Very cool paper, especially since the Chinle Formation in Petrified Forest National Park also contains shark egg capsules (Palaeoxyris). The Petrified Forest specimens are the only ones known from North America.
Fischer, J., Voigt, S., Schneider, J. W., Buchwitz, M., and & S. Voigt. 2011. A selachian
freshwater fauna from the Triassic of Kyrgyzstan and its implication for Mesozoic shark nurseries. Journal of Vertebrate Paleontology 31:937-953.
http://dx.doi.org/10.1080/02724634.2011.601729
Abstract - Habitat partitioning and site fidelity of spawning grounds are well-documented phenomena in extant selachians, but little is known about the reproductive strategies of their fossil relatives. Here we describe the selachian fauna of the Middle to Late Triassic Madygen Formation in southwestern Kyrgyzstan, Central Asia, based on several dozen tooth crowns and egg capsules. The material is assigned to three new taxa: Lonchidion ferganensis, sp. nov., and Palaeoxyris alterna, sp. nov., being teeth and egg capsules of hybodontid sharks, and Fayolia sharovi, sp. nov., being egg capsules of probable xenacanthids. Teeth of L. ferganensis, sp. nov., were almost exclusively found in pelecypod-rich shallow lacustrine mudstones and belong to juvenile individuals. Oxygen and strontium isotope data of tooth enameloid indicate freshwater conditions of the ambient water at the time of tooth mineralization. The egg capsules are common findings in near-shore lake deposits as well. Considering the mass co-occurrence of juvenile teeth and egg capsules in the study area, we propose that hybodontid/ xenacanthid sharks recurrently occupied littoral zones of the Madygen lake for spawning. The small number of full-grown individuals points to habitat partitioning of juveniles and adults wherefore the study site is interpreted as a shark nursery. The oviposition strategies inferred from this fossil example are remarkably similar to those of modern sharks, suggesting that the reproductive patterns seen in extant sharks originated well before the Cenozoic.
The Chinle specimens are the only unequivocally known remains from the Mesozoic of the US. For the Palaezoic there is a mass occurence in Mazon Creek.
ReplyDeleteThe problem with the Chinle is the general lack of egg capsules. We have the 4 described specimens from the Blue Mesa Fm. But thats all so far. Otherwise the Chinle is full of xenacanth and hybodont sharks, which were, to our knowledge, oviparous fishes. So, were are their eggs? The same pattern known from Madygen were probably also existend in North America. Maybe eggs are already recovered but mistakenly identified as plant remains waiting in several collections for their rediscovery.