The lizard biters

The answer to the puzzle is that both were named Saurodectes, meaning ‘lizard biter’. One is an insect from the Early Cretaceous of Siberia, while the other is an early Triassic procolophonoid parareptile found in South Africa. I was part of the team that found the procolophonoid although I can’t claim that I found the specimen. In fact I found precious little while Ross Damiani found 'Saurodectes' despite being severely hampered by a broken ankle. Some people are just gifted when it comes to field-work and I am not one of them. The insect has priority over the name and we had to rename our procolophonoid Saurodektes (Modesto et al. 2004). Not that there is much shame in proposing a name that is preoccupied by an arthropod. With so many arthropods it seems to happen all the time. I got my first look at the real Saurodectes when I purchased Grimaldi and Engel’s magnificent tome ‘Evolution of the Insects’. And what a fascinating insect it is.
Described as a kind of louse, Saurodectes vrsanskyi (Rasnitsyn and Zherikhin 1999) has an unusual set of characters. Some of these such as the single claw at the end of its legs, short, widely spaced legs and membranous distensible abdomen are typical of ectoparasitic insects but the very large eyes and lack of spiny setae are not. What those handle-bar like structures sticking out its head are is anybody's guess. A recent survey of fossil lice could not find any convincing characters that definately placed the fossil amongst the lice (Pthiraptera) but could not suggest any alternative relationships either (Dalgleish et al. 2006).


The head of Saurodectes, from Grimaldi and Engel (2005).

The original describers (Rasnitsyn and Zherikhin, 1999) suggested that it was a pterosaur parasite on the basis that it was too big at 17 mm to parasitise Mesozoic mammals but had single clawed feet like modern mammal lice. This is seen as an adaptation to gripping hair shafts, and that since pterosaurs were also hairy then it was supposed that Saurodectes plied its way through ptero-fuzz. However I don’t see a close correspondance between the claws of modern mammal lice and those of Saurodectes. Actually this is not the only weird Mesozoic insect that has been claimed to be a pterosaur parasite. Sauropthirus longipes, a scorpionfly relative from the same formation as Saurodectes has also been hypothesized to have found its living on pterosaurs. Actually the stiff, backwardly pointed spines and eyelessness of this insect seems to be more fitting with this kind of lifestyle. It is, of course, not impossible for both of these to be pterosaur parasites but it strikes me that some of the odd features of Saurodectes may be explicable if it lived on the scaly hide of a large non-feathered dinosaur. In modern lice there is a loose correlation between parasite size and host size indicating that Saurodectes had a large host. Furthermore backwardly pointing setae may be of little use on a host that lacks filamentous integument. Eyes may also be of use to a large, exposed ectoparasite, not sheltering under a dense pelt of hair. Whatever the habits and relationships of Saurodectes, there can be little doubt there must have been hordes of parasites making a living off of dinosaurs that we have yet to learn about.

References

Dalgleish RC, Palma RL, Price RD, Smith VS (2006) Fossil lice (Phthiraptera) reconsidered. Systematic Entomology 31: 648-651.

Grimaldi D, Engel MS (2005) The evolution of Insects. Cambridge University Press.

Modesto SP, Damiani R, Neveling J, Yates AM (2004) Saurodektes gen. nov., a new generic name for the owenettid parareptile Saurodectes Modesto et al., 2003. Journal of Vertebrate Palaeontology 24: 970.

Rasnitsyn AP, Zherikhin VV (1999) First fossil chewing louse from the Lower Cretaceous of Baissa, Transbaikalia (Insecta,Pediculida ¼ Phthiriaptera, Saurodectidae fam. n.). Russian Entomological Journal 8: 253–255.