INVERTEBRATE AND VERTEBRATE TRACE FOSSILS FROM THE LATE TRIASSIC PASSAIC FORMATION, NEWARK BASIN, NEW JERSEY

The Late Triassic Newark Basin of Pennsylvania and New Jersey is well known for its spectacular trace fossil assemblages. While much knowledge has been gained from this extraordinary record, new sites continue to add depth to what is known.

Recent excavations in the Passaic Formation near Manville, New Jersey have yielded an ichnofauna preserved in the muds of a Late Triassic lake-shore environment. One particularly dramatic surface documents a shoreline scene with sculpted sediments, running water marks, raindrop impressions, ripples, and a variety of trace fossil phenomena. Most striking are several single grooved trails of differing widths, depths and behaviors. These trails exhibit various styles of locomotion including straight, curved, looping, angular and meandering. Feeding traces and a possible dwelling trace are also visible in association with these impressions. Some of the more shallow of these trails may be referrable to Herpystezoum, which is considered to be the trail of an annelid. However, others display deep channels with thick ridges on each side of the groove. Trails with these features are usually thought to be those of mollusks and would be attributed to them here if not for the occurrence of a roughly circular form preserved in epirelief at the termination of one of the trails. Although inconclusively, this structure appears to document the mortality of the tracemaker and more closely resembles an insect, possibly a beetle.

Trails with two parallel grooves have also been found and are referrable to the ichnogenus Diplopodichnus. Many slabs representative of several different horizons were collected that contain walking arthropod trackways including very abundant Diplichnites and a single occurrence of Acanthichnus. Scoyenia burrows also occur but not abundantly. The invertebrate trace fossil assemblage here is typical of the Scoyenia ichnofacies.

The theropod dinosaur track Grallator is present along with poorly-preserved small reptile tracks probably referrable to the lacertilian ichnogenus Rhynchosauroides. Investigations are ongoing at this locality and additions to this fauna are expected.