Category Archives: Mammals

Polar Bear populations

In an earlier post about the effects of climate change I made the point that there is a lack of intellectual honesty in the political climate change debate and a comment on that article provides a perfect example.

The commenter quoted an opinion piece by Gerald Warner. Mr. Warner cites population estimates by the International Union for Conservation of Nature (IUCN) Polar Bear Specialist Group that summarizes 19 sub-populations of bears. The summary of the population status is that 8 are declining, 3 are stable, 1 is increasing, and the other 7 are unknown. They currently estimate a world population of approximately 25,000 individuals. (See the footnote)

The most flagrant claim made by Mr. Warner is “the actual statistics” that since 1970 polar bear population has quintupled from 5,000 to an estimated 25,000 individuals.

A quick search revealed an article by Terence Jeffrey that gives at least partial references for “the actual statistics.” In his article, Jeffrey relates a history of scientific polar bear population estimates over the last five decades. An honest reading of his article shows that less was known early on and with increased efforts made to study polar bear numbers, we have better estimates now. Who would have guessed?

Quoting from Jeffrey, in 1965 world population of polar bears was estimated to be “5,000 to 8,000 animals,” “over 10,000” or “17,000 to 19,000 animals.” So, the apparent basis of “the actual statistics” of Mr. Warner comes from the extreme lowest estimate of bear populations in the 1960s to the estimate of the modern populations to get a quintupling. I am not sure in which universe this counts as “actual statistics.”

All of this clearly demonstrates one of the main points I made in the earlier story—the dishonest manipulation of scientific information for the express purpose of confounding the public is all too common in the political debate of climate. I am afraid it is only going to get worse, and my stated hope for intellectual honesty in politics is looking less likely all the time.

International Union for Conservation of Nature (IUCN) Polar Bear Specialist Group. http://pbsg.npolar.no/en/index.html

Jeffrey, T. 2008. The great polar bear population puzzle. http://www.humanevents.com/article.php?id=26627

Warner, G. 2010. Climategate: two more bricks fall out of the wall of deceit—rainforests and polar bears. http://blogs.telegraph.co.uk/news/geraldwarner/100030204/climategate-two-more-bricks-fall-out-of-the-ipcc-wall-of-deceit-rainforests-and-polar-bears/

Footnote: I wanted to examine the trends in the known population numbers a bit more as given by the IUCN, so here are some observations. Of the 19 sub-populations, they currently estimate the population of 14 and declare a status for 12 of them. By taking an average of the high and low population estimate for each of the given areas, the sum is 18,461.5 bears. This is the sum of the averages for all the estimated areas. There are 5 areas with un-estimated populations, so there are more bears in the world. Plus, the average may not be the best estimate for each area and is no doubt low for some areas and high for others. So, a total global estimate of 25,000 is reasonable enough.

If we sum the estimated populations by status (declining, increasing, stable, and unknown) we see that 52% of the known population is classed as declining; 2% are classed as increasing; 19% are classed as stable; and 28% have an unknown status.

So, over half the known population of polar bears are in declining populations. More than a quarter are unknown as to their population status. Almost 20% appear at this time to be stable in population numbers, and 2% seem to be increasing. I fail to see how anyone could construe these data to say that “polar bears appear to thrive on warming” (quote from Warner).

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.

New species are still being uncovered at the Gray Fossil Site

Dr. Steven Wallace holds the beaver tooth recently discovered at the Gray fossil site. (Brian Bishop / Johnson City Press)

The Gray Fossil Site near Johnson City, Tennessee is full of surprises. The site dates to the late Miocene in age, and preserves a diverse fauna of critters. It is highly unusual to have deposits of this age preserved in the Appalachian region as most of the sediments have been stripped away from the underlying crystalline bedrock. But in this unusual setting, sediments that filled a sinkhole were preserved, along with a lot of evidence of past life from the region.

Researchers have not yet “scratched the surface” of the deposit despite several years of excavation. Core samples indicate that the deposit covers several acres and is over 100 feet thick (Wallace et al., 2002). Many species have been identified from the site including: fish; alligator; snakes; turtles; amphibians; a proboscidean; the world’s largest single collection of tapirs; rhinos; a short-faced bear; ground sloth; a saber-toothed cat; and a red panda.

They have recently added beaver to the list.

Steven Wallace and his team have identified the specimen as Dipoides, a member of an extinct line of beavers which includes the giant beaver Castoroides. Dipoides has a stratigraphic range extending from the Hemphillian to the late Blancan (Kurten and Anderson, 1980), or approximately 9 million to 3 million years ago (Prothero, 1998).

Today, you can visit a large interpretive center at the site, and watch summer excavations. It is expected that an annex will be started soon to provide even more space for visitor activities. Check it out on line at www.grayfossilmuseum.com, and watch for continued news coming from Johnson City, Tennessee in paleontology.

References:

KURTEN, B., AND E. ANDERSON. 1980. Pleistocene Mammals of North America. Columbia University Press, New York, 443 p.

PROTHERO, D. R. 1998. The chronological, climatic, and paleogeographic background to North American mammalian evolution, p. 9-36. In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary Mammals of North America. Cambridge University Press, New York.

WALLACE, S. C., J. NAVE, AND K. BURDICK. 2002. Preliminary report on the recently discovered Gray Fossil Site (Miocene), Washington Co., Tennessee: with comments on observed paleopathologies and the advantages of a large sample. Journal of Vertebrate Paleontology, 22(Supplement to Number 3):117A.

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