Rare dinosaur bone found in western Massachusetts

A Mount Holyoke College geologist looking for ornamental garden stones, chanced upon a dark-colored fossil bone, which he later identified as the distal (outer) end of the right humerus (long upper-arm) of a large neotheropod. The bone dates to the Lower Jurassic period, between 201 million and 174.1 million years ago.

Professor Mark McMenamin and his wife, Dianna, found the fossil in Amherst, Massachusetts, which is part of the Portland Formation of the Hartford Basin in western Massachusetts. Although dinosaur tracks can be found in the area, dinosaur bone material is rare.

The discovery appears in the September 2021 issue of the journal Academia Letters.

Theropod comes from the Greek words for wild beast and foot, and neotheropod means new theropod.

An important find 

The find, McMenamin says, is "the first discovery of bone material from a very large carnivorous dinosaur in the Hartford Basin. This animal may be the largest predatory dinosaur of the Early Jurassic."

He estimates that the neotheropod was more than 9.4 meters (about 30 feet) long. His analysis is based on comparison with specimen dinosaur bones from the Early Jurassic period that have been found elsewhere.

The bone validates the previous discovery of large dinosaur tracks in the area, McMenamin reports.

"We have known about the dinosaur tracks for a long time, ever since Pliny Moody discovered the tracks of `Noah's Raven' in 1802," he said. "Some of these tracks are quite large, reaching more than half a meter in length. Until now we have not uncovered bone material derived from these larger animals."

McMenamin suggests that the rarity of neotheropod tracks may indicate that the neotheropod had an aquatic lifestyle, swimming in lakes. As yet, the dinosaur is not specifically named.

Asked what led him to suggest the aquatic nature of the neotheropod, McMenamin noted the aquatic character of the geological formation.

"The Portland Formation is Early Jurassic in age [approximately 200 million years ago], and consists of lacustrine (lake) and fluvial (river) sedimentary rocks such as shales and sandstones," he said. "The sediments were deposited in a rift basin that formed when the supercontinent Pangea was pulled apart by tectonic forces." 

He cited further lines of evidence of an aquatic or semi-aquatic lifestyle, noting, "First, the bone is very dense, as is the case for Cretaceous spinosaurids. Second, there is evidence for swimming dinosaurs in the Portland Formation strata, in the form of kick marks made by a dinosaur's hind feet while swimming. Third, there were abundant coelacanth and semionotid fishes in the lakes. These would have served as an ample food supply for a large swimming dinosaur."

Unnamed until further analysis 

"I have not published the repository data for this dinosaur because I do not want anyone else to name the creature before our analyses are complete," McMenamin said. "This actually happened shortly after the discovery and misidentification of the Indonesian coelacanth, and has caused quite a scandal.

"We have also recently reported, from Portland Formation strata again, the wing bones of a Jurassic pterosaur," he added. "There is much we have to learn about the Early Jurassic fauna of the Hartford Basin. Further discoveries will be of great scientific interest [including] new fossils from the Early Jurassic have the potential to expand our knowledge of the early evolutionary histories of dinosaurs, pterosaurs, and other creatures of the Mesozoic."

***

M. McMenamin, "Large neotheropod from the Lower Jurassic of Massachusetts," Academia Letters, September 2021. DOI:10.20935/AL3591