Acleistorhinus is NOT a Lanthanosuchid

In their influential JVP paper, DeBraga and Reisz (1996) nested the tiny, round-head Acleistorhinus (Fig. 1) with the much larger flat-head, Lanthanosuchus (Fig.1 ). They erected the clade Lanthanosuchoidea and defined it as the most recent common ancestor of Lanthanosuchidae and Acleistorhinus. They also defined “Parareptilia” and “Ankyramorphorpha,” none of which makes any sense in the large reptile tree.

Well, one look at these taxa and their closest kin on the large reptile tree falsifies that relationship rather neatly. The details do too.

Acleistorhinus is a sister to Milleretta (RC14) and Eunotosaurus. Lanthanosuchus is more closely related to Romeriscus and Macroleter, all three of the flathead variety.

Figure 1. Acleistorhinus is a sister to Milleretta (RC14) and Eunotosaurus. Lanthanosuchus is more closely related to Romeriscus and Macroleter, all three of the flathead variety. Pretty easy to see when they’re all lined up like this. 

Parareptilia (Olsen 1947)
We talked about the uselessness of the paraphyletic clade “Parareptilia” before. DeBraga and Reisz (1996) defined it as the most recent common ancestor of millerettids, Acleistorhinus, lanthanosuchids, Macroleter, Procolophonia and all of its descendants. According to the large reptile tree that most recent common ancestor is a sister to Romeria primus, just two nodes away from the most basal reptile known, Cephalerpeton. Delete Procolophon from this list and you get a most recent common ancestor close to the RC14 specimen of Milleretta (Fig. 1). This definition includes all living lizards and snakes as well, so many parareptiles are actually reptiles. Evidently the definition was formulated at a time when all “parareptiles” were thought to have been monophyletic and extinct. That’s no longer the case.

Ankyramorpha
DeBraga and Reisz (1996) defined “Ankyramorpha” as the most recent common ancestor of Procolophonia, Macroleter, Lanthanosuchidae, Acleistorhinus and all its descendants. Unfortunately, according to the large reptile tree, that definition includes the exact same taxa as Parareptilia. Dropping millerettids doesn’t change a thing.

Lanthanosuchoidea
DeBraga and Reisz (1996) defined “Lanthanosuchoidea” as the most recent common ancestor of Lanthanosuchidae and Acleistorhinus. In the large reptile tree that taxon is Milleretta RC14, so sans Procolophon, this clade is the same as the two previous ones since the two defining taxa are in separate clades. Lanthanosuchus belongs with Romeriscus and Macroleter. All have a wide flat skull and several other defining traits. Acleistorhinus belongs with Milleretta RC14 and Eunotosaurus (Fig. 1).

DeBraga and Reisz (1996) analyzed the relationships of Acleistorhinus using 8 taxa and 60 characters. With such a short taxon  list they obviously presupposed where Acleistorhinus would nest prior to creating their inclusion set. Their Procolophonia included procolophonids, pareiasaurs and turtles. These are paraphyletic in the large reptile tree (now 338 taxa and growing). Their Millerettidae included Milleretta, Millerosaurus and Milleropsis. These are also paraphyletic. Now Millerettidae includes only Milleretta and desendants (listed above), and no longer includes Millerosaurus and Milleropsis. Those nest  on the opposite branch of the Reptilia, the new Archosauromorpha, among the protodiapsids.

References
Cisneros et al 2004. A procolophonid reptile with temporal fenestration from the Middle Triassic of Brazil. Proceedings of the Royal Society London B (2004) 271, 1541–1546
DOI 10.1098/rspb.2004.2748
Daly E 1969. 
A new procolophonoid reptile from the Lower Permian of Oklahoma. Journal of Paleontology 43: 676-687.
DeBraga M 2001The postcranial anatomy of Procolophon (Parareptilia: Procolophonidae) and its implications for the origin of turtles. PhD thesis, University of Toronto.
DeBragra M 2003. The postcranial skeleton, phylogenetic position and probable lifestyle of the Early Triassic reptile Procolophon trigoniceps. Canadian Journal of Earth Sciences 40: 527-556.
DeBraga M and Reisz RR 1996. The Early Permian reptile Acleistorhinus pteroticus and its phylogenetic position. Journal of Vertebrate Paleontology 16(3): 384–395.
Efremov JA 1946. On the subclass Batrachosauria – an intermediary group between amphians and reptiles. USSR Academy of Sciences Bulletin, Biology series 1946:615-638.

Batrachosauria web page
wiki/Lanthanosuchus

wiki/Acleistorhinus

1 thought on “Acleistorhinus is NOT a Lanthanosuchid

  1. I’m surprised you’ve reconstructed Romeriscus. It’s extremely badly preserved and probably a nomen dubium.

Leave a Reply

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

WordPress.com Logo

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

Google photo

You are commenting using your Google 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.