SCIENCE / MEDICINE : Tar Pits Suggest Altruism Among Saber-Toothed Tigers : Prehistoric Pride
Few creatures that roamed what is now Southern California thousands of years ago were a match for the fierce saber-toothed tiger, a predator that dined regularly on animals many times its size.
With long, saber-shaped teeth protruding from its upper jaw, the magnificent beast carved its living out of what was then a pine-covered rain forest, long before the Los Angeles Basin became the arid land that it is today. But when its hunting days were over, and a crippled or aging cat could no longer attack the elephants or great bisons that wandered through its kingdom, scientists believed that it became an outcast, deprived of the sustenance it needed to maintain life.
But new evidence suggests that these great beasts, extinct for around 10,000 years, lived a far more structured--and altruistic--life than had been thought. Wounded cats apparently were allowed to dine on the victims of other members of the pride, and even protected from other predators who would seek them out in their time of weakness.
That remarkable jump in the understanding of a long-extinct animal is unfolding in work at the La Brea Tar Pits in Los Angeles, the world’s richest deposit of fossilized, vertebra animals.
Unraveling the social life of an extinct creature is perhaps the most uncertain ground for men and women who try to piece history together from the scattered remains of that which came this way before us. Yet fossils, even tiny fragments, can tell much about the lives of ancient beasts, even as to how they spent their time and whether their kinfolk cared what happened to them.
Piecing those precious bits of information together is what modern paleontology is all about, and today, scientists are making considerable strides in the painfully slow process of reading history from its debris.
That even includes how the great cats protected and served each other, and possibly why the huge bison that roamed the region failed to adapt to changing conditions while their descendants continued to survive elsewhere in the world.
“We are starting to get an idea of the social behavior” of the saber-toothed tigers, said Christopher A. Shaw, a paleontologist on the staff of the George C. Page Museum, located on the same grounds as the tar pits. That is particularly difficult because the great cats have no living descendants.
In hopes of learning more about the beasts, Shaw teamed up with a retired surgeon, Fred Heald, and together they have opened a new window onto a scene that disappeared from the Earth many years ago.
The two men are studying thousands of bones and bone fragments excavated in the fossil-rich tar pits, which for about 30,000 years captured animals that had the misfortune of wandering through when the tar was hot and sticky, thus trapping their feet and eventually preserving their remains so that people such as Shaw and Heald could try to figure it all out so many years later.
Specifically, Shaw and Heald are studying bone pathology and the healing process that took place after some of the great cats were injured at the dinner table.
Some of the bones, particularly an extremely mangled hip bone from one cat, reveal that the beasts had a violent life, as just about everyone had believed, but in many cases they survived long after injuries that would have left them so crippled they could no longer prey on large beasts.
“We are reinforcing a lot of early ideas,” Shaw said, “and adding a little more meat to whether they were active predators. Nearly everybody feels they were.”
Some of the injuries studied by the scientists show that the cats engaged in fierce combat while trying to capture food.
“Dinner was a big, heavy animal that had to be dealt with,” Shaw said.
In some cases the injuries were extreme, suggesting that an elephant may have stomped on the hip of its attacker, for example, yet the bones also indicate that many cats lived long after such injuries occurred.
“There are some amazing healing pathologies here,” Shaw said. For example, some bones reflect long-term wearing after the injury was inflicted, and bone deposits that grew up abound the injury show that the beast survived for some time.
“That indicates the saber-tooth tigers cooperated in survival,” he said.
That is a dramatic departure from the popular conception of giant cats that depended entirely on their own resources for survival. But Shaw believes that the record is quite compelling.
“It all starts with the bone,” he said as he held up a hip joint that had been severely mangled. “That animal had to be stomped upon when it was a juvenile (yet it lived to be an adult). That tells you that the animal went through a period of healing. It wasn’t killed outright.
“This animal was so crippled it could not have hunted effectively enough to sustain its own life.”
Shaw said it would not have been possible for an injured cat to survive long by picking the bones of other beasts captured by the tar pits, because not enough animals got trapped to provide very much food during the lifetime of any one cat.
“There wasn’t enough to sustain a population of saber-tooth cats,” Shaw said. That means the cats survived only because they were “active predators.”
So how did a severly mangled juvenile live long enough to reach adulthood if it could no longer kill its own dinner? Shaw said the most plausible explanation is that they survived because other members of the pride allowed them to dine on meals they did not provide, and even protected them from other predators.
“We feel these animals had a social organization,” he said.
Other cats most likely “let them feed at kills” and protected them from such beasts as the packs of wolves that also roamed the area.
“We feel this is what happened with these cats,” he added. “They had a social order that allowed them to remain with the pride. That is exciting.”
That is not what some paleontologists had believed, and additional research at the museum also suggests strongly that some other widely held beliefs may not be true, either.
It has long been thought, for example, that it was the appearance of humans on the scene that spelled death to some species, including the great bison. Early man was an aggressive hunter, and records clearly show that in many cases great herds of bison were decimated by overly zealous humans.
That has led many to believe that humans, not nature, wiped out a type of bison that is now extinct.
“We no longer think that was the case,” said Eric Scott, who is in charge of the annual summer dig at La Brea.
Current evidence suggests that major climatic changes that altered the bison’s habitat, coupled perhaps with the creatures’ unwillingness to explore other territories, led to its demise.
Page Museum associate curator George Jefferson has done extensive studies of the bison bones found at La Brea, leading him to conclude that a major warming trend at the end of the Ice Age around 11,000 years ago changed the habitat.
“We see a drop in precipitation of about 50%,” Jefferson said.
“If you change the climate, the vegetation is disrupted,” he said. A drier climate, for example, “would provide less ground cover,” leading to greater erosion and a loss of food supplies.
Unfortunately, the change in climate also brought an end to the effectiveness of the tar pits as collection centers for ancient artifacts. Bones rarely became trapped in the tar, which was covered by dirt instead of vegetation. The dirt swept over the area during seasonal rain and wind storms, washing away many of the bones in seasonal streams.
So the record at La Brea ends just before the extinction of the bison, but not without leaving a few priceless clues.
By examining fossilized food fragments from the jaws of bison trapped in the tar, Jefferson has concluded that the beasts had a very limited migratory pattern. The food came from the hills surrounding the basin, suggesting that the bison spent their winters in the mountains on the edge of the desert, and wandered into the basin during the summer.
And determing just how old the creatures were when they perished in the black grave has allowed Jefferson to reach an important conclusion. A precise spacing in the ages indicates that members of the same herd returned over and over to the same area, where some became trapped when they were 1 year old while others died when they were 2 or 3.
That is a distinctly different pattern from the modern bison, which is a direct descendant of the extinct beast that roamed the basin so long ago.
“Current studies suggest that modern bison do not have a regular migratory pattern,” Jefferson said. “What they do is they go from the best feeding grounds to the best feeding grounds, from river drainage to river drainage” rather than returning to the same area year after year.
The record at La Brea, by contrast, “suggests a repetitive, annual visit,” he said.
The fact that modern bison survived the human onslaught, coupled with evidence that the extinct creatures may have become too dependent on a changing landscape, “suggests that humans probably weren’t that significant” in the death of the extinct bison, he added.
All of these conclusions are somewhat tentative, of course, because the world of paleontology is littered with strongly held beliefs that gave way in the face of new evidence. One needs look no further than La Brea to see that.
