Shark skull evolution updated
Short one today,
updating an older graphic with the latest ReptileEvolution images in order (Fig. 1).
More taxa =
more parsimony, smoother transitions, greater detail, more support.
Chronologically
Loganellia is Early Silurian, so more primitive taxa are earlier, in the Ordovician.
Jaws
start with Chondrosteus.
Multiple opercula (gill openings)
begin with Rhincodon.
Marginal teeth
start with Ginglymostoma.
Nasals extend beyond the jaws
(convergent with or reversal to sturgeons) with Ginglymostoma and Sphyrna, the hammerhead.
Nasals extend waaay beyond the jaws
in guitarfish (Rhinobatos) + sawfish (Pristis) on one branch and Squaloraja + the goblin shark (Mitsukurina) on another by convergence.
Nasals are much smaller
in Isistius and Ozarcus leading to Hybodus and bony fish, which also return to a single gill opening (as in Prohalecites Fig. 2, Amia, Fig. 1).
Ancestors of Gregorius also evolve to
the moray eel (Gymnothorax, not shown), Harpagofutator (Figs. 1, 2), Edestes, and Helicoprion (Fig. 1).
Ancestors of Gregorius also evolve to
spiny sharks, like Homalacanthus (Early Devonian, Fig. 2) so all more primitive taxa appeared earlier, in the Silurian.
Ratfish and Iniopterygians
arise from horn sharks like Heterodontus. These taxa also reduce the number of gill openings.
Torpedo rays
arise from hammerheads. Other skates, rays and manta rays have separate origins.
Paddlefish (Polyodon)
with a single gill opening arise from basking sharks (Cetorhinus) with multiple gill openings.
This appears to be a novel hypothesis
of interrelationships (Fig. 3). If someone proposed this earlier, let me know so I can promote that citation.
Don’t put all your ‘faith’ in one to a dozen traits
(like gill opeinings) in order to exclude taxa. That’s called “Pulling a Larry Martin.” Expand your taxon list and see where evolution takes your cladogram.
According to the LRT,
humans, bats, frogs, dinosaurs and pterosaurs all have shark ancestors, so we are all sharks. Something else to get used to.
Source: https://pterosaurheresies.wordpress.com/2021/06/04/shark-skull-evolution-updated/
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