avidly Name Meaning:  Wide Wing  Lake Dwelling

http://mmsaccounting.ca/tag/mms-accounting/ Geologic Era: Ordovician through Late Permian  

http://vboda7.org/calendar/?time=month Location Discovered: New York

Dhaulpur Size:   Up to 1.2 meters long (most specimens range from 13-23 cm)

Estimated Range: Modern USA 

Extinction Date:  Late Permian

These animals are often referred to as “sea scorpions.”  No living sea scorpions exist today, but their relatives include modern land scorpions, spiders, and the horseshoe crab.  The arthropods were and still are one of the most successful animal groups.  Our Eurypterus specimens are roughly average in size, with the larger specimen being around 6 inches in length.  The smaller one, were it complete, would probably be around 3-4 inches in length.  Our specimen is from the Silurian Era. 

Euripterid bodies are divided into three parts:  the prosoma (head), opisthosoma (body), and telson (tail).  The prosoma and opisthosoma were covered by a shell-like carapace, probably similar to modern scorpions.  The telson, as you can see in the picture below, has distinct barbs along its edges.  The limbs used for walking would have been near the front of the head, while the paddle like, longer limbs were more toward the back of the head.  Part of the paddle limb and smaller forelimb can be seen on the right side of the larger specimen.  

Eurypterids were capable of swimming, and would have employed an up and down rowing motion with their large paddles.  Probable prey included smaller invertebrates living in the sediments, such as worms and smaller arthropods.  It is not known if they were venomous, as modern scorpions are, but the barbed telson would have been suitable weapon for prey capture even without venom. 

An interesting fact about our Eurypterid is that it is probably not a fossil of a complete animal.  Like modern arthropods, eurypterids would have periodically gone through ecdysis, or molting, of their exoskeleton.  It is the remnants of these shed exoskeletons that are usually found, with whole animals being relatively rare.  Ours is probably a shed exoskeleton because of its broken appearance, especially the smaller specimen and the possible fragments of a third.  After shedding, the Eurypterid would have grown rapidly before its new exoskeleton became too hard to accommodate growth.

Eurypterids became extinct during the Permian-Triassic extinction, which wiped out around 90% of marine species, as well as around 70% of terrestrial species.  Eurypterids were already in decline at this point, facing fierce competition from more advanced bony fishes.  It is not certain what caused the Permian-Triassic extinction event, but hypotheses range from hydrogen sulfide venting on the ocean floor to a nearby supernova irradiating the Earth.  Whatever the reason for the mass extinction, it paved the way for new species to take over vacant ecological niches, such as marine reptiles and early dinosaurs.

Image Credits:

Life Reconstruction:  By ObsidianSoul Background Water_floor.jpg from: Dimitris Siskopoulos from Alexandroupolis, Greece (Own work Water_floor.jpg) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Paddling:  By Obsidian Soul (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons