TOO YOUNG OR TOO SMALL? THE EFFECT OF SIZE AND LIFE STAGE ON TERRESTRIAL VERTEBRATE TAPHONOMY

Juveniles suffer high rates of loss due to predation and environmental factors, so overproduction of offspring is a common survival trait for many species. Juveniles should make up a large portion of any population. Despite this, they tend to be underrepresented in the fossil record. Juvenile bones have different levels of mineralization, size, proportion, mass and density compared to later life stages. All of these factors have the potential to impact the weathering and breakdown of bones prior to fossilization.

This study represents an attempt to begin to separate out the effects of developmental stage, size and proportion in the weathering of vertebrate remains. We compared the weathering stages of the bones of domestic fetal pigs to that of juvenile domestic rabbits of roughly the same body mass, and large juvenile domestic pigs from six months to a year old. The remains were placed in scavenger-proof enclosures exposed to the elements. The bones were gathered at one- and two-year intervals and examined for evidence of weathering and loss due to breakdown.

Comparison of the remains shows a similar overall level of weathering across all groups at each time period. At the one-year interval ~ 40 – 50% of the major skeletal elements show signs of weathering. At the two-year mark that amount increases to ~ 62 – 72%. The smaller vertebrate remains seem more vulnerable to deeper destruction of the bone (cracking through and loss of outer layers of bone) earlier on than the much larger animals. Rate of recovery of skeletal elements was similar between the first and second year of the study. Overall fewer major skeletal elements from the rabbits were recovered compared to other animals. Despite being more calcified than the fetal bones, these were more gracile and easier to transport via overland flow. They were also possibly more attractive to scavengers looking for minerals than the fetal remains and easier to carry than the larger bones.