page_title: Eusarcana
section_title: Tail spike
hierarchical_section_title: Eusarcana / Paleobiology / Tail spike
caption_attribution_description: Paracarcinosoma (Eusarcus) scorpionis. The Eurypterida of New York. Volume 2. New York State Museum Memoir 14, plate 32
context_page_description: Eusarcana is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Eusarcana have been discovered in deposits ranging in age from the Early Silurian to the Early Devonian. Classified as part of the family Carcinosomatidae, the genus contains three species, E. acrocephalus, E. obesus and E. scorpionis, from the Silurian-Devonian of Scotland, the Czech Republic and the United States respectively.
  Eusarcana is known for its odd proportions and features; the broad abdomen, thin and long tail, spined and forward-facing walking appendages and sharp and curved tail spike differentiate it from most other eurypterids, but are shared with other carcinosomatid eurypterids. The triangular carapace, oddly positioned forward-facing eyes differentiate the genus further from its closest relatives. At 80 centimetres in length, E. scorpionis represents a moderately large species of eurypterid, and far exceeded other representatives of the genus in size, such as the 4 cm long E. obesus.
  Originally described under the name Eusarcus, this name was preoccupied by a genus of living harvestmen in the family Gonyleptidae.
context_section_description: In the Pridoli-age Buffalo waterlime fauna where E. scorpionis lived, it represented one of the larger members of the ecosystem, being at least half as long as the larger predatory eurypterids of the genus Pterygotus. With Eusarcana not having large and powerful pincers like the larger pterygotid eurypterids, which not only represented potential competitors but also dangerous predators, the only obvious organ it could use for defense was the pointed and sharp tail spike.
  The narrowed tail is so long and extended that it exceeds the principal parts of the body, the head and abdomen, in length. The fact that the tail has been preserved as curved in several fossil specimens proves that it would have been flexible in life, with the apparent curvature of the spike on its end making it a dangerous weapon. If curved forwards over the rest of the body, the spike would be positioned with its point turned upwards, effectively acting similar to a scimitar.
  The similarity between the spike of Eusarcana and that of scorpions opens up the possibility that the tail spike might possibly have possessed poison glands. Though the state in which the specimens have been preserved does not allow determination of either the absence or presence of a poison canal or pores for transferring the venom to potential victims, the shape of Eusarcana suggests that it was a rather slow and inactive animal that was not very agile, possibly adapted for burrowing or ambush predation. In such a lifestyle, a venomous and agile tail spike would greatly aid in securing prey and defense in absence of other prehensile and powerful organs with long reach.
caption: Fossil specimen of E. scorpionis with intact tail spike.
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