ICHNITE RECORD OF TERRESTRIAL TETRAPOD ABUNDANCE
AND DIVERSITY THROUGH A CRITICAL PERIOD IN EARTH
HISTORY, JACKSONWALD SYNCLINE, NEWARK BASIN,
NEW JERSEY AND PENNSYLVANIA
SILVESTRI, ShayMaria M., Dept. of Geological Sciences, Rutgers
University, Piscataway, NJ, 08855-1179
The study area, in the Jacksonwald syncline of the Newark basin,
Pennsylvania, contains numerous intervals of abundant terrestrial
tetrapod footprint-bearing horizons that occur mainly in the regressive
portions of Van Houten lacustrine sedimentary cycles. These 20,000-
year cycles represent lake transgression, highstand, and regression
driven by climatic changres. Thus Van Houten cycles provide a
precise time control against which rates of terrestrial tetrapod radiation
and extinction can be measured. The study area also contains the
palynologically-determined Triassic-Jurassic boundary. A continuous
drill core through section correlative to field sites, coupled with
paleomagnetic data for both core and field sites, allows unambiguous
stratigraphic placement of strata from field sites and therefore precise
stratigraphic placement of ichnites.
Extremely abundant ichnofaunal horizons from latest Triassic strata
reveal a rich and diverse assemblage of terrestrial tetrapod footprints.
Ichnites present include Atreipus milfordensis and Atreipus spp.
produced by small herbiverous quadrupedal dinosaurs; Batrachopus
deweyii and Batrachopus spp., crocodilian footprints;
Brachychirotherium parvum and Brachychirotherium spp., rauisuchid
and stagonolepid tracks; Chirotherium lulli, chirothere footprints;
Grallator spp., the tracks of a small carnivorous dinosaur;
Gwyneddichnium majore and Gwyneddichnium spp., produced by
minute amphibians; Rhynchosauroides brunswickii and
Rhynchosauroides spp. the tracks of small sphenodontids; and a new,
currently unnamed taxon.
The earliest Jurassic assemblage in the study locality is much
reduced and composed predominantly of latest Triassic survivors,
mainly larger-sized Grallator, and extremely rare Rhynchosauroides,
with the addition of Anomoepus.
Previous work showed the diverse latest Triassic assemblage
present to within 400,000 years of the Triassic-Jurassic boundary.
Recent research at new exposures in the Jacksonwald syncline area
reveals another new Late Triassic taxon, and allows the extension of
several ichnite ranges.
Stratigraphic analysis of new field sites shows: 1) the local fauna
was abundant and increasing in diversity in the very latest Triassic, and
2) faunal turnover from a rich latest Trassic assemblage to a sparse
Jurassic assemblage occurs within a single Van Houten cycle, or within
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