Teraterpeton news – SVP abstract 2016

Updated January 06, 2019
with new data in the form of photos of the skull of Teraterpeton and a new nesting with Trilophosaurus to match the original nesting by Sues in 2011.

To start with
in the large reptile tree the genus Teraterpeton (Fig. 1, Late Triassic) nests as a sister to Trilophosaurus as a rhynchocephalian lepidosaur.

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

From the Pritchard and Sues 2016 abstract (abridged)
Teraterpeton hrynewichorum, from the Upper Triassic (Carnian) Wolfville Formation of Nova Scotia, is one of the more unusual early archosauromorphs, with an elongate edentulous snout, transversely broadened and cusped teeth, and a closed lateral temporal fenestra. Initial phylogenetic analyses recovered this species as the sister taxon to Trilophosaurus spp.

  1. New material of Teraterpeton includes the first-known complete pelvic girdle and hind limbs and the proximal portion of the tail. These bones differ radically from those in Trilophosaurus, and present a striking mosaic of anatomical features for an early saurian
  2. The ilium has an elongate, dorsoventrally tall anterior process similar to that of hyperodapedontine rhynchosaurs.
  3. The pelvis has a well-developed thyroid fenestra, a feature shared by Tanystropheidae, Kuehneosauridae, and Lepidosauria. 
  4. The calcaneum is ventrally concave, as in Azendohsaurus.
  5. The fifth metatarsal is proximodistally short, comparable to the condition in Tanystropheidae.
  6. Much as in the manus, the pedal unguals of Teraterpeton are transversely flattened and dorsoventrally deep. 
  7. Phylogenetic analysis of 57 taxa of Permo-Triassic diapsids and 315 characters supports the placement of Teraterpeton as the sister-taxon of Trilophosaurus in a clade that also includes Azendohsauridae and, rather unexpectedly, Kuehneosauridae.
  8.  In the current phylogeny, the aforementioned amalgam of characters in Teraterpeton were all acquired independently from the other saurian lineages. We partitioned the dataset based on anatomical region to examine metrics of homoplasy across early Sauria. The CI of the partitions are not markedly different, but the RI of the pelvic girdle and hindlimb partitions are markedly higher than the others. Although the characters in the hindquarters partitions underwent a similar number of homoplastic changes, a higher proportion of them contribute to the overall structure of this phylogenetic reconstruction. The mosaic condition in Teraterpeton underscores the importance of thorough taxon sampling for understanding the dynamics of character change in Triassic reptiles and the use of apomorphies in identifying fragmentary fossils.”

Notes

  1. Seems like Prtichard and Sues do not reject the Trilophosaurus relationship.
  2. No trilophosaurids or rhynchosaurs have a thyroid fenestra. Other than Amotosaurus, no tanystropheids have a thyroid fenestra. Rather a separate pubis and ischium are not joined ventrally.
  3. I don’t see any other examples of ventrally concave calcaneal tubers in candidate taxa, nor is this apparent in the Nesbitt et al. 2015 reconstruction of Azendohsaurus.
  4. No candidate taxa have a metatarsal 5 as short as the one in Tanystropheus.
  5. They may have just metaphorically ‘shot themselves in the foot’ as kuehneosaurids are unrelated to any previously mentioned candidate taxa. They are the arboreal gliding reptiles. This throws doubt on any and all of their scoring and results.
  6. None of the candidate taxa listed by Pritchard and Sues have an antorbital fenestra or a long narrow snout with a very short cranial/temporal region like Teraterpeton has (Fig. 1). It’s an autapomorphy or taphonomic damage.

References
Pritchard AC, Sues H-D 2016. Mosaic evolution of the early saurian post cranium revealed by the postcranial skeleton of Teraterpeton hrynewichorum (Archosauromorpha, Late Triassic). Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

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