The Procolophonidae

The Procolophonidae are odd, little-to-medium-sized, plant-eating reptiles that evolved from a sister to the basal diadectid, Orobates, survived the Permian extinction, but did not survive the Triassic. Here are a few of them (Fig. 1).

Figure 1. Click to enlarge. Procolophonids including Procolophon, Pentaedrusaurus, Colobomycter, Hypsognathus and Leptopleuron. Orobates is the outgroup taxon.

Figure 1. Click to enlarge. Procolophonids including Procolophon, Pentaedrusaurus, Colobomycter, Hypsognathus and Leptopleuron to scale. Orobates is the outgroup taxon. Note the large front teeth on Orobates and Colobomycter and the miniaturization that occurred between them. Arrows indicate more derived taxa. 

Yesterday we looked at the orbit in Hypsognathus. As procolophonids evolved, the orbits migrated to the top of the skull and elongated to accommodate the bulge of the temporal muscles. Procolophonids also evolved horns developed on the cheeks.

Most workers consider owenettids to be basal to procolophonids, but actually owenettids are basal to lepidosauriformes. Milleretta and diadectids like Orobates are basal to both Diadectes and Colobomycter + Procolophon. The large reptile tree tests more taxa giving each taxon more opportunities to nest more parsimoniously. This clade gave rise to no descendants.

Broom 1939 coined the term Procolophonoidea to include the Owenettidae and the Procolophonidae, but the two clades are not directly related.

Seeley 1888 coined the term Procolophonia to incude the above taxa plus the Pareiasauria, but the Pareiasauria are not related to Procolophon and kin despite the convergent development of expanded cheek bones.

Laurin & Gauthier 1996 define the Procolophonia cladistically as “The most recent common ancestor of pareiasaurs, procolophonids, and testudines (Chelonia), and all its descendants. The most recent common ancestor of these taxa, according to the large reptile tree, is Milleretta and all of its descendants include all living and extinct lizards, probably not what they intended.

deBraga & Reisz 1996 coined the term Ankyramorpha to include the above taxa plus Lanthanosuchus and Acleistorhinus, two taxa that are not even related to each other according to the large reptile tree. See what happens when you exclude pertinent sister taxa? We really need the large reptile tree to set the stage for smaller studies.

Romer 1964 coined the term Procolophonomorpha to include Nyctiphruretus and the above taxa.

Jalil and Janvier (2005) considered the clade  Procolophonomorpha = to Ankyramorpha.

References
deBraga M and Rieppel O. 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal of the Linnean Society, 120: 281-354.
Jalil N-E and Janvier P 2005. Les pareiasaures (Amniota, Parareptilia) du Permien supérieur du Bassin d’Argana, Maroc. Geodiversitas, 27(1): 35-132.
Ruta M, Cisneros JC, Liebrecht T, Tsuji LA and Müller J 2011. Amniotes through major biological crises: Faunal turnover among Parareptiles and the end-Permian mass extinction. Palaeontology 54(5):1117.

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