Journal
PALAEONTOLOGY
Volume 59, Issue 3, Pages 329-336Publisher
WILEY
DOI: 10.1111/pala.12235
Keywords
Mazon Creek; Pennsylvanian; Hemichordata; Enteropneusta; Harrimaniidae; deposit feeding
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Funding
- Natural Sciences and Engineering Research Council of Canada (NSERC)
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The limited fossil record of enteropneust hemichordates (acorn worms) and the few external features that distinguish the four families have provided a challenge to our understanding of the evolution of the group and their various feeding adaptations. The middle Pennsylvanian Saccoglossus testa sp. nov. from the Mazon Creek, Westfalian D Carbonate Formation, Francis Creek Shale of northern Illinois provides evidence for the exploitation of surface sediments. Saccoglossus testa has a long proboscis characteristic of the extant genus Saccoglossus, a specialist in surface deposit feeding. The collar is as long as it is wide. The anterior trunk lacks a distinctively wide branchial region. These three features distinguish it from its sympatric enteropneust species Mazoglossus ramsdelli Bardack that has a proboscis characteristic of an infaunal deposit feeder. It is the seventh known species of fossil enteropneust, including a resting trace of a Lower Triassic fossil that has collar lips that characterize the extant deep-sea family Torquaratoridae, and which represents a second parallel evolution of surface deposit feeding. An analysis of the seven fossils shows that the earliest Enteropneusta had a relatively simple harrimaniid-like body plan, and that the spengelid, the torquaratorid and lastly the most complex ptychoderid body plan appeared in that chronological order.
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