AMPHIBIAN BODY IMPRESSIONS FROM THE MISSISSIPPIAN MAUCH CHUNK FORMATION, EASTERN PENNSYLVANIA

An exceptional case of preservation of three body impressions of Mississippian temnospondyl amphibians provides direct evidence of body shape, texture of the integument and possible social behavior in 330-million-year old amphibians.These impressions are from the Mississippian (Visean) Mauch Chunk Formation near Pottsville, Schuylkill County, eastern Pennsylvania, USA. The three body impressions are preserved on a reddish brown, fine-grained sandstone slab with a clay drape. On one side of the slab, two tetrapod body impressions preserve nearly complete head, body and limb outlines in convex hyporelief; on the other side of the slab a sinusoidal ridge represents a median body/tail drag associated with an incompletely-preserved body impression, also in convex hyporelief. The shovel-shaped head, robust limbs, relatively short trunk and smooth integument readily distinguish the Mauch Chunk impressions from Hermundurichnus and Sauropleura, the only named body impressions of Paleozoic tetrapods. The footprints of the Mauch Chunk body impressions can be assigned to the ichnogenus Batrachichnus, which indicates that they are of a temnospondyl. This adds to the sparse and earliest records of temnospondyls, which are of Visean age. The smooth integument of the impressions does not support the presence of ventral scales or armor in the earliest temnospondyls, but body proportions of the Mauch Chunk body impressions indicate a relatively terrestrial temnospondyl not matched by any taxon now known from fossil skeletal remains. Three closely-associated impressions on a single bedding plane suggest some sort of gregarious behavior in Mississippian temnospondyls. The head-to-tail overlap of two of the impressions may indicate that internal fertilization and associated courtship behavior evolved independently in one group of amphibians more than 300 million years ago.