From: Olsen, P. E., and Rainforth, E. C., 2002, Continental tetrapod
ichnofaunal sucession and turnover in the Newark Supergroup (?Middle-Upper
Triassic and Lower Jurassic, eastern North America) and temporally equivalent
strata in Morocco. Journal of Vertebrate Paleontology, v. 22, no. 3, supp., p.
93A-94A.
CONTINENTAL TETRAPOD ICHNOFAUNAL SUCCESSTON AND TURNOVER IN THE NEWARK
SUPERGROUP (?MIDDLE-UPPER TRIASSIC AND LOWER JURASSIC, EASTERN NORTH AMERICA)
AND TEMPORALLY-EQUIVALENT STRATA IN MOROCCO
OLSEN,
Paul E., and RAINFORTH, Emma C., Lamont-Doherty Earth Observatory, Columbia
University, 61 Rt. 9W, Palisades, NY 10964.
Three distinct assemblages characterize the
>34-million-year track record in the Newark Supergroup and coeval Moroccan
strata. The oldest, Atlas-type (Deep River, Moroccan basins), is characterized
by numerous Apatopus; unnamed, sometimes very large (>30 cm)
?bipedal tetradactyls; Brachychirotherium; ?Chirotherium; Rhynchosauoides; and far
less common indeterminate tridactyls. Grallatorids appear to be absent.
Conventionally considered Early-Late Carnian, the strata may extend into the
Ladinian.
The
Passaic-type assemblage (Dan River, Culpeper, Gettysburg, Newark, Fundy basins;
Late Carnian to the Triassic-Jurassic boundary [TJB]) is the most diverse and
long-ranging. Theropod prints increase in size and abundance: the small and
quite rare Grallator parallellum occurs throughout, but by the end
of the Triassic (202 Ma) both Grallator, and the larger Anchisauripus are common.
The ornithischian track Atreipus is abundant from the base (~228 Ma)
to ~207 Ma but absent thereafter. Other common forms include Rhynchosauroides, Brachychirotherium, Gwynnedichnium and Apatopus; far rarer
are Procolophonichnium, Chirotherium and a new
dinosaurian genus. The latest Triassic has several batrachopids.
The
youngest (Connecticut Valley-type) assemblage (Culpeper, Newark, Hartford,
Deerfield, Fundy basins; basal Hettangian [202 Ma] to base of Sinemurian [~200
Ma]) is much less diverse, with only grallatorids, Batrachopus and Rhynchosauroides basally. Eubrontes is an
abundant grallatorid, appearing within 10,000 years after the TJB. Above this,
the assemblage remains quite stereotyped through the end of the Newarkian
record. Grallatorids, Anomoepus and Batrachopus are
abundant; Rhynchosauroides and Amheghinichnus are much
rarer. In the northern basins, Otozoum is also present and can be
common.
Ichnofaunal
change is slow through the Late Triassic except at the TJB, where the turnover
between Passaic and Connecticut Valley-type assemblages, characterized by a 20%
increase in the maximum size of theropod tracks, occurs in <30,000 years.
The transition between Atlas and Passaic-type assemblages also seems unusually
rapid, but sampling is still too sparse to assess the pace of change.