Origin of two clades of spiny sharks and one of spiny shark descendants
According to Wikipedia, representing traditional thinking,
“Acanthodians are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and chimaeras. Acanthodians possess a mosaic of features shared with both osteichthyans (bony fish) and chondrichthyans (cartilaginous fish). In general body shape, they were similar to modern sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteians (gars, bowfins).”
Figure 1. Subset of the LRT focusing on two clades of spiny sharks arising from placoderms close to catfish. So spiny sharks are not basal to extant sharks.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/02/spiny_shark_origins588.gif?w=60″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/02/spiny_shark_origins588.gif?w=204″ class=”size-full wp-image-84121″ src=”https://pterosaurheresies.files.wordpress.com/2024/02/spiny_shark_origins588.gif” alt=”Figure 1. Subset of the LRT focusing on two clades of spiny sharks arising from placoderms close to catfish. So spiny sharks are not basal to extant sharks.” width=”584″ height=”2931″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/02/spiny_shark_origins588.gif?w=584&h=2931 584w, https://pterosaurheresies.files.wordpress.com/2024/02/spiny_shark_origins588.gif?w=30&h=150 30w, https://pterosaurheresies.files.wordpress.com/2024/02/spiny_shark_origins588.gif?w=60&h=300 60w, https://pterosaurheresies.files.wordpress.com/2024/02/spiny_shark_origins588.gif 618w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Subset of the LRT focusing on two clades of spiny sharks arising from placoderms close to catfish. So spiny sharks are not basal to extant sharks.
According to the LRT
acanthodians are not basal to Chondrichthyes. The closest living relatives are catfish (Fig 1) and they are derived from placoderms like Coccosteus.
Figure 2. Ischnacanthus is basal to a third lineage of fish, starting with Sauropsis. This clade includes all bony fish not related to the lineage leading to tetrapods.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/01/ischnacanthus-sauropsis588-2.jpg?w=97″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/01/ischnacanthus-sauropsis588-2.jpg?w=333″ class=”size-full wp-image-83539″ src=”https://pterosaurheresies.files.wordpress.com/2024/01/ischnacanthus-sauropsis588-2.jpg” alt=”Figure 2. Ischnacanthus is basal to a third lineage of fish, starting with Sauropsis. This clade includes all bony fish not related to the lineage leading to tetrapods.” width=”584″ height=”1798″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/01/ischnacanthus-sauropsis588-2.jpg?w=584&h=1798 584w, https://pterosaurheresies.files.wordpress.com/2024/01/ischnacanthus-sauropsis588-2.jpg?w=49&h=150 49w, https://pterosaurheresies.files.wordpress.com/2024/01/ischnacanthus-sauropsis588-2.jpg?w=97&h=300 97w, https://pterosaurheresies.files.wordpress.com/2024/01/ischnacanthus-sauropsis588-2.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Ischnacanthus is basal to a third lineage of fish, starting with Sauropsis. This clade includes all bony fish not related to the lineage leading to tetrapods.
Ischnacanthus is a notable exception.
nesting with Sauropsis, connecting spiny sharks to pachycormiforms, bowfins, coelacanths, salmon, sailfish and a long list of other bony fish not related to tetrapods.
References
wiki/Climatius
wiki/Acanthodii
wiki/Brachyacanthus
wiki/Ptomacanthus
wiki/Brochoadmones
wiki/Diplacanthus
wiki/Ictalurus
wiki/Trichomycterus
wiki/Mesacanthus
wiki/Triazeugacanthus
wiki/Homalacanthus
wiki/Acanthodes
wiki/Ischnacanthus
Source: https://pterosaurheresies.wordpress.com/2024/02/07/origin-of-two-clades-of-spiny-sharks-and-one-of-spiny-shark-descendants/
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