A Diapsid Faunule from the Lower Jurassic Of

provide a test for the hypothesis of faunal change at the Triassic-Jurassic boundary recently proposed by OLSEN and SUES (1986). They are remarkable for the numerical abundance and quality of preservation of the bones, the lithological diversity of fossil-bearing deposits, and the excellent degree of stratigraphic resolution. The vertebrate remains from the McCoy Brook Formation currently represent the oldest well-dated terrestrial tetrapod assemblage from the Jurassic. The Fundy Group of the Newark Supergroup is a 1000 m thick sequence of red clastic sediments, minor strata of carbonates, and extrusive tholeiitic basalts. Vertebrate remains occur in the basal portion of the 200+ m thick McCoy Brook Formation, the youngest formation of the Fundy Group. The bone-bearing strata fill a penecontemporaneously faulted, irregular upper surface of the North Mountain Basalt. Vertebrate fossils occur in four different types of facies within the McCoy Brook Formation at Wasson Bluff near Parrsboro (Minas Basin): 1) a brown fluviolacustrine sandstone with remains of protosuchid crocodilians and sphenodontians; 2) thin beds of brown sandstone with basalt clasts and siltstone chips, sandwiched between eolian deposits dominated by prosauropod dinosaurs and sphenodontians; 3) basalt agglomerate with red mudstone matrix containing bones of tritheledontid synapsids and protosuchid and sphenosuchid crocodylomorphs; and 4) a lacustrine limestone and interbedded basalt agglomerate with semionotid fishes and ornithischian dinosaurs. ~alynofloras dominated by Corollina meveriana, radiometric dates for the North Mountain Basalt, and comparisons of the reptilian footprint assemblages with those from other basins of the Newark Supergroup strongly suggest an Early Jurassic, specifically Hettangian, date for the lower portion of the McCoy Brook Formation. Characteristic Late Triassic archosaurs such as phytosaurs, aetosaurs, ornithosuchians and rauisuchians all appear to be absent from the new assemblages. In addition to tritheledontid synapsids, remains of sphenodontian lepidosaurs, crocodylomorph archosaurs, and dinosaurs have been recovered to date. Most specimens are well-preserved but disarticulated bones. An incomplete skeleton of an anchisaurid prosauropod and a virtually uncrushed partial skull and mandible of a sphenodontid represent notable exceptions.