The genesis of the manta ray

Manta is different than other rays.
That difference is reflected in the large reptile tree (LRT, 1694+ taxa). Manta does not nest with other rays, despite a long list of convergent traits. In the LRT Manta nests with the extant whale shark, Rhincodon, but closer to the Early Devonian taxon, Turinia (Fig. 2). Traditionally this boneless enigma is considered a thelodont. But, hey, we’re all thelodonts in a phylogenetic sense, like birds are dinosaurs and mammals are synapsids. Manta and Rhincodon have just changed less than the rest of the vertebrates. Flat and low Loganellia is an Early Silurian sister without the ray-like morphology.

Manta has one of the largest
brain-body ratios in the animal kingdom.

Manta birostris (formerly Cephalopterus manta, Bancroft 1829; up to 5.5m in length) is the extant manta ray. Traditinally a derived member of the guitarfish, skates and rays clade, Manta nests here with Rhincodon, including an anteriorly facing mouth, nares inside the mouth, tiny blankets of teeth and a diet of planktonic prey. The cephalic fins are like the lobes of cownose rays, but detached anteriorly. So, what to make of this ray with a whale shark mouth, nose, eyes and teeth?

Turinia pagei (originally Thelodus pagei Traquair 1896, 1898, Powrie 1870, Donoghue and Smith 2001; Early Devonian, 410mya) nests with the extant manta ray (Manta) in the LRT. This ventral view preserves soft tissue and only faint impressions of cartilaginous skeletal material with an open stomach cavity and a simple gut extending to the cloaca. The gill chamber was enormous. The pectoral fins had already reached the orbit and the weak tail is transitioning to a whip. The gill openings were ventral to the large pectoral fins. Tiny pelvic fins remain, as in Manta.

References
Bancroft EN 1829. On the Fish known in Jamaica as the Sea-Devil. The Zoological Journal. 4: 444–457.
Donoghue PCJ and Smith MP 2001. The anatomy of Turinia pagei (Powrie), and the phylogenetic status of the Thelodonti. Transactions of the Royal Society of Edinburgh: Earth Sciences 92:15–37.
Powrie J 1870. On the earliest known vestiges of vertebrate life; being a description of the fish remains of the Old Red Sandstone rocks of Forfarshire. Edinburgh Geological Society Transactions 1: 284–301.
Traquair RH 1896. The extinct vertebrate animals of the Moray Firth area. Pp. 235–285 in Harvie-Brown J.A and Buckley TE (eds.): A Vertebrate Fauna of the Moray Firth Basin, Vol. II. Harvie Brown and Buckley, Edinburgh.
Traquair RH 1898. Report on fossils fishes. Summary of Progress of the Geological Survey of the United Kingdom for 1897: 72-76.
Swenson JD et al. 2018. How the Devil Ray Got Its Horns: The Evolution and Development of Cephalic Lobes in Myliobatid Stingrays (Batoidea: Myliobatidae). Front. Ecol. Evol, published online November 13, 2018; doi: 10.3389/fevo.2018.00181
White WT et al. 2018. Phylogeny of the manta and devilrays (Chondrichthyes: mobulidae), with an updated taxonomic arrangement for the family. Zoological Journal of the Linnean Society, 2018, 182, 50–75.

wiki/Loganellia
wiki/Turinia
wiki/Manta