FROM THE TOMB OF THE FIRST STEGOSAURUS: A PRELIMINARY REPORT ON NEW SMALL VERTEBRATE SPECIMENS FROM LAKES' QUARRY 5, MORRISON FORMATION OF MORRISON, COLORADO

In 1877 Morrison, Colorado yielded the first rich samples of giant dinosaurs from the American Late Jurassic. Arthur Lakes discovered the type specimen for the genus Stegosaurus (S. armatus, Yale Peabody Museum specimen 1850) in fluvial sandstone he dubbed Quarry 5. The sandstone matrix around the specimen is so exceptionally hard that it discouraged further preparation.

Beginning in 2007, advancements in fossil preparation tools allowed a dedicated staff of volunteers to take on the tedious task of cleaning the type of Stegosaurus. An unexpected by-product is the discovery of small bones and teeth mingled with the stegosaur material, such as two small allosaur crowns. Up till now, small non-dinosaurian vertebrates have been poorly documented at Morrison.

Lakes reported “pterodactyl” and “turtle shell” fragments but identifications were doubtful and all specimens have been lost. Lakes did recover a single skull of the goniopholid crocodilian “Diplosaurus felise” (Yale Peabody Museum specimen 517), from Quarry 5, but no other aquatic vertebrate elements have been demonstrated.

The new preparation has revealed a turtle carapace plate with a surface ornamentation that was hitherto unknown for Morrison Formation chelonians. The new specimen shows a pustulate texture of closely crowded but separate rounded bulges that do not coalesce into ridges. Such micro-pustulate texture is well known among Early Cretaceous solemydid turtles, e.g. Naomichelys from the Cloverly Formation of Montana and Helochelydra from the English Middle Purbeck. Thus the Quarry 5 turtle apparently extends the temporal range for the family Solemydidae into the Kimmeridgian-Tithonian of the Late Jurassic.

Generally, fishes are rare from Morrison Formation quarries with the exception of the ceratodont lungfish. The new preparation of Quarry 5 blocks has recovered a lower tooth plate of a small, primitive ceratodontid lungfish. The geometry of the tooth plate is most similar to Ceratodus guntheri, but the angle between the first and second ridge is shallower than C. guntheri, and the ridge crests are very sharp, especially on the first ridge.

All these additions to the Quarry 5 sandstone fauna have been produced by preparation of only 4,000 cc of rock requiring about 330 hours of labor. Clearly the richness of the fauna has been gravely underestimated.