Ray-like fish can be confusing
especially if more of the exterior than the interior is preserved (Figs. 2-4). Scoring for the large reptile tree (LRT, 1786+ taxa is based largely on bones, but also on proportions and shapes in detail and overall.
To make matters worse,
ray-like fish like to wrap and fuse their pectoral fins around their face. I mean, who else does that? This one trait is convergent across three clades. Traditional workers suffering from taxon deletion keep mantas, skates and rays in one clade, the invalidated Batoidea, which we looked at earlier here and here.
(Fig. 1) is known from skeletal casts (hollow shapes in stone).
(Jaekel 1921; 6cm snout tip to synacrural length; Mb.f 510.2; Fig. 1; Late Devonian) was originally considered a type of placoderm different from the rest, but here nests basal to the manta ray, Manta (Fig. 6). The purported dorsal nostrils are instead left and right fontanelles that merge in Manta. The toothless mouth parts were largely transverse and faced forward, as in Manta. The tooth-bearing elements: premaxilla, maxilla and dentary were not present. The post parietal and tabulars were detached from the parietal as in Manta. The purported operculum is the supratemporal. Gill openings could be ventral.
a traditionally related taxon, Gemuendina (Figs. 2–4), is known from exquisitely preserved dermal materials with very little of the skeleton visible beneath. Perhaps someday µCT scans will reveal the interior architecture. (PhD candidates, are you listening?)
(Traquair 1903; 30cm to 1m; Early Devonian; Figs. 2–4) was originally considered a placoderm close to Jagorina (Fig. 1). Here both are related to Manta (Figs. 5–6). The famous and often copied diagram above only loosely matches the in situ specimen (Figs. 3–4). The purported dorsal eyes are not dorsal, but tiny and lateral. The purported dorsal nostrils are instead left and right fontanelles that merge in Manta. The purported jutting mouth oriented upward now appears to be a pair of curled under cephalic fins, as in Manta. A mosaic of tessellated scales covers the body, obscuring the skeleton.
Gemuendina is an excellent specimen,
unfortunately obscuring too much of the interior architecture upon which the LRT is built.
In the above photo
(Fig. 4) I could not find the large eyes and jutting mouth illustrated by Gross 1963 (Fig. 2). But I could find soft remains of cephalic fins and tiny lateral eyes, as in Manta (Figs. 5, 6).
(Fig. 5) form a clade of early gnathostomes lacking marginal teeth as adults. Since more primitive sturgeons have marginal teeth as hatchlings, data is needed on the embryos and hatchlings of whale sharks and mantas to see if they have marginal teeth that are ultimately lost. (PhD candidates, are you listening?)
Both extant taxa (whale sharks + manta rays)
have carpets of palatal teeth that look like patches of sharp-to-blunt scales.
This clade of marginally toothless gnathostomes
all feed on free-swimming open-water plankton, rather than the benthic (buried) prey other rays and skates prefer with their ventral mouths full of pavement-like teeth. They filter vast quantities of sea water in a large gill chamber (Fig. 7).
My earlier attempts at understanding
Gemuendina were hampered by not knowing the skin was so thick it obscured the skeleton beneath. Hopefully that mistake is repaired now. If not, further corrections will be made. The addition of Jargorina to the LRT and the deletion of Gemuendina from the LRT brings a more complete understanding of this clade and its ray-like, filter-feeding members.
Gross W 1963. Gemuendina stuertzi Traquair. Notizblatt des Hessischen Landesanstalt für Bodenforschung 91, 36–73.
Jaekel O 1921. Die Stellung der Pala¨ontologie zu einigen Problemen der Biologie und Phylogenie. Pal Zeit 3:213–239.
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.