Wednesday, June 15, 2011
The Many-Finned Dolphin
Cetaceans are undoubtedly the strangest of mammals, and I don't find an extra dorsal fin or 'anal fin' to be all that improbable compared with, say, the Sperm Whale's nose, the Narwhal's tusk, or Odobenocetops in general. An extra dorsal fin is not without precedent thanks to the Cornish Bottlenose Snooky, and there have been other sightings of supernumerarily-finned cetaceans, some of which reportedly looked quite unlike known species (see Raynal and Sylvestre (1991) for a review). Rather than a surviving cryptid, the speculative dolphin above is a descendant from a Lagenorhynchus species (maybe L. albirostris or L. acutus) which has taken its thunniform body shape to new extremes. The coloration and shapes of the head and foreflipper are the result of blending together a few Lagenorhynchus species, however the body shape is inspired by Dall's Porpoise, Pilot Whales, Eastern Spinner Dolphin, and scombrid fishes. The general working theory here is that since since the keels already resemble low dorsal fins in some cases, perhaps with some selection they could develop into proper fins.
This is of course not a final draft and could be subject to major change - I could see the extra fin forming separately from a keel (probably losing the 'anal fin'), the males exhibiting a forward-canting (first) dorsal fin like Dall's Porpoise and the Spinner Dolphin, sexual dimorphism resulting in other changes in fin shape and coloration, and a shifting phylogenetic identity. At any rate, there's still going to be an extra-finned cetacean in this final project, and it may very well not be the strangest cetacean out there.