Perfectly preserved insects dating from the Triassic found in dinosaur droppings

230 million years ago, during the Late Triassic, a dinosaur of the genus of Silesaurus was grazing on a pile of green algae near a body of water in present-day Poland. During its meal, the animal also ingested insects which it then ejected in the form of excrement. And recently, a team of researchers found the dinosaur droppings containing the perfectly preserved fossilized beetles.

These insects are the first to be described from fossilized droppings, and they are unlike anything we’ve previously found in amber. Not only are these insects much older, but their legs and antennae are so intact that the researchers were able to accurately reconstruct their three-dimensional shape. The new species was named Triamyxa coprolithica.

« I was really amazed at how well preserved the beetles were, when we modeled them on screen it was like they were looking us straight in the eye Explains paleontologist Martin Qvarnström from Uppsala University in Sweden. The Triassic is considered a crucial period for the evolution of insects, especially for beetles, which are the most diverse order of organisms today.

230 million year old beetles

Unfortunately, many beetle fossils from this era only give us a footprint of the species, not a three-dimensional view. Amber deposits are the exception. However, they usually don’t date back more than 140 million years. The beetles found in dinosaur droppings are almost twice as old.

Full view of one of the fossilized insects. © Qvarnström et al. 2021

After careful analysis, the researchers placed the new species of beetle in its own family, the Triamyxidae. Given some similarities, they suspect that the insects are an extinct offshoot of a small suborder of beetles, known as the Myxophaga, of which only a few fossils have been found.

ventral view fossilized insect

ventral view fossilized insect
Ventral views of the beetle. © Qvarnström et al. 2021

Today, modern myxophagous beetles can be found in large numbers on mats of green algae, usually near water; the finding suggests that their former parents may have been abundant in similar aquatic environments. The fossilized excreta, known as the coprolite, is believed to have come from a two-meter-long dinosaur, called Silesaurus opolensis, which feeds primarily on plants but also appears to have a penchant for insects. The number of beetles in his droppings certainly suggests that.

Silesaurus: his diet was certainly omnivorous

These insects being small and so numerous, researchers believe they were likely an accompaniment to the main meal. If a dinosaur munched on green algae near shore, for example, any beetle it consumed along the way would be a crisp addition and, if digested, a nutritious addition to the meal.

Given their tiny and sturdy bodies, the researchers believe that beetles would have had a better chance of surviving dinosaur digestion compared to other insects. Anything that had a soft body would have been easily broken down. ” Although Silesaurus appears to have ingested many individuals of T. coprolithica, the beetle was probably too small to have been the only prey targeted. », Explains Qvarnström.

reconstitution silesaurus opolensis

reconstitution silesaurus opolensis
Reenactment showing Silesaurus opolensis in its natural environment. © Joanna K.

« Instead, Triamyxa likely shared its habitat with larger beetles, which are represented by disarticulated remains in coprolites, and other prey, which have never been found in coprolites in any recognizable form. It therefore seems probable that Silesaurus was omnivorous, and that part of his diet was composed of insects.s ».

Coprolites: a promising tool for studying the evolution of insects

The discovery led the authors to believe that coprolites could provide an excellent window into the early evolution of insects. Fossilized feces may be more difficult for the human eye to see, but using a micro-scanner, the researchers were able to make out all the tiny details on T. coprolithica.

It wasn’t until the Lower Cretaceous that tree resin was abundant enough to capture the first insects in action and fossilize them. During the Triassic there was much less tree resin around which means we don’t have amber deposits to reveal what insects looked like at that time.

Sources : Current Biology
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