Researchers have uncovered a unique 50-million-year-old specimen of an extinct katydid species with its muscles, digestive tract, glands, and even one testicle still intact. Marking a likely first-of-its-kind find, the detailed fossil has provided vital new information into the evolutionary history of katydids.
Belonging to the genus Arethaea, also known as thread-legged katydids in reference to their grass-like limbs, the extinct species has been named Arethaea solterae after the lead author’s colleague and retired insect pathologist Leellen Solter.
“Katydids are very rare in the fossil record, so any new katydid fossil you find represents a new data point in the evolutionary history of katydids,” Sam Heads, study lead and director of the Prairie Research Institute’s Center for Paleontology, said in a statement. “Now we know that about 50 million years ago, this genus had already evolved and already had a morphology that mimics the grass in which it lives and hides from predators.”
While Heads describes finding gut traces in specimens from this area as “not so unusual”, after further microscopic investigation, the team uncovered evidence of thoracic muscle fibers associated with the wings or flank muscles, tissue known as a “fat body”, and even the inclusion of one testicle.
“Part of the digestive tract is preserved, a part of the midgut we call the ventriculus,” Heads said. “There are these little tubules that all seem to connect to a round structure – and that can only be a testis and accessory glands that are associated with the testis.”
Heads analyzed these findings in comparison to several dissected katydid specimens and found an almost identical anatomical structure, stating “the testis, the accessory glands and the ventriculus were all the same in the present-day katydids. I was just blown away by it.”
The area the fossil was retrieved from is well-known for its abundance of perfectly preserved fossils. Extending into the three states, the Green River Formation is a famous fossil bed that contains detailed records of the region’s flora and fauna. But despite the area’s reputation, researchers were still shocked by the find.
“I was not expecting to see that kind of structure preserved in a rock compression. I’ve never seen that before,” said Heads. “To my knowledge, this is the first example of this level of preservation.”
The study is published in Palaeoentomology.