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 
~20,000 years.