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.
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