Middle Jurassic (Bajocian and Bathonian) Dinosaur Megatracksites, Bighorn Basin, Wyoming, U.S.A

Abstract

Two previously unknown rare Middle Jurassic dinosaur megatracksites are reported from the Bighorn Basin of northern Wyoming in the Western Interior of the United States. These trace fossils occur in carbonate units once thought to be totally marine in origin, and constitute the two most extensive Middle Jurassic dinosaur tracksites currently known in North America. The youngest of these occurs primarily along a single horizon at or near the top of the ''basal member'' of the ''lower'' Sundance Formation, is mid-Bathonian in age, and dates to ϳ167 ma. This discovery necessitates a major change in the paleogeographic reconstructions for Wyoming for this period. The older tracksites occur at multiple horizons within a 1 m interval in the middle part of the Gypsum Spring Formation. This interval is uppermost Bajocian in age and dates to ϳ170 ma.Terrestrial tracks found, to date, have been all bipedal tridactyl dinosaur prints. At least some of these prints can be attributed to theropods. Possible swim tracks of bipedal dinosaurs are also present in the Gypsum Spring Formation. Digitigrade prints dominate the Sundance trackways, with both plantigrade and digitigrade prints being preserved in the Gypsum Spring trackways. The Sundance track-bearing surface locally covers 7.5 square kilometers in the vicinity of Shell, Wyoming. Other tracks occur apparently on the same horizon approximately 25 kilometers to the west, north of the town of Greybull. The Gypsum Spring megatracksite is locally preserved across the same 25 kilometer east-west expanse, with the Gypsum Spring megatracksite more extensive in a north-south direction with tracks occurring locally across a 100 kilometer extent. Conservative estimates for the trackway density based on regional mapping in the Sundance tracksite discovery area near Shell suggests that over 150,000 in situ tracks may be preserved per square kilometer in the Sundance Formation in this area. Comparable estimates have not been made for other areas.Similarities between the two megatracksites include their formation and preservation in upper intertidal to supratidal sediments deposited under at least seasonally arid conditions. Microbial mat growth on the ancient tidal flats apparently initiated the preservation of these prints.

The Maastrichtian–Danian Maimará tracksite (Yacoraite Formation, Salta Group), Quebrada de Humahuaca, Argentina: environments and ichnofacies implications

“…It suggests water in movement and a soft ground on which tracks have been preserved. Subaerial exposure may be related to variations in tides, and probably wind action (Kvale et al, 2001;Pazos et al, 2012), although the tracks may have been preserved in the presence of a film of water. Sparite patches indicate obliterated porosity.…”

“…Although the origin of the tracks is unknown and further studies are needed, their particular morphology allows them to be compared to those associated with swim tracks (e.g., Kvale et al, 2001;Ezquerra et al, 2007;Vila et al, 2014). 6.10.…”

“…The comprehensive analysis of mixed suites, formed by vertebrate and invertebrate trace fossils, is an interesting approach to addressing such carbonatic/clastic environments. This kind of work has recently advanced, having already been applied successfully in carbonatic/clastic marine shoreline environments, among others, by Kvale et al (2001) and Pazos et al (2012); in fluvial systems and/or lacustrine environments by Melchor et al (2006), de Gibert and Sáez (2009), Krapovickas et al (2009) and Voigt et al (2013); and inclusive in fluvial-eolian environments by Krapovickas et al (2010). On the basis of the current state of the art, it is suggestive the treatment of such a kind of mixed suites, regarding the expansion of the continental ichnofacies model.…”

An Updated Review of the Avian Footprint Record from the Yacoraite Formation (Maastrichtian-Danian), Northwestern Argentina

“…Structures suggesting cracked microbial mats of the ichnoassemblage II in Maimar a and Quebrada del Tap on are indicative of dry phases that produce mat decay in the mudflat area (Gehling 1999;Catuneanu 2006). The relevant role of microbial mats in track preservation of peritidal environments has been previously observed (e.g., Kvale et al 2001;Marty, Strasser, and Meyer 2009;Carmona et al 2011Carmona et al , 2012Bournod 2011, 2012;Fern andez and Pazos 2013).…”

Unconformity generation and the shift from storm‐dominated to tide‐dominated processes in a Jurassic retroarc foreland basin: Insights from ichnology

“…F I G U R E 2 Chronostratigraphic framework of Middle and Upper Jurassic strata and unconformities (J-1 through J-5) in southern and eastern Wyoming, the Bighorn, and Wind River basins. Data from Peterson (1954aPeterson ( , 1954b, Pipiringos (1957), Pipiringos and O'Sullivan (1978), Imlay (1952Imlay ( , 1967Imlay ( , 1980, Kvale et al (2001), Danise and Holland (2017), Holland and Wright (2020). The J-3 does not extend into Wyoming.…”