Cosmoselachus: likely closer to omitted taxa
Bronson, Pradel, Denton and Maisey 2024
bring us a new chondrichthyan, Cosmoselachus (Fig 1), from the Late Missisisippian of Arkansas USA. The authors reported, “Cosmoselachus mehlingi n. gen., n. sp. possesses a unique operculum comprised of cartilaginous branchial rays that are fused together to form a corrugated structure extending over the gill openings.”
“Unique” is rare to absent in evolution. So, where have we seen something like that before?
Figure 1. Top: Extant Chlamydoselachus. Middle: Cosmoselachus. Bottom: Thrinacoselache.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/03/cosmoselachus-mehlingi588.gif?w=114″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/03/cosmoselachus-mehlingi588.gif?w=389″ class=”size-full wp-image-84815″ src=”https://pterosaurheresies.files.wordpress.com/2024/03/cosmoselachus-mehlingi588.gif?w=584&h=1537″ alt=”Figure 1. Top: Extant Chlamydoselachus. Middle: Cosmoselachus. Bottom: Thrinacoselache. ” width=”584″ height=”1537″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/03/cosmoselachus-mehlingi588.gif?w=584&h=1537 584w, https://pterosaurheresies.files.wordpress.com/2024/03/cosmoselachus-mehlingi588.gif?w=57&h=150 57w, https://pterosaurheresies.files.wordpress.com/2024/03/cosmoselachus-mehlingi588.gif?w=114&h=300 114w, https://pterosaurheresies.files.wordpress.com/2024/03/cosmoselachus-mehlingi588.gif 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Top: Extant Chlamydoselachus. Middle: Cosmoselachus. Bottom: Thrinacoselache. Original µCT scan applied colors are changed to DGS colors here for site consistency.
Unfortunately
the front half of the skull of Cosmoselachue is missing (Fig 1), but what remains compares well with extant Chlamydoselachus and Middle Carboniferous Thrinacoselache (Fig 1). Both were omitted from the Bronson et al analysis.
Figure 2. Bear Gulch formation Thrinacoselache alongside Chlamydoselachus, the frilled shark.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2021/11/thrinacoselache_to_scale588.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2021/11/thrinacoselache_to_scale588.jpg?w=584″ class=”size-full wp-image-61571″ src=”https://pterosaurheresies.files.wordpress.com/2021/11/thrinacoselache_to_scale588.jpg?w=584&h=214″ alt=”Figure 2. Bear Gulch formation Thrinacoselache alongside Chlamydoselachus, the frilled shark. ” width=”584″ height=”214″ srcset=”https://pterosaurheresies.files.wordpress.com/2021/11/thrinacoselache_to_scale588.jpg?w=584&h=214 584w, https://pterosaurheresies.files.wordpress.com/2021/11/thrinacoselache_to_scale588.jpg?w=150&h=55 150w, https://pterosaurheresies.files.wordpress.com/2021/11/thrinacoselache_to_scale588.jpg?w=300&h=110 300w, https://pterosaurheresies.files.wordpress.com/2021/11/thrinacoselache_to_scale588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Bear Gulch formation Thrinacoselache alongside Chlamydoselachus, the frilled shark.
Chlamydoselachus was mentioned several times in the text
but no extant taxa, other than Squalus, were included in analysis. The Thrinacoselache paper (Grogan and Lund 2008) was not cited.
Figure 3. Ventral view of Chalmydoselachus showing two sets of gills: one retained by bony fish, the others retained by sharks and rays.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg?w=584″ class=”size-full wp-image-36761″ src=”https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg?w=584&h=437″ alt=”Figure 3. Ventral view of Chalmydoselachus showing two sets of gills: one retained by bony fish, the others retained by sharks.” width=”584″ height=”437″ srcset=”https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg?w=584&h=437 584w, https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg?w=150&h=112 150w, https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg?w=300&h=225 300w, https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg?w=768&h=575 768w, https://pterosaurheresies.files.wordpress.com/2019/05/chlamydoselachus-gills588.jpg 788w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Ventral view of Chalmydoselachus showing two sets of gills, one with an operculum-like structure and the other a traditional set of shark gill openings. The captions on the photo are outdated, applied when very few fish were included in the LRT.
Cosmoselachus will not be added
to the large reptile tree (LRT, 2315 taxa) due to the preservation of so little skull, here restored (Fig 1, frame 4). Bronson et al nested Cosmoselachus with Ferromirum (Fig 4). That can happen when Chlamydoselachus and Thrinacoselache are not included.
Figure 1. Ferromirum a Late Devonian shark in several views from Frey et al. 2020 and colorized here.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/03/ferromirum_basal_shark588.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/03/ferromirum_basal_shark588.jpg?w=584″ class=”size-full wp-image-84822″ src=”https://pterosaurheresies.files.wordpress.com/2024/03/ferromirum_basal_shark588.jpg?w=584&h=530″ alt=”Figure 1. Ferromirum a Late Devonian shark in several views from Frey et al. 2020 and colorized here.” width=”584″ height=”530″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/03/ferromirum_basal_shark588.jpg?w=584&h=530 584w, https://pterosaurheresies.files.wordpress.com/2024/03/ferromirum_basal_shark588.jpg?w=150&h=136 150w, https://pterosaurheresies.files.wordpress.com/2024/03/ferromirum_basal_shark588.jpg?w=300&h=272 300w, https://pterosaurheresies.files.wordpress.com/2024/03/ferromirum_basal_shark588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 4. Ferromirum a Late Devonian shark in several views from Frey et al. 2020 and colorized here.
Bronson et al reported,
“Features of the dentition and elongate Meckel’s cartilages, as well as phylogenetic analysis by both parsimony and likelihood, place Cosmoselachus n. gen. among the symmoriiform chondrichthyans. However, phylogenetic analysis provides
conflicting hypotheses of the affinity between holocephalans and other chondrichthyans.”
Adding taxa, including extant taxa, and including a long list of placoderms and other traditionally omitted taxa, resolves this issue.
Coincidentally,
the skull of Chlamydoselachus needed an update, (Fig 1).
Chlamydoselachus anguineus
(Garman 1884; 2m in length) was the basalmost shark + bony fish in the LRT, but that was before hundreds of fish were added to the LRT. Now Chlamydoselachus nests between the Megachasma clade and the Cetorhinus clade.
According to Wikipedia,
“The shark’s body featured primitive anatomic traits, such as long jaws with trident-shaped, multi-cusp teeth; amphistyly, the direct articulation of the jaws to the cranium, at a point behind the eyes; and a quasi-cartilaginous notochord (a proto-spinal-column) composed of indistinct vertebrae.
“From that anatomy, Garman proposed that the frilled shark was related to the Cladoselache genus that existed during the Devonian period (419–359 mya).
In contrast to Garman’s thesis, the ichthyologist Theodore Gill and the paleontologist Edward Drinker Cope, suggested that the frilled shark’s evolutionary tree indicated relation to the Hybodontiformes (hybodonts), which were the dominant species of shark during the Mesozoic era (252–66 mya); and Cope categorized the Chlamydoselachus anguineus species to the fossil genus Xenacanthus that existed from the late Devonian period to the end of the Triassic period of the Mesozoic era.”
The LRT nests all these sharks close to the base of sharks and close to one another.
By contrast, holocephalians (= Chimaeriformes) arise from a Devonian sister to Isurus, the mako shark (Fig 5), another taxon not tested in the Bronson et al analysis.
Figure 1. Isurus, Callorhinchus and the Late Devonian shark, CMNH 9280, are transitional taxa at the origin of the Chimeriformes in the LRT.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2023/04/origin-chimaeriformes_isurus-callorhinchus588.jpg?w=204″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2023/04/origin-chimaeriformes_isurus-callorhinchus588.jpg?w=584″ class=”size-full wp-image-77461″ src=”https://pterosaurheresies.files.wordpress.com/2023/04/origin-chimaeriformes_isurus-callorhinchus588.jpg?w=584&h=858″ alt=”Figure 1. Isurus, Callorhinchus and the Late Devonian shark, CMNH 9280, are transitional taxa at the origin of the Chimeriformes in the LRT.” width=”584″ height=”858″ srcset=”https://pterosaurheresies.files.wordpress.com/2023/04/origin-chimaeriformes_isurus-callorhinchus588.jpg?w=584&h=858 584w, https://pterosaurheresies.files.wordpress.com/2023/04/origin-chimaeriformes_isurus-callorhinchus588.jpg?w=102&h=150 102w, https://pterosaurheresies.files.wordpress.com/2023/04/origin-chimaeriformes_isurus-callorhinchus588.jpg?w=204&h=300 204w, https://pterosaurheresies.files.wordpress.com/2023/04/origin-chimaeriformes_isurus-callorhinchus588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 5. Isurus, Callorhinchus and the Late Devonian shark, CMNH 9280, are transitional taxa at the origin of the Chimeriformes in the LRT.
If anyone knows why
Bronson et al discussed similarities between Cosmoselachus and Chlamydoselachus (Fig 1) without adding Chlamydoselachus to their phylogenetic analysis, I’d like to hear that backstory. It just doesn’t make sense.
References
Bronson AW, Pradel A, Denton JSS and Maisey G 2024. A new operculate symmoriiform chondrichthyan from the Late Mississippian Fayetteville Shale (Arkansas, United States). Geodiversitas 46 (4): 101-117.
https://doi.org/10.5252/geodiversitas2024v46a4.
Garman S 1884. An Extraordinary Shark. Bulletin of the Essex Institute: 47–55.
Grogan ED and Lund R 2008. A basal elasmobranch, Thrinacoselache gracia n. gen and sp., (Thrinacodontidae, new family) from the Bear Gulch Limestone, Serpukhovian of Montana, USA. Journal of Vertebrate Paleontology. 28 (4): 970–988.
Maisey J 1989. Hamiltonichthys mapesi, g. & sp. nov. (Chondrichthyes; Elasmobranchii), from the Upper Pennsylvanian of Kansas. American Museum Novitates 2931:42pp.
wiki/Frilled_shark
wiki/Thrinacoselache
wiki/Cosmoselachus
wiki/Frilled_shark
Source: https://pterosaurheresies.wordpress.com/2024/03/09/cosmoselachus-likely-closer-to-omitted-taxa/
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