T134 Clear as Mud: Stratigraphic, Diagenetic, Sedimentologic, Geomechanical Analyses, and Modern Analogs of Ancient Mudrock Systems

Monday, 23 October 2017
1:30 PM - 5:30 PM
Ballroom 6C

BOOMERANG-HEADS AND TIGER SHARK MANDERS: EMPOYING TEXAS RED BEDS AMPHIBIA TO DOCUMENT BOTTOM MUD IN THE EARLY PERMIAN

Paper number: T134-15
Program: Technical Sessions
Time: 5:10 PM – 5:30 PM

Authors

Abstract

Amphibians are now, and probably always have been extraordinarily sensitive to mud quality. Neotenic species, like mudpuppies, with flattened bodies and sluggish benthic life style, retain gills and/or skin respiration through adulthood and so are severely dependent upon oxygenated bottom water. The Texas Red Beds sample a dozen amphibian families through the entire Early Permian, when seasonal aridity increased and permanent bodies of fresh water decreased. The embolomeres combine elongated bodies, tall posterior skulls, deep tails and short limbs, indicating a preference for hunting high in the water column, near the surface. Circular thoracic cross sections show that ribcage movements could power aerial breathing. Therefore, embolomeres should be present in pond environments with dark sediment and ironstone nodules. The prediction is confirmed by their abundance in the “boggy” sites Briar Creek and Geraldine. In contrast, trimerorhachids and boomerang-headed diplocaulids retain vertically flattened bodies and weak limbs all through their life cycle. Rib cages were incapable of heavy aerial breathing. These amphibians should favor well-oxygenated bottom sediments. The prediction is confirmed; the two families increase as caliche becomes more common and ironstone disappears.

Boomerang-heads have exceptionally weak limbs limiting excursions out of drying ponds in search of water. Thus we’d expect aestivating habits, a prediction confirmed by abundant skeletons preserved in burrows. Largest of Texas amphibians are Eryops and kin, with skulls exceeding half a meter. The limbs are very strong and adapted for terrestrial excursions; the unusually straight ribs suggest some costal breathing. Therefore eryopids should not be limited by bottom conditions. This prediction is confirmed: eryopids are most eurytopic of amphibians, common in “boggy sites” and in channels adjacent to oxidized soils. Red Beds amphibians prove to be reliable habitat indicators that can test notions about depositional environments.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-307062

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