The Razorback Dolphin is a descendant of the Common Bottlenose Dolphin (Tursiops truncatus) which has converged upon 'River Dolphins'. This isn't as unlikely as might be supposed as T. truncatus is not just pelagic, but also occurs in bays, estuaries, and the lower reaches of rivers (Reeves et al. 2002); individuals even live in the Rio de Ais (Stolen and Barlow 2003). Like the ancestral species, this species has normal-sized eyes, non-paddle-shaped flippers, and a falcate (first) dorsal fin; the beak length, large melon, and body shape appear closer in morphology to Inia or Platanista. I could imagine some rather strange things happening internally in the melon region - it's the cetacean thing to do. Taken together, these features suggest an animal adapted for riverine habits which is still capable of competing in brackish and near-shore marine waters. Ais, after all, does not have an extensive river system which can support an entire species, maybe a sub-population at best.
And there are dorsal finlets. Presumably these formed through a similar genetic pathway as the thunniform dolphin's extra fins despite the radically different body plans and habitats of the species. It's tempting to give the Razorback and Thunniform dolphin a common T. truncatus ancestor, although I suspect these would be too neat and tidy for evolution.
The primary inspiration for this species is once again a cryptid, the Sawtooth Dolphin observed by Jeremy Wade. The individual probably got its appearance from an injury, and I could imagine the coincidental appearance of the Razorback Dolphin causing some confusion for whoever is exploring Ais.
References:
Reeves, R. R., Stewart, B. S., Clapham, P. J., and Powell, J. A. (2002) National Audubon Society Guide to Marine Mammals of the World. Alfred A. Knopf: New York.
Stolen, M. K., and Barlow, J. (2003). A model life table for Bottlenose Dolphins (Tursiops truncatus) from the Indian River Lagoon System, Florida U.S.A. Marine Mammal Science 19(4), 630-649. Available.
Good work, people! Glad to see your blog alive, and waiting for new ideas! I'm also into speculative biology, and work at one project (with good team, I say!). Waiting for new posts and ideas.
ReplyDeleteI'm glad you like it!
ReplyDeleteYour project is excellent by the way, too few speculative evolution projects out there give sufficient attention to fish and inverts. I was surprised to see that you had also speculated about parasitic loricariids - there must just be something potentially leech-like about them.
By the way, what is the giant loricariid species pictured in post on Great Snapper from above?
ReplyDeleteAnd by the way again, in my world there are almost no cetaceans. You think they will survive in the future. I must stay in borders of my project, but what about the following idea:
ReplyDeleteSlowly-moving cetacean living in coastal waters. It has manatee-like appearance, short head, fat body and shovel-like tail fin. It almost lacks dorsal fin and has rather long fins acting like legs. Its front part of lower jaw is toothless and chisel-like and is used to tear off colonies of bivalves, and teeth in back part of jaws are grindling. This animal can live both in sea and river water, feeding on clams, snails and crustaceans (crabs, crayfishes).
Stay tuned, Markus has been working on something similar in habitat and diet to what you've described, except it will belong to a cetacean radiation with a radically different body plan from the norm (it's almost the exact opposite of manatee-like, in fact).
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