North-western Pennsylvania Yields Up a Prehistoric Secret
Patience is one thing that geologists and palaeontologists need plenty of and when it comes to excavating and putting together one of the most ferocious marine predators known from the Palaeozoic fossil record, the patience of even the most dedicated scientist can be tried.
Monster Fish Awaiting Discovery
In a secret location in Erie County (north-western Pennsylvania, United States), Scott McKenzie, assistant professor of geology at Mercyhurst University (Erie County), is returning to a site where the fossilised dermal armour plating of a giant Placoderm is slowly eroding out of a stream bed gully. The landowners are reluctant to permit a full excavation in the heavily wooded area so the assistant professor and his team have to wait for nature to do its job and slowly erode the fossilised pieces of dermal head shield from out of the sandy shale matrix. For Scott, visiting the site at regular intervals to inspect the fossil bearing rock can be quite a depressing business. With luck, he might be able to obtain enough material within a decade or so to make a presentable exhibit within the University’s Sincak Natural History Collection, where assistant professor McKenzie is the curator.
What were the Placoderms?
Placoderms were primitive jawed fish. They are named Placoderms “plated skins” after the wide, flat bony plates that covered the head and the anterior portions of the body. They share a number of anatomical features with sharks and rays, for example they had a body skeleton made of cartilage. Most forms were relatively small, growing to less than sixty centimetres in length, but others were giants and the Erie County specimen represents a specimen of one of the most ferocious of all marine animals known to science – Dunkleosteus.
Top Predator of the Late Devonian
Dunkleosteus was an enormous, prehistoric fish with an armoured head made up of several interlocking bony plates that covered up to thirty percent of this predator’s total length. The Placoderms (armoured fish); evolved in the Silurian geological period from ancestors that had no true teeth. Instead this group of fish developed a pair of sharp bony plates that hung from the top jaw, whilst the edges of the lower jaw were also bony and extremely sharp. The jaws could be closed together like a pair of self-sharpening shears and were powerful enough to cut a two metre long, primitive shark in half. Most specimens of Dunkleosteus (D. terrelli) come from Ohio, so the discovery of a specimen in Pennsylvania might lead to the establishment of a brand new species of this type of armoured fishy carnivore.
The strata from which the dermal armour of this fossilised fish is being eroded from has been estimated to be around 365 million years old (Late Devonian). During this period in Earth’s History much of the eastern part of the United States was underwater, this marine environment would have been a dangerous place to visit with the likes of Dunkleosteus in the water, an apex predator of the Late Devonian.
Spring Thaw Brings Hope of New Fossil Discoveries
With the spring thaw Scott and his team are hopeful that more pieces of the body armour will have been revealed. It is very unlikely that elements of the cartilaginous skeleton will have been preserved, but with the jaws and armoured head potentially being the size of a small car, the specimen once prepared and assembled will make a fine addition to the University’s natural history collection.
Scott commented that Dunkleosteus was arguably the most terrifying creature on the planet in the Late Devonian. Scientists have postulated that this large, marine predator could open its huge jaws so fast that they created a suction force that pulled any unfortunate fish or sea scorpion into the mouth. Once in the mouth the sharp, shear-like bony plates would have sliced and diced up the victim. For the moment the field team are restricted to surface collecting as the landowners have ruled out the possibility of a formal excavation and in any case, digging may damage some of the fossil pieces that remain buried.
Specimen May Have Been Eight Metres in Length
Although, the Erie County specimen is not as big as some of the fossils of Dunkleosteus found in Ohio, it is no tiddler. The geologist calculates that the fossils represent an individual between five and eight metres in length and it probably weighed more than 1,000 kilogrammes. He remains unsure whether this fossil material represents a specimen of D. terrelli or a new species. This does represent the largest fish of its kind found in the Erie County area and an animal that could have given the legendary beast of Lake Erie, affectionately known as “Bessie” by locals a run for its money.
Hoping to Make a Museum Display in the Future
The assistant professor and his team, kindly put on display at the University a number of pieces of the fossil specimen that they had already found, the bony plates although fragmented are an exciting discovery and the team are eager to see what the winter weather has managed to erode out of the matrix so that they can add to their collection. At the moment the disarticulated and disassociated fossil pieces represent a 365 million year old jigsaw puzzle.
A true inspiration to students and other scientists the dedication of Scott and his team as they try to piece together the county’s very own prehistoric monster is to be admired. Fingers crossed for them, let’s hope that the wintry weather and the spring thaw provides them with yet more fossils for them to study as they continue their quest to prepare and mount their very own Dunkleosteus museum exhibit.
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