Sallan et al. 2020 return again to
Tanyrhinichthys mcallisteri (Gottfried, 1987; Stack, Hodnett, Lucas and Sallan 2018; Figs. 1, 2; 15 cm length) and focus on its long rostrum, imagining a bottom-dweller, sturgeon-like lifestyle. Oddly they fail to phylogenetically connect it with extinct and extant paddlefish (Figs. 3, 4). In the large reptile tree (LRT, 1498+ taxa; subset Fig. 5) Tanyrhinichthys nests basal to paddlefish, just a few nodes away from sturgeons.
At that node
Tanyrhinichthys was a late-surviving (Carboniferous) last common ancestor of sharks + bony fish. That’s a big dealin the LRT, but it was overlooked by the authors, due to taxon exclusion and mistaking sturgeons for typical rayfin fish. Based on that phylogeny, Tanyrhinichthys had a Silurian genesis. Perhaps that is why it retained an osteostracan-like armored exoskeleton and was so difficult to nest by prior workers.
Tanyrhinichthys is an iconic transitional taxon in the LRT.
This hypothesis of interrelationships was overlooked by all prior authors due to taxon exclusion and some mislabeling of skull elements (Fig. 2), all repaired here.
Tanyrhinichthys had deep jaws and marginal teeth,
so it nests crownward of Chondrosteus (which had jaws, but no marginal teeth), apart from sturgeons (which lack jaws and marginal teeth). Paddlefish, like Polyodon, have teeth as juveniles (Fig. 3), but lose them as adults (Fig. 4). Both have underslung, shark-like jaws, as in Tanyrhinichthys. This taxon gives rise to sharks, ratfish, and all manner of bony fish… except sturgeons, mantas, whale sharks and kin, which are all more primitive (Fig. 5).
Stack et al. followed tradition
in assuming sturgeons are aberrant actinopterygian (ray-fin) fish. The LRT does not make assumptions, but tests all possibilities and included taxa. In the LRT (fish subset in Fig. 5) sturgeons have an extendible toothless oral cavity, the first step toward the jaws seen in Chondrosteus and all later taxa. They are not aberrant derived taxa.
From the abstract
“The earliest ray-finned fishes (Actinopterygii) with elongate rostra are poorly known, obscuring the earliest appearances of a now widespread feature in actinopterygians.”
This may be an exaggeration. The LRT tests several long rostra taxa. Several nest close to one another. Note the authors are already assuming Tanyrhinichthys is an actinopterygian just because it has ray-fins. Only a comprehensive cladogram can determine whether or not ray fin fish are monophyletic. They are not, according to the LRT, unless sharks are included, which is not the intent of the clade name or definition.
“We redescribe Tanyrhinichthys mcallisteri, a long-rostrumed actinopterygian from the Upper Pennsylvanian (Missourian) of the Kinney Brick Quarry, New Mexico. Tanyrhinichthys has a lengthened rostrum bearing a sensory canal, ventrally inserted paired fins, posteriorly placed median fins unequal in size and shape, and a heterocercal caudal fin. Tanyrhinichthys shares these features with sturgeons, but lacks chondrostean synapomorphies, indicating convergence on a bottom-feeding lifestyle.”
Note: The authors mention sturgeons, but oddly fail to mention paddlefish, so far.
“Elongate rostra evolved independently in two lineages of bottom-dwelling, freshwater actinopterygians in the Late Pennsylvanian of Euramerica, as well as in at least one North American chondrichthyan (Bandringa rayi).”
“The near-simultaneous appearance of novel ecomorphologies among multiple, distantly related lineages of actinopterygians and chondrichthyans was common during the Carboniferous radiation of fishes.
This statement assumes Tanyrhinichthys is an actinopterygian. In the LRT Tanyrhinichthys precedes the shark – bony fish split, despite having ray fins. (Don’t make the mistake of ‘Pulling a Larry Martin.’)
Quotes from ScienceDaily.com, focusing on the new paper:
“Sturgeon are considered a ‘primitive’ species, but what we’re showing is that the sturgeon lifestyle is something that’s been selected for in certain conditions and has evolved over and over again,” says Sallan, senior author on the work.
Not so, according to the LRT where sturgeons and paddlefish are related with Chondrosteus between them.
The Sallen et al. 2020 abstract,
continues to press the resemblance of Tanyrhinichys to sturgeons, while avoiding paddlefish.
“Tanyrhinichthys mcallisteri, a member of the diverse and well-preserved fish fauna within the Upper Pennsylvanian (Missourian) Atrasado Formation of the Kinney Brick Quarry (KBQ), is a small (standard length ~15 cm), elongated actinopterygian with a lengthened rostrum. New material suggests that Tanyrhinichthys was a bottom feeder morphologically similar to the modern sturgeon (Acipenser). Like sturgeon, Tanyrhinichthys had a rostrum that extended past its lower jaw and a resultant small, subterminal mouth, as well as a number of other convergent features, including a long anal fin set forward of the dorsal, large lateral line scales, and an anteriorly-deepened body with ventral insertion of the paired fins. Two other long-rostrumed actinopterygians, an unnamed taxon from Indiana and Phanerorhynchus from the U.K., are known from similarly-aged, Pennsylvanian freshwater coal deposits. Various skeletal features indicate that these long-rostrumed fishes were not closely related.
In the LRT these ‘long-rostrumed fishes’ are all related. So where are comparisons to paddlefish? They immediately follow:
“As supported by the existence of the paddlefish-like shark Bandringa in similarly aged deposits from Illinois, there was widespread convergence on a bottom-feeding freshwater morphotype amongst Pennsylvanian fishes.”
“Tanyrhinichthys falls into a group of fishes with short electro-sensory rostra with less skeletal support anteriorly, likely facilitating a bottom-roving feeding strategy. This group of fishes includes living taxa (sturgeon, paddlefish, and armored catfishes), along with fossil taxa such as Phanerorhynchus. Although there are some exceptions, it appears that long-rostrumed fishes are driven to evolve grossly similar structures in pursuit of distinctive life modes.”
Thus the authors make only the vaguest of connections between Tanyrhinichthys and paddlefish.
re: Gottfried 1987 (below): the clade ‘Aeduelliform’ seems to have been used only by him and him alone. A Google search revealed no other attributions or usages.
Gottfried MD 1987. A Pennsylvanian aeduelliform (Osteichthyes, Actinopterygii) from North America with comments on aeduelliform interrelationships.
7Paläontologische Zeitschrift 61(1):141-148.
Stack J, Hodnett JM, Lucas S and Sallan L 2018. Tanyrhinichthys, a long-rostrumed Carboniferous ray-finned fish (Actinopterygii), and the evolution of elogate snouts in fishes. Journal of Vertebrate Paleontology abstracts 2018.
Sallan L, Lucas SG, Hodnett J-P and Stack J 2020. Tanyrhinichthys mcallisteri, a long-rostrumed Pennsylvanian ray-finned fish (Actinopterygii) and the simultaneous appearance of novel ecomorphologies in Late Palaeozoic fishes. Zoological Journal of the Linnean Society, 2020; DOI: 10.1093/zoolinnean/zlaa044