Washington, June 25 ( ANI ): A very distinctive creature known as a pareiasaur roamed the desert in what is now northern Niger during the Permian era.
Although at first blush these features seem to suggest that Bunostegos was an evolutionarily advanced pareiasaur, it also had many primitive characteristics.
Pareiasaurs were large, herbivorous reptiles that were common across Pangea (single supercontinent) during the Middle and Late Permian, about 266-252 million years ago.
Most pareiasaurs had bony knobs on their skulls, but Bunostegos sported the largest, most bulbous ones ever discovered.
Tsuji's analysis showed that Bunostegos was actually more closely related to older and more primitive pareiasaurs, leading to two conclusions: first, that its knobby noggin was the result of convergent evolution, and second, that its genealogical lineage had been isolated for millions of years.
The published strict consensus of the 6 MPTs of the Muller and Tsuji (2007) analysis found the position of Nyctiphruretus and the Bolosauridae (Eudibamus and Belebey) unresolved within a grouping including the other Mezen River non-pareiasaur parareptiles, pareiasaurs and procolophonoids (Muller and Tsuji 2007 fig.
Scoring for the pareiasaur Bradysaurus was changed to '2' and Procolophon was scored as '1' (see discussion for this scoring in section 4.
1997): Pareiasaur phylogeny and the origin of turtles.
The phylogenetic analyses of Lee (1995), Tsuji (2006) and Muller and Tsuji (2007), however, do not support the view of Nyctiphruretus as a basal 'procolophon' and instead recognise Nyctiphruretus as a non-procolophonoid parareptile, possibly more closely related to pareiasaurs than procolophonoids (Tsuji, 2006).
There are two states for this character, single cusp (0) or two or more cusps (1), in Tsuji (2006), and only pareiasaurs (Bradysaurus and Scutosaurus) are coded as having state one.
In Tsuji (2006) 'Parareptilia' includes millerettids, lanthanosuchids, bolosaurs, procolophonoids, pareiasaurs, and 'nyctipthruretians' (Macroleter and Nyctiphruretus) and Mesosauria is the sister-group of 'Parareptilia'.
In fact, bootstrap support was much better (56 %) for a clade consisting of Macroleter and the pareiasaurs (Scutosaurus and Bradysaurus) that was not recovered in the MPT of this analysis but was present in the MPT of Tsuji (2006).