12-2 Trampled Ground in an Exceptional Tracksite, Lower Cretaceous Glen Rose Formation, Texas: Implications for Dinosaur Behavior and Paleoenvironment

Session: Advances in ichnology: walking in Memphis and other records of behavior (Posters)

Poster Booth No.: 87

Presenting Author:

Joshua Colasante

Authors:

Colasante, Joshua M.¹, Pittman, Jeffrey G.², Hasiotis, Stephen T.³

(1) Department of Geology, University of Kansas, Lawrence, KS, USA, (2) Ouachita Mountains Biological Station, Mena, AR, USA, (3) Department of Geology, University of Kansas, Lawrence, KS, USA,

Abstract:

The middle part of the Lower Cretaceous (early Albian) Glen Rose Formation contains several track-bearing horizons within a ~3 m succession of carbonate deposits exposed along the confluence of Fall Creek and the Lampasas River, in southeastern Lampasas County, Texas. One of these intervals consists of a ~50-cm-thick carbonate mudstone unit that contains hundreds of dinosaur tracks exposed in a 100 m–long by 14 m–wide outcrop observed in plan-view and in cross-section; this deposit was first reported on by Pittman in 1990. The tracks are predominately tridactyl and show a large variation in preservation of form due to medium consistency and the overlapping of prints, here tentatively assigned to cf. Irenesauripus and cf. Columbosauripus (theropod? tracks) as well as Brontopodus birdi (sauropod tracks). Azimuth measurements for direction of travel were taken on 130 of the tridactyl tracks based on the compass bearing of the track midline and plotted on a stereonet. Although chaotic in appearance, the plotted azimuths show that these track directions were nonrandom and strongly bimodal. The dominant track direction was eastward (73 tracks), with orientations between 85°–90°, and a secondary westward track direction (57 tracks) between 265°–275°. No other track directions were recorded outside this bimodal range (e.g., no track orientations perpendicular to the bimodal axis). This implies that the dinosaurs had a preferential direction of travel that was approximately 180° or in an easterly–westerly direction.

The trampled carbonate mudstone unit is massive, exhibiting an ichnofabric index of 6 (>100% bioturbation) and contains the trace fossils Arenicolites and Teichichnus. This trace-fossil assemblage, combined with the lack of evidence of bedding, subaerial exposure, and/or pedogenesis, indicates that the trampled ground was produced under subaqueous conditions within a protected shallow marine environment, such as a lagoon. Two hypotheses are proposed for the orientation of the dinosaur tracks within the trampled ground. The dinosaurs were moving in a preferred direction: 1) following the fall of low tide and the rise of high tide; or 2) traveling parallel to the shoreline across a back-barrier lagoon. The remainder of this study will focus on resolving the paleoenvironmental and paleoecological settings of the Glen Rose Formation at this locality.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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