Rare 50-million-year-old fossil reveals exquisitely preserved insect organs

Heads, who is also the director of the Prairie Research Institute’s Center for Paleontology, added: “But perhaps the most striking feature of this fossil is the really exceptional, remarkable preservation of internal organs – organs that you just don’t see in fossils.”

The intact fossil belongs to a new insect species 

After meticulously examining the remains, the team noted that the fossil belongs to a new but extinct species, which they named Arethaea solterae.

The extinct species belonged to the genus Arethaea, while the second name comes from a retired insect pathologist, Leellen Solter.  

The fossil depicts the insect's internal system in great detail, including the digestive canal, muscle fiber traces, testicles, and small tubule-like structures.

The team was astounded by the exceptional preservation of the interior components, as soft tissues barely survive for such a long time. 

The researchers examined the internal anatomy of many dissected katydid specimens from the same genus to confirm their findings. And their observations of the preserved soft tissues were validated. 

The arethaea genus today includes ​​katydids with strange thread-like legs. The discovery of this fossil will be useful to fill in the evolutionary gaps about the physical structure of this group of insects. 

“Obviously, having a fossil species of a modern genus is really significant because it confirms the antiquity of this lineage,” Heads said. “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.”

The study findings have been reported in the journal Palaeoentomology.

Study abstract:

Orthoptera (grasshoppers, crickets, and katydids) are abundant and diverse in the lower–middle Eocene Green River Formation of the Piceance Basin in northwestern Colorado, though remain almost entirely unstudied. Here, we describe a new species of the katydid genus Arethaea Stål (Tettigoniidae: Phaneropterinae: Insarini) from the Parachute Creek Member at a locality near Meeker in Rio Blanco County. Arethaea solterae Heads, Thomas & Hedlund sp. nov. is the first fossil member of the genus and the first tettigoniid described from the Green River Formation. The holotype and only known specimen is remarkable for the exceptional preservation of internal organs including the anterior midgut (ventriculus) and what appear to be a testis, accessory glands, and possible fat body.