Cleaning up mistakes part 4 – Two kinds of Tangasaurus?
Earlier here and here we looked at new nestings within the large reptile tree resulting from corrections to existing data brought on by reexamination following the addition of new taxa. Today we’ll look at one more.
Claudiosaurus had a long neck. Closely related Hovasaurus did not.
A sister to Tangasaurus had a long neck. The lectotype of Tangasaurus did not (Fig. 1). Earlier we looked at the long-necked version. I recently found the Currie (1982) paper describing and illustrating the lectotype (in blue below), hence this blog.
Figure 1. Tangasaurus in long-necked variety and short-necked lectotype (in blue). Strangely, of the 30 or so specimens known, none preserve the skull in total, nor is a complete tail preserved. There are other differences here, including rib length, relative limb length. Those are the jaws of the electrotype at far left. Note, the pectoral girdle has been upgraded from a previous reconstruction.
All the above named taxa descended from long-necked ancestral diapsids, like Eudibamus, Petrolacosaurus, Araeoscelis and Adelosaurus. And long necks continued in many, but not all subsequent taxa. I find it odd that such closely related taxa had such distinctly different neck lengths. It’s a chin scratcher.
What I also find interesting at this node at the base of the Enaliosauria is the development of aquatic and marine descendants, like Claudiosaurus and its descendants from bipedal, lizardy ancestors, like Eudibamus. This is all the more interesting because we see similar evolutionary patterns at the base of the Archosauria (small Triassic bipedal crocs evolve to become the large aquatic crocs of the Jurassic and present day) and at the base of the Tritosauria (small presumably occasionally bipedal huehuecuetzpallids evolve to become large aquatic tanystropheids).
Currie (1982) made note of the sternum in Tangasaurus, along with the elongated neural spines on the tail as traits shared with Hovasaurus. The limbs are robust in Tangasaurus, as in Galesphyrus, another basal diapsid.
Earlier I nested Tangasaurus at the base of the thadeosaur clade leading to dinos and crocs. The new nesting takes Tangasaurus back to the base of the Enaliosauria not far from Hovasaurus and Adelosaurus and these taxa precede Claudiosaurus and the core of the Enaliosauria.
Clearly the two putative Tangasaurus specimens are not congeneric, but they are most closely related to each other among all the taxa tested. One may need to be renamed. Sure would be nice to find a skull someday.
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
Currie P 1982. The osteology and relationships of Tangasaurus mennelli Haughton. Annals of The South African Museum 86:247-265. http://biostor.org/reference/111508
2012-12-30 11:47:16
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