43 Paleontology of the Colorado Plateau and Environs (Posters)

Wednesday, 16 May 2018
8:30 AM - 6:30 PM
Outdoor Tents

MORE THAN CHELICHNUS IN THE LOWER PERMIAN COCONINO SANDSTONE: NEW TETRAPOD FOOTPRINT LOCALITIES IN COCONINO COUNTY, ARIZONA

Paper number: 43-1
Program: Theme Sessions
Time: 8:30 AM – 6:30 PM

Authors

Abstract

Newly discovered tetrapod footprint localities in the Apache-Sitgreaves National Forest of Coconino County, Arizona, are in the upper part of the lower Permian (Leonardian) Coconino Sandstone. These sites are in a narrow stratigraphic interval < 5 m thick and are exposed over a strike distance of about 1 km. The tetrapod footprints belong to two morphotypes, neither of which is the classic Chelichnus. Both are the plantigrade footprints of quadrupeds. The larger footprints are wider than long (L: W = 4-5:3-4 cm), have a pentadactyl manus and pes, digits with pointed tips that are straight to slightly recurved, digit IV is longest or subequal to III, and digits I and V are shortest and of subequal length. The trackway pattern is of pes and manus imprints rotated outward from the midline, and the manus imprint slightly lateral to that of the pes. These tracks most closely resemble “Hylopus hermitanus” from the red-bed Hermit Shale, later made the type species of “Gilmoreichnus,” a problematic ichnotaxon likely made by a synapsid. The smaller tracks are also wider than long (L:W = 1-2: 2-3 cm), have a pentadactyl manus and pes with short, straight digits that have either pointed or rounded tips. Digits I and V are shortest and divergent from the longer and forward pointing digits II-IV. The trackway pattern is chaotic/disorganized. These small Coconino tracks closely resemble mammal-like tracks of the Mesozoic, especially Cretaceous Catocapes from Angola. For the last 20 years, ichnologists have considered Chelichnus to be the only ichnogenus of tetrapod footprints in the Coconino Sandstone, though it has a broad, vague diagnosis that encompasses some very disparate morphotypes. Indeed, the diagnosis of Chelichnus needs to be revisited in order to understand better the ichnodiversity of Coconino tetrapod tracks. The newly discovered sites also show that Coconino tetrapod ichnodiversity was more than just Chelichnus. However, the likely synapsid origin of the newly discovered tracks conforms to the idea that the majority of tetrapod footprints in lower Permian eolianites were made by synapsids. “Gilmoreichnus” has been considered a synapsid track, and the presence of this morphology in both Permian red-bed and eolian strata makes it a facies-crossing ichnotaxon, regardless of its correct ichnotaxonomic name.

Geological Society of America Abstracts with Programs. Vol. 50, No. 5

doi: 10.1130/abs/2018RM-313462

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