Occithrissops

Occithrissops is an extinct genus of prehistoric ray-finned fish of the Jurassic, known for its fearsome yet small appearance. The genus name of Occithrissops derives from the Latin word "Occi" (killing) and the Greek words "thriss" (fish) and "ṓps" (“face”). Similar in relationship to the Thrissops, it was a slightly larger predatory teleost fish with serrated pelvic fins, a cleft tail, and a bony tongue similar to the Arapaima and formerly mentioned Thrissops, bearing small teeth for catching small slippery prey like squid, invertebrates and fish.^[1] The bony tongue assisted the fish in consuming hard shelled invertebrates which included small nektonic Jurassic ammonites, which despite the growing decline of ammonoids were still prevalent and plentiful for their time.^[2]

Appearance

Occithrissops skulls and spines shared similarities to modern day osteoglossiformes. It had a thick skull and cleft pectoral fins, a body shape built towards fast pursuit in marine environments as opposed to the living osteoglossiforms which have elongated fins more suited to maneuvering in heavily obstructed rivers.^[3] They were a anadromous species, a term which comes from the Greek anadromos, meaning "running upward". They would migrate into fresh-water to spawn, albeit not as successfully as other anadromous species, as Occithrissops and other open-ocean osteoglossiformes did not survive the Triassic-Jurassic extinction event, while other members retreated to Gondwana rivers before the continent broke up.

Paleobiology

Occithrissops was a small but violent nektonic carnivore, residing in an ecological niche similar to the barracuda and the piranha. It was distributed throughout the Jurassic Oceans, congregating frequently and preying upon smaller forage fish of the period. Larger adults would become solitary while younger members continued to congregate for protection. It is believed that they participated in Lepidophagy. Thrissops were believed to be their primary prey, or a competitor for prey. They were common prey to many predators of that area including Leedsichthys, many Ichthyosaur species and Plesiosaur members.

Natural Threats

The Occithrissops, despite being an agile and advanced piscivorous predatory fish, only reached a maximum length of 1.8 metres (5.9 ft), outsized by a large menagerie of different species that generally preyed upon it, or were specialized ecologically to hunt for fish species that included it. Being a pelagic forage fish made it an accessible, predictable and easy prey for Jurassic marine reptiles. The appearance of the first metriorhynchid crocodilians appeared during the height of the epoch in which Occithrissops were most common, and many partial specimens were found in the stomachs of recovered metriorhynchid fossils.^[4] This fish's teeth were small and tailored towards capture rather than inflicting any defensive wounds to any predators larger than itself.

Disappearance

Occithrissops and many other small marine Jurassic fish were subject to massive oceanic acidification and sea-level fluctuations^[5] along with massive fish kills and a possible decline of phytoplankton which many Jurassic keystone species relied upon to survive.^[6] This would reduce the amount of members living in the ocean, making the pressures of predation from very large predators such as ichthyosaurs, pliosaurs, and marine crocodilians of the families Teleosauridae and Metriorhynchidae too high. The disappearance of Occithrissops and other small fish was followed by the Triassic–Jurassic extinction event.

See also

• Prehistoric fish
• List of prehistoric bony fish

References