Fedexia: a Late Carboniferous trematopid from Pennsylvania

Fedexia striegeli was a trematopid temnospondyl from Late Pennsylvanian rocks in western Pennsylvania. It is known from one specimen, a three-dimensionally preserved skull with articulated lower jaws and the first two vertebrae. That unusual preservation makes the head unusually informative, while the rest of the skeleton and most aspects of the animal’s life remain unknown. It is one of the early land-capable forms in the ancient amphibian catalogue.

Quick facts

A skull found beside Pittsburgh

University of Pittsburgh student Adam Striegel discovered the fossil in 2004 on a geology field trip near Pittsburgh International Airport. The remains came from the lower Casselman Formation, part of the Conemaugh Group. David Berman, Amy Henrici, David Brezinski and Albert Kollar described the animal in 2010 as a new genus and species. The holotype, CM 76867, entered the vertebrate-palaeontology collection of Carnegie Museum of Natural History.

The specimen preserves most of the skull in three dimensions, portions of both lower jaws, and the atlas and axis at the front of the vertebral column. A small stapes, a bone of the middle ear, is also preserved in position. These elements give researchers a strong anatomical basis for the head and its connection to the neck. No articulated trunk, limbs or tail are known for Fedexia, so familiar full-body images necessarily draw on related animals.

The name combines a reference to FedEx, which owned the land, with the species epithet striegeli for the discoverer. The find is therefore tied to a specific locality and collecting event, rather than to a broad collection of look-alike bones from several sites.

Traits of a trematopid

Fedexia belongs to Trematopidae, a group within the dissorophoid temnospondyls. Its classification rests on a combination of cranial characters, including the shape of the skull and the elongated external nostril typical of trematopids. Features of the palate and rear of the skull help distinguish it from other members of the group. The published family placement is a phylogenetic interpretation based on those anatomical comparisons.

The nostril is divided into front and rear portions. Researchers have proposed that the posterior chamber might have housed a gland or contributed to the sense of smell, but neither soft tissue nor a preserved function is available. The bony outline is observable; the proposed physiology remains a hypothesis. Its teeth and jaws indicate a predatory animal, yet no gut contents identify a particular prey.

The three-dimensional skull makes some measurements reliable, but estimates of total length are much less secure. Since no complete skeleton links the head to the tail, scaling from other trematopids can only provide a comparison. Claims about a precise length, gait or hunting strategy go beyond the single known specimen.

Age and the changing Carboniferous landscape

The lower Casselman Formation is Late Pennsylvanian, within the upper part of the Carboniferous. The original description used the regional term early Virgilian and discussed an age close to 300 million years. Correlating North American stages with the international timescale involves uncertainty, so the formation and regional stage are safer labels than a falsely exact date.

Berman and colleagues presented Fedexia as evidence that trematopids were established in terrestrial settings during a climatic interval that included warmer and drier conditions. This interpretation links the fossil record, anatomical traits and regional palaeoclimate. It does not establish that this one animal experienced a particular drought, or that drying alone produced terrestrial adaptations. Other trematopids and related land-capable tetrapods complicate any simple “first” claim.

The fossil-bearing rocks formed in a continental environment with rivers, floodplains and vegetated ground. A specimen in sediment records where it was buried, not necessarily where it lived every day. An image can place a trematopid in a plausible landscape, but vegetation, colour, skin and behaviour are artistic choices.

What the discovery can and cannot show

Fedexia is significant because a single, carefully preserved skull can document a named trematopid and support comparisons with other early tetrapods. It adds a Late Pennsylvanian occurrence to the group’s history. Its evidence is strongest for cranial anatomy, taxonomic placement and geological provenance. The record is silent about reproduction, growth, disease, exact diet and the proportions of the body.

It was an amphibian-grade temnospondyl, not a modern frog or salamander. The broad term “amphibian” describes an evolutionary group, but should not be taken to mean that every aspect of its physiology matched living amphibians. The best reconstruction keeps the preserved head distinct from the body plan inferred from relatives.