Rotten Hill: A Late Triassic bonebed in the Texas Panhandle, USA by S. G. Lucas, L. F. Rinehart, A. B. Heckert, A. P. Hunt and J. A. Spielmann New Mexico Museum of Natural History and Science, Bulletin 72: 1-97. 2016.
This 118-page volume presents a complete osteology and paleobiological analysis of a large population sample of the Triassic temnospondyl amphibian Eocyclotosaurus from a bonebed in northern New Mexico. If you are interested in ordering Bulletin 72, it costs $20 and you can contact Beth Ricker, Store Manager for the NMMNH&S, at beth@ naturalhistoryfoundation.org to place orders.
Abstract—The Rotten Hill bonebed is a Late Triassic fossil locality in the Texas Panhandle discovered by Floyd V. Studer in 1926, and collected primarily by WPA-funded excavations during the late 1930s and early 1940s. This locality is in the lower part of the Tecovas Formation (Chinle Group) and is of Adamanian (late Carnian) age. Forensic taphonomic analysis indicates it is a mass death assemblage that was hydraulically concentrated. The Rotten Hill bonebed is a low diversity multitaxic and monodominant bonebed; the vast majority of the bones are of the metoposaurid Koskinonodon perfectum.
It closely resembles other Chinle Group metoposaurid-dominated bonebeds that suggest aggregation of a group of metoposaurids, followed by catastrophic mortality, complete disarticulation and disassociation of the skeletons, culminated by rapid transport and burial. Fossil taxa from the Rotten Hill bonebed are the unionoidan bivalve Plesioelliptio sp., the coprolite ichnogenera Alacocopros, Eucoprus and Heteropolacopros; various fishes known from ichtyoliths; a rhynchosaur; a sphenodontid; the archosauriform Vancleavea; the trilophosaurs Trilophosaurus and Spinosuchus; the phytosaur Smilosuchus; a probable poposaurid (cf. Postosuchus), the aetosaurs Desmatosuchus and cf. Stagonolepis; a shuvosaurid; and the metoposaurids Apachesaurus gregorii and K. perfectum. K. perfectum is represented by numerous skulls, lower jaws, vertebrae, girdle and limb bones representing a minimum number of 68 individuals based on recovered interclavicles. We describe the osteology and variation of these bones, which allows us to present a revised diagnosis of Koskinonodon that employs new postcranial characters to differentiate it from other metoposaurid genera. We also compiled and analyzed a morphometric database of the Rotten Hill Koskinonodon to conclude that bone growth varied from isometry to allometry and suggests a loss in limb robustness during ontogeny that likely indicates a transition from a partly terrestrial to a more aquatic lifestyle. Probability plotting to test for size groups in the Rotten Hill Koskinodonon identifies 10-11 groups that we interpret as yearly age cohorts and use to plot a growth curve. This indicates indeterminate growth in K. perfectum and that the Rotten Hill sample represents a population of breeding adults, some of which survived at least 10-11 years after reaching sexual maturity. This is a growth curve also characteristic of some living salamanders. We infer that K. perfectum employed some mechanism, such as disparate feeding strategies, or another ecological factor that enforced separation of adults and juveniles, to reduce predation on juveniles by conspecifics and minimize the competition for food resources between the ontogenetic stages.