Clupeopsis: a large anchovy with a single vomer fang

Capobianco et al. 2020 bring us a µCT scan update
on a previously described large early Eocene anchovy with a single large vomer fang: Clupeopsis (MRHNB IG 8630; Casier 1946; Fig. 1).

They report, “Numerous features of the neurocranium, suspensorium and branchial skeleton place these taxa on the engraulid (anchovy) stem as the earliest known representatives of the clade.”

Figure 1. Clupeopsis from Capobianco et al. 2020 and colorized using DGS methods here.

Figure 1. Clupeopsis from Capobianco et al. 2020 and colorized using DGS methods here. Note: the cheek plate is composed of four bones, not just one as indicated by the tracings of the µCT scans. Colors make bone identification and delineation much easier. Let’s say goodbye to line drawings.

True, but by contrast, 
the large reptile tree (LRT, 1691 taxa; subset Fig. x) includes the Late Triassic flying fish, Thoracopterus (Fig. 3), in the same clade. So Thoracopterus is the earliest member of that clade. Thoracopterus is not mentioned in the Capobianco et al. text.

Figure 2. Engraulis skull greatly resembles that of Clupeopsis.

Figure 2. The anchovy, Engraulis skull greatly resembles that of Clupeopsis.

Clupeopsis was recognized
as a giant anchovy when it was first described, hence, its name, which refers back to the Clupeiformes (= anchovies and kin). Capobianco et al. bring us news of the giant vomer revealed by µCT scans, along with another giant vomer in a sister taxon missing too many dermal bones to be tested here.

Figure 3. Thoracopterus skull.

Figure 3. Thoracopterus skull.

Unrelated Update:
The recent addition of the Jurassic osteoglossiform, Ohmdenia (Fig. 5), attracted the weird Cretaceous swordfish-mimic Protosphyraena (Fig. 4), a traditionally hard-to-nest fish in the LRT (subset Fig. x) and elsewhere. This clade of large predators share spine-like fins and mirror-image dorsal and anal fins. A modern relative is the Amazon predator, arowana ( genus: Osteoglossum). These taxa are not far from spiny sharks (Fig. x).

Figure 1. Protosphyraena museum mount. Length about 3m. Note the advanced placement of the pelvic fins.

Figure 4. Protosphyraena museum mount. Length about 3m. Note the advanced placement of the pelvic fins.

In addition,
several traditional, extinct shark-like taxa (e.g. Xenacanthus, Hybodus) now nest in a sister clade to the ratfish + shark clade (= Elasmobranchiil; Fig. x). Previously these nested as stem bony fish close to another traditional chondrichthyan, Gregorius, which remains a stem bony fish. Now the sturgeons, paddlefish and Chondrosteus nest closer together, all basal to the shark/bony fish dichotomy. This split is one node away from the great bony fish dichotomy separating spiny sharks and kin from the majority of traditional ray fins, most of which appear in the fossil record after the Jurassic.

Figure 1. From bottom to top: Ohmdenia in situ, as reconstructed by Friedman 2011, as traced by Friedman 2011 (colors added) and as reconstructed here.

Figure 5. From bottom to top: Ohmdenia in situ, as reconstructed by Friedman 2011, as traced by Friedman 2011 (colors added) and as reconstructed here.

For operculum aficionados:
This means the operculum (gill cover) originated several times by convergence in [Plan A]: 1) sturgeons, 2) paddlefish, 3) ratfish, and 4) traditional bony fish… or [Plan B] the operculum was convergently lost in 1) whale sharks = mantas and 2) traditional sharks. More study should illuminate which is correct, if not a mixture of both in some fashion.

Figure x. Newly revised fish subset of the LRT

Figure x. Newly revised fish subset of the LRT

The above family tree changes came about by 
applying the experience gained on more recent additions to earlier taxa. For instance, I re-identified the elements of the fused skull of Chimaera (the ratfish or chimaera) without the initial bias I had a year ago to find lots of bones (like the jugal, squamosal, premaxilla, maxilla and dentary) that don’t appear until later in derived taxa. This is what happens when tinkering with information not yet in papers or textbooks and while attempting to falsify original hypotheses. Follow this lead and be willing to let go of invalid hypotheses when better solutions appear.


References
Capobianco A, Beckett HT, Steurbaut E, Gingerich PD, Carnevale G, Friedman 
M 2020. Large-bodied sabre-toothed anchovies reveal unanticipated ecological diversity in early Palaeogene teleosts. Royal Society Open Science 7: 192260.
Casier E 1946. La faune ichthyologique de l’Yprésien de la Belgique. Mémoires du Musée
Royal d’Histoire Naturelle de Belgique 104, 1–267.

https://www.livescience.com/ancient-anchovy-fangs-saber-tooth.html

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