Sirens are a very weird, long-bodied group of salamanders today restricted to North America but with a fossil record that perhaps involves other continents (that’s a story for another time). I’ve written about them at some length before: see this article on sirens from June 2016 for a primer on the group. Sirens are certainly weird, but they’re also certainly salamanders, as – once again – verified by numerous aspects of anatomy and genetics.
Indeed, sirens are so weird that much of the older literature lists them as representing some sort of unique salamander sub-group, termed either Trachystomata or Meantes. Back in the 1950s this was especially popular among researchers who did actually think that sirens might not be salamanders at all but, rather, direct descendants of a long-bodied, limbless group of fossil tetrapods called the aïstopods. That’s right: based on their analysis of fossil siren vertebrae from Florida, Coleman Goin and Walter Auffenberg actually speculated that sirens might be modern-day aïstopods (Goin & Auffenberg 1955). And Goin & Goin’s (1962) textbook An Introduction to Herpetology made fleeting reference to this hypothesis, noting that siren vertebrae resemble those of aïstopods.
Aïstopods are otherwise known only from the fossil record of the Carboniferous and Permian and are thought long-extinct, so this proposed relationship would be a big deal to say the least. Not only would we have copious soft tissue and molecular data on an otherwise unsampled section of the tree of life, the existence of living aïstopods would of course help us work out exactly what these weird animals are, since there are competing ideas…
Admittedly, this ‘living aïstopod’ idea has been scarcely discussed outside of those citations mentioned above. The late J. Alan Holman was good enough, however, to cover it in his Fossil Salamanders of North America (Holman 2006). What I especially like about his treatment is that he writes of the thrill that he and his fellow students felt at the time: “This generated much excitement among us graduate students at the University of Florida, and the possibility of having 330 million year old fossils swimming around in our local lakes made us ecstatic” (Holman 2006, p. 45). But, alas, it was not to be: siren anatomy and genetics shows that they are salamanders, weird though they may be.
More stuff on amphibian evolution soon. For previous Tet Zoo articles on ‘non-standard hypotheses’, see...
- Aquatic proto-people and the theory hypothesis of initial bipedalism
- Goodbye from the stem-haematotherm, goodbye from me
- The ‘Birds Come First’ hypothesis of dinosaur evolution
- Birds Come First – oh no they don’t!
- We flightless primates
- Amphisbaenians and the origins of mammals
- The ‘Tree-Kangaroos Come First’ hypothesis
- The Haematothermia hypothesis
- Nonstandard Ideas in Amphibian Evolution, Part 1
- Nonstandard Ideas in Amphibian Evolution, Part 2: Salamanders and Caecilians Evolved Independently of all other tetrapods
Refs - -
Cox, B. 1975. The Prehistoric World. Galley Press, London.
Goin, C. J. & Auffenberg, W. 1955. The fossil salamanders of the family Sirenidae. Bulletin of the Museum of Comparative Zoology, Harvard University 113, 497-514.
Goin, C. J. & Goin, O. B. 1962. Introduction to Herpetology. W. H. Freeman, San Francisco and London.