A temnospondyl trackway from the early Mesozoic of western Gondwana and its implications for basal tetrapod locomotion

MARSICANO, CLAUDIA; WILSON, JEFF; SMITH, ROGER

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2014

1932-6203

Background: Temnospondyls are one of the earliest radiations of limbed vertebrates. Skeletal remains of more than 190genera have been identified from late Paleozoic and early Mesozoic rocks. Paleozoic temnospondyls comprise mainly smallto medium sized forms of diverse habits ranging from fully aquatic to fully terrestrial. Accordingly, their ichnological recordincludes tracks described from many Laurasian localities. Mesozoic temnospondyls, in contrast, include mostly medium tolarge aquatic or semi-aquatic forms. Exceedingly few fossil tracks or trackways have been attributed to Mesozoictemnospondyls, and as a consequence very little is known of their locomotor capabilities on land.Methodology/Principal Findings: We report a ca. 200 Ma trackway, Episcopopus ventrosus, from Lesotho, southern Africathat was made by a 3.5 m-long animal. This relatively long trackway records the trackmaker dragging its body along a wetsubstrate using only the tips of its digits, which in the manus left characteristic drag marks. Based on detailed mapping,casting, and laser scanning of the best-preserved part of the trackway, we identified synapomorphies (e.g., tetradactylmanus, pentadactyl pes) and symplesiomorphies (e.g., absence of claws) in the Episcopopus trackway that indicate atemnospondyl trackmaker.Conclusions/Significance: Our analysis shows that the Episcopopus trackmaker progressed with a sprawling posture, usinga lateral-sequence walk. Its forelimbs were the major propulsive elements and there was little lateral bending of the trunk.We suggest this locomotor style, which differs dramatically from the hindlimb-driven locomotion of salamanders and otherextant terrestrial tetrapods can be explained by the forwardly shifted center of mass resulting from the relatively large headsand heavily pectoral girdles of temnospondyls.