Tag Archives: Ice Age

What to call the giant cat from the Ice Age?

The Ice Age of the recent past was a fascinating time, full of superlative animals, especially the mammalian megafauna of North America. The Ice Age, also referred to as the Pleistocene epoch, lasted from 1.9 million years ago to 10,000 years ago, and was characterized by a series of glacial advances and retreats across much of the Northern Hemisphere. It was also a time of animal migrations between continents and of many species being exceptionally large.

Giant ground sloths, the giant short faced bear, saber-toothed cats, mammoths, and mastodons all tromped through what was to later become our backyards. Many people are surprised to learn that North America was also home to a very large cat, larger than the modern lion, given the scientific name Panthera atrox.

This big cat lived mostly across the western half of North America, and ranged into South America as far as Peru. Its remains are plentiful in the tar pits of Rancho La Brea. It is clear that this is a big animal. Estimates of body size suggest a weight of about 1,000 pounds, and that it stood 4 feet at the shoulder. For comparison, the modern African lion weighs in at about 375 pounds. This American cat would have been the second largest mammalian predator, right behind the giant short faced bear. (See How big was the Giant Short-faced bear?)

The giant American cat, Panthera atrox

However, understanding how this animal relates to other large cats has been difficult. Scientists have noticed similarities between P. atrox and the modern lion, tiger, and jaguar. For many years, P. atrox was thought to be a subspecies of the lion, and so it has popularly been called the American Lion, and even the American Cave Lion. If it is closely related to the African lion, it suggests that lions migrated out of Asia and into the New World during the Ice Age, expanding as far south as South America, and becoming extinct at the end of the age. Several other species are known to have done this, so that is not so unusual. But is it an accurate story?

In a recent paper on the subject (Christiansen and Harris 2009), researchers have come up with a different idea. They examined the skull and jaws of the big American cat and compared it with lions, tigers, and jaguars. They used a wide range of measurements to create a mathematical model of each species, and compared them to each other. The result? Panthera atrox does not seem to be a lion at all, but rather is closest to the modern jaguar.

Jaguars came into the New World from Asia during the early Pleistocene. It seems then that P. atrox and the modern jaguar species, P. onca, are derived from the early jaguar that came into North America, and that lions never made that long trek across. If these researchers are correct, we should not call this magnificent cat the American Lion.

A jaguar, Panthera onca. By Pascal Blachier from Savoie, France.

So, what should we call it? Jaguars are native to the New World, so the word “American” seems a bit redundant in the name. And the simple scale and grandeur of the cat requires some adjective. “Mega Jaguar” seems a bit plain to me. What do you suggest?

Christiansen, P. and Harris, J. M. 2009. Craniomandibular morphology and phylogenetic affinities of Panthera atrox: implications for the evolution and paleobiology of the lion lineage. Journal of Vertebrate Paleontology 29(3):934-945.

Mammoth protein designed to be cool

Researchers were recently able to isolate and study woolly mammoth hemoglobin and compare it to the modern African and Asian elephants. They isolated the genes from DNA that code for the creation of hemoglobin, the protein that carries oxygen in our blood. This was done for both the modern elephant species, as well as from DNA from mammoth bone from Siberia. They observed some minor differences between all the species, so the researchers wondered if the difference in the mammoth’s blood might have helped it survive in cold climates.

Hemoglobin supplies our body with oxygen by carrying it around in our blood stream and then releasing it to our tissues. When our tissues need more oxygen, like for muscles that are working hard, hemoglobin more easily releases oxygen because of the higher temperatures created by the heat generated by the muscle. However, in colder temperatures, hemoglobin does not give up oxygen as easily. This is potentially a real problem in colder climates. To keep the hemoglobin to working effectively an animal might need to expend valuable energy to maintain a higher body temperature.

The researchers (Campbell et al. 2010) wondered if the slight differences in woolly mammoth hemoglobin might have been an adaptation for living in colder temperatures. They inserted the Asian elephant genes that make hemoglobin into the common bacteria, Escherichia coli, and allowed the bacteria to act on the genes, thereby making Asian elephant hemoglobin. This process is not new as it is commonly used to have bacteria produce proteins that are identical to human-made proteins, like insulin.

To get the bacteria to make mammoth hemoglobin, they needed to modify the Asian elephant genes the same way they observed, then let the bacteria make the hemoglobin of a mammoth—thousands of years after the mammoths last did it themselves. Researchers could then compare the protein of the two species directly. The result was that mammoth hemoglobin released oxygen much more effectively at lower temperatures.

Woolly mammoths from Alan Turner (2004), National Geographic Prehistoric Mammals.

Woolly mammoths were adapted to colder climates in a number of ways, such as compact bodies, small ears, short tails, and long woolly hair. This result strongly suggests that their bodies were also changed at the molecular level for life in cold, high latitude climates during the Ice Age. It would be very interesting to see if other mammoth species, such as the Columbian mammoth, for example, shared this adaptation. But I suppose that will have to wait until we can get good DNA from that species. All in good time.

Campbell, K. L. et al. 2010. Substitutions in woolly mammoth hemoglobin confer biochemical properties adaptive for cold tolerance. Nature Genetics 42:536-540.

Musk ox say no to hunting

As we face the uncertain effects of climate change ourselves in the future it is instructive to look back in time to see how other species fared. (See also a geologic perspective on the effects of climate change.) Paleontology is one of the main sciences involved in this research and so proves to be very relevant to this modern issue.

A recurring mystery in paleontology is the cause of the most recent major extinction event at the end of the Pleistocene or Ice Age. Many large species of mammals, collectively referred to as megafauna, became extinct relatively recently, a mere 10,000 years ago more or less. Charismatic animals such as mammoths, mastodons, giant ground sloths, and saber toothed cats vanished from the Earth forever.

It has long been debated what the primary cause of this extinction event was. Just as with other major extinctions observed in the fossil record, there are a number of suspected causes for Ice Age extinctions: disease, climate changes, and extra-terrestrial phenomena like asteroids. But the Ice Age extinctions have another factor that previous extinction events do not have—the emergence of humans as a major player upon the landscape. Did human activities, maybe the over hunting of the megafauna, drive them to extinction?

Many studies have tried to get at this question, but it is very difficult to separate all the confounding issues from each other to focus on just one to test its potential effects. A new study however was able to do just this.

In a recent paper (Campos et al., 2010) DNA material was extracted and analyzed from one of the species that did survive the Ice Age extinctions, the musk oxen. This Ice Age relic lives today mainly in the high-latitudes of Greenland and Canada, but was once more wide-spread. Indeed, its remains have even found as far south as Nebraska, New York, and Ohio during the Pleistocene.

Musk oxen are well adapted to the extremes of arctic living with sturdy bodies and thick coats of hair.

The researchers collected samples from across the musk oxen’s former range for the last 60,000 years. They examined the DNA to look for patterns of population dynamics over that period. Basically, when a population is strong and has many members the DNA samples show an increase in diversity—more genetic variation in the mix. When populations suffer and numbers decrease the results show up in the DNA as a decrease in diversity, sometimes referred to as a genetic bottleneck. So, the DNA diversity over time shows a proxy for population numbers and health.

Therefore, if humans were a prime driver of population declines for musk oxen at the end of the Ice Age we would expect to see genetic bottlenecks within the DNA corresponding to the timing of human activity within the musk oxen’s range.

The DNA results show that the geographic origin of all the musk oxen DNA is northeast Siberia with a large diverse population. However, the population in that region crashed about 45,000 years ago. After that population decline, there was a world-wide genetic diversity increase about 30,000 years, followed by another decline about 18,000 years ago, and finally a slight recovery about 5,000 years to the modern relict populations.

With these data we can directly test for the first time the correlation of population declines of the musk ox with human activity. And, in fact, they do not correlate very well, suggesting that humans played little role in the population dynamics of musk oxen.

So, if not humans, what then was driving the populations to decline? The most likely cause was environmental changes, particularly climate changes. The Pleistocene is characterized by shifts in climate patterns with the best-known effect being glacial advance and retreat over the last 2 million years. It seems, at least in the case of musk oxen populations, that the pattern of boom and bust was driven by their ability to adapt to climatic changes in their environment. Musk oxen almost went the way of the mammoths and succumbed fully to extinction, but managed to just hold on by their horns in greatly reduced numbers until today.

Of course, whether they, or any other species that are similarly at risk, will weather the next several decades, and any modern climate changes, remains to be seen. The effects of climate change may well prove to be too much for them after all.

CAMPOS, P. F., E. WILLERSLEV, A. SHER, L. ORLANDO, E. AXELSSON, A. TIKHONOV, K. AARIS-SØRENSEN, A. D. GREENWOOD, R.-D. KAHLKE, P. KOSINTSEV, T. KRAKHMALNAYA, T. KUZNETSOVA, P. LEMEY, R. MACPHEE, C. A. NORRIS, K. SHEPHERD, M. A. SUCHARD, G. D. ZAZULA, B. SHAPIRO, AND M. T. P. GILBERT. 2010. Ancient DNA analyses exclude humans as the driving force behind late Pleistocene musk ox (Ovibos moschatus) population dynamics. Proceeding of the National Academy of Sciences.

Giant Short-Faced Bear Reexamined

As the old saying goes, looks can be deceiving. That is the theme of a new paper on the Giant Short-Faced Bear (GSFB), Arctodus simus, recently published in the Journal of Vertebrate Paleontology (Figueirido et al., 2010).

We have explored this beast in other posts (see below), and will no doubt do so in the future, as it is one of my favorite animals because of the fascinating paradoxes that it presents. Bears as a group often do not do what we think they should do!

The GSFB is the largest mammalian carnivore known, fossil or recent. First discovered in Northern California and described by Cope in 1879, remains of this species have since been recognized from Alaska to Mexico, and from the west coast east to Pennsylvania in North America. It lived from about 1 million years to about 10,000 years ago. It is likely that they became extinct as an ultimate effect of climate change at the end of the Ice Age.

Kurten (1967) was one of the first to look at the GSFB in much detail, and he made a number of observations that have come to define this bear: shortened face like a cat, and extremely long limbs compared to body length. Kurten argued that those adaptations show a hypercarnivore, a cat-like giant predatory bear, with long runner’s legs and a bite-style like the large cats.

There is something very appealing in this picture: a huge cat-like bear running down prey and dominating the Ice Age landscape. Alas, science cannot be based on drama or romantic notions, and this image of the GSFB gets reexamined from time to time, with other authors coming to different conclusions. Some have pointed out the ambiguity of the limb proportions, or compared the GSFB to its closest living relative, the South American spectacled bear, and concluded that it was primarily omnivorous with a diet rich in plants (Emslie and Czaplewski, 1985).

The question of what the GSFBs were eating, at least, seemed to have been dramatically concluded in a couple of papers during the mid-1990s (Bocherens et al., 1995; Matheus, 1995). Those authors explored the carbon and nitrogen stable isotopes preserved in skeletal material. You are what you eat as differing amounts of these elements are deposited in body tissues depending on their dietary sources, and the isotope data clearly show that the GSFB were eating mostly meat in their diet.

In the most recent paper, Figueirido and colleagues also re-examine Kurten’s cat-like interpretations of the GSFB. For example, they challenge the very notion that the GSFB was short-faced at all. While a casual observation of the skull seems to “bear” that out, they compared the skull and face length with other bears, and it seems that what makes the skull of the GSFB look short-faced is really the depth of the snout and the height of the skull overall, creating an illusion of short-facedness.

Snout lengths relative to skull length in living bears and in the GSFB.

They also ran a number of statistical analyses on the dimensions of the skulls of bears with other carnivores to see if differences in feeding behavior might be teased out this way. Feeding strategy, such as cat-like hypercarnivory or hyena-like bone-crushing, might be visible in the skull proportions. They concluded that the GSFB had a skull shape not like that of a cat, but more similar to modern brown bears (Ursus arctos). Brown bears are omnivorous and will certainly eat meat, but also have a significant amount of plant matter in their diet. So, those authors suggest the skull shape does not support a hypercarnivorous behavior.

Figueirido et al. also examined the claim that the GSFB had extremely long legs. They compared total limb length to overall body weight among modern bears and the GSFB. Their results suggest that the limb length is just what it should be for a bear of the overall size of the GSFB, and not especially long when compared to other bears.

Nothing in science is sacred and I applaud Figueirido et al. for critically looking at past interpretations. However, the answers to our questions continue to elude us. If they are right that the GSFB was not especially short-faced, and that the limbs were not especially long, and the skull was not especially cat-like, none of that really nails down the behavior of this giant species, as they point out. And bears in particular have a tremendous range of feeding adaptations and behaviors that do not fit the mold.

For example, modern bear behavior goes from one extreme represented by the polar bear, which lives on the arctic sea ice and eats almost nothing but seals, to the giant panda living in Asian forests and eats almost nothing but bamboo (but they too will eat meat if given the chance). And between those extremes is a lot of variation. There is really no reason to think that the GSFB was not also variable in its diet and behavior to some degree. But the isotope evidence is hard to argue with at the moment: they seem to have eaten a lot of meat.

The question remains though, how did they get their meat? Did they chase down their prey in long pursuits, or ambush them from short range, or act as the neighborhood bully and chase smaller carnivores from their kills? We don’t yet know but we will keep looking.

BOCHERENS, H., S. D. EMSLIE, D. BILLIOU, AND A. MARIOTTI. 1995. Stable isotopes (C13, N15) and paleodiet of the giant short-faced bear (Arctodus simus). Comptes Rendus de l’Acadƒemie des Sciences Paris, 320, serie IIa:779-784.

EMSLIE, S. D., AND N. J. CZAPLEWSKI. 1985. A new record of giant short-faced bear, Arctodus simus, from western North America with a re-evaluation of its paleobiology. Contributions in Science, 371:1-12.

FIGUEIRIDO, B., J. A. PEREZ-CLAROS, V. TORREGROSA, A. MARTIN-SERRA, AND P. PALMQVIST. 2010. Demythologizing Arctodus simus, the ‘short-faced’ long-legged and predaceous bear that never was. Journal of Vertebrate Paleontology, 30(1):262-275.

KURTEN, B. 1967. Pleistocene bears of North America; 2. genus Arctodus, short-faced bears. Acta Zoologica Fennica, 117:1-60.

MATHEUS, P. E. 1995. Diet and co-ecology of Pleistocene short-faced bears and brown bears in eastern Beringia. Quaternary Research, 44:447-453.

Giant Short-Faced Bear: a Northern California Original

In 1878, James D. Richardson explored Potter Creek Cave in Shasta County, California. He found the skull of a bear beneath several inches of cave dirt, and he sent the specimen to Edward D. Cope, who determined that it was the type specimen for a new species of American “cave bear” (Cope, 1879).

Reconstruction of the Giant Short-faced Bear, Arctodus

When a scientist studies an animal and determines that it is something new to science, they set up a name for it and designate a type specimen. The type specimen, or type, holds a special significance as the “name bearer” for the entire species, and subsequent investigations of that species make reference to the type. They are often kept in special collections within the museums that hold them, or at least given special protection over other specimens. For example, they often are not loaned out as other specimens in the museum collection might be, so there is less risk of damage. (For a description of geologic type sections, see formations).

All too often the type specimens of fossil species have been based on fragmentary material or poor descriptions, making a full understanding of the species more difficult. A famous example of this is the story of the dinosaur Apatosaurus.

Apatosaurus was named by Cope’s rival, O. C. Marsh (Marsh, 1877). Both Cope and Marsh were rushing to describe more fossil species than the other, and their famous rivalry led to shoddy work by both men on occasion. Marsh said the type specimen of Apatosaurus was a “nearly complete specimen in excellent preservation.” However, he only briefly described the vertebrae of this new animal in his haste to publish the new name.

Later, Marsh published the name Brontosaurus, with a few comments on the pelvis and vertebrae of that type (Marsh, 1879). Brontosaurus soon became widely known to the public, and to many, represented the quintessential dinosaur. However, by 1903 Elmer Riggs recognized that Apatosaurus and Brontosaurus were in fact the same species of dinosaur, and since Apatosaurus was named two years before Brontosaurus, that name had priority and was the name that should be used (Riggs, 1903). However, the old name Brontosaurus was in such popular usage that it took many decades for the public to catch on. Now, it seems that every young dinosaur buff knows of this name change and is comfortable with it.

Since the first Short-faced Bear fossil to be recognized in North America was from Northern California, the type specimen, and the name of the bear, Arctodus simus, will be forever linked to the region. This “American Cave Bear” is now known from over 100 localities from Alaska to Mexico, east coast to west (Richards et al., 1996). It was a wide-spread species of the late Pleistocene Ice Age.

What is perhaps most striking about this bear is its size. Arctodus is the largest mammalian carnivore ever discovered. It is larger than any of the modern bears, tigers, or lions by a significant degree. An estimate for the largest Arctodus found to date suggests that if the individual was “lean” it weighed from 1,300 to 1,400 pounds (Nelson and Madsen, 1983). In contrast, a male lion weighs about 450 pounds. (See How big was the GSFB?)

So this imposing carnivore of the Ice Age roamed across North America, and the North State can forever claim it as its own. A full skeletal mount of this beast can be seen in the new Gateway Science Museum at Chico State.

COPE, E. D. 1879. The cave bear of California. American Naturalist, 13:791.

MARSH, O. C. 1877. Notice of new dinosaurian reptiles from the Jurassic Formation. American Journal of Science, 14:514-516.

MARSH, O. C. 1879. Notice of new Jurassic reptiles. American Journal of Science, 18:501-505.

NELSON, M. E., AND J. H. MADSEN, JR. 1983. A giant short-faced bear (Arctodus simus) from the Pleistocene of northern Utah. Transactions of the Kansas Academy of Science, 86(1):1-9.

RICHARDS, R. L., C. S. CHURCHER, AND W. D. TURNBULL. 1996. Distribution and size variation in North American short-faced bears, Arctodus simus, p. 191-246. In K. M. Stewart and K. L. Seymour (eds.), Palaeoecology and Palaeoenvironments of Late Cenozoic Mammals: Tributes to the Career of C.S. Churcher. University of Toronto Press, Toronto.

RIGGS, E. S. 1903. Structure and relationships of opisthocoelian dinosaurs. Part
1: Apatosaurus Marsh. Field Columbian Museum, Geological Series, 2:165-196.

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