FEATHERS, TAILS OR CLAWS? – A KINEMATIC-TAPHONOMIC RE-INTERPRETATION OF SOME CONNECTICUT VALLEY ICHNOTAXA

Among the myriad of Connecticut Valley (Early Jurassic, Newark Supergroup) ichnotaxa named and described by Edward Hitchcock are ichnites with features he identified as tail drags and possible feather impressions and drag-marks; subsequent workers have also suggested that some of these features are feather-related. Tarsodactylus caudatus, an ichnospecies Hitchcock (1858) thought was made by an animal dragging it's tail (as the ichnospecies-name suggests), is instead a trackway of an animal dragging it's claws along the substrate as it walked; the ‘tail' traces diverge and terminate at the footprint, in line with the position of the clawprints. A similar phenomenon is seen on AC (Amherst College) 1/7, a specimen referred to Eubrontes lyellii, which has been interpreted instead by some workers (e.g. Gierlinski 1996) to be feather impressions. The type (and only) specimen of ‘Plesiornis' mirabilis, AC 51/16, was believed by Hitchcock to have been made by an animal that rested on all fours, it's lower limbs leaving behind groove-like impressions, with a possible feather impression adjacent to the trackway. However, this specimen (and therefore the ichnospecies) is actually a composite trackway of an Anomoepus-type trackway overprinting a grallatorid-type trackway; the grooves described by Hitchcock are claw-drags (of the grallatorid) leading into the pes prints, and the feather-like impression is simply wrinkling of the substrate as the claws dragged over it. Similar wrinkling is seen on the claw drags of other specimens, as well as on tail drags (e.g. Gigandipus caudatus). This wrinkling is due to the interaction of the body-part with the substrate. There is currently no ichnological evidence for feathers among the thousands of known specimens from the Connecticut Valley.

References

Gierlinski, G. 1996. Feather-like impressions in a theropod resting trace from the Lower Jurassic of Massachusetts. Pp. 179-184 in M. Morales (ed.), The Continental Jurassic. Mus. Northern Ariz. Bull. No. 60.

Hitchcock, E. 1858. Ichnology of New England. Boston, Mass., Commonwealth of Massachusetts.