July 2010


Enhanced Forelimb Strength in Sabertooth Cats

The most ridiculous manifestation of sabertooth cats in popular culure may be the novel Hunter. In this book, a group of scientists manages to create a cross between a human and a sabertooth cat, who escapes and must be tracked down before he reaches civilization.

You don't have to enter the depths of science fiction craziness to be frightened by sabertooth cats. Depending on the species, they were roughly three feet tall, weighed up to a thousand pounds, and had those famously large canines (up to almost a foot long).

The average person may think that their canines are all the sabertooth cats would need to kill prey. However, the general scientific consensus is that their forelimbs were important to restrain prey, minimizing the risk of damage to their canines.

Unambiguous analysis of forelimb bone resistance to compression and bending would help settle this question. Such an analysis has been carried out by Julie Meachen-Samuels and Blaire Van Valkenburgh (University of California Los Angeles, United States).

Sabertooth cat forelimb bones.

The scientists directly measured bone lengths and thicknesses by taking x-ray measurements of Smilodon fatalis (a species of sabertooth cat) humerus bones (the forelimb bone, which runs from the shoulder to the elbow). They calculated (1) resistance to compression in the axial direction (i.e. along the length of the bone), (2) rigidity to non-axial compression, and (3) resistance to bending about the craniocaudal (head to tail) and mediolateral (inside to outside) planes using this data.

They found that the forelimb bones are both thicker and more resistant to bending than corresponding bones in modern cats. However, their femur (thigh bone) is similar to modern cats.

Sabertooth cats' front legs were far more powerful than their back legs, relative to modern cats. This makes sabertooth cats fundamentally different from modern cats, who typically kill with a crushing bite to the neck.

Modern cats don't have the huge canines of sabertooth cats, and thus aren't at as much risk of losing important teeth when killing their prey. This new data strongly suggests that sabertooth cats could use their well-developed forelimb to restrain prey, likely to enable slashing bites to get the job done quickly.

Enhanced forealimb relative to hindlimbs have been seen in other species, but they serve to facilitate digging or swimming. Another possible explanation is an adaptation to climbing, but this is less likely due to these cats' huge size.

A reason for sabertooth cat decline?

This forelimb adaptation of sabertooth cats is energetically costly. It consequently stands to reason that it imparted an evolutionary advantage.

The scientists speculate that it may have nevertheless led to their decline. After large prey disappeared from their habitat roughly 10,000 years ago, the predominant prey was smaller and likely more agile, leaving sabertooth cats (less agile) with the same huge canines but without catchable food.

ResearchBlogging.org for more information:
Meachen-Samuels, J. A., & Van Valkenburgh, B. (2010). Radiographs Reveal Exceptional Forelimb Strength in the Sabertooth Cat, Smilodon fatalis PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011412