ribs. Bone from the shale is typically compressed and flattened, while bone in the conglomerate has retained its original shape. Bones of several amphibians of varying size are present. The largest pelvis probably came from an individual whose total length exceeded six feet.
Many of the bones clearly represent amphibians from the subclass Labyrinthodontia, an important group of primitive amphibians. Described remains of early labyrinthodonts from the Devonian of Greenland and the Carboniferous of Scotland illustrate the skeletal anatomy of similar primitive amphibians. Early amphibians superficially resembled salamanders; they possessed elongate bodies, short limbs, and required water in which to lay their non-amniotic eggs to complete their reproductive cycle. Many primitive amphibians were quite large, however, some measuring six to ten feet in length. They were covered with bony scales, and the size and shape of their teeth demonstrate that they were voracious predators whose diet probably consisted mainly of fish. The environment in which they thrived probably was one of shallow, fresh- to brackish-water pools, ponds, and streams in lowlands marginal to the sea.
The bone bed and associated sediments were deposited during a time interval after the regression of the St. Louis seas, but prior to the transgression of the seas which deposited the younger Pella Formation. During this time period an unconformity, or surface of erosion, was developed upon the St. Louis limestones. Formation of karst from the dissolution of limestones and perhaps deeper evaporite (gypsum) beds, plus erosion by flowing water sculpted subtle relief into an otherwise flat landscape. Streams and water-filled depressions on this surface were probably excellent locations for amphibians to feed and reproduce. More importantly though, these same depressions served as sites where skeletons and bones would be deposited, buried, and preserved from the destructive effects of weathering and decay.