Fossil discovery with a bite: Investigators unearth and describe two new species of ancient shark
Fossil evidence of two new species of ancient shark has been unearthed in Kentucky's Mammoth Cave system, dating to around 325 million years ago.
Palaeontologists discovered the fossil remains of two shark species dating back to 325 million years ago in the 400-mile-long cave system in Kentucky's Mammoth Cave National Park. The fossils were identified as two new species of ancient shark, named Troglocladodus trimblei (T. trimblei) and Glikmanius careforum (G. careforum).
The right conditions for preservation
Mammoth Cave is a spectacular geological formation built through the deposition of layers of Palaeozoic limestone bedrock. The Mississippian and Ordovician periods of around 541 and 252 million years ago saw widespread marine deposition, resulting in limestone layers rich in fossilised marine organisms such as crinoids, brachiopods, and trilobites.
The Mammoth Cave system comprises tubes, sinkholes, and openings, providing unique fossil preservation sites. The stable temperature, absence of solar radiation, and oscillating weather conditions mean that cave systems provide a favourable environment for well-preserved fossil specimens. As many as 70 species of ancient fish have been identified across 25 caves and passages within the Mammoth Cave system.
Diversity and behaviour of the shark species
By analysing the fossilised teeth of adult and juvenile T. trimblei (named after Barclay Trimble, Mammath Cave park's superintendent), the researchers concluded that the unique shark species belongs to a new genus. Its teeth were described as branched and trident-like which influenced the creation of its name, Troglocladodus, meaning "cave branching tooth." In addition to Mammoth Cave, fossil teeth of T. trimblei were also identified in the Bangor Formation in Alabama.
The researchers also identified G. careforum teeth in Mammoth Cave, along with the Bangor and Hartselle Formations. The structure of the mandible provided clues that the shark had a short head and formidable bite, which it may have used to crunch up bony fish and orthocones (ancient creatures with long conical shells and tentacles), as well as smaller sharks. Incomplete fossil remains of G. careforum (comprising of its jaws and gills) remain in Mammoth Cave because they are too fragile to excavate and reside within an area of the caves that is hard to access by the researchers.
The age of these fossils suggests that the Glikmanius genus originated 50 million years earlier than previously considered.