Pterygotus is an extinct genus of the order Eurypterida which is a group known as "sea scorpions". The eurypterids flourished during the Silurian and the Devonian 3). Most of the eurypterids group may have been present by the Middle Ordovician. They either radiated rapidly after their occurrence, or earlier groups of them may have an origin in the Cambrian 3).
The eurypterids are known as large arthropods groups, acutualy, the pterugotids are among the largest known arthropods to have existed with a body length of approximately 2.5 m 2), 3).
Pterygotid has six paired prosomal (head and thorax) appendages. The first pair of limbs is chelicerae, limbs II - IV are feeding and/or walking, limbs V is walking, and limbs VI is paddle-like form adapting for swimming 1), 3). Pterygotus may have ability to cross open stretches of ocean and may be the pnly group udertaking oceanic excursions 6). The chelicera of the pterygotid is large.
Although pterygotids were among the chief predators in the middle Palaeozoic world, the chelicerae of Pterugotids were adapted for cutting and grasping, not crushing, suggesting that they were scavenging or browsing 5). In the Early Devonian sea, the pterygotids may have been preyed by the paleozoic fishes, especially sharks 5).
The eurypterids were sexual dimorphism. There is a model of mating that the male deposits a spermatophore on the bottom and the female retrieves and storages it in the spemathecae, allowing the timing of egg production and fertilization to be controlled 1). In the ancient lagoon, a pair of eurypterids may have danced face to face with each other.
The eurypterids may have mated and moulted en masse. They may have migrated seasonally into quiet and fluctuating salinity levels environments, such as nearshore, lagoons, brackish water estuaries, to protect themselves from other predators during ecdysis, or to prevent spermatophore from disruption by strong stream 1).
Probably, the eurypterids had a dual respratory system, an aquatic respiratory organ and an accessory arerial respiratory organ 4). Accordingly, they may have been able to breathe some while on land.
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