Tactile tails: a new hypothesis for the function of the elongate tails of diplodocid sauropods

Abstract

ABSTRACT Tail elongation is a trait common to many sauropod dinosaurs. In certain members of Diplodocidae, for example, the total caudal vertebrae count is as high as 70 to 80 bones, making a total estimated tail length for mature animals that is in excess of 10 metres. A number of competing hypotheses have been suggested to explain the function of this ‘hyper-elongate’ tail including use as a counterbalance, use as a defensive weapon, use as a sonic-boom-generating ‘bull-whip’ or use as a feature for sexual display. Here, a new hypothesis is presented for the function of sauropods’ hyper-elongate tails – herding co-ordination. Many sauropods are known, from multiple independent lines of evidence, to have been herding animals that moved in large groups over wide ranges; it is proposed that the elongation of the tails in many of the more massive sauropod lineages may have evolved to allow for simple and efficient communication between individuals via near continuous animal-to-animal contact during herd movement and migration. This contact, it is suggested, would have facilitated speedier, more compacted and more efficient mass movement of the animals as a group, and reduced the need for continual slowing and stopping to maintain herd formation. Institutional abbreviations: AMNH: American Museum of Natural History, New York, USA; CM: Carnegie Museum of Natural History, Pittsburgh, USA; HMN: Natural History Museum, Berlin, Germany; OMHN: Sam Noble Oklahoma Museum of Natural History, Oklahoma, USA