A trace fossil made by a walking crayfish or crayfish-like arthropod from the Lower Jurassic Moenave Formation of southwestern Utah, USA

Abstract

New invertebrate trace fossils from the Lower Jurassic Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm (SGDS) continue to expand the ichnofauna at the site. A previously unstudied arthropod locomotory trace, SGDS 1290, comprises two widely spaced, thick, gently undulating paramedial impressions flanked externally by small, tapered to elongate tracks with a staggered to alternating arrangement. The specimen is not a variant of any existing ichnospecies, but bears a striking resemblance to modern, experimentally generated crayfish walking traces, suggesting a crayfish or crayfish-like maker for the fossil. Because of its uniqueness, we place it in a new ichnospecies, Siskemia eurypyge. It is the first fossil crayfish or crayfish-like locomotion trace ever recorded.

A review of the glacial environment arthropod trace fossils Umfolozia and Warvichnium with the description of new ichnotaxa

“…Q, Copeza triremis (traced from Hitchcock 1858 by Rose et al . 2021). R, Lithographus hieroglyphicus (traced from Hitchcock 1858 by Rose et al .…”

“…R, Lithographus hieroglyphicus (traced from Hitchcock 1858 by Rose et al . 2021). S, Stiallia berriana (traced from Smith 1909 by Rose et al .…”

“…S, Stiallia berriana (traced from Smith 1909 by Rose et al . 2021). T, Arcuites bertiensis (holotype; traced from Vrazo & Ciurca 2018, fig.…”

“…2O) has elongated tracks as in U. terere , but differs by: (1) having paired continuous medial linear impressions that are simple; and (2) having a series of up to four tracks with a larger separation between sets of tracks (Walker 1985). Siskemia eurypyge Rose et al ., 2021 (Fig. 2P) differs from U. terere by having: (1) sinuous medial impressions with occasional intermittence and alternating symmetry; and (2) tracks that are ellipsoidal to circular in shape and occur in series of two to three tracks (Rose et al .…”

“…2P) differs from U. terere by having: (1) sinuous medial impressions with occasional intermittence and alternating symmetry; and (2) tracks that are ellipsoidal to circular in shape and occur in series of two to three tracks (Rose et al . 2021).…”