SVP abstracts – Origin of aquatic reptiles?

Sobral and Schoch 2019
bring us news on a taxon at the genesis of aquatic reptiles.

I presume that means
no sea turtles, no marine iguanas, no mosasaurs, no sea crocs, no penguins. If so, the LRT already provides a long list of diapsid taxa at the base of the Enaliosauria (Fig. 1; including mesosaurs, ichthyosaurs, thalattosaurs, placodonts, pachypleurosaurs and plesiosaurs) along with other basal aquatic marine younginiforms (Fig. 2), a monophyletic clade distinct from terrestrial younginiforms that gave rise to protorosaurs and archosauriforms.

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 1. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

From the abstract:
“The Middle Triassic was a time of major changes in terrestrial tetrapod faunas, but the fossil record of this interval is largely obscure.”

Why do paleontologists always paint themselves into a corner like this? To make their discoveries more newsworthy?

“This is unfortunate, since many modern groups originated or diversified during this time. However, recent excavations in the upper Middle Triassic of Germany have revealed several new taxa, most of which are much smaller than those found in other tetrapod-bearing basins of similar age.”

Here’s Galesphyris (Fig. 2) at the base of the aquatic younginiforms in the LRT.

Figure 3. Spinoaequalis and descendant marine younginiformes.

Figure 3. Spinoaequalis and descendant marine younginiformes. These give rise to plesiosaurs, placodonts, mesosaurs, ichthyosaurs and thalattosuchians. Click to enlarge.

Sobral and Shoch continue:
“Here, we report a new taxon from the Vellberg limestone quarry comprised of skull bones distinct from other diapsids from this locality. It is diagnosed by a long maxilla with a far posteriorly reaching tooth row; a long and stout ventral process of the postfrontal; exclusion of the postorbital from the lower temporal fenestra due to a contact between the anteroventral process of the squamosal and the dorsal process of the jugal; and a tall quadrate + quadratojugal complex.”

“Some anatomical aspects of the new taxon are similar to stem diapsids such as Elachistosuchus huenei from similar deposits of Northern Germany and of uncertain phylogenetic affinity.”

In the LRT Elachistosuchus (Fig. 3) nests certainly between proterosuchids and choristoderes (Fig. 4). Neither are related to aquatic younginiforms.

Figure 1. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 3. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 4. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera.

Figure 4. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera.

“A phylogenetic analysis retrieved both taxa in an “ichthyosauromorph” clade, included in an almost exclusively aquatic group. The new taxon, Hupehsuchus, and Elachistosuchus appear as successive sister-taxa to Ichthyopterygia.”

This is not supported by the LRT where Hupehsuchus (Fig. 5) and Elachistosuchus (Fig. 3) are not related  to one another. The outgroups to the Ichthyopterygia (Fig. 1) are the Thalattosuchia, Mesosauria and basal Sauropterygia (pachypleurosaurs).

Figure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

Figure 5. Basal Ichthyosauria in the LRT, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and ThesaurusFigure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

“It is interesting to note that many of the autapomorphic characters of the new taxon pertain to elements related to the lower temporal fenestra. In particular, the contact between the jugal and squamosal is unusual, but is also found in sauropterygians, saurosphargids, Hupehsuchus, and Wumengosaurus, as well as in rhynchocephalians.”

Oh, why did they have to add rhynchocephalians? They were doing so well! Readers beware, convergence is rampant (= everywhere) in the Reptilia. Don’t rely on one, two or a dozen traits. If you do, you’ll be pulling a Larry Martin. Only rely on the last common ancestor in a valid cladogram to determine relationships.

“Derived ichthyosaurs show the typical jugal-quadratojugal contact, but via an unusual dorsal contact between the two. The jugal–squamosal contact may thus represent a transitional state to the anatomy observed in later ichthyosaurs, reinforcing the interpretation of the ‘ventral cheek embayment’ of basal ‘euryapsids’ as a ventrally open lower temporal fenestra.”

“Thus, the new taxon has implications for the origin of secondarily aquatic groups, and therefore also paleobiogeographic significance. The appearance of placodontians has been traced to central Europe, but ichthyopterygians are believed to have originated in the Eastern Tethys. The new taxon indicates that the earliest evolutionary history of these groups may have occurred in the Western Tethys, associated with the Germanic Basin. This new material emphasizes the importance of sampling small-bodied taxa in the understanding of reptile evolution.”

The Lower Keuper is Carnian, early Late Triassic. Galesphyris is older. It comes from the Late Permian, perhaps representing an early Early Permian genesis.


References
Sobral G and Shoch R 2019. A small diapsid from the Lower Keuper of Germany and the origin of aquatic reptiles. Journal of Vertebrate Paleontology abstracts.