A LATE JURASSIC LACUSTRINE BIOTA FROM THE MORRISON FORMATION OF COLORADO

Several Morrison Formation quarries in Temple Canyon, near Cañon City, Colorado are yielding a diverse biota from a laterally extensive freshwater limestone and associated overlying carbonate mudstone units. The fossiliferous lacustrine limestone unit varies in thickness from 10 to 50 centimeters and grades upward into fossiliferous carbonate mudstones. A diverse flora is represented by cycads, conifers, ginkos, ferns, and horsetails. An abundant invertebrate fauna consists of ostracodes, concostrachans, prosobranch and pulmonate gastropods, caddisflies (represented by numerous larval cases) and an orthopteran hindwing, representing the first unambiguous insect body fossil from the Morrison formation of North America.

Abundant fish remains, ranging from isolated scales to complete articulated specimens, have been recovered from the Temple Canyon localities. At least six distinct fish taxa can be identified. Halecomorphs are represented by one species of amiid amiiform and a basal halecomorph possibly equivalent to the 'parasemionotiform' grade. Teleosts are represented by a single species of 'pholidophoriform' grade. Two other species of actinopterygian are also represented; a semionotid neopterygian and a coccolepid 'paleoniscimorph'. The dipnoan 'Ceratodus' guentheri is represented by a nearly complete skull and rare isolated scales. Identifiable tetrapod material is rare, and only the chelonian Glyptops sp. and a possible anuran have been recovered to date.

Prosobranch gastropods and ostracodes typically indicate open, perennial, well-oxygenated waters. However, the presence of pulmonate gastropods and conchostracans generally suggests oxygen-poor, sometimes ephemeral conditions, possibly indicting that varying water conditions existed within the lake system.