Megalograptus – A Predator in our Ancient Ordovician Ocean
Posted On: 08/16/2017 - 2:51pm, Posted By: Brenda Hunda, Curator of Invertebrate Paleontology
The rocks in the Cincinnati region are world famous. They preserve and reveal vast amounts of information on an important interval in Earth’s history, the Late Ordovician Period (approximately 450 million years ago), when a shallow, warm tropical sea covered this region. The diversity and abundance of life at this time was astounding, as evidenced by the amazing fossils preserved within these rocks. It was an ecosystem dominated by invertebrate animals, and as such, invertebrates occupied every ecological role in the marine environment. We perhaps tend to think of invertebrate animals as passive and benign as compared to their vertebrate counterparts, but invertebrate predators did exist, and they could be quite large.
A donation of a eurypterid third appendage (they are also known as sea scorpions), along with previously collected material in the Invertebrate Paleontology collections, has shed light on the morphology, paleoecology, and paleobiology of these ancient marine predators.
The third appendage of Megalograptus ohioensis IP53976. Appendage is approximately 18 cm long.
Megalograptus ohioensis is a chelicerate arthropod, most closely related to horseshoe crabs and arachnids (scorpions and spiders). It was one of the largest creatures in the Cincinnati sea floor community, reaching a length of over 50 cm, although there is fossil evidence that they could reach 4 feet in length! Megalograptus is also significant because is it one of the oldest eurypterids in the fossil record, and one of the most unusual. Of particular note is its large third appendage, which is unlike that of any other eurypterid known. It is striking for its length and the long spines directed toward the center. Exactly how Megalograptus used this appendage is uncertain. The basket-like structure of the long spines suggests that the animal might have raked them through the sediment in order to extract prey in a sieve-like fashion. With predators like Megalograptus around, perhaps scuba diving in the Ordovician ocean wasn’t so safe after all!
Specimens of Megalograptus ohioensis are quite rare and unique to the Cincinnati region. When donations of material like this are made to our collections it’s exciting for scientists who want to study these amazing creatures. Each specimen opens a window and reveals something different about our regional natural history. Museums rely upon amateur collectors to bring important finds like this to their attention, as the passion and dedication of “non-professional paleontologists” often leads them to make great discoveries.
A reconstruction of Megalograptus ohioensis. Note the large 3rd appendage.