The socio-sexual behaviour of extant archosaurs: implications for understanding dinosaur behaviour

Abstract

Dinosaur behaviour has little legacy in the fossil record and the rarity of fossil soft tissues makes it difficult to evaluate. Indirect evidence from bonebeds, trackways, nesting traces and in-group comparisons with extant Archosauria suggests that the only substantive arguments to be made for dinosaur sociality concern cranial ornamentation and herding behaviour. There is currently no reliable method to determine gender from skeletal remains. Dinosaur reproductive anatomy was a unique combination of crocodilian and avian characters and extant models indicate that dinosaurs copulated using a reptilian ‘leg over back’ posture. Reliable evidence for post-hatching care in dinosaurs is lacking and extant archosaurs yield little insight. A hypothesis is proposed that for the majority of dinosaurs there was no post-hatching care provided which would have allowed adults energy acquisition that would otherwise have been required for defence and provisioning to be redirected towards growth and increased fecundity, both traits for which there is fossil evidence. Arguments suggesting that the more advanced aspects of extant avian care boasting an explicit coelurosaurian theropod origin are rejected as these behaviours appear unique to the Neornithes. Three ancestral care hypotheses are tested and none conform in a satisfactory manner with body fossil and ichnological evidence.

Keywords:

• dinosauria
• mating
• parental care
• aves
• crocodilians
• reproduction

Acknowledgements

Many zoological institutes kindly provided unreleased videofilm and photographs of animal sexual behaviour which were used for comparative modelling and in that respect I wish to thank the following individuals in particular. Andy Hartley of the Whipsnade Zoological Park in the UK and Dr Lorenzo Fersen of Tiergarten Nürnberg in Germany both provided film of Indian Rhinoceros (R. unicornis) copulation; Dvr Králové Zoo in the Czech Republic supplied similar records for the Northern White Rhinoceros (C. simum cottoni) and Terri Roth with the Cincinnati Zoo furnished videofilm describing Sumatran Rhinoceros (D. sumatrensis) reproduction. Dr David Kirshner provided detailed data regarding Lace Monitor (V. varius) mating and records of Elephant Seal (Mirounga spp.) copulation were furnished by both Sarah Lurcock and Jane Stevens. Many of the illustrations in this thesis were commissioned from Brad McFeeters based on detailed text descriptions provided by the author who once again extends his thanks and regards. Critical proofreading and detailed reviews of the manuscript were kindly provided by Dr Phil Senter, Dr David Martill, Dr Dave Unwin and Mrs Amanda Hart.