PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 110(1):1-17. 1997. Cretaceous anuran and dinosaur footprints from the Patuxent Formation of Virginia Robert E. Weems and Jon M. Bachman (REW) Mail Stop 926A, U.S. Geological Survey, Reston, Virginia 20192, U.S.A.; (JMB) 115 Windsor Circle, Fredericksburg, Virginia 22405, U.S.A. Abstract. — Footprints of an anuran (gen. et sp. indet.), a theropod dinosaur (Megalosauropus sp.), and an ornithopod dinosaur {Amblydactylus sp.) have been recovered from the Lower Cretaceous Patuxent Formation in Stafford County, Virginia. These footprints are the first record of terrestrial vertebrates from Cretaceous strata in Virginia, and their discovery suggests that the scarcity of bones and teeth in the Patuxent probably is an artifact of preservation. The anuran trackway provides the oldest known direct evidence for hopping loco-motion among these amphibians. The Patuxent Formation has yielded an abundant fossil macroflora from Maryland and Virginia (Fontaine 1889; Ward et al. 1905; Berry 1908, 1910a, 1910b, 1910c, 1911a, 1911b, 1911c, 191 Id; Clark & Mil-ler 1912; Brenner 1967; Wolfe 1972; Doyle & Hickey 1975; Skog 1982, 1988, 1992; Hickey 1986), as well as a diverse paly-noflora (Brenner 1963, Hughes & Moody 1966, Doyle 1977, Doyle & Robbins 1977). In sharp contrast, the only vertebrate ma-terial reported from this unit is a fish skel-eton, found somewhere in the James River valley of Virginia (Berry 1911a). There-fore, it is significant that footprints of an anuran and two kinds of dinosaur have been found north of Fredericksburg, Virginia, in Stafford County (Fig. 1). These prints pro-vide our first glimpse of the Cretaceous ver-tebrate fauna that once existed in Virginia. The Lower Cretaceous Arundel Formation, which overlies the Patuxent Formation in Maryland but not in Virginia (Fig. 2), has produced a diverse but fragmentary verte-brate fauna that includes turtles, crocodiles, and dinosaurs (Lull 1911a, 1911b; Gilmore 1921; Ostrom 1970; Galton & Jensen 1979; Kranz 1989; Weishampel 1990; Martin & Brett-Surman 1992). The diversity of this fauna suggests that a diverse fauna also may have existed while the slightly older Patuxent sediments were accumulating. Un-til the discovery of the footprints described here, however, no direct evidence for such a fauna was available. Location, age, and geologic setting. — The footprints described here were found by Jon Bachman in strata of the Lower Cre-taceous Patuxent Formation in a roadcut on the east side of U.S. Route 1, located 0.25 mi south of Potomac Creek in Stafford County, Virginia (Fig. 1). In its outcrop belt, the Patuxent Formation is approxi-mately 200 to 300 ft thick (Clark & Miller 1912). The unit dips gently and thickens to the east, becoming about 575 ft thick twen-ty-five mi east-southeast of Fredericksburg, near Oak Grove (Reinhardt et al. 1980). In the Fredericksburg region, pre-Mesozoic crystalline rocks directly underlie the Pa-tuxent Formation with profound unconfor-mity. These rocks crop out along the floor of Potomac Creek well to the west of U.S. Route 1 . Because the footprint-bearing out-crop is located toward the eastern margin of the Patuxent outcrop belt, the footprints probably come from the upper half of that formation. However, faults are known ir om the general vicinity of the footprint -1 aring outcrop (Mixon & Newell 197 7 so the
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