| Tristychius | |
|---|---|
 | |
| Restoration ofTristychius | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Family: | †Tristychiidae |
| Genus: | †Tristychius Agassiz,1837[1] |
| Type species | |
| †Tristychius arcuatus Agassiz, 1837 | |
Tristychius (fromGreek:τρειςtreis, 'three' andGreek:στῐ́χοςstíkhos 'row')[2] is an extinct genus ofeuselachianchondrichthyan from theCarboniferous period (Visean). Fossils ofT. arcuatus, the type and only species, including fin spines have been found inScotland.
Tristychius was a small animal, up to about 60 centimetres (2 ft) long. It had aheterocercalcaudal fin, and large spines on two dorsal fins.[3] Unlike other chondrichthyans that have three basal plates on pectoral fin (propterygium, mesopterygium and metapterygium), its pectoral fin had only two basal plates and lacked mesopterygium.[4] Even through it is one of the earliest known stem-elasmobranchs, it is estimated to be a specializedsuction feedingbenthic predator, eitherambushing or using stealth to approach its prey.[5] While historically considered ahybodont, a 2016 study considered it to be a basal euselachian, with hybodonts more closely related to Neoselachii (the group of modern sharks and rays) than toTristychius. The study placed the genus in the familyTristychiidae along withAcronemus.[6]
Holocephali (chimaeras and relatives) | |||||||||||||||||||
| Euselachii |
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