Reinterpretation of Climactichnites Logan 1860 to include subsurface burrows, and erection of Musculopodus for resting traces of the trailmaker

Abstract

Based on a thorough examination of field and museum Climactichnites specimens, two species of this trace are recognized, each representing a unique behavioral variant produced by a soft-bodied animal in Late Cambrian intertidal environments. C. wilsoni represents surface-produced trails, whereas C. youngi is re-erected for burrows produced below the surface. Burrowing behavior is supported by: 1) the presence of C. youngi within, rather than on, the surface of beds; 2) the orientation of some burrows inclined to bedding; and 3) the occasional presence of distinct burrow fills. Burrows can also be distinguished morphologically from surface traces by the absence of lateral ridges and the presence of fine, mm-scale striations or grooves superimposed on the transverse bars and furrows. Burrowing behavior for the Climactichnites trailmaker was previously unknown and thus represents a new, although not entirely unexpected, behavior for this mollusk or mollusk-like animal. The body impression of the sedentary animal is removed to Musculopodus sedentarius n. igen. and isp. In the future, Musculopodus may be expanded to include the resting traces of other soft-bodied animals known from the fossil record. Currently, Climactichnites is known only from very shallow to emergent strata of North America; reports of this fossil in other parts of the world are misidentified trails produced by other animals.