Cladoselache enters the LRT

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)

Figure A. Classic diagram of Cladoselache skull, colors added.

Figure A. Classic diagram of Cladoselache skull, colors added.

Figure 1. Classic reconstruction of Cladoselache, a shark-like taxon basal to sturgeons and catfish+placoderms in the LRT.

Figure 1. Classic reconstruction of Cladoselache, a shark-like taxon basal to sturgeons and catfish+placoderms in the LRT.

The iconic Devonian shark, Cladoselache
(Fig. 1), enters the large reptile tree (LRT, 1463 taxa) nesting with the extant mako shark, Isurus. That’s to be expected. They are both traditional sharks.

FigurFigure 1. Cladoselache specimen in ventral view. Note the rostrum and mandible tip have been restored as a gray tone here. e 1. Cladoselache specimen in ventral view. Note the rostrum and mandible tip have been restored as a gray tone here.

Figure 1. Cladoselache specimen in ventral view. Note the rostrum and mandible tip have been restored as a gray tone here. Prior workers imagined a bullet-shaped skull, but see figure 2. This may be a flatter taxon in vivo that previously illustrated.

Surprisingly,
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.

Figure 2. Cladoselache skull and pectoral fins in dorsal view. Colors added. Note the disc-shaped rostrum, different than the iconic bullet-shaped rostrum we are all used to seeing.

Figure 2. Cladoselache skull and pectoral fins in dorsal view. Colors added. Note the disc-shaped rostrum, different than the iconic bullet-shaped rostrum we are all used to seeing.

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.

Figure 6. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

Figure x. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

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.


References
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.

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