Phonodus and Colobomycter still bother me
Phonodus and Colobomycter (Fig. 1) are represented by small partial skulls of unusual morphology.
Figure 1. Basal placodonts to scale.
Vaughn (1958) initially considered Colobomycter an eothyrid and for good reason, considering the length of its cone-shaped teeth. Modesto and Reisz (1999) considered it a parareptile close to Acleistorhinus. We talked about Colobomycter earlier here.
Phonodus was considered a sister to Procolophon by Modesto et al. (2010, Fig. 2). We talked about Phonodus earlier here.
Figure 2. Which one does not belong? Procolophon (in box) nests far from these other enaliosaur taxa. Phonodus demonstrates the closure and arching of the lateral temporal fenestra in placodonts from a Claudiosaur-like ancestor. The ghosted area between the arrows indicates hypothetical reconstruction.
I nested both with the shelled placodonts. Moving either to other nodes on the tree adds ten steps and that’s based on not that many skull traits.
Colobomycter is from the Early Permian. Phonodus is from the Early Triassic. Both have the long low naris of Claudiosaurus (Fig. 2). Phonodus has button-like teeth. Colobomycter has a premaxillary tusk and no button-like teeth.
What bothers me is the lack of post-crania. If both are related to shelled placodonts, there should be some shells (carapace +plastron) around. So far shells have not been found. The small size is also a curiosity.
What also bothers me is the low placement of the naris. Other placodonts have a dorsolateral naris, but Phonodus shares this and other traits with Henodus (Fig. 2). The low large naris in Colobomycter hearkens back to Claudiosaurus.
Both have been considered “enigmas” and for good reason. They really don’t look that much like placodonts either, except Phonodus does have those button-like teeth. Perhaps these represent other branches of this strange-toothed family and perhaps provide some course of evolution toward their other strange morphologies.
Like I said, move them anywhere else on the large reptile tree and the nesting becomes almost instantly less parsimonious. So, we’ll leave it to the matrix until further specimens arrive to settle this issue.
Sometimes it just is not that easy. That’s what bothers me. BTW, Sean Modesto (pers. comm) has not tested these taxa against members of the Placodontia. Maybe someday.
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
Vaughn PP 1958. On a new pelycosaur from the Lower Permian of Oklahoma, and on the origin of the family Caseidae. Journal of Paleontology 32:981–991.
Modesto SP and Reisz R R 1999. Colobomycter pholeter from the Lower Permian of Oklahoma: a parareptile, not a protorothyridid. Journal of Vertebrate Paleontology 19(3): 466–472.
Modesto SP and Reisz RR 2008. New material of Colobomycter pholeter, a small parareptile from the Lower Permian of Oklahoma. Journal of Vertebrate Paleontology 28 (3): 677–684.
Modesto SP, Scott DM, Botha-Brink J and Reisz RR 2010. A new and unusual procolophonid parareptile from the Lower Triassic Katberg Formation of South Africa. Journal of Vertebrate Paleontology 30 (3): 715–723. doi:10.1080/02724631003758003.
wiki/Colobomycter
2012-11-01 21:02:36
Source: http://pterosaurheresies.wordpress.com/2012/11/02/phonodus-and-colobomycter-still-bother-me/
Source:
