Hibbertopteridae

Hibbertopteridae Temporal range: Middle Devonian - Late Permian, 387.7–251.9 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Drawings of the carapace of Hibbertopterus scouleri, from above (upper drawing) and below (lower drawing) and of the ornamentation of the posterior side of the head (enlarged, left) by Henry Woodward, 1866-1878.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Order:	†Eurypterida
Suborder:	†Stylonurina
Superfamily:	†Mycteropoidea
Family:	†Hibbertopteridae Kjellesvig-Waering, 1959
Type genus
†Hibbertopterus Kjellesvig-Waering, 1959
Genera
†Campylocephalus †Hibbertopterus †Vernonopterus
Synonyms
Cyrtoctenidae Waterston et al., 1985

Hibbertopteridae (the name deriving from the type genus Hibbertopterus, meaning "Hibbert's wing") is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Mycteropoidea. Hibbertopterids were large, broad and heavy animals unlike virtually every other group of eurypterids, which are commonly streamlined and lightweight. Their bizarre morphology is so unusual that they in the past have been thought to represent an entirely distinct order of chelicerates. Fossils of the family first appear in deposits of Middle Devonian age and the last known fossils representing hibbertopterids are known from deposits of Late Permian age. The hibbertopterids represent the last known living eurypterids, going extinct during the Permian–Triassic extinction event or shortly before.^[1]

Although eurypterids are commonly known as "sea scorpions", hibbertopterids inhabited freshwater swamps and rivers and were unable to swim since they lacked swimming paddles, a feature they shared with their entire suborder, the Stylonurina. Hibbertopterids fed using a method referred to as sweep-feeding, in which the animal would rake through the soft sediment of their substrate with specialised blades on their forward-facing appendages to capture small invertebrates. Though this method of feeding was present in other mycteropoids and in stylonuroids, it was at its most advanced stage within the derived Hibbertopteridae.

The hibbertopterids were the largest of all stylonurine eurypterids, with both Hibbertopterus at 180–200 centimetres (5.9–6.6 ft) and Campylocephalus at 140 centimetres (4.6 feet) representing giant eurypterids in their own right. Though longer eurypterids are known from the eurypterine suborder, notably the largest known arthropod of all time, Jaekelopterus, at 230–260 centimetres (7.5–8.5 ft), hibbertopterids were far bulkier than any of the largest eurypterine eurypterids and as such likely represent the overall heaviest animals in the order.