Tanystropheus (T/2793 Exemplar C. T/2917 Exemplar K. T/2819 Exemplar Q of Wild 1973) was not a terrestrial predator, but a bipedal, vertically oriented aquatic predator (see below). One can imagine Tanystropheus sitting on the sea floor, emitting a bubble net from its long tracheal reservoir of dead air, rising from below to eat squid and fish concentrated into a small ball near the surface.

Distinct from Macrocnemus, the skull of Tanystropheus had an upturned premaxilla with elongated procumbent teeth. The postorbital and jugal were more robust. The temporal fenestrae were smaller and the quadrate was shorter.

The cervicals were greatly elongated and their number had increased to twelve. Two anterior chevrons were greatly elongated, the so-called heterotopic bones, or these are novel ossifications that may be associated with gender. If so they may have extended the area devoted to egg retention. As in some lizards, including pterosaurs, Tanystropheus likely retained the egg and embryo within its body until shortly before hatching.Given the isometric development associated with this clade, the eggs may have been very long.

The scapula shape was similar to the the smaller specimen of Macrocnemus, with no hint of a strap-like extension. Only four carpals were ossified. Metacarpals II-IV were nearly the same length. Manual digits III and IV were subequal with more similar phalangeal lengths.

The pubis extended more anteriorly. The ischium was broader ventrally. Only a few tarsals were ossified. Metatarsal III was longer than IV. The proximal phalanges were longer than the distal ones. Pedal 5.1 extended further than metacarpal IV, convergent with Cosesaurus.

A marine lifestyle has been established for this taxon based on the sediments in which it is found and on the presence of squid hooks in the torso. These are considered part of the Tanystropheus diet but may have been artifacts following deposition in the sea. Comparisons to Dinocephalosaurus indicate that Tanystropheus has no obvious marine adaptations. However, it would be ideally suited to feeding from the bough of a tree while stationed at its base. Larger Tanystropheus would be suited to taller trees. Tanystropheus may have become adapted to plucking arboreal reptiles out of trees. Smaller ones might have fed on tree-clinging insects, as their cusped teeth indicate. Height may have been key during fights for mating privileges and territory. If taller ones were more successful, their genes would be passed on.

A purported “juvenile” Tanystropheus (Li 2007) was slightly larger than the A specimen and had fish bones in its gut area. The skull is unknown. Since juveniles were identical to adults, without similar specimens nearby, or eggshells, there is no way to tell if this specimen was indeed a juvenile or just small. The skull is unknown. The lack of ossification in the carpus is not a sign of immaturity, but a trait shared by other clade members, large and small, beginning with Huehuecuetzpalli.

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Spiekman SNF, Fraser NC and Scheyer TM 2021. A new phylogenetic hypothesis of Tanystropheidae (Diapsida, Archosauromorpha) and other “protorosaurs”, and its implications for the early evolution of stem archosaurs. PeerJ 9:e11143 DOI 10.7717/peerj.11143

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