Congratulations are in order: well done Dave Hughes, David Marjanovi? and Allen Hazen in particular. No, the creature shown yesterday is not a squabrat from The Dark Crystal (if there is such a thing), Romer’s hellasaur, an old picture of a colugo, a proto-bat, proto-pterosaur, arboreal theropod, antiquated archaeopterygid, tree shrew, climbing duck-possum, arboreal gorgonopsian, proto-ropen, or one of Dougal Dixon’s arbrosaurs: it is, instead, the hypothetical stem-haematotherm depicted in Philippe Janvier’s 1984 article on the Haematothermia concept. It made an appearance both within the article (yesterday’s picture) and on the cover (the original is in lurid colour, but I only have a black and white photocopy: what you see here – and below – is a low-res scan). Janvier’s article is in Spanish and my limited efforts at translating leave me confused as to exactly what Janvier made of the concept: he described it as an exciting idea, but one that failed to take account of the vast amount of data supporting the conventional notion that birds are closer to crocodilians than to mammals (Janvier 1984)…
According to the haematotherm theory, birds and mammals are sister-taxa, united by their endothermy, fully divided heart, respiratory turbinates, and by nerve and vascular characters, as well as others. The best known proponent of this concept has been Brian Gardiner; he published a few reasonably lengthy papers on the subject in high-impact journals, the best known of which is Gardiner (1982). Unfortunately, Gardiner has since become best known for this above all else, whereas his writings on vertebrate phylogeny in general, Piltdown, and on Darwin’s correspondence should be better known. I met him a few years ago (2002 I think) when he acted as external examiner for Alberto Vasconcellos’ Phd thesis, and he was still very keen on the idea then, arguing that if I was happy with the ‘traditional’ version of amniote relationships then that was up to me (i.e., I was stupid). Gardiner didn’t start the whole haematotherm thing however: Søren Løvtrup published on the theory earlier (Løvtrup 1977) and later provided a supporting paper (Løvtrup 1985). Both Løvtrup and Gardiner cited and discussed old observations by John Ray (from 1693!) and Richard Owen (from 1866), both of whom supported the idea of a bird-mammal group that did not include other tetrapods. Owen (1866) actually named this group Haematothermia: Løvtrup and Gardiner seemed to have overlooked this, and consistently used the alternative spelling Haemothermia.
As was later discussed by a whole string of authors (e.g., Gauthier et al. 1988a, b, Kemp 1988, Benton 1985, 1991), one can only conclude that birds and mammals share characters not seen in other tetrapods by ignoring and excluding a vast amount of contradictory data. Løvtrup and Gardiner both ignored fossils, relied predominantly on soft tissue characters, and included only a handful of characters (literally, three or four) that contradicted the favoured topology and supported the traditional one: neither author included or discussed the huge number of bony and soft tissue characters that unite crocodilians and birds, for example. Furthermore, nearly all of the haematotherm ‘synapomorphies’ could be shown to be more widely distributed than proposed, non-homologous, or just plain wrong (e.g., Benton 1985, pp. 103-106).
As I’m sure I’ve said before, I admit to being a huge fan of what are politely termed non-standard theories, and what are less politely termed as fringe nonsense. Alternative theories like the haematotherm concept can be a good thing, because they force workers to tighten up ‘traditional’ models and to marshal a more convincing supporting data set, but they can also cause people to waste a lot of time when they could be doing something more useful! Whatever, we will be looking at a few non-standard theories in the near future, stay tuned…
And on the subject of using time constructively, I need to go – I am now away for the Big Cats in Britain conference and will be back next week. Have fun in my absence: remember to keep an eye on SV-POW! and also on the continuing debacle that is aetogate.
Refs – -
Benton, M. J. 1985. Classification and phylogeny of the diapsid reptiles. Zoological Journal of the Linnean Society 84, 97-164.
- . 1991. Amniote phylogeny. In Schultze, H.-P. & Trueb, L. (eds) Origins of the Higher Groups of Tetrapods: Controversy and Consensus. Cornel University Press (Ithaca, London), pp. 317-330.
Gardiner, B. G. 1982. Tetrapod classification. Zoological Journal of the Linnean Society 74, 207-32.
Gauthier, J. A., Kluge, A. G. & Rowe, T. 1988a. Amniote phylogeny and the importance of fossils. Cladistics 4, 105-209.
- ., Kluge, A. G. & Rowe, T. 1988b. The early evolution of the Amniota. In Benton, M. J. (ed) The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Clarendon Press (Oxford), pp. 103-155
Janvier, P. 1984. El divorcio del ave y del cocodrilo. Mundo Cientifico 32, 14-16.
Kemp, T. S. 1988. Haemothermia or Archosauria? The interrelationships of mammals, birds, and crocodiles. Zoological Journal of the Linnean Society 92, 67-104.
Løvtrup, S. 1977. The Phylogeny of Vertebrata. John Wiley, London.
- . 1985. On the classification of the taxon Tetrapoda. Systematic Zoology 34, 463-470.
Owen, R. 1866. On the Anatomy of Vertebrates, Volume 2. Longmans Green and Co., London.