Fischer, J., S. Voigt, J. W. Schneider, M. Buchwitz & 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. [Abstract]
Aha: Egg capsules and microvertebrate fossils can be a worthwile study object after all. (Event though Jan Fischer, my fellow grad student at the Geological Institute in Freiberg, had an interview with a critical local newsreporter who doubted that anybody could ever be interested in something like that.)
Jan and colleagues describe chondrichthyan egg capsule fossils from the Madygen Formation and refer them to Palaeoxyris, a capsule type usually assigned to hybodont sharks, and Fayolia, probably produced by xenacanth sharks. These fossils are accompagnied by nearby finds teeth of hybodont shark teeth - most of them are tiny and probably belonged to juveniles of the newly erected species Lonchidion ferganensis.
Oxygen isotope analysis of the teeth and their comparison to hybodont teeth from other localities yields a clear freshwater signal for the Madygen samples, indicating that the shark offspring indeed inhabited a freshwater habitat.
Facial analysis of the sedimentary succession of the Madygen Formation demonstrates the presence of wide-spread shallow and vegetated shore areas during the Middle Triassic which could have functioned as a shark nursery, i.e. a separate and ecologically distinct habitat for juveniles which was not invaded by adult sharks of the same species.