Earlier we looked at basal anomodonts, noting that Biseridens should not be part of this inclusion set because it is a basal dinocephalian. Instead Microurania (Fig. 1) and Stenocybus should be included as they nest in that basal position in the large reptile tree.
There are few references for the rarely studied Russian therapsid Microurania (Ivakhnenko 1995, 2003, Middle Permian, Lower Tatarian), and only one illustration that I know of. Yet it is an important transitional taxon leading to the base of the Dicynodontia.
Figure 1. All that is known of Microurania, a basal therapsid, basal anomodont and dicynodont precursor. Image from Ivakhnenko 2003.
Close to Stenocybus and Nikkasaurus at the base of the Therapsida, the proto-dicynodont Microurania (Fig. 1) retained upper and lower single canines. It was considered a biarmosuchian but nests in the therapsid subset of the large reptile tree closer to Otsheria and Venjukovia {now Ulemica] (Fig.1) at the base of the Anomodontia.
The holotype (PIN 4337/1) is a partial skull with leaf-like postcanine teeth similar to those in Phthinosuchus.
Microurania has a shorter snout than Biarmosuchus, closer to Stenocybus with which it shares procumbent teeth. Microurania retained canines, unlike Nikkasaurus.
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Figure 2. Basal therapsids and sisters to their ancestors. The short skull of Stenocybus is retained by anomodonts like Microurania, dromasaurs and dicynodonts. This also demonstrates the present diphyletic therapsids with two lineages arising from basal ophiacodonts.
Figure 4. Basal therapsid family tree. Biseridens nests far from the anomodonts and Microurania.
Plain Jane/Brown Sparrow
Microurania is one of those plain Jane / brown sparrow unspectacular sorts of reptiles. Frankly, it looks kind of boring. The ironic reality is, such “generic” taxa are exactly where evolution is making key transitions. They are blends, hybrids, part this and part that.
Microurania does not have the elevated suborbital/cheek region found in Otsheria, Venjukovia [now UIlemica] and Eodicynodon. The large canines found in dicynodonts may be new traits. Immediate predecessors do not have such large canine teeth.
The Therapsida may turn out to be essentially diphyletic. Stenocybus and the Anomodontia form one branch. Nikkasaurus and the rest of the Therapsida (including mammals) form the other branch. Ophiacodon is currently the most completely known common ancestor, but two scrappy double-canine taxa may be transitional forms.
References
Ivakhnenko MF 1995. New primitive therapsids from the Permian of Eastern Europe, Paleontol. Zh. 1995(4):110–119.
Ivakhnenko MF 2003. Eotherapsids from the East European Placket (Late Permian). Paleontological Journal, 37, Suppl. 4: S339-S464.
The Pterosaur Heresies 