A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains, Australia

Abstract

A diverse assemblage of late Pleistocene marsupial trackways on a lake bed in south-western Victoria provides the first information relating to the gaits and morphology of several megafaunal species, and represents the most speciose and best preserved megafaunal footprint site in Australia. The 60e110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid Diprotodon optatum, a macropodid (probably Protemnodon sp.) and a large vombatid (perhaps Ramsayia magna or 'Phascolomys' medius) and possible prints of the marsupial lion, Thylacoleo carnifex. The footprints were imprinted within a short time period, demonstrating the association of the taxa present, rather than the time-averaged accumulations usually observed in skeletal fossil deposits. Individual manus and pes prints are distinguishable in some trackways, and in many cases some digital pad morphology is also present. Several parameters traditionally used to differentiate ichnotaxa, including trackway gauge and the degree of print in-turning relative to the midline, are shown to be subject to significant intraspecific variation in marsupials. Sexual dimorphism in the trackway proportions of Diprotodon, and its potential for occurrence in all large bodied, quadrupedal marsupials, is identified here for the first time.

Contemporaneous Trace and Body Fossils from a Late Pleistocene Lakebed in Victoria, Australia, Allow Assessment of Bias in the Fossil Record

“…Although the dolomitic limestone is currently being stripped by modern erosional processes, its presence is a factor in the preservation of both the trackways and the skeletal accumulations. The upper surface, on which the trackways are preserved [12], is organised into sand bars of wavelength 10–15 m and amplitude 10–15 cm which trend north-south and prograded eastward. Carey et al [12] noted that a small component of smectite in the sandstone was probably responsible for the fine moulding of the trackways, and that the impregnation with calcitic cement of the uppermost 10 mm of most of the trackway surface was critical to the preservation of the trackways.…”

“…Carey et al [12] used a variety of dating techniques to estimate the age of the VVP trackways deposit. The analyses included OSL dating of the matrix in which the bones of SA2 were preserved, yielding a minimum age of 57 ka, and OSL dating of the volcaniclastic host to the trackways, yielding a minimum age of 75 ka.…”

“…Careful stratigraphic examination of the site by Carey et al [12] revealed that, with one or two possible exceptions, the trackways were most likely restricted to a single bedding surface. The presence of features such as ejecta, marginal ridges and adhesion ridges in the diprotodontid and macropodid trackways (Figure 2) rules out the possibility of the tracks being underprints, and foot-pad detail in the tracks of the smaller quadrupeds also suggests a short period of accumulation of the footprints.…”

“…(a) large macropodid tracks, identified in [12] as probably belonging to the extinct macropodid Protemnodon , illustrating deformational characteristics that give clues as to the paleoenvironment of the trackway surface; (b) diprotodontid pes print, identified in [12] as belonging to Diprotodon ; (c) a diprotodontid pes print overprinting a vombatid trackway; (d) possible Thylacoleo prints, black arrows point to digital impressions; all scale bars equal 100 mm, yellow arrows point to marginal ridges, red arrows to ejecta and white arrows to adhesion ridges.…”

“…The rarity of documented Pleistocene vertebrate trace fossils, as compared to body fossils, has been noted both within Australia [11], [12] and worldwide [13]. It has also been observed that the paleoecological investigation of dinosaurian ichnocoenoses (trace fossils from a number of taxa recorded in a single horizon [14]) is uncommon [2], [10].…”