Another lateral temporal fenestra!

Figure 1. Emeroleter skull showing lateral temporal fenestra, as also shown in its sisters Macroleter, Romeriscus and Lanthanosuchus. Images from Tsuji, Müller and Reisz 2012.

This looks like a regular break (Fig. 1), but Emeroleter nests between taxa that also have a lateral temporal fenestra (Fig. 2). So this could be a real lateral temporal fenestra made ragged over the last tens of millions of years.

Figure 2. Macroleter, Emeroleter, Romeriscus and Lanthanosuchus in phylogenetic order and to scale. All have a lateral temporal fenestral, even if small. This is a better evolutionary sequence leading to Lanthanosuchus than Acleistorhinus can provide.

At this stage in lepidosaurormorph evolution, taxa were just beginning to experiment with the lateral temporal fenestra, which was “here to stay” in owenettids, like Sauropareion.

However, the last time we see the lower temporal bar (jugal/ quadratojugal connection) is right here (Fig. 2) until these two bones are reconnected again in basal sphenodontians, drepanosaurs and fenestrasaurs.

DeBraga and Reisz (1996) and Cisneros (2004) reported that Acleistorhinus was the sister to Lanthanosuchus. However, the large reptile tree indicates a better match with Romeriscus, Emeroleter and Macroleter. Acleistorhinus makes a better sister to the turtle-like millerettid, Eunotosaurus.

Tsuji et al. 2012 reported, “A clade consisting of the nycteroleters and pareiasaurs, here termed Pareiasauromorpha, is supported by both methods.” Unfortunately, it is not supported by the large reptile tree, unless all subsequent taxa that have these taxa at their base are also called pareiasauromorphs, and that would include all turtles, lizards and snakes, and Lanthanosuchus, which Tsuji et al. 2102 also nested with Acleistorhinus far from Emeroleter. 

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 
deBraga M and Reisz RR 1996. The Early Permian reptile Acleistorhinus pteroticus and its phylogenetic position. Journal of Vertebrate Paleontology 16(3): 384–395. doi:10.1080/02724634.1996.10011328.
Modesto SP, Damiana RJ and Sues H-D 2002. A reappraisal of Coletta seca, a basal procolophonid reptile from the lower Triassic of South Africa. Palaentology 45(5):883-895.
Tsuji, Müller and Reisz 2012. Anatomy of Emeroleter levis and the Phylogeny of the Nycteroleter Parareptiles. Journal of Vertebrate Paleontology 32 (1): 45-67. doi:10.1080/02724634.2012.626004.

wiki/Emeroleter

 

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.

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 2001. The 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

Assembling the Squamate Tree of Life – part 1

Some of the heaviest hitters in paleontology joined forces to produce a 300-page paper (including tons of photos and the data matrix) of squamate phylogeny, including several fossil taxa. Gauthier et al. (2012) takes the reader through the history of squamate studies, discusses some of long standing problems and some of the new molecular studies. 141 extant and 51 extinct species were included. The outgroup consisted of three Rhynchocephalians. 610 characters were tested. 112 trees were recovered, chiefly at the base of the Iguania. The homoplasy index was 0.82, so a great deal of homoplay was present. This was a huge study and powerful due to its size.

Happily most of the Gauthier (2012) tree echoed the results of prior trees and the large reptile tree. At the base of both: Huehuecuetzpalli followed by Iguania and Scleroglossa with the latter divided into Gekkota, Scincomorpha and Anguimorpha. Major differences include: 1) Mosasaurs and their kin at the base of the Scleroglossa. 2) Eichstattisaurus at the base of the Gekkota, 3) Amphisbaenia as the sister to a 4) monophyletic Serpentes (snakes). The large reptile tree found 1) mosasaurs to nest with varanids, 2) Eichstattisaurus to nest with basal snakes close to mosasaurs and their kin, far from the Gekkota, 3) amphisbaenids as sisters to skinks, 4) and diphyletic clades of snakes arising from sisters to Lanthanotus and Adriosaurus.

Figure 1. Click to enlarge. The Gauthier et al. 2012 family tree of the squamates, color added for large clades.

We’ll look at these differences point by point in coming blogs and attempt to dissect the differences and why they occurred.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Gauthier, JA, Kearney M, Maisano JA, Rieppel O and Behkke ADB 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1):3-308. online here.

What is Saurorictus?

Figure 1. Saurorictus australis reconstructed. The parietal, outlined in gray, is largely unknown. Click for more info.

Saurorictus australis
Captorhinids were basal lepidosauromorph reptiles that appeared in the Early Permian and evolved multiple tooth rows by the Late Permian.  Saurorictus (Modesto and Smith 2001) SAM PK-8666 was originally considered a late-surviving single-tooth row captorhinid that had “very slender marginal teeth” and reportedly lacked a supratemporal.

Figure 2. Saurorictus, Macroleter and Lanthanosuchus demonstrating the evolution of one to another and another of these three sister taxa. The derived sister taxon is Nyctiphruretus. An ancestor includes a sister to Orobates. The size increase is important.

A Larger Tree Nests Saurorictus Elsewhere
Here the large reptile tree nested Saurorictus with Lanthanosuchus and Macroleter, far from the captorhinids.  Like another sister, Nyctiphruretus, Saurorictus lacked an indented squamosal and lacked a lateral temporal fenestra. To move Saurorictus to the captorhinids requires an additional 17 steps. Saurorictus also nests between Stephanospondylus (which leads to turtles) and Nyctiphruretus (which leads to owenettids and lepidosauriformes). So this is a key taxon. And a tiny one!

Figure 3. The supratemporal in Saurorictus (ST, in pink) was originally considered a part of the parietal which is reasonable given their paradigm that Saurorictus was a captorhinid.

Missing a Supratemporal? Maybe Not.
The worst preservation in SAM PK-8666 occurs on the skull roof. The parietal is barely present and the pineal opening is nowhere to be found. Just dorsal to the squamosal is a plate-like bone that Modesto and Smith (2001) considered a parietal lacking a supratemporal between it and the squamosal. The skull of Saurorictus does indeed resemble that of captorhinids in general. The supratemporal in captorhinids is a tiny splint of bone and such a bone is indeed missing. I added the Saurorictus data (lacking a supratemporal) to the large reptile tree and was surprised to see it nested with Lanthosuchus and Macroleter, taxa with a large, plate-like supratemporal. Now the lack of a supratemporal seemed to be a very odd autapomorphy. Reexamining the published image (Modesto and Smith 2001) of Saurorictus I realized that the corner of bone originally labeled as a parietal was a large and mislabeled plate-like supratemporal, matching sister taxa.

Figure 4. Saurorictus nests with Macroleter and Lanthanosuchus.

Different and Similar
At first it would appear odd that round-skulled Saurorictus should nest with the cantilevered skulls of Macroleter and Lanthanosuchus, but round-skulled Nyctiphruretus also nests nearby. Diadectes and Procolophon also nest nearby, but Orobates is a more basal sister that shares certain plesiomorphic traits with Saurorictus. Here, apparently, we’re seeing a small, simple, pleisomorphic taxon that gives rise to the various odder, more derived sisters.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Modesto SP and Smith RMH 2001. A new Late Permian captorhinid reptile: a first record from the South African Karoo. Journal of Vertebrate Paleontology 21(3): 405–409.

wiki/Saurorictus