Carcinosoma newlini

Carcinosoma is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Carcinosoma are restricted to deposits of late Silurian age. Classified as part of the family Carcinosomatidae, which the genus lends its name to, Carcinosoma contains seven species from North America and Great Britain. Carcinosomatid eurypterids had unusual proportions and features compared to other eurypterids, with a broad abdomen, thin and long tail and spined and forward-facing walking appendages.

Carcinosoma was among the largest eurypterids, with isolated fossil remains consisting of a 12.7 centimeters long metastoma of the species C. punctatum indicating a full length of 2.2 meters. Fossil prosomal appendages referred to the species could possibly increase this estimate to an overall length of around 2.5 meters. This massive size makes C. punctatum the largest of all known carcinosomatoid eurypterids and it rivals the largest pterygotid eurypterids, such as the 2.5-meter long Jaekelopterus.

Carcinosoma was first described under the name Eurysoma by British American geologist and paleobotanist Edward Waller Claypole in 1890, who named the type species of the new genus E. newlini in honor of a C. E. Newlin who had collected the fossils. The Eurysoma specimens had been discovered in deposits of Early Pridoli age in the Kokomo Formation of Indiana alongside several other eurypterid specimens, all of which at the time were referred to Eurypterus lacustris.

The walking legs of Carcinosoma were turned forward, which also directed the large spines on the appendages forward. In C. newlini, these flat and forward-facing legs are thought to have been used to create a trap to capture prey in. The strong structures seen in C. newlini are not reflected in other carcinosomatids. For instance, the appendages of Eusarcana were much more weakly developed and would not have served as an effective weapon.

As the opisthosoma of Carcinosoma wasn't as streamlined as that of more active eurypterids and on account of its unique telson morphology, it is believed that Carcinosoma was not a very active swimmer. It is unlikely to have been well adapted to a completely nektonic lifestyle and is more likely to have been nektobenthic. The flat metasoma of Carcinosoma was probably used as at least partially as aid when swimming, suggested by the pretelson being slightly expanded in comparison to other eurypterid.