19 Council on Undergraduate Research (Posters) II

Friday, 19 May 2006
8:00 AM - 11:40 AM

QUADRUPED TRACKS FROM THE LOWER JURASSIC MOENAVE FORMATION (HETTANGIAN), ST. GEORGE DINOSAUR DISCOVERY SITE AT JOHNSON FARM, WASHINGTON COUNTY, UTAH

Paper number: 19-19
Program: THEME SESSIONS
Time: 8:00 AM – 11:40 AM

Authors

Abstract

A large collection of small quadruped footprints from the Lower Jurassic Whitmore Point Member, Moenave Formation (Hettangian), St. George Dinosaur Discovery Site at Johnson Farm (SGDS), St. George, Utah, were preserved on mudflats and beaches along the western edge of ancient Lake Dixie, an oasis that formed during the deposition of the Wingate erg to the east and northeast. A unit consisting of fine-grained sandstone, siltstone, and mudstone, referred to as the “Top Surface” of four track-bearing horizons, has over 350 mapped quadruped tracks. The “Top Surface” is located approximately 53 m above the top of the Dinosaur Canyon Member at the SGDS. There are a variety of quadruped tracks in this location, many of which include both manus and pes prints. By far the most common tracks belong to the ichnotaxon Batrachopus, attributed to a small crocodylomorph, possibly Protosuchus, which is well known from the Dinosaur Canyon Member in northeastern Arizona.

Measurements of the quadruped tracks and partial trackways, as well as acetate tracings and photographs, confirm the majority of footprints are indeed Batrachopus. Three other forms are recognized from SGDS: (1) possible sphenodontian tracks with elongate manual and pedal digits, potentially pertaining to the poorly known ichnotaxon Exocampe; (2) small (size ranges:2.7-2.8cm lengths; 1.3-1.7cm widths), four-toed, highly digitigrade pes prints resembling synapsid tracks from the Early Jurassic of Argentina, though these tracks may be extramorphological variants of Batrachopus; and (3) larger (size ranges:4.2-6cm lengths; 3.4-5cm widths), possible synapsid pes prints with four, and sometimes five, digits, nearly all showing partial metatarsal impressions. One of these five-toed specimens exhibits clear claw marks and is covered with skin impressions.