Urumqia – a very basal lepidosauromorph

Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Lower Permian.

Figure 1. Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Late Permian.

Here’s a gephyrostegid/basal amniote/basal lepidosauromorph
you may not have heard of. (Remember lepidosauromorphs in the large reptile tree constitute about half of all amniotes). It is considered China’s oldest known tetrapod.

Urumqia liudaowanensis (Zhang et al. 1984, Fig. 1) ~20 cm snout-vent length, Late Permian Lucaogou Formation), was originally considered a discosaurid seymouriamorph. Here it nests at the base of the lepidosauromorph reptiles. Shifting Urumqia to the discosaurid seymouriamorphs adds 39 steps to the large reptile tree.

Derived from 
Gephyostegus bohemicusUrumqia was basal to Bruketererpeton, Thuringothyris, and all lepdiosaurs, turtles, diadectids, pterosaurs and other various lepidosauromorphs starting with Saurorictus and Cephalerpeton. Phylogenetically Urumqia must have made a first appearance in the Viséan (335 mya, Mississipian, Carboniferous) despite its late appearance in the Late Permian (255 mya).

Figure 1. Basal amniotes to scale. Click to enlarge.

Figure 2. Basal amniotes to scale. Click to enlarge. Urumqia nests on the right hand column with Cephalerpeton and Thuringothyris.

Distinct from G. bohemicus,
Urumqia had shorter limbs, longer (but not long) posterior dorsal ribs and a robust tail with elongate caudals. The palate included a suborbital fenestra. The cheek may have included a small lateral temporal fenestra convergent with others. The carpals and tarsals were poorly ossified.

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Figure 3. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Notably
the posterior dorsal ribs were much shorter than the gastralia. So the gastralia create a wide posterior torso, ideal for carrying large amniote eggs (Fig. 3), as we learned earlier.

The new topology of basal reptiles
is based on the inclusion of several more species based taxa not previously considered. This new topology show that synapsids were not the first clade to branch off. Rather all taxa closer to archosaurs (here considered the new Archosauromorpha) split from all taxa closer to lepidosaurs (here considered the new Lepidosauromorpha) at the onset of the Reptilia (=Amniota).

References
Zhang F, Li Y, and Wan X. 1984. A new occurrence of Permian seymouriamorphs in Xinjiang, China. Vertebrate Palasiatica22(4):294-306.

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