Revisiting Aquilolamna using Cladoselache kepleri as a Bauplan

For your consideration:
Early Cretaceous Aquilolamna (Fig 1) now nests with Late Devonian Cladoselache kepleri (Fig 1) in the large reptile tree (LRT-2311 taxa). These two nest in a previously overlooked clade that had its genesis in flat-head placoderms like Bianchengichthys (Fig 4). At this unfinished point in the construction of this cladogram, several members of the traditional clade Chondrichthyes now appear to have had separate origins in the LRT.

Sometimes it takes a related genus to provide a familiar Bauplan for unfamiliar taxa. The recent addition of Cladoselache kepleri (Fig 1) to the LRT finally provided a Bauplan that was lacking in 2021 when Aquilolamna first entered the LRT with Palaeospondylus, itself a Middle Devonian enigma taxon, nesting in the LRT close to the extant torpedo ray, Tetronarce.

In phylogenetic analysis always look for a better match for problem taxa. So keep adding taxa (not characters) to resolve your cladogram.

Several hundred million years separate Aquilolamna from Cladoselache.
Even so, the two share a long list of traits exclusive of other tested taxa.

Figure 2. Revised tracing of the Aquilolamna skull. ” data-image-caption=”

Figure 2. Revised tracing of the Aquilolamna skull.

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/02/aquilolamna_skull588.gif?w=238″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/02/aquilolamna_skull588.gif?w=584″ src=”https://pterosaurheresies.files.wordpress.com/2024/02/aquilolamna_skull588.gif?w=588″ alt=”Figure 2. Revised tracing of the Aquilolamna skull.” class=”wp-image-84291″ style=”width:588px;height:auto” srcset=”https://pterosaurheresies.files.wordpress.com/2024/02/aquilolamna_skull588.gif 588w, https://pterosaurheresies.files.wordpress.com/2024/02/aquilolamna_skull588.gif?w=119 119w, https://pterosaurheresies.files.wordpress.com/2024/02/aquilolamna_skull588.gif?w=238 238w” sizes=”(max-width: 588px) 100vw, 588px” />

Cladoselache kepleri is easier to understand
because the morphological elements are more distinct (Figs 1, 4). Aquilolamna is less distinct, harder to score. That’s why a Bauplan, a Rosetta Stone, a blueprint, a guide, is sometimes needed to present possibilities for interpretation. Over time you will start to develop an eye for traits that should or should not be present based on comparative anatomy.

Aquilolamna milarcae
(Vullo et al. 2021; 1.6m; Tuorcian, Early Cretaceous, INAH 2544 P.F.17) was described as a manta-like plankton feeder with wide terminal jaws and lalcking pelvic fins. Here Aquilolamna nests with Cladoselache kepleri apart from Cladoselache fyleri. Some skull labels provided by Vullo et al. are reinterpreted here (Fig 3).

Figure 1c. Cladoselache kepleri nests with these flathead sharks derived from flathead placoderms in the LRT ” data-image-caption=”

Figure 1c. Cladoselache kepleri nests with these flathead sharks derived from flathead placoderms in the LRT

” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/02/gladbachus.dickosteus.fossil588.jpg?w=121″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/02/gladbachus.dickosteus.fossil588.jpg?w=412″ src=”https://pterosaurheresies.files.wordpress.com/2024/02/gladbachus.dickosteus.fossil588.jpg” alt=”Figure 1c. Cladoselache kepleri nests with these flathead sharks derived from flathead placoderms in the LRT” class=”wp-image-84251″ />

Squatinactis caudispainatus
(Lund and Zangrel 1874, Lund 1988, Late Carboniferous, CMNH 461133) is known from elements similar to those found in Aquilolamna, but with transitional proportions. Lund reported, “The pectoral fin structure is unique among Chondrichthyes… Lack of adequate detail prohibits assignment other than as a derived sister taxon of Cladoselache.”

Vullo et al mentioned Squatinactis (which is how it came to my attention) without getting into details. Cladoselache kepleri was not mentioned.

References
Lund R and Zangrel 1974. Squatinactis caudispinatus, a new elasmobranch from the Upper Mississippian of Montana.. Annals of the Carnegie Museum 45:43–54.
Lund R 1988. New information on Squatinactis caudispinatus (Chondrichthyes, Cladodontida) from the Chesterian Bear Gulch limestone of Montana. Journal of Vertebrate Paleontology8(3):340–342.
Vullo R, Frey E, Ifrim C, Gonzalez Gonzalez MA, Stinnesbeck ES and Stinnesbeck W 2021. Manta-like planktivorous sharks in Late Cretaceous oceans. Science 371(6535): 1253-1256. DOI: 10.1126/science.abc1490

wiki/Aquilolamna
wiki/Squatinactis