New Early Jurassic Tetrapod Assemblages Constrain into the Jurassic, thus decreasing the magni­ tude of the extinction event at the boundary Triassic-Jurassic Tetrapod Extinction Event (6). Although more recent discoveries of vertebrates (7, 8) have brought the ranges of many Triassic families to near the Triassic­ p. E. OLSEN, N. H. SHUBIN,* M. H. ANDERS Jurassic boundary and extended the ranges of many Early Jurassic forms into the Juras­ The discovery of the first definitively correlated earliest Jurassic (200 million years sic and Cretaceous (8), the dearth of well­ before present) tetrapod assemblage (Fundy basin, Newark Supergroup, Nova Scotia) dated earliest Jurassic assemblages has pre­ allows reevaluation of the duration of the Triassic-Jurassic tetrapod extinction event. vented precise dating of the extinctions that Present are tritheledont and mammal-like reptiles, prosauropod, theropod, and occurred at or after the boundary. ornithischian dinosaurs, protosuchian and sphenosuchian crocodylomorphs, spheno­ We describe four newly discovered di­ dontids, and hybodont, semionotid, and palaeonisciform fishes. All of the families are verse vertebrate assemblages within a well­ known from Late Triassic and Jurassic strata from elsewhere; however, pollen and correlated earliest Jurassic sequence from spore, radiometric, and geochemical correlation indicate an early Hettangian age for Nova Scotia, Canada, which fill this gap. these assemblages. Because all ''typical Triassic" forms are absent from these assem­ They are important for four main reasons: blages, most Triassic-Jurassic tetrapod extinctions occurred before this time and (i) the fossil remains are unusually abun­ without the introduction of new families. As was previously suggested by studies of dant, (ii) a large range offossil-bearing facies marine invertebrates, this pattern is consistent with a global extinction event at the and paleoenvironments is represented, (iii) a Triassic-Jurassic boundary. The Manicouagan impact structure of Quebec provides high degree of stratigraphic resolution is dates broadly compatible with the Triassic-Jurassic boundary and, following the permitted, and (iv) togeth,er with related impact theory of mass extinctions, may be implicated in the cause. assemblages, the pattern of extinctions is plausibly representative of global changes. HE TRIASSIC-JURASSIC BOUNDARY ture of the faunal transition with one ex­ The new data permit a much more refined T marks one of the more significant of treme suggesting a dramatic, catastrophic look at the Triassic-Jurassic transition and the 13 or so (1-5) mass extinctions turnover (1) and the other suggesting a that punctuate the Phanerowic. Late Trias­ gradual change spread over tens of millions P. E. Olsen, Department of Geological Sciences and Lamont-Doherty Geological Observatory of Columbia sic continental faunas were dominated by of years (6). At the time the first hypothesis University, Palisades, NY 10964. diverse quadrupedal archosauromorph rep­ was formulated, virtually all the strata de­ N. H. Shubin, Museum of Comparative Zoology, Har­ vard University, Cambridge, MA 02138. tiles, labyrinthodont amphibians, and mam­ scribed in this report as Early Jurassic were M. H. Anders, Department of Geology and Geophysics, mal-like reptiles. By the late Early Jurassic, considered Triassic in age (1, 6). Their University of California, Berkeley, CA 94720. dinosaurs, crocodylomorphs, mammals, and reassignment to the Jurassic extended the *Present address: Department of Paleontology, Univer­ essentially modem small reptiles and am­ range of many supposedly Triassic families sity of California at Rerkeley, Berkeley, CA 94720. phibians were dominant and the terrestrial fauna had attained the basic composition it A Newark Supergroup B would keep for the next 140 million years / Newark (4, 6). extrusive dates Standard Despite its crucial position, the Triassic­ 180 ages Jurassic tetrapod transition is poorly known, ~4 the main problem being the absence of definitive earliest Jurassic deposits (4, 6). T These stratigraphic difficulties underlie a Fundy 189 190 Basin range of conflicting hypotheses on the na- p Manicouagan dates 198 Fig. 1. (A) The Newark Supergroup (black), s showing the position of the Fundy Basin, other a 195 t--H- Newark Supergroup deposits, and the Manicoua­ 200 200 gan impact structure: 1, Newark Basin; 2, Hart­ ford Basin; 3, Fundy Basin; and 4, Manicouagan impact structure. (B) Correlation of major por­ tions of Fundy Basin section of Newark Super­ N b group [from (12)], Newark igneous (29) and 210 Manicouagan dates (27), and standard ages. Time scale compiled from Webb and Odin and Kenne­ I dy (29). In stratigraphic columns, gray is domi­ 215 nantly cyclic lacustrine sediments, white is domi­ nantly fiuvial sediments, and black is extrusive 220 c basalt flows. Abbreviations of units are as follows: ' ,,;r(:r ) '----' 1, WolfVille Formation; 2, Blomidon Formation; 'v""</ j I.. o 10 #dates 3, North Mountain Basalt and sedimentary in­ > ' 225 terbeds; and 4, Scots Bay and McCoy Brook I • t \ , formations. Dates are: a, 206 ± 6 million years t ;\ ,,' 230 L (K-Ar); b, 215 ± 4 million years (K-Ar); c, / , 1> / , ;J' 212.9 ± 0.4 million years (Ar/Ar); d, 209 ± 5 I , , I '> million years (Rb-Sr) (26, 27). Standard ages are: ,,,""_.r' ---- 235 ,,,.,,... .... ""' A, Anisian; C, Carnian; H, Hettangian; L, Ladin­ A ian, N, Norian; P, Pliensbachian; S, Sinemurian; and T, Toarcian. O- km- 400I 240 28 AUGUST 1987 REPORTS !025 may allow tests of the major hypotheses of sian (early Middle Triassic) to Hettangian penecontemporaneously faulted and highly faunal change. (earliest Jurassic) age are recognized (Fig. 1 irregular upper surface of the extrusive The tetrapod remains occur within the and Table 1). The new assemblages occur in North Mountain Basalt. Four separate facies upper part of the early Mesowic Fundy basal beds of the youngest formation of the of the McCoy Brook Formation have pro­ Group of the Newark Supergroup, a 1000- Fundy Group, the McCoy Brook Forma­ duced reptile assemblages at Wasson Bluff: m thick sequence consisting of red elastics, tion, at Wasson Bluff near Parrsboro, Nova (i) a brown fluvio-lacustrine sandstone, minor carbonates, and extrusive tholeiitic Scotia. The basal, bone-producing portions dominated by sphenodontids and protosu­ basalts. Five conformable formations of Ani- of the McCoy Brook Formation fill the chid crocodiles; (ii) thin brown sandstone beds with basalt debris and siltstone chips sandwiched between eolian dune sets, domi­ Standard ages nated by prosauropods and sphenodontids; Family (iii) basalt talus cones, dominated by proto­ I s I A I L IC I N I H I Sin I p I T I Aal I B I suchid and sphenosuchid crocodylomorphs Uranocentrodontidae Benthosuchi·dae -- and tritheledont mammal-like reptiles; and Indobrachyopidae -- (iv) a lacustrine muddy limestone and inter­ Rytidosteidae -- bedded basalt talus cone, dominated by se­ Dissorophidae -- Lystrosauridae -- mionotid fishes and ornithischian dinosaurs. Myosauridae -- A fauna! list is given in Table 2. Cynognathidae Triassic Jurassic The age of the lower McCoy Brook as­ Erythrosuchidae -- Diademodontidae semblages is constrained by three lines of Brachyopidae data. Pollen and spore assemblages from the Ctenosauriscidae Shansiodontidae -- upper Blomidon Formation (9, 10), the type Proterosuchidae -- Scots Bay Formation (11), and the McCoy Kannemeyeriidae Brook Formation (10) are dominated by Traversodontidae Trematosauridae Corollina meyeriana, suggesting a Hettan­ Stahleckeriidae gian or younger age (12). Reptile footprint Rhynchosauridae assemblages from the basal McCoy Brook Chiniquodontidae Proterochampsidae Formation and Scots Bay Formation are of Lagosuchidae -- "Connecticut Valley" aspect (Table 2), Erpetosuchidae which indicates an Early Jurassic age (13). Scleromochlidae -- -- 40 39 Procolophonidae Conventional K-Ar, Ar/ Ar, and K-Ar Prolacertidae isochron (14) dates from the North Moun­ Mastodonosauridae tain Basalt strongly suggest an Early Jurassic Rauisuchidae Trilophosauridae (Hettangian) age. Tanystropheidae More precise dating and geographic con­ Plagiosauridae trol are afforded by correlation with the Metoposauridae Ca pi tosauri.dae southern Newark basins. The geochemistry Ornithosuchidae of the underlying North Mountain Basalt, Stagonolepididae pollen and spore data, and lacustrine cycles Phytosauridae Kuehneosauridae all point to a close synchroneity of events in Drepanosauridae the northern and southern Newark basins. Proganochelyidae Whole rock and trace element geochemis­ Kuehneotheriidae Haramiyidae tries of the North Mountain Basalt correlate Tritheledontidae with the oldest of the high Fe20rhigh Melanorosauridae Ti02 tholeiites of the more southern New­ Gephyrosauridae Heterodontosauridae ark basins (15). Strata interbedded between "Scelidosauridae" basalts of the more southern basins consist­ Chigutisauridae I ently produce Hettangian palynoflorules Anchisauridae "lissamphibians" and, in the Newark Basin, the Triassic­ Procompsognathidae Jurassic boundary is palynologically fixed at Fabrosauridae about 30 m below the oldest basalt (Orange Sphenodontidae Stegomosuchidae Mountain) (12), suggesting that the North Sphenosuchidae Mountain Basalt-Blomidon Formation con­ "Dimorphodontidae" tact lies within 10 m above the Triassic­ "Eudimorphodontidae" Morganucodontidae Jurassic boundary (9). Finally, in the New­ Tritylodontidae ark and Hartford basins, the hierarchy of Megalosauridae