94th Annual Meeting UNIVERSITY of NEVADA Las Vegas, Nevada June 16 - 19, 2013

Symposium Abstracts

(10) Dinosaurs and Their Neighbors

Tracks of Synapsids and Arthropods in the Aztec Sandstone of Southern Nevada, STEPHEN M ROWLAND* and HEATHER M STOLLER (Department of Geoscience, Box 454010, University of Nevada, 4505 Maryland Parkway, Las Vegas, NV 89154; [email protected], [email protected]). Numerous sites with synapsid and/or arthropod tracks have been discovered in the Lower-Middle Jurassic Aztec Sandstone of Southern Nevada. Synapsida includes mammals and therapsids (aka ‘protomammals’ or ‘mammal-like reptiles’). The most common synapsid tracks belong to the ichnogenus Brasilichnium. These tracks are roughly oval, ranging in width from 2.2 cm to 4.1 cm, usually with an impression of the hindfoot (pes)—but not the front foot (manus)—preserved. Based on its size, the Brasilichnium trackmaker was a squirrel-size animal that was almost certainly a therapsid. Brasilichnium trackways sometimes occur in multiple parallel sets, which strongly suggests that the trackmaker lived gregariously, like prarie dogs and meercats. Two additional synapsid track types do not appear to match any described ichnogenera. One is similar to large Brasilichnium tracks, but is morphologically distinct. The other unnamed synapsid track type consists of tiny footprints the size that a mouse would make, with a stride of about 10 cm. These are our ’10-cm strider’ trackways, we have documented at several localities. We have identified three types of arthropod tracks. One is a well-known Permian and Mesozoic track called Octopodichnus, which may be the track of a scorpion. A more common track type in the Aztec Sandstone is Paleohelcura, which is almost certainly the track of a scorpion. A third type of arthropod track consists of a meter-scale network of burrows, each burrow being 5-7 mm in diameter; we interpret this burrow network to be the nest of an unknown colonial insect.

Tracks of Dinosaurs in the Aztec Sandstone of Southern Nevada: A Progress Report, HEATHER M STOLLER* and STEPHEN M ROWLAND ( Department of Geoscience, University of Nevada, Las Vegas, 4505 Maryland Parkway Las Vegas, NV 89154-4010, [email protected], [email protected]). This investigation focuses on dinosaur tracks in Aztec Sandstone exposures in Red Rock Canyon National Conservation Area and Valley of Fire State Park of southern Nevada, and the Mescal Range of southern California. These three locations preserve different examples of ichnotaxa, allowing me to specifically focus on details of each track and interpret the environment in which the track was laid. Once all details regarding the tracks in these locations are collected, the first complete list of tracks and trackways of dinosaurs, synapsids, and arthropods will be available, permitting a comparison to the tracks in the correlative Navajo Sandstone. Preliminary observations indicate all of the dinosaur tracks appear to be undertracks, which formed on a surface some distance beneath the surface on which the dinosaur walked or ran; most are assigned to the ichnogenus Grallator. To date, 17 tracksites have been documented, with details of individual tracks and trackways recorded at each site as well. Using the trackway dimensions, which are proportional to the animal’s hip height, it is possible to calculate the speed the trackmaker was traveling. The speed of Grallator trackmakers in one location will be compared with those at other locations, which will reveal details regarding the animal’s behavior in all locations. For example, of those speeds calculated to date, the dinosaur was moving approximately 3.8 mph. A more detailed paleoecology study is being prepared as well. Alongside of these data, the paleoenvironment of the Aztec Sandstone will also be reconstructed to provide information about the environment present in the Jurassic, and detailed maps have been created for each trackway at each location.

Nevada’s Mid-Cretaceous Biota, JOSHUA BONDE (Geoscience Department, University of Nevada Las Vegas, 4505 S. Maryland Pkwy, Las Vegas, NV 89154-4010; [email protected]). Over the past ten years there has been a leap in our understanding of the Cretaceous biota of the state of Nevada. Vertebrate fossils are now known from a number of different sites across the state, spanning from the ?Barremian through to the Cenomanian. Deposits from east-central Nevada represent organisms preserved within a Sevier piggy-back basin. Fauna from this unit include: hybodontids, holosteans, testudines, crocodilians, armored dinosaurs, two types of ornithopods, theropods, and perhaps some sauropod material. Cretaceous deposits from southern Nevada represent the foredeep of the Sevier retroarc foreland. Fauna preserved from this unit include: holosteans, dipnoans, testudines, crocodilians, armored dinosaur, two types of ornithopod, two types of theropods, and sauropods. These faunas are most similar in composition to contemporaneous faunas from east-central Utah, implying some ecological continuity from the more coastal deposits of Utah to the more tectonically active regions of Nevada.

Campanian Dinosaurs of the Southern Basin and Range Province, ROBERT McCORD (Arizona Museum of Natural History, 53 N Macdonald St., Mesa, AZ 85201; [email protected]). Although not as famous or as spectacular as Campanian Age faunas of the northern Western Interior, a remarkable, diverse, and little known record of Campanian dinosaurs is preserved in the Fort Crittenden Formation of Arizona, the Ringbone Formation of New Mexico, and the Corral de Enmedio Formation of Sonora. Study of these faunas is hampered by spotty exposures and generally disarticulated remains making even generic identifications difficult. Despite these issues, continued work is being rewarded by increasing knowledge of a surprisingly diverse fauna. Taxa known to date include: ? allosauroid, small ?dromaeosaur, large dromaeosaur, tyrannosaur, ?titanosaur, hadrosaur, chasmosaur, centrosaur, and ankylosaur sensu stricto. Dinosaur trackways, skin impressions, and eggshell are also known as well as pollen, wood, invertebrates, fish, turtle, lizard, and crocodilian remains. Although likely separate sedimentary basins these deposits represent similar intermontane lacustrine, deltaic and riparian systems created by early Laramide uplift with similar source areas. Geochemical evidence suggests seasonal aridity and frequent wildfires. This area represents a productive, unique snapshot of southern, upland dinosaurs of Laramidia.

POSTER PRESENTATION

A Review of the Paleogeography, Sedimentology and Paleontology of the Jurassic and Cretaceous Eolian Sandstones of Gondwana, MARTIN COBOS-NUNEZ, and STEPHEN M ROWLAND (Department of Geosciences, University of Nevada Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154; [email protected]). The Aztec/Navajo/Nugget lithosome of western North America represents an extensive Early Jurassic dunefield deserts inhabited by a diverse fauna of theropod dinosaurs, therapsids, and arthropods. A comparable desert existed in Gondwana during the Jurassic and Early Cretaceous, but it is much less studied. It is represented by the Botucatu Formation of Brazil and the Twyfenfontein Formation of South Africa. The objective of this study is to review the published literature in Portuguese, Spanish and English concerning the paleogeography, sedimentology, and paleontology of Early Jurassic to Early Cretaceous dunefield deserts of Gondwana, and compare these with the Aztec/Navajo/Nugget desert of western North America. Of particular interest are trackways of Brasilichnium, which are found within the Botucatu Formation, and also in the Navajo/Aztec/Nugget sandstones. The published reports on these trackways show that similar trackmakers existed in different regions of Gondwana. These trackways were produced by, although the species of the trackmaker has not been identified. Preliminary results suggest that the Botucatu Formation covers a region of 1.5 million km2 that can be up to 100 m thick, whereas the Aztec/ Navajo/Nugget Sandstone covers a region of 350,000 km2 and up to 670 m thick. The Botucatu Formation expands over what is currently southern Brazil and parts of eastern of Paraguay, Uruguay, and Argentina. The Navajo, Aztec, Nugget Sandstone covers what is now parts of western and mid-west United States. The Botucatu Formation covers more area regionally, but is much thinner, and its broad pieces of exposed dunes are spread widely over South America. The Aztec/Navajo/Nugget Sandstone covers less area, but is much thicker than the Botucatu Formation.