The extant Opah now has an Early Jurassic sister in the LRT: Dapedium

“Opa!” is a Greek toast
usually yelled out by customers when the waiter brings out the flaming cheese.

Opah is also a big, colorful deep-bodied fish
(genus: Lampris, Fig 1) languidly swimming today’s oceans. Earlier in the large reptile tree (LRT, 2108 taxa, subset Fig 3) Lampris nested close to the much smaller flying fish, Exocoetus.

A reexamination and rescoring of traits
now nests the small deep-bodied Early Jurassic fish, Dapedium (Fig 1) as a sister to Lampris. The strong resemblance has gone unnoticed everywhere, even here, until today. Flying fish now nest on the other side of the two tested jacks, the swift-swimming Seriola rivoliana and Seriola zonata.

Figure 1. Lampris, the opah (in color, x-ray and diagram, now has a Jurassic sister, Dapedium (above and to scale in the middle.

Dapedium caelatum
(Leach 1822; Thies and Hauff 2011, Thies and Waschkewitz 2015, Smithwick 2015; Lower Jurassic; UHH 2; Fig 1) nests with the much larger extant Lampris in the LRT. Note the ganoid scales absent in Lampris. The skulls are nearly identical. That deep triangular mandible is a character found in many related taxa in the LRT.

According to Thies and Hauff 2011,
“Dapedium Leach 1822 is a neopterygian genus containing deep-bodied fi shes of medium size that were first discovered by early 19th century fossil collectors at the famous Lower Liassic outcrops at Lyme Regis, southern England. The stratigraphical range of the genus is restricted to approximately 25 My from the Late Triassic (Rhaetian) to the Earliest Middle Jurassic. The geographical distribution includes Europe and India encompassing the Mesotethys seaway.”

Lampris guttatus
(Brünnich 1788; up to 2m in length) is the extant opah, a large, colorful, slow-moving discoidal fish. It was the first fish to be considered endothermic. Note the deep coracoids that anchord pectoral muscles to power the flapping pectoral fins. The mouth is toothless. It eats small fish and squid. Traditionally Lampris nests with the oarfish, Regalecus. That is corrected in the LRT (subset Fig 3).

Figure 2. Nematalosa, the extant bony bream from Australia is a river fish basal to the opah + Dapedium in the LRT.
Figure 3. Subset of the LRT focusing on derived ray-fish close to Lampris and Dapedium.

Nematalosa erebi
(Regan 1917; originally Fluvialosa erebi, Chatoessus erebi Günther 1868; length 18cm) is the extant bony bream. It was traditionally considered a member of the Clupeidae (herrings), but here nests basal to jacks, flying flish and opahs. As in more primitive taxa the circumorbital ring is retained. Some specimens of Dapedium retain this ring. Others do not. Note the enormous tabular (light red). This toothless taxon feeds on benthic algae, detritus and small invertebrates.

Thies and Waschkewitz 2015 reported,
“Dapedium is the sister group of the ginglymodian fishes [Semionotiformes + Lepisosteiformes].”

That’s where the LRT used to nest Dapedium. Neither Lampris nor Nematalosa were mentioned in any previous Dapedium study. That means taxon exclusion continues to be the number one problem affecting paleontology.

References
Brünnich MT 1788. Om en ny fiskart, den draabeplettede pladefish, fanget ved Helsingör i Nordsöen 1786. K. Danske Selsk. Skrift. N. Saml. 3: 398-407.
Leach WE 1822. Dapedium politum. P. 45 in HT de la Beche Remarks on the geology of the south coast of England, from Bridport Harbour, Dorset, to Babbacombe Bay,
Devon. Volume 1, Transactions of the Geological Society of London, Series 2. Geological Society of London, London.
Smithwick F 2015. Feeding ecology of the deep-bodied fish Dapedium (Actinopterygii, Neopterygii) from the Lower Lias (Sinemurian) of Dorset, England. Palaeontology 58(2):293–311.
Thies D and Waschkewitz 2011. A new species of Dapedium LEACH, 1822 (Actinopterygii,
Neopterygii, Semionotiformes) from the Early Jurassic of South Germany. Palaeodiversity 4: 185–221; Stuttgart 30:185–221.
Thies D and Waschkewitz 2015. Redescription of Dapedium pholidotum (Agassiz, 1832)
(Actinopterygii, Neopterygii) from the Lower Jurassic Posidonia Shale, with comments on the phylogenetic position of Dapedium Leach, 1822. Journal of Systematic Palaeontology, DOI: 10.1080/14772019.2015.1043361

wiki/Lampris
wiki/Exocoetus_volitans
wiki/Dapedium

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