Yesterday we looked at primitive archosauromorpha at the base of the Amniota. Today we’ll look at basal lepidosauromorpha.
Figure 1. Cladogram of basal amniotes, a subset of the large reptile tree. Dots represent phylogenetic size reductions. Bootstrap scores are shown. Archosauromorpha in gray. Lepidosauromorpha in black at the bottom.
Figure 2. A new reconstruction of Gephyrostegus bohemicus. This species lived 30 million years after the origin of the Amniota in the Visean, 340 mya. Note the lack of posterior dorsal ribs. This trait shared by all basalmost amniotes, may provide additional space for massive eggs in gravid females, but is also shared with males, if there were males back then.
As mentioned earlier, the Amniota is divided at its base into Lepidosauromorpha (taxa closer to lepidosaurs) and Archosauromorpha. Gephyrotegus bohemicus (Fig. 2) is the last common ancestor and Silvanerpeton is the outgroup anamniote.
Figure 3. Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Lower Permian. Formerly considered a sister to Utegenia, an anamniote, it now nests as the basalmost of all lepidosauromorpha.
Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Upper Permian, was originally considered a discosaurid seymouriamorph close to Utegenia. Here (Fig. 1) it nests at the base of the lepidosauromorph reptiles despite its late appearance in the fossil record. Note the gastalia are much wider than the dorsal ribs, likely to retain large eggs in gravid females. Distinct from G. bohemicus, Urumqia had shorter limbs, longer posterior dorsal ribs and a robust tail with elongate caudals. The palate included a larger suborbital fenestra, not homologous to later taxa with this trait. The cheek included a small lateral temporal fenestra. The carpals and tarsals are poorly ossified.
Figure 4. Bruktererpeton, a gephyrostegid and a basal lepidosauromorph amniote.
Bruktererpeton fiebigi — (Boy and Bandel, 1973; Fig. 3) is an older (Namurian/ Bashkirian, 320 Ma) sister to Gephyrostegus bohemicus (Ruta, Jefferey and Coates, 2003; Klembara et al., 2014). The pectoral girdle and limbs are more gracile. The scapula is taller. The intercentra are smaller. Other traditional amniote traits, if present, are not preserved.
Figure 5. Thuringothyris. A basal lepidosauromorph.
Thuringothyris mahlendorffae — (Boy and Martens, 1991; type: MNG 7729; (Müller et al., 2006) referred MNG 10183; Artinskian, Early Permian, 280 Ma) is half the size of Bruktererpeton and documents all traditional amniote traits. Note the derived shape of the humerus and the reduced intercentra.
Traditional amniote traits include:
- loss/fusion of the intertemporal
- absence of the otic notch
- loss/reduction of palatal fangs
- appearance/expansion of the transverse flange of the pterygoid
- loss of labyrinthine infolding of the marginal teeth
- reduction of the intercentra
- addition of a second sacral vertebra
- narrowing and elongation of the humeral shaft
- appearance of the astragalus from fused tarsal elements.
Figure 6. Cephalerpeton. A basal lepidosauromorph.
Cephalerpeton — (Gregory 1948) representing a new sister clade to the Captorhinomorpha, Cephalerpeton had an elongate humuerus with a narrow shaft. The much larger and later Reiszorhinus is a sister.
Figure 7. Two specimens of Concordia, a basal lepidosauromorph.
Concordia — (Müller & Reisz 2005, Stephanian, Late Pennsylvanian, Carboniferous, 4 cm skull length) was considered the oldest known captorhinid, but here (Fig. 1) it nests with Cephalerpeton as a sister to captorhinids.
Figure 8. Romeria texana, a basal capitorhinomorph, lepidosauromorph, amniote.
Romeria texana —(Price1937) Artinskian, Early Permian, ~280 mya, ~25 mm skull length, was the basalmost captorhinid. Here (Fig, 1) the skull is wider and flatter.
Figure 9. Saurorictus, a basal lepidosauromorph in the lineage of Milleretta, compared to sister taxa.
Saurorictus — (Modesto and Smith 2001, SAM PK-8666, skull length ~2.2 cm, estimated total length 15 cm, Late Permian), derived from a sister to Thuringothyris, Concordia and Cephalerpeton, Saurorictus is the taxon basal to all other lepidosauromorpha including diadectomorpha, chelonia and lepidosauria. (sorry, cut off from bottom of cladogram, Fig. 1). It was considered the most complete captorhinid from the Late Permian.
Figure 10. Basal amniotes to scale. Click to enlarge.
Here, Fig. 10, there is a size reduction in ‘second generation’ basal amniotes/basal lepidosauromorpha. You’ll note that several former anamniotes now nest within the amniota. They were judged anamniotes by the skeletal traits, not by their phylogenetic nesting, which has not been adequately tested until now.
Boy JA and Bandel K 1973. Bruktererpeton fiebigi n.gen.n.sp. (Amphibia: Gephyrostegida). Der erste Tetrapode aus dem Rheinisch-Westfälischen Karbon (Namur B; W-Deutschland). Palaeontographica 145: 39–77.
Boy JA and Martens T 1991. Ein neues captorhinomorphes Reptil aus dem thüringischen Rotliegend (Unter-Perm; Ost-Deutschland). Palaeontologische Zeitschrift 65 (3-4): 363–389.
Gregory JT 1948. The structure of Cephalerpeton and affinities of the Microsauria. American Journal of Science 246:550–568
Modesto SP and Smith RMH 2001. A new Late Permian captorhinid reptile: a first record from the South African Karoo. Journal of Vertebrate Paleontology 21(3): 405–409.
Müller J, Berman DS, Henrici AC, Martens T and Suminda S 2006. The basal reptile Thuringothyris mahlendorffae (Amniota:Eureptilia) from the Lower Permian of Germany. Journal of Paleontology 80:726-739.
Müller J and Reisz RR 2005. An early captorhinid reptile (Amniota: Eureptilia) from the Upper Carboniferous of Hamilton, Kansas. Journal of Vertebrate Paleontology. 25(3): 561-568.
Price LI 1937. Two new cotylosaurs from the Permian of Texas. Proceedings of the New England Zoölogical Club 16:97-102.
Zhang F, Li Y, and Wan X. 1984. A new occurrence of Permian seymouriamorphs in Xinjiang, China. Vertebrate Palasiatica22(4):294-306.