Abstract
BackgroundTemnospondyls are one of the earliest radiations of limbed vertebrates. Skeletal remains of more than 190 genera have been identified from late Paleozoic and early Mesozoic rocks. Paleozoic temnospondyls comprise mainly small to medium sized forms of diverse habits ranging from fully aquatic to fully terrestrial. Accordingly, their ichnological record includes tracks described from many Laurasian localities. Mesozoic temnospondyls, in contrast, include mostly medium to large aquatic or semi-aquatic forms. Exceedingly few fossil tracks or trackways have been attributed to Mesozoic temnospondyls, and as a consequence very little is known of their locomotor capabilities on land.Methodology/Principal FindingsWe report a ca. 200 Ma trackway, Episcopopus ventrosus, from Lesotho, southern Africa that was made by a 3.5 m-long animal. This relatively long trackway records the trackmaker dragging its body along a wet substrate 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., tetradactyl manus, pentadactyl pes) and symplesiomorphies (e.g., absence of claws) in the Episcopopus trackway that indicate a temnospondyl trackmaker.Conclusions/SignificanceOur analysis shows that the Episcopopus trackmaker progressed with a sprawling posture, using a 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 other extant terrestrial tetrapods can be explained by the forwardly shifted center of mass resulting from the relatively large heads and heavily pectoral girdles of temnospondyls.
Highlights
The Moyeni tracksite in Lesotho, southern Africa, preserves a diverse assemblage of large- and medium-sized tetrapod tracks (Fig. 1)
The Moyeni tracksite was first described by Paul Ellenberger [3], who mapped the surface and identified numerous tetrapod trackways made by several trackmakers preserved in what he interpreted as an emergent sandbank formed at the mouth of a river flowing into a large lake (Fig. 2)
200 million years ago in the part of western Gondwana that is the southern African country of Lesotho, a partially emerged, microbial-matted sand bar on the inner bank of a river bend was repeatedly traversed by dinosaurs and other tetrapods
Summary
The Moyeni tracksite in Lesotho, southern Africa, preserves a diverse assemblage of large- and medium-sized tetrapod tracks (Fig. 1). The flanks of the bar remained sculpted by low amplitude, small current ripples orientated tangential to slope. These surfaces were subsequently draped with a veneer of silty clay that settled out of suspension. Paleozoic temnospondyls comprise mainly small to medium sized forms of diverse habits ranging from fully aquatic to fully terrestrial. Their ichnological record includes tracks described from many Laurasian localities. Few fossil tracks or trackways have been attributed to Mesozoic temnospondyls, and as a consequence very little is known of their locomotor capabilities on land
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