Dapedium
Dapedium is an extinct genus of primitive marine neopterygian ray-finned fish. The first-described finding was an example of D. politum, found in the Lower Lias of Lyme Regis, on the Jurassic Coast of England. Dapedium lived in the Late Triassic to the Middle Jurassic period, from the late Norian to the early Aalenian.
Evolution
Dapedium is one of the most diverse and abundant genera of ganoid fish from the early Jurassic of Europe. Its remains are known from many appropriately-aged lagerstätten throughout western Europe, with some records also known from eastern Europe. It appears to have been relatively rare during the Triassic, especially compared to other members of its family, but saw a large burst in diversification in the wake of the Triassic-Jurassic extinction event. It is thought that most Triassic dapediids had highly specialized feeding strategies or had less armor compared to the heavily-scaled, generalist Dapedium, allowing it to survive the extinction event. These adaptations may have also enabled Dapedium to survive a second extinction event, the Toarcian Oceanic Anoxic Event, although the abundance of Dapedium saw a dramatic decline after that, and it went extinct shortly afterwards. Dapedium was apparently a poor disperser, as despite its ecological success, there are no records of it outside Europe.Species
The following species are known:- D. angulifer - Early Jurassic of England
- D. ballei Maxwell & López-Arbarello, 2018 - Middle Jurassic of Germany
- D. caelatum Quenstedt, 1858 - Early Jurassic of Germany
- D. colei Agassiz, 1835 - Early Jurassic of England
- D. dorsalis - Early Jurassic of England
- D. granulatum Agassiz, 1835 - late Hettangian/earliest late Sinemurian of England
- D. magnevillei - early Toarcian of France
- D. milloti Sauvage, 1891 - early Toarcian of France
- D. noricum Tintori, 1983 - Late Triassic of Italy
- D. orbis Agassiz, 1836 - Hettangian/Pliensbachian of England
- D. pholidotum - early-middle Toarcian of Germany
- D. politum Leach, 1822 - early Sinemurian to earliest late Sinemurian of England
- D. punctatum Agassiz, 1835 - early Sinemurian to Pliensbachian of England
- D. stollorum Thies & Hauff, 2011 - early-middle Toarcian of Germany
Appearance
The various species of Dapedium ranged from long, and all had an oval to near-circular body. The skin was covered with thick, rhomboid, ganoid scales. The smallest species so far found is D. noricum.The skull was armoured with bony dermal plates, which were especially plentiful in the orbital region. These bones bore irregular tubercles. The small pectoral and pelvic fins, along with the extended dorsal and anal fins formed a functional unit with the tail. The tail was short and stout, providing the power for a sudden change in direction while the fish was swimming.
The upper jaw of Dapedium was moveable and could protrude from the mouth, enabling a wider gape to capture larger prey.