Who's Who at Red Hill
Red Hill is a Late Devonian (Famennian Stage) fossil site located in central Pennsylvania. Its geology tells us that Red Hill was formed about 361 million years ago by a large lowland river with extensive floodplains. An impressive variety of animal and plant fossils have been recovered from this site, the most renowned of which are the earliest known tetrapods from North America.
The fossils from Red Hill have come from two broad types of deposits. Most of the vertebrate fossils, including the tetrapods, have been recovered from the shallow channel margin deposits. Vertebrate fossils have also been recovered from the floodplain pond (or overbank pond) deposits. In addition, the pond deposits have yielded an abundance of plant fossils as well as some invertebrates.
Shallow Channel Margin
The shallow channel margin deposits are made up red sandy siltstone sediments, but lenses of coarser red sandstone are also present. Most of the vertebrate fossils consist of disarticulated (separated) bones that show little sign of transport or reworking. Associated skeletal elements have been found in several lenses, as have articulated specimens of smaller fishes. Most if not all of the vertebrates apparently came from the floodplain exysystem.
At least 13 vertebrate taxa have been recovered from the shallow channel margin deposits. This makes Red Hill the most diverse vertebrate assemblage associated with Late Devonian tetrapods. Turrisaspis elektor was the most numerous species, but Phyllolepis, Ageleodus, Gyracanthus, and an assortment of lobe-fin fishes are frequently collected. These vertebrates ranged from the formidible Hyneria lindae, which may have exceeded 3 m in length, to the diminutive Turrisapsis and ray-fin fishes (<10 cm).
- Placoderms (armored fishes)
- Chondrichthyans (sharks)
- Acanthodians (spiny-fin fishes)
- Actinopterygians (ray-fin fishes)
- Sarcopterygians (lobe-fin fishes)
Floodplain Pond Facies
The floodplain pond deposit at Red Hill is made up of greenish-gray mudstone and very fine grained sandstone. The small grain size of these rocks indicate that they were laid down in sluggish waters. Their gray-green color was the result of reducing conditions caused by the decomposition of abundant plant debris. Thin layers of gray-green rock are found thoughout Red Hill, but a 1.5 m thick layer extends through much of the exposure. This layer is believed to be an floodplain pond.
The quiet waters of the floodplain pond increase the chances that some of the plants and animals in or near it will become fossilized. In fact, many of the vertebrate fossils found here are articulated (their bones have not been scattered), whereas most fossils from the shallow river margin are disarticulated (scattered). The abundance of delicate plant fossils and the presence of fragile invertebrates are also the result of favorable conditions.
A total of six vertebrate taxa have been collected from the floodplain pond. Articulated specimens of the ray-fin fish, Limnomis delaneyi and an undescribed rhizodont have been collected here, which suggest that these species were residents. The other vertebrates were represented by smaller bone fragments and individual scales, suggesting that these taxa may have been washed into the lake during flooding.
A large progymnosperm tree, Archaeopteris, and an ancient fern, Rhacophyton, account for most of the identifiable plant fossils, but a relatively diverse assortment of other vascular plants was also found. These include two arborescent lycopsids, barinophytes, another ancient fern, and early seed plants.
- Trachaeophytes (vascular plants):
- Scientific Papers:
- Daeschler, E.B. and W. Cressler. 1997. "Paleoecology of Red Hill: A Late Devonian tetrapod site in Pennsylvania" (abstract). J. Vert. Paleo. 17(3) Supplement: 41A.
- Image Credits: