Researchers from the University of Cincinnati have recently discovered not one but two ancient parasites that would attach themselves to marine fossils. Parasite interactions on fossils have been notoriously hard to find, due to the fact that parasites mostly live on the soft tissue of their host. The discovery of these parasites also gives us a glimpse as to how the parasites and the creatures they lived on evolved over 200 million years.
The effect of the parasites were first discovered on ancient crinoid fossils. Modern crinoids are marine animals like sea lilies and live in both deep and shallow water.
The first of the two parasites was a small spiny snail that lived near the anus of the crinoid, feeding on the expelled waste. However, researchers discovered that as the snail evolved it would eventually use its tongue to drill a feed tube directly into the gut of the crinoid. Another interesting evolutionary turn took place with the development of spines on both the crinoid as well as the snail.
“We connected the spine growth to the rise of fish predators in the Devonian Period. About 360-to-420 million years ago there was a revolution of swimming predators, such as sharks, that could swim above the bottom of the sea and go after hard-shelled prey. Although the crinoids may not have been very delectable, based on living forms, the gastropods may well have been delicious ‘escargot’ to these larger predators. In this sense, the crinoids that hosted the snails were ‘targeted’ by the predators, which was detrimental to both the crinoids and their attached snails.”
The second parasite discovered on these crinoids was an ancient parasitic worm that is now extinct. The parasites would drill out large areas on the skeleton of the animal, leaving large pits. Some of the fossils had a majority of thier body covered in these pitted areas.
“The parasites never really were so harmful that they killed the hosts, but persisted in ‘ecological standoffs,’ even through major biological crises. Eventually, however, both groups became extinct.”