Eurypterids
Sea scorpions — the largest arthropods that ever lived, reaching 2.5m and ruling Palaeozoic oceans, rivers, and estuaries for 200 million years.
Overview
Eurypterids — sea scorpions — were chelicerate arthropods that radiated from Ordovician into Permian seas, from small crawlers to Jaekelopterus, at around 2.5 m the largest arthropod that ever lived. Some later forms migrated into estuaries and fresh water.
Quick Facts
Key Characteristics
- •Body of a prosoma (head shield) and segmented opisthosoma ending in a telson — a spike or paddle
- •Grasping chelicerae and pointed walking legs; a broad swimming paddle in eurypterines
- •Book gills for respiration
- •Compound eyes and simple ocelli
- •Some grew to 2.5 m — the largest known arthropods
Fossil Record
Eurypterids preserve best in fine, low-oxygen sediments: the Bertie Waterlime of New York (Eurypterus remipes, the state fossil), Lesmahagow in Scotland, and Silurian deposits of Estonia and Ontario yield whole specimens.
Global Distribution
Primarily North America and Europe, with additional records in Asia and Australia.
Evolutionary & Scientific Importance
Sea scorpions illuminate arthropod gigantism (tied to high oxygen and lack of vertebrate competition), the chelicerate invasion of fresh water, and the ecosystems that seeded the later arachnid radiation on land.
Classification
Eurypterids are chelicerates — closer to horseshoe crabs and arachnids than to crustaceans.