A new jugal for Acleistorhinus

Earlier work by yours truly
on Acleistorhinus relied on drawings of the specimen (Fig. 3). Here (Fig. 1) a DGS tracing (colorizing skull bones) of photos from the original paper (Daly 1969) reveals a slightly new interpretation of the skull, and the jugal in particular.

Figure 1. Acleistorhinus skull with bones colorized (on left) along with reconstructions in dorsal and lateral view (on right). Note the distinct jugal restored here with two posterior processes arising from the postorbital process, as in Delorhynchus.

Figure 1. Acleistorhinus skull with bones colorized (on left) along with reconstructions in dorsal and lateral view (on right). Note the distinct jugal restored here with two posterior processes arising from the postorbital process, as in Delorhynchus. Click to enlarge. Note the holes in several skull bones. The middle posterior process of the jugal is broken in situ and overlying the lower posterior process. Essentially both Delorhynchus and Acleistorhinus had dual lateral temporal fenestrae.

Acleistorhinus pteroticus (Daly 1969) Early Permian, ~3.5 cm skull length was consiered by DeBraga (2001, 2003) and DeBraga Reisz (1996) to be a Parareptile related to Lanthanosuchus, which is a clear mismatch. Daly (1969) considered Acleistorhinus a procolophonid. Here, in the large reptile tree, Acleistorhinus is derived from a sister to the RC14 specimen of Milleretta, is a sister to Delorhynchus (below; Reisz, Macdougall  and Modesto 2014) and phylogenetically precedes the turtle-like (but not relatedEunotosaurus (Fig. 2).

Figure 2. Acleistorhinus compared to sister taxa, Delorhynchus and Eunotosaurus.

Figure 2. Acleistorhinus compared to sister taxa, Delorhynchus and Eunotosaurus.

The middle posterior process of the jugal in Acleistorhinus
is broken in situ and overlying the lower posterior process. Essentially both Delorhynchus and Acleistorhinus had dual lateral temporal fenestrae.

Since both Eunotosaurus and Milleretta 
had expanded ribs, it is likely that Acleistorhinus did so too. We do not know the post-crania at present.

Figure 3. The earlier attempt at reconstructing the skull of Acleistorhinus based on drawings in

Figure 3. The earlier attempt at reconstructing the skull of Acleistorhinus based on drawings in DeBraga and Reisz 1996. The interpretation of the temple region changes the most between this version and figure 1. No other taxa have such a temporal region, but the new interpretation resembles that of Delorhynchus. 

The new data
on Acleistorhinus did not change its placement in the large reptile tree. I did not have access to any of the specimens listed above. Even so, the new data further unites two taxa, Delorhynchus and Acleistorhinus, that had been earlier united by a suite of traits. Colorizing the bones greatly helps produce the reconstruction.

References
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.
Reisz RR, Macdougall MJ and Modesto S 2014. A new species of the parareptile genus Delorhynchus, based on articulated skeletal remains from Richards Spur, Lower Permian of Oklahoma. Journal of Vertebrate Paleontology 34:1033–1043.

wiki/Acleistorhinus

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