A MID-DEVONIAN LAGERSTÄTTE FROM THE CATSKILLS (NEW YORK, USA) REVEALS INVERTEBRATES FROM AN EARLY FRESHWATER ECOSYSTEM

The Catskills region of New York state is home to multiple Devonian-age deposits that have produced important fossils for reconstructing early terrestrial ecosystems, such as the oldest forests and silk-producing spider relatives. Here we report on the first known aquatic fossil fauna from the region, part of an exceptionally preserved community at a freshwater-terrestrial interface in the Middle Devonian Plattekill Formation, located in Cairo Quarry. A deposit of organic-rich shales in the quarry produces abundant fossils preserved with details as fine as 10µm. Using HF maceration to extract fossils, we isolated hundreds of specimens of plants, algae, arthropods, and other organisms, many with enigmatic affinities. Crustaceans make up much of the identifiable animal material, with valves of ostracods (preserved on rock surfaces) and spinicaudatan clam shrimp being the most numerous. Appendages and body segments from an undescribed branchiopod taxon, apparently related to anostracans (fairy shrimps), are commonly found. This crustacean possesses a combination of morphological traits previously unseen in branchiopods that place it as an early-diverging member of the clade, shedding light on character evolution in an ecologically and economically important group of freshwater invertebrates. Small, stalked spindle-shaped structures found in the shales closely resemble egg cases of extant turbellarian flatworms. The stalks have been found fixed to the thalli of liverworts, plausibly representing a Paleozoic animal-plant interaction between two rarely fossilized clades. Other fossil morphotypes found in the shales include arthropod segments likely belonging to terrestrial myriapods and arachnids. We interpret the depositional setting as a lake margin—possibly an oxbow lake—within a regional estuarine environment. The Lagerstätte at Cairo Quarry provides a window into a key period in the development of early freshwater and terrestrial ecosystems, in which connections between the aquatic and terrestrial realms may have played major evolutionary and ecological roles. Further study of the site, and comparisons with freshwater paleocommunities from other parts of the Devonian like the Rhynie Chert and Strud biota, will contribute to a deeper understanding of ecosystems from this time.