PRELIMINARY REPORT ON NEW VERTEBRATE BURROW LOCALITIES IN THE LOWER JURASSIC NAVAJO SANDSTONE, MOAB AREA, SOUTHEASTERN UTAH: ARCHITECTURAL AND SURFICIAL BURROW MORPHOLOGIES INDICATIVE OF MAMMALS OR THERAPSIDS, AND SOCIAL BEHAVIOR

New localities of vertebrate burrow complexes in wet interdune eolian deposits in the lower part of the Lower Jurassic Navajo Sandstone in and around Canyonlands National Park, near Moab, Utah, provide new information that attributes these structures to mammals or therapsids. Furthermore, the complexity and interconnectedness of burrows within these burrow complexes suggest highly gregarious or social behavior.

The architectural burrow morphology is relatively complex. Burrow complexes are composed of high density, often branched, and interconnected networks of tunnels, short shafts, spiral tunnels, and chambers in low relief, mound-like areas about 0.5 m in preserved relief that cover roughly a 5 x 7 m to 10 x 15 m square area. Mounds are often associated closely with other mound-like complexes. Many of the tunnels, shafts, and burrows weather in three-dimensional relief, showing clearly the complex interrelationship all the burrow components. Burrow diameters are strongly elliptical and have a width-to-height ratio of 1:1.4 to 1:1.9. The vast majority burrow segments are horizontal to subhorizontal tunnels; rarer vertical to subvertical shafts have ratios of 1:1.2 to 1:1.4. Burrows appear to be filled passively with sand.

Relatively smooth burrow walls dominate the surficial burrow morphology. Very little detailed morphology has been observed on the burrow walls. Some of the better-preserved burrows, however, exhibit asymmetrically scalloped surfaces, particularly along the walls of subhorizontal to horizontal tunnels. Scalloped areas range from 2 to 4 cm wide and protrude 0.5 to 2 cm outward from the walls. They are asymmetrical because one end protrudes outward, whereas the other end is flush with the burrow wall.

The architectural and surficial burrow morphologies of these burrows compare very well to extant burrows constructed by mammals with gregarious to social behavior. The scalloped markings on the Navajo burrow walls are very similar to markings found on horizontal and vertical casts of modern mole and ground squirrel burrows. Multiple individuals living together best explains the highly complex Navajo burrow systems, rather than one individual making multiple, interconnected burrows. The Navajo burrow patterns are similar superficially to burrows complexes constructed by extant naked mole-rats and prairie dogs.