Stylonurina

Stylonurina Temporal range: Middle Ordovician - Late Permian, 460–251.9 Ma PreꞒ Ꞓ O S D C P T J K Pg N
The defining characteristic of stylonurine eurypterids is that the sixth pair of legs remain normal limbs used for walking. Reconstructed leg of Parastylonurus.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Order:	†Eurypterida
Suborder:	†Stylonurina Diener, 1924
Clades
†Rhenopteroidea †Stylonuroidea †Kokomopteroidea †Mycteropoidea Incertae sedis †Stylonuroides
Synonyms[1]
Woodwardopterina Kjellesvig-Waering, 1959 Hibbertopterina Størmer, 1974

Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from deposits primarily in Europe and North America, but also in Siberia.^[2]

Compared to the other suborder, Eurypterina, the stylonurines were comparatively rare and retained their posterior prosomal appendages for walking. Despite their rarity, the stylonurines have the longest temporal range of the two suborders. The suborder contains some of the oldest known eurypterids, such as Brachyopterus, from the Middle Ordovician as well as the youngest known eurypterids, from the Late Permian. They remained rare throughout the Ordovician and Silurian, though the radiation of the mycteropoids (a group of large sweep-feeding forms) in the Late Devonian and Carboniferous is the last major radiation of the eurypterids before their extinction in the Permian.^[3]

Though the Eurypterina contains several famous giant eurypterids such as Pterygotus and Jaekelopterus, the Stylonurina gave rise to large forms as well, several larger than a metre in length. The largest known stylonurine was Hibbertopterus scouleri, with a potential length of almost 2 metres (6 ft 7 in).^[4]