REVISITING ARTHUR LAKES’ LOST QUARRIES: INITIAL SURVEY OF UNDESCRIBED YALE PEABODY JURASSIC MORRISON FOSSIL MATERIAL COLLECTED FROM MORRISON CO (1877-1879)

The Yale Peabody Museum (YPM) collections contain extensive fossil material collected by Arthur Lakes’ excavations (1877-1879) into the Jurassic Morrison Formation near the town of Morrison, CO. In this area, the Morrison Formation consists of a quartz cemented quartz arenite, with fluvial to ephemeral lacustrine depositional environments. The YPM collections include fossil material from six sites.

Quarry 1 are fluvial deposits with numerous clay rip-up clasts within channel lag deposits. The YPM collections survey uncovered the first diplodocid teeth from Quarry 1 as well as crocodillimorph material (tooth crown) and undescribed post-cranial material from a camarasaurid. Quarry 5, the type location for Stegosaurus armatus, is fluvial sandstone. This site contains sauropod cranial elements, originally misattributed to S.armatus, as well as proximal-caudal and pedal material from S.armatus. Additionally, the partial cranium of a crocodilimorph was identified. Quarry 8 is a gray alluvial mudrock. Localized reducing conditions preserved diagnostic post-cranial material from A.ajax and material from a potential stegosaurid. Quarry 10, the type location for Apatosaurus ajax, is an ephemeral lacustrine environment with limited degrees of biodiversity. This survey expands the biodiversity present including rediscovered turtle material at this site. Quarry 11 is fluvial sandstone with high degrees of quartz cementation. Channel lags contain fragmentary, but describable, fossil material with microsites in adjacent overbank deposits. New material include theropod and camarasaur crowns and fragmentary rib material. Nugent’s Quarry is an overbank environment with a variety of undescribed fossil material. This site contains fragmentary theropod limbs, turtle shell, fragmentary stegosaur and sauropod material including the partial ischium of A.ajax.

This survey reveals that within the local Morrison formation, apatosaurs are unusually common and aquatic crocodilimorphs and turtles are comparatively rare; supporting the interpretation of ephemeral bodies of water at this locality during the time of deposition. The recent survey of undescribed material underscores the importance for maintaining historical collections and periodically reexamining these specimens under more recent paradigms.