I’m rushing around frantically trying to get everything done before I leave for HiliLand on Saturday, so don’t expect much. Since people seemed to like the evolution post on ring species yesterday, I might do another tomorow on a new paper on the hooded crow/carrion crow hybrid zone (a famous area where two “species” meet and sometimes mate) in Europe. But for the nonce have a look at some animals: pronghorn antelopes sent by Stephen Barnard from Idaho (maybe I’ll just call him “SB” from now on, since everyone knows his photos), as well as a landscape taken from where he lives.
As I’ve explained before, pronghorn antelopes (Antilocapra americana) aren’t really antelopes: they’re the only species in the family Antilocapridae. Every other species in that family is extinct. Here’s a group photographed by Stephen (click all pictures to enlarge):
Wikipedia says this, though I haven’t verified it:
The pronghorn is the fastest land mammal in the Western Hemisphere, being built for maximum predator evasion through running. The top speed is very hard to measure accurately and varies between individuals; it can run 35 mph for 4 mi (56 km/h for 6 km), 42 mph for 1 mi (67 km/h for 1.6 km); and 55 mph for 0.5 mi (88.5 km/h for .8 km). It is often cited as the second-fastest land animal, second only to the cheetah. It can, however, sustain high speeds longer than cheetahs.
True antelopes are Old World creatures found in Africa and Eurasia (examples are the impala, the dik-dik, the sable antelope, the wildebeest, and the Thompson’s gazelle). I did a TimeTree search to find out the evolutionary relationship between the pronghorn and other deerlike mammals. (You should all know about the TimeTree site; put in any two species and you’ll find their divergence time and the scientific references for it. I’ll do a post someday on the weird counterintuitive relationships you can find using this site.)
Here’s the relationship between the pronghorn and a true antelope; their lineages diverged about 29 million years ago.
Here’s the divergence between pronghorns and giraffes. It’s not much different!
And the relationship between two “true” antelopes, whose ancestors diverged about half that long ago:
What this says is that the pronghorn is no more closely related to “true” antelopes than it is to the giraffe, which of course isn’t an “antelope” at all. The pronghorn, limited to North America, is a truly unusual species.
And now a landscape shot of where they live, also from SB:
sub
Responding to both bits of this post:
a) I’m sure many of us would welcome more posts in the vein of the ring species one, in particular when they give more “popular” explanations of what is in your book Speciation (hopefully this comment doesn’t violate the Roolz, as the point is raised in the post above)
b) Thanks to all of the photographers whose work appears here
Beautiful photos Stephen, as always. What a lovely place to live. It looks quite green for mid-July. Must have had a damp spring and early summer (like last year).
When we drove across ID, MT, WY, and SD last summer (late July) I was amazed at how green it was. I’d never (crossing the high plains many, many times since 1973, my first trip) seen it that green that late in summer.
If SB keeps sending photos like those above half of the followers of WEIT will start thinking about moving out there!
I had heard that the closest living relative of the pronghorn was the giraffe–but the older divergence time than the impala suggests this is not true. I guess I’ll have to wade into this question–I’ll be doing a geology field trip to Wyoming in just a couple of weeks, and I should have my biology straight as well!
Well, the impala/pronghorn and giraffe/pronghorn divergence are within error limits the same. I wasn’t able to find a good phylogeny of the artiodactyls, but one I had showed several groups, including pronghorns, branching off at the same time, so there may not be one artiodactyl group that is more closely related to pronghorns than other artiodactyls. It could be a “star” phylogeny, in which several groups branched off at about the same time.
Of course there are extinct species of pronghorn relatives that are more closely related to living pronghorns than the African antelopes, in that their common ancestor lived more recently. But those species are all kaput.
“I’ll be doing a geology field trip to Wyoming in just a couple of weeks”
Lucky you! Where and looking at what?
Thanks Jerry and John for your comments!
The field trip is part of an undergraduate class that does a grand tour around Wyoming. (Their first 4-5 weeks are focused on the Spring Creek Preserve near Laramie, which features dinosaur-bearning Morrison Formation exposures and a variety of other geological, biological, and archeological features.)
I’ll be looking at some Precambrian rocks in the Medicine Bows and Tetons, some of the rocks in Yellowstone and the Beartooths north of Yellowstone, and some miscellaneous Cenozoic sedimentary rocks in the basins in between these areas.
From the point of view of rocks, I’m most looking forward to some roughly 2.3 Byr old rocks in the Medicine Bows that are supposed to be ancient glacial tills. What is particularly interesting about these is that they are supposed to have been deposited at low elevations in tropical latitudes, and thus they are evidence for a ‘snowball Earth’ interval much older than the better studied ~575-775 Myr interval.
I’ve never been to the Medicine Bows, but I took a hike in the Snowy Range a few years back and was very impressed by the geology: greenschists, various other schists, quartzites, and some very cool metaconglomerates. Also a bit of stromatolitic limestone a bit lower down (in elevation; presumably up-section). And nice birds too.
You have to be careful with Timetree output; you have to understand the assumptions that go into any particular estimate. First, each number is the average of all the estimates in their database. The pronghorn-impala date relies on a single study (Hassanin et al. 2003), and that study found pronghorns to be closer to giraffes than impalas. But the pronghorn-giraffe date is the average of three studies, only one of which is Hassanin et al. The fact is that none of the three studies clearly resolves the relationships of the three groups, which can change based on small differences in method of analysis. Since the divergence date estimates depend on the tree, those also change depending on analysis. And the results of one study can’t be compared to the average of three studies.
So the end result is what Jerry says: these three groups all diverged somewhere around 30 million years ago, give or take a few million, and the Timetrees site doesn’t tell us anything about the order of those divergences.
I’m sure there must be some more recent research on this subject with a much larger data set than any referenced by Timetrees. But I haven’t been able to find any yet. Is there a mammal phylogeneticist in the house?
Where did they diverge from- N America or Asia?
How would you tell?
Where the ancestral fossils are found, for example horses were from N.America, spread to Eurasia & Africa, became extinct in N.America & were re-introduced by humans. similarly with camelids – N.American in origin eg http://science.nbcnews.com/_news/2013/03/05/17184574-ancestor-of-the-camel-was-an-arctic-giant?lite
Not always a good clue, especially if the fossil record isn’t good. But I’ll admit it might work for most large ungulates.
From poking around in the internet I have learned there are several subspecies of pronghorn, distributed over the Western U.S. and Mexico.
The various extinct species that I found look pronghorny, but they differ in the form and numbers of their horns. Some are pretty weird.
Here is a posting from Tetrapod Zoology about extinct pronghorns.
Nice photos! Those pronghorns look very exotic.
Great Pictures… another amazing animal but it makes you realize how impoverished the mammals of North America are…
Is the crow article the Science one from Poelstra et al?
Pretty please do one on that 🙂
That last photo — what’s the white stuff on top of the mountains?
I’m guessing that’s not from your property. Is it looking back on it?
And how did you do the pano…?
b&
what’s the white stuff on top of the mountains?
Have you never left the southern flatlands or is there a joke I’m not getting?
This is the Sawtooth Basin, headwaters of the Main Fork of the Salmon River, about 90 miles north and over Galena Summit from where I now live. Those are the Sawtooth Mountains in the background. I lived here for 12 years and still have a cabin in Stanley.
The pano was done with Photomatrix Light.
Apologies in advance, I know this is off topic. Have you seen the latest Deepakity? [www.charismanews.com/us/44670-new-age-dr-deepak-chopra-issues-1-million-challenge-to-militant-new-atheists]
This has been posted on here and here.
Ah, I don’t trust the mean given in the Time Tree website. The expert result is much better, because you can locate individual chapters of the book here:
http://www.timetree.org/book.php
Each chapter contains explanations, methodologies, details, and discussions of the studies, the genetic material they use, and to what degree you can place confidence in the results. The chapter for the pronghorn (Cetartiodactlya, or basically whales and even-toed hoofed mammals) can be found here:
http://www.timetree.org/pdf/Gatesy2009Chap81.pdf
The best part is that of the chapters focused on groups of animals, each contains a diagram of the timetree used, and the table of data showing the expert result and comparing that to the individuals studies used to produce it. In that chapter, the pronghorn (antilocapridae) is the outgroup of all the ruminants, which include giraffes and deer (giraffidae and cervidae, respectively). The pronghorns diverged about 31.6 million years ago from the rest of the ruminants.
Unfortunately, the book chapters don’t give individual species, and never go lower in taxa than the family. It also tends to be really patchy in some areas: for instance, there’s a whole chapter on sea urchins, but no chapter on echnioderms in general; some chapters only contain one or two splits and that’s it (like the owl and crocodylian chapters); the true fly and cephalopod chapters contain two lineages that aren’t connected and don’t contain any information about when they split: and you need to know what the taxa are called, or else you won’t be able to tell what group is what, so get Wikipedia on hand ready to look some up if you don’t have a clue. Also, some dates contradict each other. For instance, the divergence between metazoa (animals) and choanoflagellates is something like 1020 million years ago in the Eukaryote chapter, but the first split within Metazoa in its own chapter occurs 200 million years earlier!
It is, however, fascinating if you want to look at the bigger picture. For one thing, it dispels the myth of the Cambrian explosion as simply an explosion of fossilisability, not of actual evolution. For another, it contains more than a few surprises: for me, one of the eye-openers was that most holometabolous (fully metamorphizing) insect orders are roughly as old as the classes of vertebrates reptiles, birds, and mammals (amniotes, collectively). In the same time frame that eventually produced the ancestors of these three vertebrates “classes”, the insects churned out something like eleven orders, from beetles, lacewings, and hornets to horseflies, butterflies, and fleas. Another one was finding that insects are a group nestled within crustacea rather than outside them; the humble water flea and brine shrimp are more closely related to dragonflies than they are to hermit crabs, cleaner shrimps, and spiny lobsters!
It’s an amazing resource, that’s for sure! 😀
Error correction: http://en.wikipedia.org/wiki/Tragulidae Chevrotains are the outgroup of ruminants, not Pronghorns. My mistake!
In that chapter, the pronghorn (antilocapridae) is the outgroup of all the ruminants, which include giraffes and deer (giraffidae and cervidae, respectively). The pronghorns diverged about 31.6 million years ago from the rest of the ruminants.
There’s definitely a problem with guide trees. Different estimates of the same taxon pair use different guide trees and get different results. The age you see is the average of multiple estimates using different trees. I’m not sure how even to interpret such a number.
Also, some of the taxonomy used to link species into higher taxa is way, way out of date and results in ludicrous age estimates, at least for birds. This isn’t a problem here, as Antilocapridae, Bovidae, and Giraffidae are clearly all monophyletic.
For one thing, it dispels the myth of the Cambrian explosion as simply an explosion of fossilisability, not of actual evolution
How so?
“There’s definitely a problem with guide trees. Different estimates of the same taxon pair use different guide trees and get different results. The age you see is the average of multiple estimates using different trees. I’m not sure how even to interpret such a number.”
What are you talking about? The methodology is pretty standard stuff: measure trees for different genetic locii, then figure out what kind of tree would be most parsimonious.
“Also, some of the taxonomy used to link species into higher taxa is way, way out of date and results in ludicrous age estimates, at least for birds.”
Again, not sure what you’re talking about. Most of the time, when the taxa are not truly monophyletic, the tree just puts “” marks around it, like “Porifera” for sponges.
“How so?”
The Metazoa chapter, for a start, shows divergences among the major animal groups ranging from 1200-700 million years ago. The first chapter contains a graph on its 8th page which shows how the fossil record and the genetic studies correlate. The fossil record notably flatlines around the Cambrian, while the genetic studies continue their trend:
http://www.timetree.org/pdf/Hedges2009Chap01.pdf
The Cambrian Explosion is, therefore, not a true explosion, at least not a true evolutionary explosion. The pieces of the chessboard had already been set up hundreds of millions of years earlier. Cyclostomata, for instance (jawless fishes), were already separate from Gnathostomata within the Ediacaran period:
http://www.timetree.org/pdf/Hedges2009Chap39.pdf
What are you talking about? The methodology is pretty standard stuff: measure trees for different genetic locii, then figure out what kind of tree would be most parsimonious.
That would certainly be true if this were, say, 1989. But no, these days maximum likelihood or Bayesian analyses are more common, and they have all sorts of parameters that have to be estimated and all sorts of different evolutionary models that might be considered. Add those many models to parsimony and neighbor-joining (still popular in some circles) and you get quite a few possible trees out of the same data, most particularly if the nodes in question are not strongly supported by the data.
Again, not sure what you’re talking about. Most of the time, when the taxa are not truly monophyletic, the tree just puts “” marks around it, like “Porifera” for sponges.
That’s true if they know about that non-monophyly. Sometimes. But if you input a pair of species, the website returns not just the trees that contains those species, but trees that contain any members of the same taxa they think (based on their taxonomy) you are trying to compare. If that taxonomy is wrong, they give you estimates based on taxa that aren’t really close relatives. Again, based on birds, if you want to compare, say, Cariama with Passer, you will get results that compare any gruiform with any passeriform. Unfortunately, Cariama isn’t really a gruiform, so bad things happen. Again, this isn’t a problem with the comparisons Jerry was doing.
The Cambrian Explosion is, therefore, not a true explosion, at least not a true evolutionary explosion.
Doesn’t that directly contradict what you said before? “…it dispels the myth of the Cambrian explosion as simply an explosion of fossilisability, not of actual evolution.” Perhaps you mistyped, and you meant to dispel the latter, not the former?
Anyway, I think the truth is somewhere in the middle. See for example Lee et al. 2013. Rates of Phenotypic and Genomic Evolution during the Cambrian Explosion, Current
Biology 23:1889-1895.
Both phenotypic and genetic evolution were estimated to be around 5 times faster in metazoans during the explosion than before or since.
Oh, that’s disappointing. I had thought TimeTree was a good resource, but now I have my doubts. You wouldn’t happen to know of a more up-to-date resource I could consult, could you?
Re: The Cambrian Explosion. Blame the confusion on my unclear writing. I was saying that it was proof that the Cambrian explosion didn’t actually happen, but that it was a normal gradual process.
Beautiful photos. They also brought out some interesting discussions. Learning all the time here.
I lived in Cheyenne, WY for 8 years. We had herds of Pronghorns on our property. Amazing mammals. Though I’ve never seen so many males together as shown in the photos.
I could also see how Wyoming would be a geologist’s paradise. The wind river canyon is spectacular.
The small group of pronghorn consists of both sexes. Male and female pronghorn both have horns. Male horns are larger averaging about twice as tall as female horns. It appears there are two bucks in the photo, one on the left behind the two females and one second from the right. It is possible there is another male in the center clump. I have seen pronghorn from Montana to the Sonoran Desert of southern Arizona in my travels around the west. My son and I drove over Galena Summit after hiking in the Sawtooth Mountains last week.
This past winter we saw pronghorn on the National Elk Refuge near Jackson, WY. Apparently fall and early winter were mild. Some members of a large herd of pronghorn that summer in Jackson Hole and the south end of Yellowstone NP did not cross the Gros Ventre Mountains to the Green River drainage south of the mountains. A few pronghorn spent the winter in Jackson Hole.
Pronghorn are common year around near my home in SE Utah. The numbers seem to have increased since my childhood.
Thanks for straightening out my antelope knowledge. And yes, I think their population is growing in WY, and they are managed well.
They were nervous but not spooked while I was photographing with a long lens. You’re right about identifying the males. Those are the ones looking at me, and another that I suspect is an immature male.
The prime predator of pronghorns used to be the American cheetah, which went extinct, along with many other large North American mammals, about 10,000 years ago. Based on what I’ve read, the American cheetah was once thought to be closely related to the cheetahs of Africa and Eurasia but more recent studies have determined it was actually most closely related to cougars (mountain lions, pumas or whatever else you want to call them).
It’s been speculated that pronghorns have more speed and endurance than they seem to need, given their common predators (primarily wolves), because they coevolved with cheetahs.