Another Look at Amotosaurus

Amotosaurus

Figure 1. Amotosaurus reconstructed from data in Fraser and Rieppel (2006).

Amotosaurus rotfeldensis SMNS 50830 (Wild 1980) was originally considered a juvenile Tanystropheus antiquus, but Fraser and Rieppel (2006) determined that only eight cervicals were present, a shagreen of denticles covered the vomers, palatines and pterygoids, the second sacral rib was bifurcate, the tarsus was well-ossified and three distal tarsals were present. Due to the ossified tarsus they considered the small specimen an adult.

Ooops…
Unfortunately Fraser and Rieppel (2006) reported that Langobardisaurus had 12 rather than 8 cervicals and so missed an important shared trait. Here Amotosaurus nests with Langobardisaurus and they shared a longer mt 4 relative to mt 3 among several other characters. The scapula is much enlarged in Amotosaurus, as in Tanystropheus. The ventral pubis and ischium are in contact with one another, as in Cosesaurus, which also shares a longer metatarsal 4. The mandible is ventrally concave as in Langobardisaurus. The posterior teeth are difficult to see, but there seems to be little indication of anything but simple compressed cone shapes present, as in Tanystropheus. Pedal 5.1 was relatively shorter.

Protorosaur? No.
Protorosaurus nested near the base of the Archosauriformes. Langobardisaurus and Amotosaurusnested within the Lepidosauriformes, within the Tritosauria.

Why Ignore Langobardisaurus?
In their conclusion,  Fraser and Rieppel (2006) practically ignored Langobardisaurus. They reported, “At present it can be said that Amotosaurus probably occupies a position intermediate between Tanystropheus and Macrocnemus.” According to the present tree, that’s a position currently occupied by Langobardisaurus, here considered the closest sister of Amotosaurus and similar in size.

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
Fraser NC and Rieppel O 2006. A new protorosaur (Diapsida) from the upper Bundsandstein of the Black Forest, Germany. Journal of Vertebrate Paleontology 26(4):866-871.
Wild R 1980. Tanystropheus (Reptilia: Squamata) and its importance for stratigraphy. Mémoires de la Société Géologique de France, N.S. 139:201–206.

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