When palaeontologists unearthed a fossilised horseshoe crab at the famous Mazon Creek Lagerstätte fossil deposit in Illinois, USA, two things stood out: the remarkable preservation of the ancient animal and more than 100 strange dimples on its shell.
The specimen represents an extinct species of horseshoe crab known as Euproops danae. By comparing it with modern horseshoe crabs, an aquatic animal related to spiders and scorpions, experts believe the curious pits suggest the individual was killed by an algal or parasitic infestation.
According to a new study published in Biology Letters, the find offers rare insight into some of the earliest known cases of animal disease in swamps during the Carboniferous, between 359 and 299 million years.
“Ancient arthropods faced many of the same ecological pressures that modern species experience today, including microbial attacks and environmental stress,” says Russell Bicknell, who led the study.
“This fossil links a specific biological event – likely microbial or algal infestation – to a broader evolutionary picture, showing that interactions between animals and microbes were already well established long before dinosaurs evolved,” adds Bicknell.
“It also ties the specimen to the Late Carboniferous world, a time when Earth’s ecosystems were undergoing significant changes that shaped the future of animal evolution.
“From an evolutionary perspective, this discovery pushes back evidence of such infestations in horseshoe crabs by more than 300 million years.”
Bicknell says the discovery adds a new piece to the ecological puzzle of these ancient animals, highlighting the pressures that shaped their evolution. It also shows the significance of Mazon Creek in documenting ancient host–parasite interactions.
- “A remarkable find": student unearths prehistoric animal on England's Jurassic Coast
- Living fossils: 10 ancient animals with prehistoric roots that are still alive today
Top image: fossil horseshoe crab. Credit: Gregory Lewbart | North Carolina State University
More amazing stories from around the world
- 'Giant' creature found in ancient sinkhole in Appalachian Mountains
- "The whole front of the mouth is just giant teeth." Prehistoric swamp monster with toilet-seat head dug up in Namibia
- Dinosaur hunters make “chilling” discovery deep in Canadian badlands
- Scientists just split open a 2-billion-year-old rock – what they found inside is truly astonishing
