Knowing that Eryobis is world where all its life has a terran origin, this mention of sharks was initially overlooked and shrugged off as a quite likely plausibility, given the incredible age of Elasmobranchs.
However, when footage of these supposed Eryobian sharks was properly examined, something about them immediately seemed off.
They did not have the 5 to 7 gill slits typically associated with sharks, instead possessing an operculum and thus only one gill opening.
They appeared to have no pelvic fins at all, their first dorsal fin looked as if it was laterally split in two and the caudal fin, while heterocercal like a shark's, appeared to have three distinct lobes.
Those among the explorers with knowledge of terran paleontology suggested that these creatures could be Holocephalians, related to the chimaera's of Earth. For quite some time, this was considered to be the most likely origin of these "sharks", since it technically fitted within the suggested Eryobian evolutionary timeline.
As specimens were examined up close and subjected to testing however, the idea that these were even Chondrichthyians at all was quickly discarded.
In pretty much all genetic tests, they came out as being closest related to the coelacanths and more specifically, with their closest relatives being the Anisospondyls.
When more fossils of prehistoric Eryobian fish were unearthed, the pieces fell into their place.
These were no sharks, they were Lagotoichthyiiformes or rather, bunnyfish.
Their close relation to the Anisospondyls now made sense, for these now land dwelling creatures are Planosolincolans and thus technically bunnyfish themselves.
The "dorsal fin split in two" are actually the pectoral fins which had shifted far up the body to act as dorsal fins and what seemed to be the pectoral fins are actually the pelvic fins that moved far to the front of the body, as is seen in all bunnyfish.
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| Reconstruction of Lagoselache durus, the likely ancestor all coeaaien and kin |
It seems that bunnyfish were hit extremely hard in the mass extinction known as the World Scarring, with most genetic evidence suggesting all modern forms can be traced to a single ancestor that lived around 120 million Eryobian years ago.
In fact, a likely candidate for this supposed ancestor has actually been found in rocks dating to the early Thyellian: a small fish named Lagoselache durus.
This fish shows the characteristic "double dorsal fins" and three lobed heterocercal caudal fin, demonstrating that this condition was ancestral to all modern forms.
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| Some examples of living coeaaien and kin |
At some point, the term "coeaai" (pronounced "koo-aye") became widely used among explorers to refer to the more shark like bunnyfish, likely a contraption of coelacanth and the ancient dutch word for shark "haai".
All the modern bunnyfish have been classified as supergroup named Lagoselachia, after the oldest known member. Despite this name, not nearly all of them look shark-like. And apparently some of the most shark-like members of this group evolved largely independently. A good example of this are the toothed coeaaien and the plated coeaaien. Both of these look very much like sharks and resemble each other quite a bit in overall anatomy, yet genetic testing suggests these split over 80 million years ago and both have many relatives that do not look particularly shark-like.
Then ofcourse there are also Lagoselachians that surrendered their ancestral body shape for that of a more typical bony fish or even turned it into something else entirely.
The modern bunnyfish and coeaaien are very diverse in body shape, yet they are not very numerous in species compared some other Eryobian fish orders. Still, they are not an uncommon sight in any Eryobian waters and often fill critical parts of the ecosystem they find themselves in.
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