SVP 15 – Erpetonyx. Still a milleropsid, not a bolosaurid

Updated February 9, 2022
with an updated tracing and reconstruction.

Modesto et al. 2015a
discuss Erpetonyx, which is still a sister to Milleropsis in the large reptile tree (not a bolosaur parareptile as originally described, Modesto et al. 2015b). And Milleropsis is not a millerosaur.

Note that Millerosauria is included as an ingroup taxon
Unfortunately Millerosaurus ornatus (Broom 1948, Watson 1957) Late Permian (Changhsingian, 30 cm est length) is based on a chimaera of over a dozen skeletons with many common elements distinct from one another. Millerosaurus has been removed from the large reptile tree. Milleropsis is a protodiapsid not related to Milleretta. Milleretta is likely the genera used for the original suprageneric taxon in the cladogram shown in Figure 1,

If this is too confusing, let me know and I’ll walk you through it.

This abstract
has already been published as a paper (Modesto et al. 2015b).

Figure 1. Skull of Erpetonyx in situ and reconstructed.

Figure 1. Skull of Erpetonyx in situ and reconstructed.

Figure 2. Erpetonyx in situ.

Figure 2. Erpetonyx in situ.

From the abstract
Erpetonyx arsenaultorum was recently erected for a single, nearly complete, and mostly articulated skeleton of a bolosaurian* parareptile** collected from the Gzhelian-age Egmont Bay Formation of Prince Edward Island. Erpetonyx arsenaultorum is autapomorphic in possessing 29 presacral vertebrae and a relatively small radiale, fifth distal carpal, and pisiform. The skull is characterized by the presence of plicidentine and by the absence of caniniform maxillary teeth. The neural arches closely resemble those of the Early Permian lanthanosuchian Delorhynchus cifelli in their broadly tongue-shaped zygapophyses, in which the lateral edges of the anterior zygapophyses pass posteriorly onto the lateral surface of the arch and form a conspicuous shelves, emphasized by an anteroventral pocket. The right carpus is well ossified. The preserved unguals are also well ossified, with a prominent flexor tubercle, a suboval proximal portion, and a stout, slightly ventrally curved tip. Together with the observation that the unguals are longer than their respective proximal phalanges, ungual morphology suggests adaptation to a fossorial or semi-fossorial lifestyle. Erpetonyx arsenaultorum is the oldest known amniote with digging adaptations, appearing ca. 3􀂱4 million years after the demise of th coal-swamp forests.

*Not a bolosaurian, but a milleropsid.
**Parareptile is an outmoded name based on traditional cladograms that have been falsified by the large reptile tree.

We looked at Erpetonyx earlier here in this blog.

Gow CE. 1972. The osteology and relationships of the Millerettidae (Reptilia: Cotylosauria). Journal of Zoology, London 167:219-264.
Modesto SP, Reisz RR, Macdougall MJ and Scott DM 2015a. Skeletal anatomy of the oldest known parareptile from the Upper Carboniferous of Priince Edward Island, Canada. Journal of Vertebrate Paleontology abstacts
Modesto SP, Scott DM, MacDougall MJ, Sues H-D, Evans DC, Reisz RR 2015b. The oldest parareptile and the early diversification of reptiles. Proceedings of the Royal Society B 282: 20141912.
Watson DMS 1957. On Millerosaurus and the Early History of the Sauropsida. Philosophical Transactions of the Royal Society of London Series B 240(673):325-400.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.