Paper No. 13
Presentation Time: 1:30 PM-5:30 PM
A PLACODERM WITH PACHYOSTEOMORPH AFFINITIES FROM THE CATSKILL FORMATION (UPPER DEVONIAN), TIOGA COUNTY, PENNSYLVANIA
Pachyosteomorph arthrodires were an advanced group of placoderms (armored fishes) with a predominately marine fossil record from the Middle-Upper Devonian. Dermal plates of large arthrodires, some displaying pachyosteomorph affinities, come from a 30-meter section of the lower half of the Catskill Formation (Famennian, Late Devonian). They were collected from a talus slope of an Interstate 99 roadcut, 8-miles north of Mansfield, PA. In this area the Catskill Formation is undifferentiated, consisting of red and gray sandstones and red siltstones. These exposures have been interpreted as lower delta plain facies. The associated ichthyofauna consists of the placoderms Bothriolepis and Phyllolepis, the porolepiform Holoptychius, an unidentified tristichopterid, and the lungfish Apatorhynchus. Of these, the presence of Phyllolepis is indicative of a non-marine environmental setting. Large arthrodires are represented at the site by a partial anterior dorsolateral and an anterior lateral plate. Both isolated elements display a fine, dermal ornament and show no signs of being reworked post-deposition. The external surface of the anterior dorsolateral plate was preserved as an impression with residual bone. This allowed for the creation a silicone peel, which facilitated morphological comparison. The anterior lateral plate displays a suite of features that suggest affinity with pachyosteomorph arthrodires. Its high and narrow proportions are consistent with the presence of a posterior, pectoral incision. The plate has a postbranchial embayment, a broad anteroventral wing with deep concavities, and a well developed obstantic process. Recognition that large, pachyosteomorph arthrodires utilized non-marine environments in the Catskill Deltaic System may prove important to future discussions of the paleoecology of large placoderms.