The skeleton of the small, early camelid Poebrotherium on display at the American Museum of Natural History. Image from Wikipedia.

Even with the young politician Jefferson Davis behind their adoption by the military, camels were a hard sell to the U.S. government. Along with other military men, Davis was convinced that camels could replace horses as the standard beasts of burden used by cavalry on the ever-expanding western frontier, but most congressmen and senators balked at the idea. When Davis tried to formally get a military appropriation for fifty camels (along with Arab trainers and other supplies) in 1851, the senators present for his speech thought the idea of cannon-carrying camels to be too frivolous to merit serious consideration, and the following year a similar request was similarly shot down.

But Davis was not to be deterred. The defeats the camel appropriation requests had suffered raised the idea's profile, and when Davis took office as the U.S. Secretary of War in 1853 he renewed his push to see American soldiers riding camels across the arid western scrub. Once again, Davis' attempt for an 1853 appropriation failed, but with some support from two midwestern senators, Davis was finally able to secure the $30,000 needed for the experiment. The "Camel Corps" project was made into law in March of 1855.

With the bureaucratic matters in order, Davis sent military officers out to the desert bordering the eastern edge of the Mediterranean Sea to gather information and procure dromedary camels to bring back to the United States. By the summer of 1856, a small herd had been offloaded and was being observed in Texas - even the local people, at first skeptical that camels could carry much weight at all, were impressed with the abilities of these animals to bear large burdens. Further tests confirmed that camels were adept at going over and through terrain which was impassible to horses and mules, and it seemed that Davis' had been right about the utility of the camels.

Despite the promise the early observations held, western military outposts were not as enthusiastic about receiving the camels. The quartermasters preferred horses, and the soldiers disliked the Arab camel caretakers even more than the camels themselves. Nevertheless, those soldiers who did use camels found them to perform as well - if not better - than horses when traveling through the desert, and the experiment continued even after Davis left office in 1857. Then came the Civil War. When the Confederacy, led by Davis, broke away from the federal government in 1861 the camel experiment was effectively halted. Many of the animals were sold off, some were set loose to go feral, and others remained at their military outposts, causing a fuss among local people who thought them to be ugly, smelly nuisances (at least until Confederate troops captured some of these outposts and let the camels run off into the desert).

On its surface, the importation of dromedary camels to the United States would seem to be a government-facilitated invasion of a foreign species. Camels are animals of northern Africa and Asia, not North America. Yet, through the perspective of geologic time, the introduction of camels to the United States is no stranger than the importation of horses to the continent by European explorers. Much like horses, camels evolved in North America before being entirely extirpated from it; the introduction of modern species to the American west was something of a homecoming for a lineage which had been absent from it for more than 10,000 years.

Although the exotic camels brought to the United States acclimated well to life in the west, not all fossil camels lived in dry, scrubby habitats. Over the course of 45 million years many different genera of camels occupied an array of habitats, from closed forests to open grasslands. One way to appreciate this diversity - both of camels and the ecosystems they inhabited - is to look at the distinctive patterns of scratches and pits left by plant food on their teeth. As communicated in a new Palaeogeography, Palaeoclimatology, Palaeoecology paper, this is precisely what scientists Gina Semprebon and Florent Rivals have done.

The word "camel" is typically attributed to two species of mammal - the dromedary and Bactrian camels - but the extant camelids encompass a wider variety of creatures, including the llamas, alpacas, vicuñas and guanacos of South America. Despite their present range, though, for the first 36 million years of their evolution camelids were restricted to North America, with their heyday occurring around 16 million years ago during the Miocene (a time when many different large mammals, including horses and predatory whales, were also undergoing evolutionary radiations). By six million years ago, the llama and camel lineages had split and camelids had spread to other continents, and the remaining North American lineages became extinct at the end of the Pleistocene along with the giant ground sloths, mammoths, saber-toothed cats, and other megafauna. Although there are no endemic camelids left in North America, camelids persisted on this continent longer than any other, and so the fossil record of North American camelids provides a rich source of information about their paleobiology.

In order to ascertain the dietary habits of the extinct North American camelids, Semprebon and Rivals looked at three different aspects of their molars: the height of their teeth (the higher the tooth crowns, the rougher the diet), mesowear (wear on tooth cusps caused by long-term feeding patterns by an individual), and microwear (pits and scratches made by food during the time shortly before the death of the animal). Together these three different kinds of data outline not only the dietary preferences of individual animals, but also shifts in dietary patterns over time, which are themselves signals of the kinds of environments inhabited by camelids at different points in earth history.

After surveying tooth characteristics in a range of camelid taxa - from the small, early genus Poebrotherium and the giraffe-like, Miocene form Aepycamelus to the recently-extinct Camelops - Semprebon and Rivals found that, in general, fossil camels had much tougher diets than their living counterparts. In terms of mesowear, specifically, fossil camelids showed higher degrees of long-term wear on their teeth from the Eocene through the early Miocene. At this point there was a brief reversal in these trends, but after the mid-Miocene fossil camelids again showed increasing amounts of wear on their molars until the mid-Pleistocene, when there was another drop. Changes in tooth crown height roughly tracked this pattern - tooth crowns became higher during times when there were elevated degrees of mesowear on camelid teeth - indicating that for much of their evolutionary history camelids consumed tough, abrasive foods with reversals occurring in the mid-Miocene and from the mid-Pleistocene to recent time. In terms of tooth crown height and mesowear, living camels and llamas are more like early camelids than most of their fossil relatives.

Tooth height (hypsodonty; left) and mesowear (right) patterns for North American camelids during their evolution. Both graphs show significant dips in the Miocene - probably related to the availability of soft browse - before rebounding and dipping again during the Pleistocene to recent time. This graph sharply contrasts with W.B. Scott's idea of camelid progress from browsers to grazers over time. From Semprebon and Rivals, 2010.

Given the patterns in tooth height and mesowear seen in other herbivorous mammals, it might be expected that many fossil camelids primarily fed on tough grasses. This does not appear to be the case. According to Semprebon and Rivals, most fossil camelids were actually browsers, but they foods they selected were tougher on their teeth. A prime example is the early Miocene genus Stenomylus. This long-limbed, antelope-like camelid had high-crowned teeth and appears to have been adapted to open, grassy habitats, but the patterns of microwear on its teeth are comparable to those of living herbivores which primarily browse on leaves. The reason for this seeming contradiction - a browser with the body of a grazer - may be that Stenomylus was a "dirty browser", or ate soft plants covered in a significant amount of grit. If this was the case, then the high-crowned teeth of camelids were not adaptations to tough grasses, but to softer foods coated in bits of hard extraneous matter which could quickly wear down teeth.

W.B. Scott's simplified diagram of camelid evolution through time. This diagram mirrors early 20th century conceptions of horse evolution in that camelids were belived to have evolved from small browsers into large grazers. From A History of Land Mammals in the Western Hemisphere (1913).

Stenomylus was not an isolated oddball. Some camelids - such as the giraffe-like Aepycamelus - browsed on "cleaner" plant foods high off the ground, and camelid Megatylopus was a grazer, but, when looked at from a wider perspective, Semprebon and Rivals found that camelids moved into open habitats relatively early in their evolution and have primarily been dirty browsers in terms of diet. As far as teeth are concerned, the grit-covered foods camelids consumed caused their teeth to converge in form with those of grazers. This similarity has misled some paleontologists in the past. In his massive 1913 treatise A History of the Land Mammals of the Western Hemisphere, paleontologist W.B Scott wrote "The mode of evolution displayed by the camels does not differ in any significant respect from that seen in the horses," and included an illustration showing how camels, too, evolved in a straightforward fashion from small browsers to large grazers. Now - thanks to the new study by Semprebon and Rivals and previous work on horses by paleontologists such as Bruce MacFadden - we know that neither camelids nor horses evolved in such a linear fashion, and camelids in particular have undergone some dental reversals as the available plant foods have changed during the past 20 million years.

So, although Jefferson Davis did bring camelids back to North America, the imported dromedaries were not equivalent to most of the camelids which lived on the continent during prehistory. The relatively narrow swath of modern camelid diversity does not contain an exact proxy for the species which have been lost from North America, and the feral camels which were loosed into the west interacted with the local flora and fauna in ways different from their prehistoric cousins. Seen in the context of their fossil relatives, though, modern camelids seem even stranger than they already are - they are evolutionary mosaics which the body of a grazer meets the diet of a browser.

Gina M. Semprebon and Florent Rivals (2010). Trends in the paleodietary habits of fossil camels from the Tertiary and Quaternary of
North America Palaeogeography, Palaeoclimatology, Palaeoecology, 295, 131-145 DOI: 10.1016/j.palaeo.2010.05.033

A coprolite from the intestine of the Yukagir mammoth. The large twigs are from willows. From van Geel et al., 2008.

If you want to know about the life and habitat of a woolly mammoth, there is scarcely a better place to look than in its dung. Found frozen in the permafrost or extracted from the intestines of well-preserved specimens, mammoth coprolites are fecal records of the plants which existed in the animal's local environment and what foods that individual was eating just prior to death. Twigs, fruits, seeds, and other plant bits are common components of mammoth coprolites, but there are also signs that mammoths sometimes picked up the dung of their own species for a little extra digestive processing.

The head of the Yukagir mammoth. From van Geel et al., 2008.

A male woolly mammoth recently discovered in northern Yakutia, Russia ate feces shortly before it died. As reported in a 2008 issue of Quaternary Research by an interdisciplinary team of scientists, the "Yukagir mammoth" was well-preserved enough that paleontologists were able to extract a coprolite from its lower intestine and sort through the plant-rich material. Traces of willows, daisies, sorrel, sedges, rushes, sweet-grass, cinquefoils, and other plants indicative of an open, grassy landscape were found, but so was a fungus - Sporormiella - which is known to grow on deposited feces. Since the fruiting bodies of this fungus would have taken about a week to develop, and there was no sign of bile acids in the coprolite which would have signaled that the ingested dung had come from another species of animal, it appears that the Yukagir mammoth ate a one-week-old mammoth patty just prior to its death.

(In investigating the mammoth carcass, the paleontologists also found evidence that the Yukagir mammoth had back problems. The scientists proposed that it had reactive spondylarthropathy, which they said was "most probably associated with inflammatory bowel disease.")

The woolly mammoth coprolite found in northwestern Alaska. From van Geel et al., 2010.

The Yukagir mammoth was not the only one to engage in coprophagy. Earlier this summer some of the same scientists reported another incident of feces-eating among woolly mammoths based upon their observations of  a coprolite found with a partial mammoth skeleton in northwestern Alaska. As described in Quaternary Science Reviews, this dung ball contained plants representative of the open, dry "mammoth steppe" habitat preferred by these animals, as well as the fungi Sporormiella and Podospora conica. And, like the Yukagir mammoth coprolite, no bile acids were found in the coprolite, meaning that the Alaska mammoth also ate a coprolite which had been dropped by a mammoth (itself or another) a week or so before.

The exact reasons why these mammoths ate dung is difficult to discern, but this behavior is not as unusual as it sounds. Young herbivorous mammals sometimes populate their guts with the appropriate digestive bacteria by eating feces, and herbivore droppings can be rich sources of plant material and fermentation products. Even living elephants have been observed to consume dung from time to time, but how regularly mammoths did so is unknown. Perhaps, the scientists behind these reports speculate, the mammoths studied so far were in a state of nutritional stress and turned to coprolites as an easy source of food shortly before their deaths. Then again, perhaps paleontologists have just missed the clues that mammoth coprophagy was regular behavior. Further sampling and research will be required to find out just how often woolly mammoths consumed dung, but at least these two studies have given scientists an idea of what to look out for while picking through mammoth shit.

References:

VANGEEL, B., APTROOT, A., BAITTINGER, C., BIRKS, H., BULL, I., CROSS, H., EVERSHED, R., GRAVENDEEL, B., KOMPANJE, E., & KUPERUS, P. (2008). The ecological implications of a Yakutian mammoth's last meal Quaternary Research, 69 (3), 361-376 DOI: 10.1016/j.yqres.2008.02.004

van Geel, B., Guthrie, R., Altmann, J., Broekens, P., Bull, I., Gill, F., Jansen, B., Nieman, A., & Gravendeel, B. (2010). Mycological evidence of coprophagy from the feces of an Alaskan Late Glacial mammoth Quaternary Science Reviews DOI: 10.1016/j.quascirev.2010.03.008

Post-script: As described by Sean, and as seen in the video below, some captive elephants go straight to the source when interested in a stinky snack:

For more on coprolites:

Fossil feces from an Indiana sinkhole preserve traces of a meat-eater's last meal

Unique fossils record the dining habits of ancient sharks

Collecting blow from a bottlenose dolphin in Baltimore's National Aquarium. From Frere et al, 2010.

For years marine biologists have relied on dart biopsies – small portions of tissue obtained by shooting a dart into an animal – to study the genetics of dolphins in the wild. The trouble is that this method can’t be used on very young animals for fear of harming them, and concerns about injury to adult animals has made dart biopsies a controversial choice for field scientists. Now, as reported in the journal PLoS One an international team of marine biologists has found a new way to gather the same information, and it involves little more than collecting a dolphin’s exhaled breath.

As described by University of Queensland scientist Celine Frère and colleagues, the air expelled through dolphin blowholes – simply called “blow” – contains lung surfactant (a mix of proteins and lipids), respiratory fluid, lung cells, and other biological materials. A previous study carried out by C.J. Hogg showed that the presence of reproductive hormones could be detected by analyzing dolphin blow, and subsequent studies have used blow to examine disease in these marine mammals. But the authors behind the new study went in a slightly different direction - if blow is so rich in biological material, might it be useful for genetic studies?

In order to test their hypothesis about dolphin blow, members of the research team used pieces of sterile filter paper stretched over a hoop in an attempt to collect the exhaled residues of wild bottlenose dolphins in Western Australia's Shark Bay. The basic collection technique worked, and even though extracting the blow from the filter paper turned out to be more difficult than expected, the scientists were able to recover some mitochondrial DNA from one specimen. While the difficulties with the filter paper hampered the laboratory aspect of the study, the scientists were encouraged by the initial result and switched to a different set of subjects thousands of miles from Shark Bay.

Frère and her co-authors turned to the captive bottlenose dolphins held at Baltimore, Maryland's National Aquarium to refine their technique. Filter paper was ditched as a collection tool in favor of polyproplene tubes which were held upended over the blowholes of six dolphins, and this modified method also proved successful in collecting dolphin blow. In contrast to the meager sample from the pilot study, though, the biological material lining the plastic tubes was rich enough to provide data on mitochondrial DNA and microsatellite DNA from each individual dolphin. Furthermore, the DNA profiles taken from blow matched the DNA profiles of each dolphin taken from blood, suggesting that blow may be just as good as blood for studying dolphin genetics.

A profile of microsatellite DNA collected from "individual 1" through blow (top three) and blood (bottom three). From Frere et al., 2010.

Wild dolphins will not just sit still and blow into a tube, however. Adapting the methodology for wild animals presents a substantial challenge, and the authors of the new study state that such efforts are currently underway in Shark Bay. If successful in the field, the new technique would allow scientists to trade in their darts for test tubes.

Reference:

Frère, C., Krzyszczyk, E., Patterson, E., Hunter, S., Ginsburg, A., & Mann, J. (2010). Thar She Blows! A Novel Method for DNA Collection from Cetacean Blow PLoS ONE, 5 (8) DOI: 10.1371/journal.pone.0012299

A male pronghorn, photographed on Antelope Island, Utah.

Capable of reaching speeds exceeding 70 kilometers per hour, the pronghorn (Antilocapra americana) is one of the fastest mammals on earth. No large North American carnivore can match it for speed - some conservationists have go so far as to suggest importing cheetahs to special parks to reinstate the evolutionary race between pronghorn and extinct big cats - yet every year many pronghorn fall prey to a canid more often considered a pest than a consummate hunter. Wolves, cougars, bears, and even eagles all prey upon pronghorn from time to time, but it is the coyote that kills more individuals than any other, especially in the northern range of Yellowstone National Park.

While traveling through northern Utah and Wyoming last summer I saw many pronghorn, but, despite their apparent abundance in the area, the Yellowstone population is quite small. Consisting of less than 300 individuals - low enough to put them at risk of being extirpated locally - the Yellowstone population primarily occupies an area along the northern border of the park. As reported last year in Western North American Naturalist by a team of ecologists led by Kerey Barnowe-Meyer, the partially-migratory group often summers in the arid, shrubby land around Gardiner, Montana in the winter but some migrate into Yellowstone during the summer.

A female pronghorn and two fawns, photographed just outside Grand Teton National Park, Wyoming.

To understand the population dynamics of the Yellowstone pronghorn and which predators posed to greatest threat to them, Barnowe-Meyer and colleagues monitored the movements and mortality of adult females and newborn fawns. During the winters of 1999-2001 and  2004-2006 the team darted adult females and placed tracking collars on them (which would also notify the scientists when the animal died) and in the spring of 1999-2001 they similarly tracked new fawns (taking care to make sure they did not place the baby pronghorn at increased predation risk). When an individual was killed the team went out to inspect the carcass and recorded whatever useful information remained about what kind of animal had killed the pronghorn, thereby providing an outline of what kinds of predators were taking pronghorn and with what frequency.

The trouble with a carcass in Yellowstone is that it does not last for long. Beyond the damage done by the attacking predator, scavengers can quickly obscure clues about what kind of animal made the kill. Nevertheless, the team was able to authenticate the cause of death in 22 cases of adult mortality, with 13 of those being attributed to predators (eight were undetermined and one was due to complications during birth). Of those thirteen the predator breakdown looked like this: 5 coyotes, 3 cougars, 1 wolf, and 4 undetermined predators. The sample was small, but, based upon the incidents in which the killer could be identified, coyotes appeared to be the most significant predators of pronghorn.

The sample of pronghorn fawns was also small, but showed a similar pattern. Of 28 tagged fawns, four survived, eight disappeared, and two died of unknown causes, leaving 14 cases of predation. Of this subset, six were killed by coyotes, five were scavenged (and may have been killed by) coyotes, one was killed by a large bird of prey, and two were killed by an unknown predator. Once again, coyotes appeared to be the most significant predator of the pronghorn, especially since they frequented the kind of habitat which pregnant females preferred for giving birth to and raising their fawns. The other predators took pronghorn opportunistically as the herbivores migrated between Wyoming and Montana, but coyotes preyed on them consistently.

What remains unknown, however, is how the predation of pronghorn by coyotes has been influenced by the reintroduction of wolves to Yellowstone in the 1990's. Coyotes are mesopredators - second-tier carnivores whose populations are controlled by apex predators - and it has been proposed that the existence of wolves in northern Yellowstone acts as a check on the number of coyotes in the area. Then again, it may be that coyotes avoid the rugged, more forested habitats which are home to other predators in favor of more open areas, thus placing adult female pronghorn and their fawns at increased predation risk. At present, the effect of wolves and top-level predators on coyotes in Yellowstone is still poorly known, but figuring out how coyotes have responded to the reintroduction of wolves may help conservationists manage what is left of the Yellowstone pronghorn population.

A male pronghorn, photographed on Antelope Island, Utah.

Female and infant pronghorn are not the only individuals to be killed by coyotes. Male pronghorn, despite their armaments, can also fall prey to the mesopredators, and one recent case identified a unique risk suffered only by the males. Much like elk, male pronghorn often fight with their horns, and every now and then two males become irrevocably stuck. As reported by Jennifer Chipault and Dustin Long in The Southwestern Naturalist, at about 8 PM on October, 2 of 2006 two male pronghorn in Vermejo Park Ranch, Colfax County, New Mexico were found locked together - the horn of one was stuck on the head or neck of the other such that they were nearly nose-to-nose. One was already in a bad state, lying on its side and breathing shallowly, and the other made frequent attempts to free himself.

The naturalists observed the pronghorn intermittently throughout the night, but they were not the only ones watching. At about 2 AM on October 3rd several coyotes were seen in the vicinity of the stuck pronghorn. The coyotes did not immediately attack, perhaps being deterred by the presence of the human observers, but when the researchers left and checked back at the site at about 6:30 AM there was little left of the pronghorn which had been lying on the ground. What remained of it was still attached to the other male. As the researchers described the scene:

The pronghorn on the ground had been partially consumed; all that remained was the head and four limbs held together by dorsal skin, backbone, pelvis, and ribcage. The head of the carcass was still attached to the head of the live, standing pronghorn, which pulled, twisted, and within ca. 1 min freed himself from the carcass.

Is the great speed of the pronghorn attributable to an evolutionary "arms race" with the extinct, fleet-footed cat Miracinonyx? Perhaps, but it would be a mistake to consider the relationship between pronghorns and their predators as only a matter of speed. Infant and female pronghorn are vulnerable to much slower predators during the fawning season, and male pronghorn may inadvertently grapple their way into very vulnerable positions. Pronghorn are not withering away while waiting for a long-lost superpredator to reappear and kickstart their evolution - they continue to be actors in the Darwinian "struggle for existence" in which the rules, and competitors, are subject to change at any time.

Kerey Barnowe-Meyer, P.J. White, Troy Davis, and John Byers (2009). Predator-Specific Mortality of Pronghorn on Yellowstone's Northern Range Western North American Naturalist, 69 (2), 186-194 DOI: 10.3398/064.069.0207

Chipault, J., & Long, D. (2010). Pronghorn (Antilocapra americana) Locked in Fight Becomes Prey of Coyotes (Canis latrans) The Southwestern Naturalist, 55 (2), 283-284 DOI: 10.1894/TAL-07.1

I can't say that all the "science" in the short is sound (Graboids are reptiles? Really?), but it's a fun look at the stars of the Tremors series.

Close up of one of the Pipe Creek Sinkhole coprolites showing structures interpreted as hair (A) and a close-up of a mold in the coprolite thought to have been made by a hair (B). From Farlow et al, 2010.

Time and again I have stressed that every fossil bone tells a story, and, in a different way, so do coprolites. Fossilized feces are small snapshots of the lives of prehistoric organisms, often preserving bits of whatever they had been eating, and while coprolites may not get top billing in museum halls, they are among the most pungent reminders that weird and wonderful organisms really did live during the remote past. As reported by paleontologists James Farlow, Karen Chin, Anne Argast, and Sean Poppy in the latest issue of the Journal of Vertebrate Paleontology, two such vestiges of ancient digestive systems have recently been found in Indiana, but what left them is something of a mystery.

Called the Pipe Creek Sinkhole, the site where the coprolites were found dates back to around five million years ago. During that time Indiana was home to a motley assemblage of mammals. As stated by the authors, remains of "insectivores, rodents, hares, peccaries, deerlike ungulates, camelids, rhinoceroses, felids, canids, skunks, and bears" have been found there, but what sort of animal left the scat behind? To find out, the scientists attempted to parse the details of the fossils through thin sections and CT scans.

One of the teeth found in a Pipe Creek Sinkhole coprolite, as seen inside the coprolite (looking at the root of the tooth) and after its removal. From Farlow et al, 2010.

What the paleontologists found was that the coprolites - measuring 50 mm long × 26 mm maximum diameter and 30 long × 26 mm maximum diameter, respectively - were similar in chemical composition to scat produced by meat-eating animals. This was confirmed by remains discovered within one of the specimens. While one coprolite lacked internal detail, the other (INSM 71.3.144.3000) preserved hairs and two teeth from a small carnivorous mammal, perhaps a skunk, indicating that whatever creature produced the scat was itself a carnivore.

The determination that the coprolites were made by a meat-eating animal narrowed down the list of suspects, but the actual identity of the scat-maker proved difficult to ascertain. The enamel of the teeth found in the coprolite was eroded away, something which has been seen in coprolites attributed to crocodiles. The trouble was that no crocodile remains had been found at Pipe Creek Sinkhole. Additionally, while the scats were similar to those made by snapping turtles observed by the scientists in aquaria, the researchers stated that they are doubtful that the scats were left by a turtle due to the relatively large size of the scats and the lack of enamel-eroded teeth in the modern samples for close comparison.

The only other candidates were the large, meat-eating or omnivorous mammals of the site. Of those animals, it seemed most likely that the scats were left by a canid, especially since experimental tests of how dogs consume and digest white-tailed deer jaws have previously confirmed that whole teeth can sometimes make their way into the stomach where their enamel is dissolved before being deposited as scat. While the authors could not rule-out a large turtle as the scat-maker, on the basis of these observations they assigned the coprolites to a wolf-sized canid. Regardless of the identity of what animal left the scat, though, it is wonderful that such signs of ancient life have been preserved, and through using techniques like those employed in this study paleontologists can begin to better resolve the paleobiology of long-dead organisms.

James O. Farlow; Karen Chin; Anne Argast;Sean Poppy (2010). Coprolites from the Pipe Creek Sinkhole (Late Neogene, Grant County, Indiana, U.S.A.) Journal of Verterbrate Paleontology, 30 (3), 959-969 : 10.1080/02724631003762906

A photograph and line drawing (left side) of the fossil dolphin Astadelphis gastaldii. The crescent-shaped line in the drawing represents the bite of a large shark, with the red portions representing damage done directly to the bone. From Bianucci et al, 2010.

Shark attacks are events of speed and violence. When they have locked-on to a prey item, sharks seem to come out of nowhere, and though they can be quite gentle with their jaws (as on occasions when they are unsure about whether something is food or not) their ranks of serrated teeth can inflict a devastating amount of damage. They are not the cruel, vicious, or bloodthirsty villains they have often been portrayed as, but instead are exquisitely-adapted predators which rely on their ability to catch and consume a variety of prey. And, just as it is among present day sharks, so it was among their prehistoric relatives.

Between 19 and 8 million years ago Maryland's Calvert Cliffs were covered by the ocean. Those shallow waters were inhabited by at least fifteen different genera of sharks, and their teeth (typically all that is left of them today) are scattered everywhere along the beaches. Indeed, they are abundant enough that paleontologists Christy Visaggi and Stephen Godfrey recently cataloged of 26,000 of them to determine what kinds of sharks lived off the shores of ancient Maryland and in what numbers.

Their findings, printed in the Journal of Vertebrate Paleontology, reveal that this place was home to a mix of both living and extinct shark genera. There were fossils from Hemipristis (snaggletooth sharks), Galeocerdo (tiger sharks), Carcharias (sand tiger sharks), Carcharhinus (a subset of requiem sharks), and Isurus (mako sharks) in addition to the famous superpredator Carcharocles megalodon, most of which came from the time interval between 19 and 14 million years ago. (Teeth from many other genera, such as those related to whale sharks and great white sharks, were also found, but were so rare that they did not constitute a significantly significant sample.) While not exactly the same as their living relatives, these Miocene sharks would have looked very familiar to us, and clearly the area that would become the Calvert Cliffs was a very productive marine ecosystem which could support such a wide array of predators. Not surprisingly, there was plenty of prey in the water, too. Although not explicitly considered in their study, Visaggi and Godfrey noted that fish, sea turtles, crocodiles, birds, seals, sea cows, and numerous whale species all lived in the same place, and every now and then a specimen of one of these animals is found showing evidence of shark attack.

In a second new paper published by Godfrey and Joshua Smith in Naturwissenschaften, the paleontologists report on one such trace. In this case the evidence is two coprolites (fossil feces) that had been washed out of the Miocene fossil deposits and found on the beach. Exactly what species produced the coprolites is unknown, but after analyzing a third specimen of the same composition found nearby the scientists determined that it had been produced by a carnivorous vertebrate other than a shark. A crocodile seemed to be a likely candidate, but the thing that made the paleontologists undertake this analysis in the first place was that the fossil feces showed characteristic tooth marks; one of the coprolites had been bitten into and the other had been severed. (You don't often see lines like "This tooth penetrated the feces to a depth of about 3 mm." in the literature.) A shark had bitten into these feces, but what kind of shark, and why?

Photographs of the coprolites CMM-V-2244 (left, lower surface) and CMM-V-3245. The specimen on the left preserves the tooth impressions of the attacking shark while the specimen on the right was severed (the numbers denote where the teeth cut through the feces). From Godfrey and Smith, 2010.

The coprolite that had been severed, given the label CMM-V-3245, was not especially helpful in identifying the biter, but the other coprolite (CMM-V-2244) preserved a row of tooth marks. The scientists made a silicone cast of the impressions to see if the punctures held any clues as to the identity of the biter. What they found was that the animal that had made them had a single row of asymmetrical teeth, and while there were as many as eight shark genera with this characteristic, most of these were deemed "innocent" on the basis of anatomical peculiarities. The best fits for the tooth marks were the genera Physogaleus and Galeocerdo (which, in fact, might be synonymous), sharks that, like their living relative the tiger shark (Galeocerdo cuvier) possessesed asymmetrical teeth in the shape of a bent A.

With the list of potential culprits successfully narrowed down Godfrey and Smith were left with the question of how the bite marks had been made. Even though coprolites are relatively common at the Calvert Cliffs site, no one had ever found a shark-bitten piece of shit before, so they had no other reference to go by. They ultimately settled on several possible scenarios.

The simplest explanation was that the shark (or sharks) which left the marks had been intentionally trying to eat the feces. "From the curvature of the toothmarks and their positions on the specimens," Godfrey and Smith write, "we reason that the majority of the fecal masses were in the sharks' mouths." Yet, strangely, the coprolites were not ingested. Even though tiger sharks have often been cast as indiscriminate when it comes to food there has been no indication that they have ever deliberately eaten feces, and so the authors looked for a different explanation.

A restoration of a "tiger shark" (either Galeocerdo or Physogaleus) attacking a crocodile. The shark could have left impressions of the feces inside the crocodile during this stage of the attack or after the viscera of the crocodile had become exposed. The restoration was created by Tim Scheirer, the premier artist when it comes to restorations of the fossil animals of the Calvert Cliffs. From Godfrey and Smith, 2010.

Another possibility was that the shark bit the coprolites to see if they were palatable. Sharks have been known to tentatively bite objects for this reason, yet if the shark in question did so, the authors noted, the bite marks would have been deeper on both sides of the coprolites (particularly CMM-V-2244). Hence the authors favored a different scenario. The pattern of the bite marks and the fact that the feces were not ingested is consistent with a reconstruction in which, during an attack on another animal, the shark either bit through the body wall and guts to leave the tooth impressions or bit the intestines after disemboweling its prey. Such an attack would have left tooth marks on the feces, which probably fell out of the intestine shortly afterward, hence "In this scenario, the shark chose not to eat the feces, which drifted away, settled out of sight, or otherwise avoided attention."

Unfortunately there is not enough information to know for certain how the coprolites from the Calvert Cliffs came to be bitten, but another discovery made on another continent is a little more straightforward. As reported in the latest issue of Palaeontology, scientists Giovanni Bianucci, Barbara Sorce, Tiziano Storai, and Walter Landini took another look at the exceptionally-preserved remains of a 3.8-3.1 million year old dolphin Astadelphis gastaldii which had been discovered in Italy during the late 19th century. Though long-forgotten, this particular specimen was significant as its bones were lacerated by the teeth of a large shark (thought to be a great white by the naturalists who originally examined it), and the team of researchers went back to these bones to see if they could reconstruct what had happened to the dolphin.

Signs of a shark attack; bite marks on the 6th-11th ribs on the left side of the Astadelphis gastaldii skeleton. This damage would have been done by the shark's lower jaw. From Bianucci et al, 2010.

Like the scientists working with the geologically older Calvert Cliffs material, one of the first steps in reconstructing the events was determining what kind of shark had bitten the skeleton. There was a diversity of large genera, both living and extinct, to choose from, but the marks seemed most consistent with those of a large shark with pointy, unserrated teeth, with the top contenders being Cosmopolitodus hastalis and its still-living relative Isurus oxyrinchus (the shortfin mako). To test this idea the researchers used teeth from both these sharks to make cutmarks on plasticine, but while the marks seemed to be consistent with the damage seen to the dolphin skeleton it was difficult to distinguish between the damage caused by each type of tooth. Likewise, even though the maximum height of Cosmopolitodus hastalis teeth was three millimeters higher than the tallest shortfin mako teeth, this alone was not enough to distinguish between the marks the two species might have left on the bone. The apparent size of the shark involved makes Cosmopolitodus hastalis a seemingly better candidate, but there was no way to tell for sure.

Nevertheless, the numerous toothmarks on the jaw, vertebrae, and ribs of the Astadelphis specimen confirm that it had been bitten by a large shark with smooth-sided, sharp teeth. Now the question was whether the bones recorded an actual hunting event or were the result of a shark scavenging an already dead dolphin. As the scientists discovered, there were traces of both types of feeding.

Sequence of a shark attack. The shark approaches from behind (A), bites the dolphin on the right side (B), and bites it again behind its dorsal fin (C). From Bianucci et al, 2010.

Based upon observations of damage done to large prey by living sharks, the authors of the study propose that a large shark killed the dolphin. As indicated by the deep cuts on the dolphin's rib bones it appears that the shark attacked the dolphin from behind and to the right. The dolphin struggled to get away, causing further trauma to the flesh and bone, and there is little doubt that after the initial bite the dolphin would be suffering catastrophic blood loss. As it died it appears that it may have rolled over onto its back, and at this point the shark bit again just behind its dorsal fin (leaving a second set of bite marks along the vertebrae). Then the shark probably began to feed on the dolphin's soft tissues, and the array of other small scrapes and marks on the ribs and jaws of the dolphin would have been inflicted by smaller scavengers who picked at the remains after the attacking shark had finished. In the ocean, bodies do not go to waste.

(Alternatively, the bite marks could represent the scavenging of a large shark which was consuming an already-dead dolphin. Distinguishing between predation and scavenging in the fossil record can be extremely difficult, and while the attack scenario is more dramatic, a scavenging event cannot be ruled out.)

Together the discoveries from Maryland and Italy provide scientists with narrow, but very informative, windows into the distant past. They remind us that fossils are not just inert remains. They are the last vestiges of living creatures and every single fossil, from the most common shell to rare treasures like shark-bitten croc poop, tell us about what ancient life was like. We cannot answer all the questions we have, but discoveries such as these allow us to reconstruct the past in way usually only possible in our imaginations.

CHRISTY C. VISAGGI and STEPHEN J. GODFREY (2010). VARIATION IN COMPOSITION AND ABUNDANCE OF MIOCENE SHARK TEETH FROM
CALVERT CLIFFS, MARYLAND Journal of Verterbrate Paleontology, 30 (1), 26-35

Godfrey, S., & Smith, J. (2010). Shark-bitten vertebrate coprolites from the Miocene of Maryland Naturwissenschaften DOI: 10.1007/s00114-010-0659-x

BIANUCCI, G., SORCE, B., STORAI, T., & LANDINI, W. (2010). Killing in the Pliocene: shark attack on a dolphin from Italy Palaeontology, 53 (2), 457-470 DOI: 10.1111/j.1475-4983.2010.00945.x

Written in Stone: Evolution, the Fossil Record, and Our Place in Nature

... the galley copies of Written in Stone. These are the uncorrected (but near-final) versions of the book which will go out to magazine editors, reviewers, and others in advance of the book's actual release on November 1st. Given that the book is now less than three months away from hitting shelves, though, there is a lot of work to do, and I have been filling much of my daily allotted writing time with answering interview questions, looking over press materials, pitching articles related to the book, and thinking about which bloggers I should contact about launching a blog book tour. It's exciting, but it also makes me a bit nervous, and I am quite anxious about how reviewers will respond to my first book (especially since I am planning my next book[s] right now).

Zeff the Amur tiger, photographed at the Bronx Zoo.

For female Amur tigers, defending your territory is not just about acquiring enough food to survive; it's also about passing down real estate to your daughter.

As described by a team of scientists led by the Wildlife Conservation Society's John Goodrich in the latest issue of the Journal of Mammalogy, a 14-year study of Amur tigers in eastern Russia's Sikhote-Alin Biosphere Zapovednik has shown that male and female tigers establish home ranges of different sizes for different reasons. After capturing and radio-collaring 32 individual tigers (adults and cubs), the team of Russian and American scientists was able to determine that male tigers maintained very large territories (about 1,385 square kilometers) which encompassed the home ranges of several females (about 390 square kilometers).

A map of Amur tiger home ranges between 1992-1997. Solid areas marked "F" designate females and dashed lines marked "M" designate males. From Goodrich et al, 2010.

The disparity in territory size was not much of a surprise. Among solitary big cats, males often have larger home ranges than females, and the reason for this difference between the sexes has to do with the different life strategies of male and female Amur tigers. Whereas young male tigers typically leave the home territory of their mother in an attempt to find a vacancy and gain access to as many females as possible, females stake out their territories based upon the resources they can provide for them and their cubs (thus their home ranges can be much smaller).

What intrigued the scientists, however, was that the home ranges of female Amur tigers contracted when they had female cubs, with their daughters taking up residence in the vacant areas. This favored the future reproductive success of the young tigresses as they did not have to face the risks usually encountered by individuals which try to establish themselves elsewhere (and often become victims of poachers). As the authors of the paper state, it appears that the adult female tigers in their study defended larger territories than they actually needed to survive, and by passing down a portion of this land to their daughters they enhanced the potential success of their offspring while mitigating competition for the same resources.

Yet, as the scientists saw firsthand, poaching can disrupt the matrilineal inheritance of territory among Amur tigers. During the early years of their study - from 1997 to 2000 - all but two of the radiocollared tigers living within the Sikhote-Alin Biosphere Zapovednik were killed by hunters. The vacancies were filled by a mix of "immigrant" animals from other areas and individuals which were related to those which had been poached, but, even after a new population became established, it took five years before a mother tiger passed down territory to her female offspring.

The spatial patterning of tigers over time detected by Goodrich and colleagues may very well complicate tiger recovery plans. If there is a large area of land in which tigers were nearly eliminated (as was the case in this study), the new tiger population will not quickly rebound to its maximum capacity. Instead female tigers which move into vacancies will defend larger territories than they require until they pass down some of that area to their daughters, and during this time the tiger population might be more susceptible to poaching as a smaller number of animals will be occupying an area which could actually support many more. But this news isn't all bad. If tigers can be successfully protected long enough for adult animals to become established, the population size and density can potentially double when the next generation of female tigers mark out their own territories within those initially carved out by their mothers. Given enough time, the tattered remnants of a tiger population can begin to recover.

References:

Goodrich, J., Miquelle, D., Smirnov, E., Kerley, L., Quigley, H., & Hornocker, M. (2010). Spatial structure of Amur (Siberian) tigers (Panthera tigris altaica) on Sikhote-Alin Biosphere Zapovednik, Russia Journal of Mammalogy, 91 (3), 737-748 DOI: 10.1644/09-MAMM-A-293.1

A restoration of Amphicyon by Charlene Letenneur. From Argot 2010.

Between 23 and 16 million years ago, just outside of where the city of Lisbon, Portugal sits today, there lived a unique mix of mammals which would have seemed both strange and familiar. From bones and footprints left in fossilized feces, paleontologists have found that rhinoceros, deer, horses, antelope, and elephants browsed and grazed in the ancient ecosystem, and many were preyed upon by archaic carnivores such as the fearsome amphicyonids (popularly known as "bear-dogs"). That such confrontations occurred can readily be inferred by the presence of large predators and prey in the same place, but direct evidence of interaction is rare. It does not require a stretch of the imagination to envision a large bear-dog grappling a fleeing antelope or rhinoceros to the ground, but how do we really know that such events took place?

Without a time machine, it can be extremely difficult to tease out the relationships between extinct organisms, but every now and then paleontologists find a rare specimen which records the interaction of two species. One such specimen, a bit of the left lower jaw from the rhinoceros Iberotherium rexmanueli, was described by scientists Miguel Antunes, Ausenda Balbino, and Léonard Ginsburg in 2006. Although rather plain-looking at first sight, the specimen is remarkable for exhibiting a series of pits and scratches that were most probably made by the bear-dog Amphicyon giganteus.

A line drawing of the anterior portion of the rhinoceros jaw showing furrows made by the incisor teeth of a large carnivoe. From Antunes et al, 2006.

The Iberotherium specimen in question is the middle portion of the animal's lower jaw; the front of the jaw is missing and the rear portion was accidentally broken off during collection. There are a number of small pits and perforations along the jaw which indicate that a carnivorous mammal stripped the flesh off it, with some of the most conspicuous damage being seen towards the front of the bone. Here, near the area of the left jaw which would have met with the front of the right jaw (called the symphysis), there are three indentations on both sides which were probably made when the carnivore gripped the jaw with its incisors.

The hypothesis that Amphicyon giganteus was probably the offending carnivore came out of a process of elimination. Although the large carnivore Dinocyon also lived around the same time, its remains have not been found from the same locality, and while the bear-dog species Amphicyon major also prowled nearby, its presence in the Lisbon beds has not been confirmed. Likewise, the size of the bite marks indicated the activity of an animal the approximate size of a brown bear, and other contemporary candidates were not large enough to fit the profile. Hence the scientists were left with only one valid candidate - Amphicyon giganteus.

But, even if we can be confident in the identification of Amphicyon giganteus as the predator in question, does the tooth-marked jaw represent a predation event or scavenging? It is impossible to know for sure. Antunes and colleagues propose that the pattern of toothmarks on the jaw suggest that the Amphicyon was holding onto and biting the rhinoceros mandible in a manner similar to how we eat corn on the cob. Hence they hypothesize that this means that the carnivore was eating a largely-intact carcass "on the spot." If true, this means that the Amphicyon either killed the rhinoceros - perhaps preying upon an individual weakened by droughts which frequently occurred during the time - or was lucky enough to happen upon an intact Iberotherium which had been killed in a flood.

Yet, as a large carnivore, Amphicyon would have also been capable of tearing off portions of a carcass - such as a head or jaws - and carrying them away to consume in relative peace. This hypothesis could also apply to either a hunting or scavenging scenario, but without the rest of the Iberotherium skeleton, it is impossible to tell exactly what happened. The toothmarks indicate that an Amphicyon fed on the rhinoceros jaw, but they can't tell us how the rhinoceros died in the first place.

References:

ANTUNES, M., BALBINO, A., & GINSBURG, L. (2006). Ichnological evidence of a Miocene rhinoceros bitten by a bear-dog (Amphicyon giganteus) Annales de Paléontologie, 92 (1), 31-39 DOI: 10.1016/j.annpal.2005.10.002

ANTUNES, M., BALBINO, A., & GINSBURG, L. (2006). Miocene Mammalian footprints in coprolites from Lisbon, Portugal Annales de Paléontologie, 92 (1), 13-30 DOI: 10.1016/j.annpal.2005.09.002

Top image from: Christine Argot (2010). Morphofunctional analysis of the postcranium of Amphicyon major (Mammalia, Carnivora, Amphicyonidae) from the Miocene of Sansan(Gers, France) compared to three extant
carnivores: Ursus arctos, Panthera leo, and Canis lupus Geodivertistas, 32 (1), 65-106