassic of Kyrgyzstan and analysis of chroniosuchian relationships. Zoological Journal of the Linnean Society 160: 515–530. doi:10.1111/j.1096-3642.2009.00613.x
Smithson TR 1994. Eldeceeon rolfei, a new reptiliomorph from the Viséan of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (3-4): 377–382.
Smithson TR & Rolfe WDI 1990. Westlothiana gen. nov. :naming the earliest known reptile. Scottish Journal of Geology no 26, pp 137–138.
Tverdochlebova GI 1972. A new Batrachosaur Genus from the Upper Permian of the South Urals, Paleontol. Zh., 1972: 95–103.