Revised November 18, 2019
with new data on Cladoselache. The dorsal skull specimen of Cladoselache appears to be distinct from the classic skull image (Fig. A) and classic overall image (Fig. B). A new cladogram with many more taxa appears here (Fig. C)
the Cladoselache specimen employed (Fig. 2) did not have the iconic bullet-shaped rostrum with a terminal mandible used in every illustration we’ve seen for this taxon. Rather, the rostrum extended some distance over the mandible and it expanded laterally, creating a disc-shape in dorsal view.
The laterally extended nasal on Cladoselache
is a trait shared with the related sturgeon, Pseudoscaphirhychus, further tying sharks and sturgeons closer together.
Cladoselache acanthopterygius (Dean 1894; Late Devonian; 1.8m) is a primitiive shark with a deeply forked tail. Most images show a terminal mouth, but the example here (Fig. 2) has a typically shark-like underslung mouth and small sharp teeth. A robust spine precedes both dorsal fins. The torso is wider than tall producing a ‘cut-water’ near the tail. The pectoral fins do not have major spines.
The cladogram topology in figure x
is not traditional. Neither is the rest of the LRT. Even so, the LRT continues to provide solutions to long-standing problems and all sister taxa document a gradual accumulation of derived traits. They look like each other, which is how evolution is supported to work.
None of this could be done
without the discoveries of countless paleontologists over the last 200 years. Additionally, none of this could be done without computer software that enables the creation of cladograms from characters and taxa, and software that enables the addition of digital colors to digital images.
Dean B 1894a. Contributions to the morphology of Cladoselache (Cladodus). Journal of Morphology 9:87–114.
Dean B 1894b. A new cladodont from the Ohio Waverly, Cladoselache newberryi, n.sp. Transactions of the New York Academy of Science, 13: 115–119.
Miller RF, Cloutier R and Turner S 2003. The oldest articulated chondrichthyan from the Early Devonian period. Nature 435:501–504.
Turner S and Miller RF 2004. New ideas about old sharks. American Scientist 93:244–252.