The Squat Factor in Defense of a Vulnerable Neck and Brain

Abstract

Pathological skeletons allow behavioral inferences for extant and extinct taxa without living analogs. Recent revisions of sauropod head, neck and tail posture suggest defensive use of their enormous tails to protect their hindquarters. Horizontal neck posture assigned to many of the sauropods, however, make the distal neck and head (brain) accessible to predation. Posterior neck proportions of even a small sauropod (e.g., 14 meter Camarasaurus) are 1.3 meters wide and 1.7 meters high, beyond the gape of contemporary predators. Anterior neck diameter (0.3 meters wide by 0.6 meters tall), however, is within the gape and accessible (vertically to large Allosaurus. Sauropod necks move maximally 20° laterally, eliminating defensive swinging away from a predator. Long bodies limit tail use during frontal attack. Some reconstructions show sauropods rearing on hind legs with anteriorly or anteroventrally extended forelegs. However, there is theoretical and physical evidence that they likely squatted with flexed knees as do other graviportal animals (e.g., elephants) in a stable, easily held posture. A unique diplodocid, KUVP 129717, with a partially healed, distal penetrating pubic symphysis injury, and a healed, deep anteroposterior dorsal claw cut metacarpal, provide clues to head and anterior neck defense. Slight remodeling, not altering injury architecture, proves the sauropod survived. The pubis wound is not explainable by tooth or claw injury and lacks the characteristic taper related to Stegosaurus spike‐derived injuries. The geometry and location suggest that the sauropod sat on a sharp, slender object, in a critical situation that prevented injury avoidance. Sauropods squatted to lay eggs, unlikely encountering a sharp object, or the animal would have repositioned to avoid pubic symphysis penetration. We suggest that the diplodocid squatted when imminent danger required anterior body elevation to raise the head and neck above predator reach. Xenarthran anteaters use this stable tripodal defensive stance, supporting partial body weight on the tail base as sauropods may have done. Further, presence of a long metacarpal claw‐derived scar suggests a defensive wound, one that could have occurred if it was elevated by squatting to the position that placed the distal neck and head out of reach of predator reach, leaving its forelimbs available for defense. Such a posture protects sauropods from even the largest Late Jurassic carnosaurs.Support or Funding InformationNot applicable.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.