Archive for the ‘evolution’ Category

new peru whale

A lot of the popular reaction to new discovery  of a 42.6-million-year-old amphibious whale in Peru has focused on the fact that this whale had four legs.  Yeah, four-legged amphibious whales first appeared in South Asia 50 million years ago, with most famous one being Pakicetus.

However, this reaction to this new discovery merely tells me that most people are unaware of how much we know about whale evolution.  Whales and dolphin, in case you didn’t know, are actually a subset of artiodactyls.  Artiodactyla is the same order that includes pigs, sheep, antelope, giraffes, cattle, and camels, and when scientists began to classify whales and dolphins this way, some creationist wag posted a strawman that scientists believed that whales evolved from cows.

No. Whales and dolphins are actually derived an ancestor that was very close the common ancestor of hippopotamuses. The clade that includes hippos and whales and dolphins is called Whippomorpha.  Literally, they just combined the word “whale” and “hippo” to create this name.

Hippos are actually much more closely related to whales and dolphins than they are to other artiodactyls, and because whales and dolphins are so well-nested in Artiodactyla, some experts now call the order Cetartiodactyla, combing the word “Cetacean” with the word “Artiodactyla.”  I personally don’t do this because we could just as easily renamed Carnivora “Pinnipedavora” because phocid seals, otariid seals, and the walrus are all derived from caniform ancestors.

Whales and dolphins, though, are derived from land-based artiodactyls. They are not derived from cows or any ruminants, though. Ruminants are highly specialized plant-eating mammals, which have a multi-chambered stomach to deal with the hard cellulose and fiber of their diets.

50 million years ago, though, there were many omnivorous and carnivorous artiodactyls.  Mesonychids, which were quite numerous millions of years before whales evolved, were essentially artiodactyl wolves that ran down their prey on hoofed feet.  When I was first reading about whale evolution as a teenager, it was believed that whales derived from Mesonychids, but now we have a more complete view of their evolution.

Pakicetus first appeared in the fossil record of South Asia. It was a sort of a semi-aquatic artiodactyl wolf, which then gave rise to Ambulocetus, a sort of mammalian crocodile-like creature.

From South Asia, these primitive whales entered the sea, and over time, they evolved into more and more specialized animals.

Four-legged whales have been found North America and Africa, but there has long been a debate about how whales dispersed from South Asia into the oceans of the world.

The discovery of this new extinct whale species called Peregocetus pacificus in Peru suggests that South Asian amphibious whales entered the now defunct Tethys Sea (which included the Mediterranean but went much further east), swam down around the Atlantic Coast of Africa, crossed the narrow distance of the Atlantic to enter South America, and then colonized North America. This colonization took about 10 million years after the whales began to become creatures of the water.

So yeah, we know a lot more about whale evolution now because of this discovery, and now the public knows that four-legged whales really were a thing.


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When Europeans arrived in the Americas, the cougar was the most widespread wild cat species, but in the modern era, after we have extirpated the cougar from most of the East, the most widespread cat is the bobcat.

It is found throughout the Lower 48, but it is conspicuously absent from most of the Midwest. In Ohio, they are found almost entirely within a short distance of West Virginia, Pennsylvania, or Kentucky. In the Northern Great Lakes states, they live towards Canada and the lakes themselves. But they are fairly numerous elsewhere.

The bobcat is a species of lynx, which is conveniently classified in the genus Lynx.  Four extant species roam across Eurasia and North America. The bobcat includes the smallest individuals of the genus, but they are the most variable in size. 13-pound queens can be found, as can toms that exceed 40 pounds in weight.

The lynx species likely evolved in North America.  The dentition of a cat from the Pliocene that has been called Felis rexroadensis suggests that it was the earliest form of lynx.  Some authorities now call this cat Lynx rexroadensis. Bjorn Kurten believed that this species is the ancestor of the Issoire lynx (Lynx issiodorensis), which is the likely ancestor of the Eurasian, Iberian, and Canada lynx.

The bobcat is either a direct descendant of rexroadensis or is derived from the Issoire lynx that came back into North America.

The latter seems more likely,  because our current understanding of the molecular evolution of the cat family finds that the lynx species last shared a common ancestor 3.2 million years ago. 

Ancestral bobcats appear in the fossil record of North America 2.6 million years ago, and the modern bobcat evolved from a population that became marooned south of the ice sheets 20,000 years ago.

So the most likely scenario is that bobcats have a deep evolutionary history in North America, but their exact line went into Eurasia and then came back.

It should also be noted that Felis rexroadensis has sometimes been placed into another species called Puma lacustris, which fits somewhere in the cougar lineage. The cougar and lynx lineages are closely related, and as you go back towards the common ancestor of both lineages,  the basal forms tend to resemble each other. However, it is well-supported now that the lynx lineage first evolved in North America and then radiated into Eurasia.

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black coyote

For most of my life, scientists believed that the present era was still the Holocene.  Glaciers retreated with a global warming trend around 11, 650. Man went from being the apex predator over much of the world and became the apex consumer. Agriculture allowed our populations to expand, and we started to give up our wandering ways and became “civilized.”

It was generally believed that the past few centuries are but a continuation of this age, but now a growing number of scientists believe we have left the Holocene and entered into the Anthropocene. Several scholars have issues with this new distinction, but I think it is quite useful. In this era, human activity is the main factor affecting climate and ecology, which is why the age is named for the Greek word for human (anthropos).

The best argument I’ve seen for when this era began is 1610.  In this scenario, the era is dated to when European disease and conquest killed off enough Native Americans and enslaved and enough African had been enslaved to allow forests to grow back in former agrarian fields.  This process started in 1492, but by 1610, enough of those trees had grown to remove enough carbon dioxide from the atmosphere to push the planet into the Little Ice Age.

Darcy Morey and Rujana Jeger have a great model for understanding dog domestication as a change in trophic strategies.  In the Pleistocene ecosystems, most wolves were mesopredators, playing second fiddle to an ecosystem full of cave lions, machairodonts, large bears, and cave hyenas. When these wolves hooked up with people, though, they hitched their wagon to the species that often behaved as the apex predators in the ecosystems.  When humans switched to agrarian lifestyles during the Holocene, humans became apex consumers, and dogs joined us as beneficiaries of being allied to that apex consumer species.  During the Holocene, many wolves became apex predators, as the cave lions and other large predators became extinct.

I’ve always liked the framework that Morey and Jeger derived in this paper, but now that we’re entering into a new geological age, maybe we need to look at the change in trophic strategies of wolves in this new age.

Morey and Jeger don’t have a good framework for what happened to wolves in the Anthropocene, but across Eurasia and North America, wolves were gone from many human-dominated landscapes by the first decades of the twentieth century.  They existed only in isolated areas in Western Europe, and in the  lower 48 states of the US, they lived only in Minnesota and in an isolated region in East Texas and Louisiana, where the taxonomically controversially red wolves were located.

Large pack-hunting wolves were really in quite a bit of trouble.  In the United States, the coyote population began to expand out of its Western core range into the Great Lakes States. They eventually made to New England and the Maritimes of Canada, and they hybridized with relict wolves and the expanding population of domestic dogs.  Coyotes eventually colonized all the Eastern states, and as they did so, they largely became the apex predators in many parts of their range.

But in the 1960s, attitudes about wolves began to change. Many nations protected wolves, and there were often introduction plans in the works.  By the early decades of the twenty-first century, wolves were making significant comebacks in Germany and Italy. The wolves in Italy were often living very much like stray domestic dogs, living large at garbage dumps. Wolves live near large cities in Germany, and how these wolves are going to adapt to living in such human dominated environments is going to be a major question for researchers.

And in throughout Eurasia, we began to see that domestic dogs were mating with wolves.  Indeed, it is now estimated that a majority of wolves in Eurasia have relatively recent dog ancestry. 

Similarly, as coyotes expanded in North America, their genes began to work their way into the wolf population.  Yes, coyotes in a large part of the US have wolf ancestry, but we also have discovered that wolves across North America have coyote ancestry. Indeed, one interesting thing about these genome comparisons is that coyotes and wolves are much more closely related than we initially gleaned form mitochondrial DNA analysis. The calculation is that the gray wolf and the coyote last shared a common ancestor around 50,000 years ago.  This recent common ancestry has a taxonomic implication, which is that coyotes are themselves a divergent form of gray wolf in much the same way domestic dogs are.

In the Anthropocene, the wolves that have done the best have been the domestic dog and the coyote. The domestic dog’s ability to ingratiate itself into human society or live very nicely as an opportunistic scavenger/hunter on the periphery of humanity is a great gift.  The coyote can live as an opportunistic scavenger/hunter as well, and it also can live very nicely as a mousing fox or pack up and hunt deer.

Gene flow among wolves, coyotes, and dogs has made these entities much more fuzzy than we once thought they were. Dog genes are working their way into both the coyote and wolf population.  Strange pelt colors are popping up in the wild animals. The black coloration in domestic dogs was conferred onto the North American wolf population during the Holocene, but this same mutation for melanism has entered the coyote and Italian wolf population in very recent years. Dogs have introduced dewclaws on the hindlegs to some wolf populations, and I have seen photos of Eastern coyotes that have those hind dewclaws as well, which likely were introduced through breeding with domestic dogs.

Coyotes in the East are evolving larger size to become better predators of deer, but becoming larger and more effective ungulate hunters will have a trade-off. As carnivorous mammals grow larger, they become more and more dependent upon large prey to survive.  Very large wolf-like coyotes will lose their ability to live well on small prey and garbage.

So in the Anthropocene, dogs remain allied to the apex consumers. Some coyotes operate as apex predators, and some wolves live as opportunistic scavengers.

And as these creatures adjust their trophic strategies in a much more predator tolerant world, the pseudo species barriers that exist among wolves, coyotes, and dogs can break down. Hybridization among these creatures is likely to be a major feature of their continued evolution, a definite feature and not a bug.

These canids  thus make the leap with us into this human dominated age, an age that is experiencing a mass extinction of amphibians and great retrenchment of large sharks and big cats.

Yet they are still there. Evolving as the winds change. Winds that we ourselves are changing and are only now starting to understand.

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This morning, I decided to subject myself to some creationist programming on one of the religious channels that every American gets with a basic TV package. I don’t know why I do this, but I consider learning what creationists do– and do both deceptively and wrongly–a great exercise in understanding my own epistemology.

The most important thing to understand about creationism, whether it is the Kent Hovind, 6,000-year-old earth type or the more sophisticated intelligent design type, is the fundamental exercise is not understanding scientific findings. Instead, it is about protecting the authority of scripture from scientific findings. The Hovind types are about denying science, wile the ID types are more into a sort syncretism between the findings of science and the need to have faith. This same sort of syncretism exists with religious people who accept evolution, too, but the intelligent design types often are a bit more into making sense of scripture and science than the theistic evolutionists.

So whenever you are subjected to creationist or intelligent design pontifications, you need to understand they are much more concerned with defending scripture against scientific findings than creating any kind of parallel scientific hypothesis that could ever compete with those of peer-reviewed science.

This particular creationist segment was concerned about speciation, and it was definitely from the school of thought that a Kent Hovind would appreciate. Because biologists do not have a hard and fast definition of species– a strength of the discipline, if you ask me–creationists are able to play games with what a species is. The piece talked about how they accepted that all the breeds of dog derived from a wolf ancestor, but then it started getting dishonest.

It showed how biologists think of lions and tigers as distinct species, but they can sometimes interbreed. However, unlike mixed breed dogs, the ligers are often sterile. The narrator of the piece didn’t seem to get that this sterility is how we know that lions and tigers are different species, because no scientist alive believes that two animals that produce offspring in which fertility is limited to this degree belong to the same species.

Instead, the narrator skipped over this glaring problem and began to explain that breeds of dog and tigers and lions were obviously derived from the same kind, and the reason why ligers are often sterile is because of a sort of hyped up “evolution” that happened after Noah’s flood.

It is certainly true that dog breeds are far more morphologically variable than lions and tigers are from each other, but dogs have a good reason for this morphological variation. They have some odd characteristics to their genomes that allow them to respond to selection pressures in rather dramatic ways. Thus, dogs vary a lot in terms of their morphology, but they don’t vary as much genetically as lions and tigers do from each other. Molecular evidence points to all extant dogs radiating within the past 15,000 years, and although some experts would put that date a bit further back, it is nowhere near the 4 million years estimated for the most recent common ancestor lions and tigers.

I don’t know how creationists square this problem, except to say that mutation rates are so much higher in some of these “species” than in others. But the mutation rate you’d have to have to match the millions of years of divergence between tiger and lion lineages would not be biologically possible. I image that the genetic load from deleterious mutations would be too much to sustain either lineage.

But that’s not what the creationists in this piece discussed. Instead, they came up with an entire theory called “polyphyletic decent.” The “kinds” of animal that came off the ark diverged into the things resembling species in phylogenetic trees that look a lot like the ones real scientists use to describe evolutionary relationships. However, unlike those phylogenetic trees there is no implication of connection between “kinds.” They are trees growing out of a single stem that diversified.

Evolution is based upon monophyletic decent. That’s why the argument that creationists often make where they posit the absurdity of an organism giving birth to another species is quite ridiculous. All living things evolve out of a particular lineage. Nothing evolves out of it. Humans will always be great apes, which will always be Old World primates, which will always be simiiformes, which will always be haplorhines, which will always be euarchontoglires, which will always be boreoeutherians, which will always be placentalian, which will always be therian mammals.

This is why so many taxonomists work hard to ensure that organisms are classified according to their descent. This descent can be traced through the morphology of the organism as well as its molecular biology.

If the creationists were right about this “polyphyletic descent” hypothesis, then you would be able to find organisms for which one can find no DNA sequences in common with any other. And one has not been found yet.

So creationists have a new thing to play around with. It will never gain acceptance among scientists.

But that is not the point. The point of creationism is to defend scripture’s inerrancy against scientific findings. It is an exercise in defending faith, not in trying to understand that which the rigors of the scientific method has revealed.

And once you understand this difference, it makes total sense why scientists don’t debate creationists. The two disciplines are trying to do entirely different things, which are not equivalent to each other. One is trying to understand the material world using measures and data that verified, while the other is trying to defend supernatural beliefs that can never be verified.

I guess I go by the Bible and say by its fruits, it will be known. The scientific method has produced all the technological advancements that have made modern life what it is. It has increased our knowledge about our place in the world and in the cosmos. Defending scripture against what science has revealed has produced little but adhering the truly faithful to the religion a bit more strongly and made a few charlatans infinitely rich. But it has not advanced us one iota, and in this current epoch, it is holding us back from confronting global problems like climate change and mass extinctions. If you can deny evolution, which is quite obvious, then you have the intellectual skill-set to deny what climate scientists are saying.

We live in an era of tribal realities. What one accepts as true depends upon which tribe one belongs. If you’re a conservative Christian in the United States, you have a different understanding of how the world is than virtually anyone else in the Western World. Part of the reason for this disconnect is that white conservative Christianity is losing the demographics battle in the United States. And in this loss in demographics is this tendency to turn to those ideas and individuals who might restore their former advantage. Belief in fundamentalist Christianity might somehow bring down the divine, which could restore it all with a miracle, and belief in Donald Trump might work out, too, because he will be nasty to all those people who are taking away this demographic advantage.

Time will eventually remove this madness from our society, but while it is there, it will do some damage. And for the climate, we don’t have that much time.

All I can do, then, is use my voice to make some sense to a few more people, and hope, the dismal tide turns sooner rather than later.

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One of the things I like about paleontology is the often creative hypotheses that get postulated in its literature. However, there are certain ideas that need better fleshing out with regard to molecular data, and sometimes, the tendency toward parallel evolution in certain clades is not adequately addressed in some of the morphological analyses that the discipline is force to use.

Among these would be the claim that arctic foxes evolved in the Himalayas. The paper that postulates a Tibetan origin for this polar species was well-publicized, as was the attendant out of Tibet hypothesis for arctic mammals. I must admit a certain amount of skepticism of the entire hypothesis, because it seems a bit of a stretch that evolution in high altitudes in the middle of a vast continent would create a lasting evolutionary lineage that could then colonize regions to the far north of that continent. It seems to me odd that you would get something like a polar bear started in the Himalayas, then have it colonize the arctic as a near marine organism.

The authors of the paper posit a Tibet origin for the arctic fox, based upon the remains of Vulpes qiuzhudingia Tibetan fox that lived over 5 million years ago. The dentition of this fox strongly resembles that of the modern arctic fox, and therefore, the authors think that the arctic fox must have derived from either this species or one that is close to it.

The authors also think that the next oldest arctic foxes were found in the arctic 3-4 million years ago, which is also interesting.

Both of these claims are interesting because the molecular data indicate that the closest relative of the arctic fox is the swift fox of North America, and what’s more, the arctic and swift foxes shared a recent common ancestor that lived about 900,000 years ago. The molecular data indicate that what we call an arctic fox today derived from the swift in the North American arctic.

So what the authors likely found with Vulpes qiuzhudingi is a parallel evolution of a more carnivorous fox in the high altitude of Tibet 5 million years ago. It might be the ancestor of “arctic foxes” found in the arctic 3-4 million years ago, but they are not the same thing that goes by Vulpes lagopus today. It is also possible that these arctic foxes that are older than 900,000 years old are another parallel evolution of more carnivorous foxes in cold climates.

This tendency toward parallel evolution matches so much of what we know about about canid evolution, and why virtually everything one reads about canid paleontology and systematic morphology needs to be confirmed with molecular data.

So yes, I do appreciated the creativity of paleontologists to describe the fauna of the world as it once was, but that darn ol’ DNA messes up the flight of fancy so many times.

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Our brains like simple answers. We love to see the cause and then the effect, and we constantly look for them in nature.  At one time, we believed that the appearance of comets in the sky would be harbingers of great doom. And even in the past century in my home state, it has long been claimed that the appearance of Mothman in the area around Pt. Pleasant corresponded with the Silver Bridge collapse.

Correlation does not equal causation. Chanticleer, that old rooster of English Medieval lore, believed that his crowing at dawn made the sun rise.  When two variables occur at the same time but don’t have any causal relationship, they are called stochastic. Stochastic is one of my favorite words from graduate school, and even today when someone posits a bogus relationship between two variables, I say “Those are stochastic variables.”  I get some odd looks, but that was the point.

In trying to understand the complex phenomena that comprise evolution, we are constantly looking for these relationships. Some of them make some good sense and are well-supported with the data. We know that predators are the driving force behind making the prey swift and nimble, and we also know that plant-eating animals are the driving force behind the development of thorns and toxic plants.

But sometimes, our desire to see patterns leads us astray.  One example of what may be an erroneous positing of stochastic variables involves one of North America’s most unusual animals.

If one were to go to Wyoming on a hunting trip, there is a good chance that the outfitter will tell you to buy “antelope tags.”  Tags, of course, are licenses that give permission to the hunter to take a particular species, and in Wyoming, there is great interest in the pursuit of antelope.

But the little secret is there are no antelope in Wyoming. Indeed, the only true antelope in the United States are gemsbok that have been introduced to specific part of New Mexico, and Texas game ranches are full of various species of Old World antelope.

But no true antelope is native to the Americas. The animal we call an “antelope” should be more appropriately called “the pronghorn.”  It is not an antelope at all, but it is the last survivor of a lineage of creatures that are much more closely related to the various giraffe species and the okapi.  The pronghorn and its extinct kin are placed in a superfamily of Artiodactyla called Giraffoidea. These animals have bony processes that stick off their heads. In the giraffe and okapi, these are called ossicones and are covered in hair. In the pronghorn, a sheath of keratin grows over the bone. This sheath is shed every year, which leads to the claim that the pronghorn is the only animal that loses its horns every year.

The animal we call a pronghorn is superficially quite similar to what we would call an antelope or gazelle in the Old World.  But these similarities arose through parallel evolution. Both gazelles and pronghorns evolved in the open land where all sorts of cursorial predators hunted them. Predation forced these animals into swiftness and nimbleness.

That part is not much up for debate.

The problem comes with a specific claim about pronghorns.  One odd feature of this species is its speed. The top speed of an adult pronghorn is 55 mph (88.5 km/h). This speed far exceeds any of its predators that were around in historical times. A pronghorn can smoke a pack of wolves or coyotes and can easily outrun a cougar or a bear.

This high speed has vexed science for quite some time, but there has been an attempt to explain how it could evolved using predation as the driving force.

The hypothesis even points to a specific predator.

At one time the cougar lineage was much more diverse than it is now.  Right now, only three cats still exist in this lineage:  the cougar/mountain lion/puma/catamount/painter/panther (all names for one species), the jaguarundi, and the cheetah of Africa and Iran.

But during the Pleistocene, there were long-limbed cats that superficially resembled the cheetahs of the Old World. They were called “American cheetahs,” but analysis of mitochondrial DNA extracted from their fossils revealed they were much more closely related to cougars. Indeed, they were more closely related to cougars than cougars are to jaguarundi, which complicates the whole move to place jaguarundis in the same genus as the cougar. The two extinct American cheetahs are currently classified in the genus Miracinonyx, while the cougar is in Puma and the jaguarundi is in Herpailurus. Because these two American “cheetahs” are closer to the cougar, placing the jaguarundi in Puma creates a paraphyletic genus. This problem could all be solved if we just placed the two American “cheetahs” into Puma, but not everyone agrees with the mitochondrial DNA assessment of their phylogeny.

Let’s just say that the current pronghorn species lived at the same time as these lithe cougars, and it has been suggested that these cheetahs are the driving force behind the evolution of the extreme speed. The person who came up with this suggestion was a pronghorn expert named John Byers. Byers does not claim that these “cheetahs” were the sole force behind the development of speed in pronghorns. Instead, he lists them among a whole guild of running predators that could have placed selection pressures on pronghorns to force them into the evolution of speed.

The claim that these “cheetahs” were the driving force behind pronghorn speed has been picked up on the popular press though. Wildlife writer Dan Flores even made this claim recently on the Joe Rogan Podcast, and one can find countless pieces on the internet (including this blog when I was a lot more naive) that the extinct North American cheetahs are the “but for” cause of the pronghorn’s fleetness.

The problem with this claim is that it leaves out the nuance of the original hypothesis, and what we’re left with is a sort of cartoon version of evolution.

On the blog Laelaps, a great amount of skepticism is leveled at this hypothesis, largely because the popular understanding of how North American cheetahs might have affected pronghorn evolution.

One problem is that no one really knows how the two species of North America cheetah lived:

We don’t know very much about the natural history of either Miracinonyx species. Their skeletons are cheetah-ish, but that’s not nearly enough to pin these carnivores as the inspiration for artiodactyl agility. In fact, the ecological context of Miracinonyx bones hints that these cats were not simply speedy specialists who prowled open grasslands.

In their 1990 study, Van Valkenburgh and collaborators noted that later Miracinonyx bones have been found from Nebraska to Pennsylvania and Florida in deposits which accumulated under varying conditions. These cats were apparently just as at home among coastal savannahs as mountain stream valleys. More recently, at the 2010 Society of Vertebrate Paleontology meeting, John-Paul Hodnett and coauthors presented a poster about Miracinonyx that frequented caves in prehistoric Grand Canyon, Arizona. There was a distinct lack of fast-running, open-savannah prey animals during the same time period – the researchers noted that the extinct mountain goat Oreamos harringtoni was the most common possibly prey animal in the area. Rather than speeding over the grasslands, Hodnett and colleagues reported, the Grand Canyon Miracinonyx may have lived like snow leopards, bounding down sheer rock faces in pursuit of mountain goats.

This isn’t to say that Miracinonyx never bolted after equally-swift prey. It’s only to point out that we don’t know much about the cat’s ecology, feeding habits, or hunting strategy. There are a few ways we could find out a bit more, though.

Coprolites attributable to Miracinonyx might contain identifiable bone fragments of the cat’s prey. And while such a find is a longshot, perhaps a trackway made by a Miracinonyx running or launching itself into pursuit could tell us about how these cats actually moved. Both lines of evidence suffer from the complexities of accurately attributing a particular trace fossil to a trace-maker, though. Another route may be to compare the isotopic clues in the teeth of Miracinonyx to those of their potential prey, as was recently done for two sabercats and a bear dog found in Spain. By ascertaining where herbivores were feeding, and how geochemical signatures of prey became locked in carnivore teeth, paleontologists could narrow down the preferred habitats and prey of Miracinonyx. Furthermore, a poster presented by Natalia Kennedy and coauthors at the 2012 SVP meeting outlined a new attempt to compare the spine of the modern cheetah to that of Miracinonyx and other extinct cats to see how skeletal anatomy influenced flexibility and lifestyle.

Miracinonyx might have been the reason for the swiftness of pronghorn. False cheetahs and archaic pronghorn overlapped in time, if not habitat, for as much as three million years. But saying Miracinonyx was certainly a speed demon that gave pronghorn a reason to run is only supported by the barest amount of evidence. If we’re going to understand the evolution and natural history of these animals, we must first untangle their histories and the specific details of their ecology. The Just-So story of how the pronghorn got its speed has yet to be tested by the evidence which resides in the fossil record.

So we really don’t know enough about the extinct North American “cheetahs” at all, and we certainly don’t know enough to make claims that they were the driving force behind the evolution of speed in pronghorns.

Further, if one reads Byers’s text on these predators, he does say that these cheetahs were “the principal agents of selection” behind the pronghorn’s speed, but the author does point out that things like dholes, wolves, and various species of Borophaginae could have been part of the mix as well.

Pronghorn don’t just have speed. They have endurance.  Endurance is one way that Old World antelope elude the speed of cheetahs, but the main way they elude them is through agile running maneuvers. Pronghorn are fast, but they don’t have the quick turns of a Thomson’s or dorcas gazelle.

If these North American “cheetahs” ran down their prey in the same way the Old World true cheetahs do, then one would expect the pronghorn to have evolved some of these tricks.

Instead, pronghorn are running machines. They can take off and go and go and go. An animal that evolved to do such a thing likely didn’t evolve to outpace a sprinting cheetah. It likely evolved to outrun endurance runners.

Dholes are known in North America’s fossil record largely from Beringia, but we do have remains of dholes from Mexico. So their distribution in North America was probably more extensive than we might have assumed, but their fossil record is still quite spotty. Dholes run down their prey in long endurance chases, and dhole predation could have been a pretty strong selection pressure on pronghorns to make them fast endurance runners.

But another species could have also provided this pressure, and its presence in North America is well-established. What’s more, it lived in roughly the same areas where pronghorn were common.

This animal was North America’s only hyena, Chasmaporthetes ossifragus. These hyenas were far less like the modern bone-crushing species of hyena. Indeed, they were quite dog-like and are part of a grouping of hyenas that were called “dog-like hyenas.” The only dog-like hyena still in existence is the aardwolf,  which eats almost nothing but termites.  Its extinct relatives, though, were pretty adept predators of ungulates. They are thought to have run down their prey in much the same way dholes and African wild dogs do today.

So it seems that the pronghorn’s speed and endurance are much more likely to have evolved in response to predation from these long-distance running predators.

Further, we really don’t know how early North American wolves hunted their quarry.  Edward’s wolf and Armbruster’s wolf were both pretty common in North America until 300,000 years ago. They may have also hunted in much the same way dholes and African wild dogs do.  We don’t know enough about their natural history either, so we can only speculate.

The truth is we really don’t know why pronghorns are so fast.  It is possible that the North American “cheetahs” were the principal driving force behind the pronghorn’s speed. It is possible, but the evidence still is wanting. Further, there are more likely candidates that should be explored as having some influence on evolution pronghorn predation avoidance behavior.

So it is possible, but right now, it looks like we have two stochastic variables. We need much more evidence for a causal relationship.

And like everything else in evolution, we need to be careful about looking for patterns where they might not exist.







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Reeves’s muntjac is native to China and Taiwan. It is not native any place in Europe, but one of the places where it has been introduced is England. The epicenter of their population in that country is Bedfordshire, where this hunt takes place.  The Dukes of Bedford were into promoting deer on their estate, Woburn Abbey, and they were instrumental in saving the Pere David’s deer from extinction. One suggestion is that the muntjac in England derived from Reeves’s muntjac that escaped Woburn Abbey, but they also could have derived from escapees from the Whipsnade Zoo.

Whatever their origin, Reeves’s muntjac have established themselves a long way from their native territory, and they do quite a bit of damage to trees.

And what usually happens is that people are encouraged to hunt the invasives, but as you can see from the selective shooting that goes on this video, the species is now being managed as a sort of game species on many estates. This development should be of no surprise, and it should be noted that island of Great Britain has only two native deer species, the red and the roe. The very common fallow deer was introduced by the Romans and then again the Normans from the European continent.

But the fallow deer is essentially managed as a native game species. The exact same thing is done with Sika deer that have been introduced to Maryland. White-tailed deer are treated the same way in the Czech Republic, as are all the deer that have been introduced to New Zealand.

Whatever their treatment as a game or invasive species, this video does provide a nice closeup of the male Reeves’s muntjac as a specimen. Of particular note are the tusks, which they use for fighting and display.  It is mentioned in this clip that they are “musk deer, ” but this is in error.

This error comes from the tusks that both muntjac and musk deer possess, but musk deer are placed in their own family (Moschidae).  True deer are Cervidae, and all the muntjac species are true deer that fall into the Cervinae subfamily (which includes red deer, fallow deer, and North American elk).  However, they are primitive Cervinae.

Musk deer differ in some morphological characters from true deer in that they don’t have facial glands, possess only a single pair of teats, and have a gallbladder.  They also never have antlers, and all species possess a scent gland on their tail.

The common ancestor of musk and true deer, though, had prominent tusks. The modern muntjac species is unique in that it still has those fangs of the earliest Cervinae.

The other true deer that is known for its tusks is the Asian water deer, which was definitely introduced to Britain thanks to escapees from Woburn Abbey. But it is not closely related to the muntjac at all.

It is also not a musk deer, even though it has much more prominent tusks than the muntjac and never has antlers. Instead, it fits within Capreolinae, the subfamily of deer that includes roe deer, moose, reindeer/caribou, and all the New World deer but the wapiti. Its prominent tusks and lack of antlers are a also primitive trait in this lineage of deer.

That muntjac and water deer are both fanged shows that more primitive animals will resemble each other more the derived forms of their respective lineages.

These cnine teeth are celebrated in North America elk lore. Their “ivory” is taken as almost as much a trophy as the antlers, and indigenous people in Canada and the US used them as jewelry. They aren’t sharp daggers like those found on muntjac and water deer, though. They are just vestigial teeth that show that the ancestor of the great bugling bull were once little fanged creatures.

These upper canines also appear in white-tailed deer on occasion as an atavism.

Beyond these little fangs, North American deer lack these primitive traits, so I find fangs on these Asian species totally fascinating.

They are windows into the past, when deer were just little beasts of the undergrowth.

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