Leptosaurus: another transitional taxon between Rhynchocephalia and Rhynchosauria

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Azendohsaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

Leptosaurus pulchellus (Fitzinger 1837, Zittel 1887, Renesto and Viohl 1997; aka: Kallimodon Cocude & Michel, 1963) SCHA 40 Late Jurassic, Tithonian Stage, Germany,
155.7 to 150.8 Ma.

Holotype: Leptosaurus neptunicus Fitzinger 1837.

Rhynchocephalians are generally not so small, but this one is, likely yet another case of miniaturization at the base or transition to a major clade. In this case the SCHA 40 specimen attributed to Leptosaurus (I haven’t seen the holotype) is basal to the much larger Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus. Priosphenodon and rhynchosaurs on the other.

The large reptile tree (still not updated) keeps adding transitional taxa without changing the tree topology. That’s a measure of its strength. And more taxa using the same number of characters keeps dropping that character/taxon ratio.

References
Renesto S and Viohl G 1997. A sphenodontid (Reptilia, Diapsida) from the late Kimmeridgian of Schamhaupten (Southern Franconian Alb, Bavaria, Germany). Archaeopteryx 15:27-46.

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