Tangasaurus: the long and the short of it

Earlier I presented Tangasaurus as “the great, great diapsid grandfather of birds and crocs,” but on reexamination a new nesting was recovered in the large reptile tree. Below corrections have been made to the earlier posting.

Tangasaurus mennelli (Haughton 1924) was a small aquatic(?) diapsid of the Late Permian. It is known from only two specimens collected in 1922 by F. P. Mennell in Tanzania. Currie (1982) reported over 300 partial specimens were attributed to Tangasaurus, but reattributed most of them elsewhere. Previous analyses by Bickelmann et al. (2009) and Reisz et al. (2011) nested Tangasaurus with Acerosodontosaurus and Hovasaurus and also with Thadeosaurus and Claudiosaurus, all basal diapsids. The large reptile tree found a similar nesting.

Tangasaurus in long-necked variety and short-necked lectotype (in blue).

Figure 1. Tangasaurus in a long-necked variety (but is it Tangasaurus?) and short-necked lectotype (in blue). According to Currie (1982) Tangasaurus is known from two specimens. A part of the poorly preserved skull is known only in the electrotype. The long-neck version is a close relative. The gastralia indicate a wide torso in the relative, not the lectotype.

Reptiles like Tangasaurus don’t get all the press they deserve. With its powerful limbs and sculling tail, Tangasaurus appears well-suited to life on land and in the water. 

 Thadeosaurus

Figure 2. Thadeosaurus, another taxon at the base of the terrestrial diapsids with a poorly known skull. Here the pectoral girdle is fused. The sternae are ossified. There were fewer cervicals and more dorsals here than in Tangasaurus.

Haughton (1924) described a long, powerful, flattened tail and presumed an aquatic existence. The long-necked specimens do not include very much of the tail and what is present does not seem particularly flattened or aquatic in design in the manner of Hovasaurus, for instance. To me, this seems like a powerful terrestrial reptile. The size of the transverse processes at the base of the tail are notable. So is their anterior curvature. These reflect the size of the caudofemoralis muscles driving the large hind limbs. The short-necked specimens had the tall flattened tail of an aquatic taxon.

Tangasaurus juvenile.

Figure 3. Long-neced Tangasaurus? juvenile. Scale unknown. Here the skull is present but hard to make out. A foot is reconstructed with PILs. The ribs indicate a narrower deeper torso. Please provide a high resolution image if you have one. I’d like to reexamine the skull, which is slightly exploded here, apparently with a leg  sticking through the jaws at the orbits.

The large reptile tree divided lizards and turtles (and kin) from mammals and archosaurs (and kin). That makes traditional diapsids diphyletic. Among the true diapsids (Petrolacosaurus and kin, derived from synapsid protodiapsids) the branches split into the Enaliosauria (marine diapsids) and the terrestrial diapsids led by Thadeosaurus.

Basal diapsids including Araeoscelis, Hovasaurus, Adelosaurus, Acerosodontosaurus, Tangasaurus and Thadeosaurus.

Figure 4. Basal diapsids including Araeoscelis, Hovasaurus, Adelosaurus, Acerosodontosaurus, Tangasaurus and Thadeosaurus, all to scale.

Now, with Tangasaurus added to the large reptile tree we have a new diapsid taxon not far from Adelosaurus (Fig. 4) at the base of the Enaliosauria.

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
Bickelmann C, Müller J and Reisz RR 2009. The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of ‘‘younginiform’’ reptiles”. Canadian Journal of Earth Sciences 49: 651–661.
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
Haughton SH 1924. On Reptilian Remains from the Karroo Beds of East Africa. Quarterly Journal of the Geological Society 80 (317): 1–11.
Reisz RR, Modesto SP and Scott DM 2011. A new Early Permian reptile and its significance in early diapsid evolutionProceedings of the Royal Society B 278 (1725): 3731–3737.

wiki/Tangasaurus

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