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Home , Cape Blomidon, Early Jurassic, Grallator, Group (stratigraphy), Jurassic, McCoy Brook Formation

Olsen, P. E., 1986, Discovery of earliest assemblage from implies catastrophic end to : Lamont (Newsletter), v. 12, p. 1-3.

Discovery of Earliest Jurassic Reptile Assemblages from Nova Scotia: Imply Catastrophic End to the Triassic and sediments record (Fig. 1). These are the remnants of the bones. Long-legged,fully terrestrial and a crucial period in the evolution of the Earth's basin fill of the rifting episode of the present relatives are by farthe most common - biota. Not only does this interval witness the origi- . , especially those mals, with at least 50 skulls and jaws uncovered. nation of the , , , of terrestrial , have traditionally been Second in abundance are small -like sphen- , , crocodiles, and , but regarded as very rare in the . odontid rhynchocephalians represented by about the Triassic-Jurassic boundary itself is the third Last summer, however, in collaboration with a 30 jaws and one nearly complete skull (Fig. 5). most significant of the thirteen or so mass extinc- team headed by developmental biologist Neil H. Third, and perhaps the most precious of all, are tions that punctuate the record. Shubin of Harvard and funded by the National remains of highly advanced -like . Unfortunately, despite its crucial position, the Geographic Society, Lamont paleontologist Paul These are the trithelodonts, the reptile group Triassic-Jurassic transition has remained one of E. Olsen discovered a of rich assemblages thought to most closely relate to mammals. Over 13 the most poorly documented successions of the of well-preserved reptiles in the earliest Jurassic trithelodont skulls and jaws have been recovered, Phanerozoic, especially for terrestrial vertebrates. part of the Fundy Group of the Newark Super- with several forms being represented - including In particular, the time-stratigraphic framework for group. These assemblages apparently just post- the Pachygenelus and Diarfhrognathus. This is continental rocks of Late Triassic and Early Jur- date the mass event, and thus they the first definitive record of these genera outside assic age has been especially problematic, with shed considerable light on what may prove to be South Africa, and the first record of the reptile well dated earliest Jurassic terrestrial skeletal one of the great biological catastrophes that group closest to mammals in North America. Least assemblages being essentially unknown. A direct helped shape the modern world. common is a suite of ornithischian, theropod, and consequence of these stratigraphic difficulties is The remains occur within the upper part prosauropod remains. This includes a a proliferation of conflicting hypotheses on the of the early Fundy Group of the Newark partial prosauropod dinosaur skeleton (collected nature of the faunal transition: from those suggest- Supergroup, a 1000-m-thickcontinental sequence in collaboration with Donald Baird of Princeton). ing a dramatic, catastrophic turnover, to those consisting of red clastics, minor carbonates, and There is a massive residuum of unidentified mate- suggesting none. extrusive tholeiitic basalts (Fig. 3). Five forma- rial that remains to be sorted through. A faunal Late Triassic and Early Jurassic continental tions spanning from the - (Middle list is given in Table II. sediments are well represented in eastern North Triassic) to (earliest Jurassic) are rec- The faunal assemblages occur in three distinct America, where they comprise the Newark Super- ognized (Table I). The new assemblages occur of the McCoy Brook Formation: 1) a brown in beds of the youngest formation of the fluvial sandstone dominated by sphenodontids, Fundy Group, the McCoy Brook Formation at and crocodilomorphs (this is also the unit which Wasson's Bluff near Parrsboro, Nova Scotia. The produced the prosauropod dinosaur skeleton); 2) upper flows of the underlying extrusive North a basalt-bearing basalt agglomerate, a probable Mountain Basalt are discontinuous in this area lahar, dominated by crocodilomorphs and the and the basal, bone-producing portions of the trithelodont mammal-like reptiles: and 3) a lacus- McCoy Brook Formation fill the highly irregular trine muddy and interbedded basalt basalt topography where the two formations inter- agglomerate dominated by semionotid fishes and tongue (Fig. 4). ornithischian dinosaurs. SO far, roughly three tons of bone-bearing matrix The real value of these assemblages is that it have been collected, containing perhaps 100,000 (continued on page 2)

Fig. 1: Just prior to the separation of the North American and African continental plate, a series of elongate riff basins formed around the incipient riffing axis. In eastern North America, these basins parallel the grain of the Appalachian Orogen and were filled with thousands of meters of continental sediments and minor tholeiitic igneous rocks. The faulted, tilted, and deeply eroded remnants are expose6 from Nova Scotia to South L Carolina and are termed the Newark Supergroup. The Fig. 2: Skull of the common primitive reptile Hypsog- ) below the Triassic-Jurassic boundary. Hypsog- Manicouagan impact structure, which dates from 210 nathus found in latest Triassic Newark Supergroup red nathus represents one of the 13 families of terrestrial ?- 4 ma, very close to the Triassic-Jurassic boundary, and sandstones from the in Nova Scotia, reptiles that went extinct at or near the boundary. according to impact theory may have been responsible Hartford Basin, and Newark Basin. In Clifton, New (Drawing by Paul Olsen, twice actual size). for a mass at the boundary. Jersey, a skeleton has been found 100 m (400,000 lova Scotia Discovery North Mountain Basalt, by pollen and spore data, thie longer-term eccentricity cycles, the entire and by lacustrine cycles. According to the regionaI Niiwark extrusive episode seems to involve less mntinued from page 1) . . evolution model of John Puffer of Rutger: j thian 500,000 years. This agrees with times foi possible to place the bone-bearing units in a and Tony Philpotts of University of Connecticut at igiieous cooling and fractionation of the basalts sveloping, high-resolution litho- and chronostrati- Storrs, the North Mountain Basalt correlates witt 1 W( Irked out by Philpotts. Because the North Moun- 'aphy in a way that has not been possible for the oldest of the high Fe20i-high TiOs tholeiites5 taiin Basalt seems to correlate with the oldest o arly Jurassic terrestrial assemblages of the more southern Newark basins. The Triassic- thie flows of the southern basins, and the Triassic utside the Newark Supergroup. The age of the Jurassic boundary is palynologically fixed at about Juirassic boundary seems to be 100,000 ; wer McCoy Brook faunules is constrained by 30 m below the oldest basalt (Orange Mountain) oilder than the oldest basalts (again based or iree separate lines of age-correlativedata: First, in the Newark Basin and all of the interbeds of climate cycles), the new reptile assemblage: ~llenand spore assemblages from the upper 5 the southern extrusive units Hettangiar1 st~ould be less than 200,000-300,000 year: I of the Blomidon Formation, the Scots Bay For- aspect microfloras. The hierarchy of lacustrini? yc iunger than the boundary. lation and the middle McCoy Brook Formation, cycles that occurs interbedded with and underly Late Triassic continental faunas were dominatec re dominated by Comllina meyeriana, strongly ing the basalt flows in the Newark Basin can bi? by diverse quadrupedal archosauromorph reptiles Jggesting a maximum of an Hettangian age. used to estimate the total length of the Newarl< large labyrinthodont amphibians, and various econd, reptile footprint faunules from the basal extrusive episode and to infer the duration of thi3 mammal-like reptiles, and remains of these arc IcCoy Brook Formation and Scots Bay Forma- interval between the new reptile assemblages an(j fo und in Nova Scotia in formations below thf 3n are of "Connecticut Valley" aspect, which indi- the Triassic-Jurassic boundary. The lacustrini? 10 cally-defined Triassic-Jurassic boundary and it ates an Early Jurassic age. Third, conventional cycles have been interpreted as responses to cli- cc wrelative strata in more southern Newark basins -Ar, and K-Ar isochron dates from the North mate changes governed by the precession cycli3B' y the Early Jurassic, dinosaurs, diversecrocodilo lountain Basalt are consistent with an Early of 21,000 years and the eccentricity cycles oif morphs, mammals, and essentially modern smal urassic age. roughly 100,000 and 400,000 years following thi3 reptiles (including sphenodontids) and amphibi Detailed correlation with the rest of the Newark Milankovitch theory of climate change. By countin!3 a1is were dominant and the terrestrial fauna attain upergroup is afforded by the whole rock and the lake-level cycles caused by the precessioiI ec j the basic composition it would retain for thi ace element geochemistry of the underlying cycles and looking at the phase relationships oif ni?xt 140 million years. The Late Triassic-Earlv Jurassic aoe assem - blages from the Newark ~u~er~rou~,especiall! thie new McCoy Brook assemblages shed consid ei¥abl light on two previous hypotheses proposei fo ir the pattern of around the Triassit bi3undary. These are: 1) that the transition wa alarupt and of a scale rivaling the mass extinction a1 t the - boundary; and 2) tha thie large number of extinctions at the boundar is an artifact of miscorrelation of strata. At thi tiime the first hypothesis was formulated, virtuall

Table 1: Formations of Fundy Group in Nova Scotia, McCoy Brook Formation (+200 m) -- - Red and brown coarse to fine fluvial and deltaic 3 STANDARD AGE 1 2 3 4 5 clastics with locally developed eolian sandstones AGES (MY) CAPE BLOMIDON FIVE ISLANDS WASSONS BLUFF MCKAY HEAD BLUE SAC and minor purple, green, and white lacustrine limestone and clastics and basalt agglomerate (lateral equivalent of Scots Bay Fm.). Scots Bay Formation (-30 m) White, green, and red lacustrine limestone and chert with minor brown fluvial and eolian sandstone (lateral equivalent of McCoy Brook Fm.). ME McCoy Brook Formation North Mountain Basalt (maximum of 270 m) Scots Bay Formation Bluish gray to green and red tholeiitic extrusive NMB North Mountain Basalt basalt flows. B Blomidon Formation w Formation Blomidon Formation (maximum of 300 m) Red and brown and green, cyclic lacustrine and CARE deltaic fine claystone to sandstone with locally - developed brown eolian sandstone and purple 'ig. 3: (A) The Fundy Basin (shown here in black) is to onlap on the faulted margin of the Fundy Basin. Nei w conglomerate. nique in the Newark Supergroup in having an extensive assemblage of Early Jurassic skeletal remains is i it (maximum of 400 m) ontinuation offshore (not shown), below the Bay of Wassons Bluff at "s,t. " Major fault zone on the north sid e Brown and red fluvial sandstone and conglomerate undy and Gulf of Maine. Numerals 1-4 show positions of the Fundy Basin is the so-called Glooscap Geofrat and subordinate mudstone with locally developed f sections shown in 8. (6)Sections measured on the ture. Abbreviations tor fossils as follows: I, ; p, polle n red and brown deltaic and lacustrine clastics and orth side of the Fundy Basin in Nova Scotia (2-5) show and spores; s, reptile bones; t, reptile footprints. thick brown eolian sandstone. marked thinning compared to the south side (1) due -

10. 4: Example of intertonguing relationship between kCoy Brook Formation and North Mountain Basalt at Ifessons Blutf, Nova Scotia, Canada. Center panel is key 3 photograph: (1) massive and vesicular flow of North fountain Basalt; (2) lacustrine limestone, sandstone, nd siltstone lapping onto sloping basalt surface: (3) iasalt agglomerate intimately mixed with lacustrine silt- tone containing abundant semionotid and palaeonisci- vmfish scales, hybodont teeth, and ornithischian finosaur bones -pinches out to lower left: (4) red silt- tone and nodular limestone; (5)large-scale cross bed- fed eolian sandstone; (6) lacustrine red and brown- iurple claystone and thin channel sandstones bearing ibundant reptile bones (mostly covered): (7) large-scale ¥rosbedded eohan sandstone all the strata dated here as Early Jurassic were redating of many supposedly Late Triassic conti, considered to be Triassic in age. Their reassign- nental rocks at first suggested that the terrestria ment to the Jurassic at first markedly decreased vertebrate extinctions were not correlative witt the number of families thought to have gone those of the invertebrates. The McCoy Broot extinct at the boundary, thus leading to the sec- assemblages and the new interpretations of thf ond hypothesis, first proposed by Olsen and Peter global pattern of extinctions strongly suggests tha Galton in 1977, that most extinctions occurred the and invertebrate extinctions were ir gradually through the Late Triassic and Early fact contemporaneous. Jurassic. The hypothesis of a sudden and dramatic Subsequent discoveries, however, brought extinction event at the Triassic-Jurassic boundary most of the Triassic extinctions back to near the affecting both marine and terrestrial assemblages boundary, yet still extended the range of many is supported by the McCoy Brook Formatior families far into the Jurassic and . discoveries. An advantage of this hypothesis i! As a consequence, extinctions once again appear that it is easily falsified by either the discovery o concentrated in the latest Triassic ( Age). "typical" Triassic families or the discovery o Moreover the high Norian extinction rate is match- uniquely Jurassic families in the McCoy Brool ed with a zero origination rate through the Hettan- Formation of correlative strata. gian. A global tabulation of the -level faunal Further corroboration of this catastrophic ex transition of the Norian-Hettangian boundary tinction hypothesis is needed. Planned effort: reveals that 43% of all continental tetrapod fami- include additional collection of the Nova Scotiar lies disappear in or at the end of the Norian. Early Jurassic localities and an intense collectior While this bespeaks an extinction event, it tells effort directly around the Triassic-Jurassic bound little as to whether it is gradual or catastrophic. ary in the Culpeper, Gettysburg, Newark, an( Utilizing families present only at the latest Norian, Hartford, Deerfield, and Fundy basins of tht at least 50% of those families are extinct by the Newark Supergroup. Actual osseous remains wil Hettangian. In the Newark Basin, typical late probably never be found in sufficient abundanct Triassic taxa such as the procolophonid reptile to examine rates of extinction across the bound (Fig. 2) and occur ary rigorously. Reptile footprints, however, are ven within 100 m of the estimated position of the abundant in the strata around the boundary ir Triassic-Jurassic boundary. Again, using lacus- several basins. Because these are good for rec trine cycles this places their extinction within the ognizing the presence of many ecologically domi 500,000 years prior to the boundary. Although by nant reptile families they can provide the statisti no means conclusive, this is suggestive of a very cally robust data needed to examine the abrupt large, catastrophic extinction. ness of the vertebrate transition where actua Earliest Jurassic faunas are thus characterized osseous remains are lacking. Coupled with stud only by the absence of "typical" Triassic families; ies of the floral transition in the same beds an( there are no new families. This is exactly the kind with the use of lacustrine cycles and a develop of transition that would be expected of a cata- ing paleomagnetic stratigraphy, the Triassic-Jur strophic extinction event such as that proposed for assic boundary can be examined in the Newarl the Cretaceous-Tertiary boundary. One would not Supergroup at a less than 10,000 year level o expect the immediate aftermath (within 200,000- resolution. Only when data are available at this 300,000 years) of a catastrophe to see the origina- level of resolution can a true catastrophic extinc tion of new families, rather the "day after" commu- tion be distinguished from a more gradual one. nities should be composed of survivors -exactly the pattern seen in the early Hettangian McCoy Brook faunules. Such a pattern of survivors has already been described for the Cretaceous-Ter- Table 11: Taxa Found in tiary boundary. McCoy Brook Formation It has long been recognized that the Triassic- ("indicates taxon is a footprint) Jurassic boundary was marked by a major extinc- Class (shaiks and rays); Subclass tion event affectina dominant marine invertebrates. ; Order Hybodontiforrnes: As Anthony alla am of has shown, all con- odonts, nearly half of the bivalve genera and aff. sp. nearly all bivalve species, almost all and Class Osteiichthyes (bony fishes); Subclass ammonite families, and most , dis- ; Order Paleonisciformes: appeared at the Triassic-Jurassic boundary. The unidentified scales and skull bones. order Semionotiforrnes: Semionotus sp.

Class Reptilia; subclass Therapsida; Order Ictidosauria: Pachygenelus sp.; Diarthrognathus sp.

Subclass ; Order Rynchocephalia (tuatarids): 3 new sphenodontids

Subclass ; Order Crocodilomorpha (crocodile-like reptiles): Cf. Stegomosuchus sp.; new sphenosuchid; Eatrachopus spp.'; moodii'.

Order Saur~chia(lizard-hipped dinosaurs): Ammosaurus sp.; cf. Syntarsus sp.; FIQ 5 Survivor of the bassic-Jurassic extinction event spp ' the same form occurs in Connecticut below the hassic- Jurassic boundary' a skull of a sphenodontid reptile from Order (-hipped dinosaurs): the Early Jurassic McCoy Brook Formation of Nova New fabrosaurid; spp.' Scotla The skull is 1 5 cm across