Fossils are often fascinating windows into the plants and animals of the past. Some of these ancient animals are different from those alive today. Often, the discovery of these prehistoric creatures are made by those who keep their eyes and ears open to what is around them. This week’s Pennsylvania Treasure tells the story of such a find. The fossil, SMP VP-12, represents an impression of the bone of an ancient armored fish that once lived in Pennsylvania.
In 1882, A. Carter, a farmer living in Susquehanna County, was ploughing his fields when he struck a rather unusual rock. While it’s common for farmers to come across rocks in their fields, this particular rock included some strange markings. The following year, Carter mentioned the odd rock to Professor E. W. Claypole, who requested that Carter send him the distinct specimen so that it might be studied further.
Claypole sought the input of other professionals, contacting many of the prominent paleontologists of the day, including J. F. Whiteaves, E. D. Cope and J. S. Newberry. Each of the experts agreed that they did not know of any known animals that would fit the description of the specimen. Claypole determined that the fossil came from a previously unknown type of ancient fish and named it Pterichthys rugosus. The name roughly translates to “rugose winged fish”. The genus Pterichthys was already known at the time.
Dr. J. S. Newberry, who studied the fossil fish of North America, took a second look at Pterichthys rugosus. He determined that it represented a distinct genus of fish, which he named Holonema, making the proper name for the fish Holonema rugosum. This moniker roughly translates as “rugose threaded fish,” so named for the weird texture on its surface.
Holonema rugosum is a type of ancient fish called an arthrodire, a group of fish known to have armor plating covering their bodies, similar to crustaceans such as crabs and lobsters today. Holonema rugosum ruled the seas before other large fish, sharks and marine reptiles such as mosasaurs and plesiosaurs evolved. Their ranks included one of the largest and potentially scariest sea creatures to ever be around, the almost school bus-sized Dunkleosteus. This group of fish had their heyday during the Devonian Period, but died out about 350 million years ago during a mass extinction event that was more extreme than the one that killed off the dinosaurs.
Holonema rugosum (SMP VP-12) was smaller than its arthrodire relative, Dunkleosteus, although still probably reaching sizes of 4 to 5 feet long. SMP VP-12 represents a piece of the animal’s body armor, namely the boney armor found on the middle of its stomach, just behind its head. Part of what makes this creature so distinct is the sculpturing, or texture on the body armor, which is quite rugose and where the species gets its name. These fish would have been large predators in the seas for more than 50 million years during the Devonian Period. Holonema rugosum would have patrolled the seas over Pennsylvania around 370 million years ago.
Other specimens of this fish have been found in Bradford and Susquehanna counties and in southern New York. Despite these other finds, the best specimen of Holonema rugosum is still the holotype, or first specimen, ploughed up in a field in 1882 and now in the paleontology collection of The State Museum. This discovery shows that amazing things are everywhere, and one never knows where or when they may show up, even in a farmer’s field in Pennsylvania.
This edition of Pennsylvania Treasures was written by Steven E. Jasinski, curator of paleontology and geology at The State Museum of Pennsylvania.
About Pennsylvania Treasures:
The Pennsylvania Historical and Museum Commission houses artifacts hailing from all eras of the commonwealth’s past. These objects represent Pennsylvania arts, culture, history, sciences, business and agriculture. PHMC curators continue to research the stories behind many of these rarely exhibited artifacts and works of art. We are sharing these Pennsylvania Treasures with the public through weekly updates.