DISCOVERY OF A SKULL OF A SMALL THEROPOD
DINOSAUR (CF. COELOPHYSIS) FROM THE LOWER
HAVEN FORMATION OF THE HARTFORD BASIN,
CONNECTICUT, USA (LATE TRIASSIC, NEWARK
OLSEN, P. E., Lamont-Doherty Earth Observatory of
Columbia University, Palisades, New York, 10964
NORELL, M. A., Department of Vertebrate Paleontology,
American Museum of Natural History, Central Park
West at 79th Street, New York, NY 10024-5192
SUES, H.-D., Department of Vertebrate Paleontology, Royal
Ontario Museum, 100 Queen's Park, Toronto, Ontario
M5S 2C6, Canada
McDONALD, N. G., Department of Earth and Environmental
Sciences, Wesleyan University, Middletown, CT
Dinosaur skeletal remains are regarded as particularly rare in the
Triassic age portion of the Newark Supergroup, despite the extreme
abundance of dinosaur footprints in some basins. In March, 1995,
however, most of a skull of a small theropod dinosaur was found in
the lower New Haven Formation, in Cheshire, CT. The skull, still
under preparation at the time of writing, is long and pointed, with a
very large antorbital fenestra, and recurved teeth that are thickly oval
in cross section. In its overall form, it is comparable to small
specimens of the Ghost Ranch Coelophysis from
the Rock Point Formation of the Chinle Group at Ghost Ranch, NM
(see Hunt and Lucas, 1991). Further preparation should allow a more
definitive identification. This is the first skull of a Triassic theropod
dinosaur from eastern North America, and the first dinosaur skull of
any sort from the Newark Supergroup found since the 19th century.
Intriguingly, the matrix containing the skull also contains what seems
to be an isolated sphenodontian premaxilla.
The source of the material is an exposure in Cheshire
consisting of gray, buff, and brown meandering river deposits
alternating with red overbank deposits (McInerney (1993) and Horne
et al., 1993). The skull was found in situ in an upright position in red
sandy mudstone. The mudstone is intensely bioturbated by Scoyenia
burrows and roots, and it passes upward into caliche-bearing red
sandy mudstone comprising a typical New Haven Formation caliche
paleosol profile. A pollen and spore assemblage from the basal part of
the New Haven Formation (Cornet, 1977) constrains the age of the
new skull to the Late Triassic, almost certainly to the Norian.
Previously described reptile taxa from the New Haven Formation include the type of Stegomus arcuatus (Marsh, 1896) , an isolated, fragmentary scapula of a phytosaur ("Belodon validus": Marsh, 1893), a small sphenodonian skull (Sues and Baird, 1993), and an excellent skull and partial skeleton of Hypsognathus fenneri (Ostrom, 1967). The relative age relations of these taxa, apart from being Norian or Rhaetian, are unknown.
The bone-bearing fluvial facies at Cheshire is one of the most
common types of fluvial facies in the Newark Supergroup, and it is
noteworthy that a similar suite of lithologies in the Durham subbasin
of the Deep River basin in North Carolina recently produced several
partial skeletons of suchian archosaurs (Olsen et. al, 1996). Because
this facies is almost never prospected for fossils in the Newark
Supergroup, the dearth of skeletal remains in Newark Supergroup
Triassic age strata may be more apparent than real.
Cornet, W. B., 1977, The Palynostratigraphy and Age of the Newark
Supergroup. [Ph.D., thesis], Department of Geosciences, Pennsylvania
State University, State College, Pennsylvania, 505 p.
Horne, G. S., McDonald, N. G., LeTourneau, P. M. and de Boer, J. Z.,
1993, Paleoenvironmental traverse across the early Mesozoic Hartford
rift basin, Connecticut, In Cheney, J. T., Hepburn, J. C., Field trip
guidebook for the northeastern United States, Boston GSA,
Contribution - Geology Department, University of Massachusetts,
v.67, Vol. 2, p. P.1-P.26.
Hunt, A. and Lucas, S., 1991, Rioarribasaurus a new name for a Late
Triassic dinosaur from New Mexico (USA). Palaeontologische
Zeitschrift, v. 65, 191-198.
Marsh, O. C., 1893, Restoration of Anchisaurus. American Journal of
Science, 3rd ser., v. 45, p. 169-170.
Marsh, O. C., 1896, A new belodont reptile (Stegomus) from the
Connecticut River sandstone. American Journal of Science, 4th ser.,
v. 2, p. 59-62.
McInerney, D. P., 1993, Fluvial architecture and contrasting fluvial
styles of the lower New Haven Arkose and mid-upper Portland
Formation, early Mesozoic Hartford Basin, central Connecticut. M.S.,
thesis, Department of Geology an Geography, University of
Massachusetts; Amherst, 271 p.
Olsen, P. E., 1980, Comparison of the vertebrate assemblages from
the Newark and Hartford basins (Early Mesozoic, Newark
Supergroup) of eastern North America: In Jacobs, L. L. (ed.), Aspects
of Vertebrate History. Flagstaff, Museum of Northern Arizona Press,
Ostrom, J. H., 1967, [on the discovery of Hypsognathus in
Connecticut]. Discovery, v. 3, p. 59.
Sues, H.-D. and Baird, D., 1993, A skull of a Sphenodontian
lepidosaur from the New Haven Arkose (Upper Triassic Norian) of
Connecticut. Journal of Vertebrate Paleontology, v.13, n.3, p.370-372.
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