A difficult thing about uncovering the history of Indiana before 286 million years ago is the lack of terrestrial organisms, or those who lived on land. Most of Indiana’s deposits from that time record marine conditions and yield fossils such as marine snails, fish, corals and trilobites. Because of this rarity, fossils showing evidence of terrestrial life from this time are valuable in the study of Indiana’s past.
The Indiana State Museum has been fortunate enough to acquire one of these rare objects. Collected many years ago, a spider-like animal by the name of Orthotarbus minutus now resides in the Museum collection. The object was found in Sullivan County and acquired from an Indiana fossil collector.
“This little arachnid was most likely a predator and like modern relatives, fed on insects and other arachnids,” said Peggy Fisherkeller, Curator of Geology. “And the amphibians and reptiles that prowled the tidal flats at this time probably ate all of them, if given the chance.”
Most of the terrestrial fossils from Indiana that have been discovered came from geologic deposits in the west-central and southwestern corner of Indiana, and most of them record plant life, with fern fossils and rush-like plants heavily represented. Very few reptile or amphibian footprints have been found – and the Indiana State Museum owns most of these.
“Even though very few terrestrial animals have been found in Indiana from this time period, they were very likely everywhere,” said Fisherkeller. “And just as bugs and spiders are very diverse today, they were probably very diverse 300 million years ago, especially here. So few were preserved because they mostly lived on land, and primarily only marine and stream channel environments were preserved in the rock record.”
This little arachnid provides a rare opportunity to study the terrestrial organisms of that period in Indiana’s history. So what can this rare object tell us about ancient environments in Indiana?
“The addition of this tiny arachnid to the museum collection helps to increase our knowledge of plant and animal interactions with climate during this time period and hopefully will fuel imaginations of future visitors,” said Fisherkeller. “Plant fossils from this time period tell us that climate was warmer than today, and we know from paleogeographic reconstructions that Indiana was located near the equator. In fact, the extinct group to which this arachnid belongs has never been found outside the paleotropics.”
This little arachnid will go on display in the Ancient Seas Gallery, most likely in the spring rotation, Fisherkeller said. It will join a dragonfly-like wing is already on display in that gallery as another example of terrestrial life in Indiana before about 286 million years ago.