Tetrapod Zoology

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ResearchBlogging.org

The Pronghorn or Pronghorn antelope* Antilocapra americana is a strikingly unique artiodactyl, endemic to western North America. Historically, it ranged from southern Manitoba and Washington in the north to northern Mexico in the south, and to western Iowa in the east. Between 40 and 50 million Pronghorns were alive in 1850; excessive hunting had reduced this number to 13000 by 1920. Subsequent conservation efforts have resulted in substantial recovery: there are currently between half a million and one million Pronghorns.

* Also known as the Cabrit, Prong Buck, Speedgoat (my favourite) or just Antelope.

Growing to about 1.5 m in total length, and with a shoulder height of approximately 1 m, the Pronghorn is a cursorial browser-grazer of plains, scrub-steppes and deserts. It’s renowned for its phenomenal running speed. Most sources (e.g., Nowak 1999, Kitchen & Maher 2001) state that it’s been clocked at 86 km/h (55 mph): a top speed of 100 km/h (62 mph) is given by some and there’s even one claim of 113 km/h (70 mph). Astonishingly, it can run 11 km in 10 minutes, giving an average running speed of 65 km/h (40 mph) (Lindstedt et al. 1991). The top speeds credited to Cheetah Acinonyx jubatus are 96-101 km/h (60-63 mph), though it’s easy to find claims of 114-120 km/h (70-75 mph) and I’m currently confused as to whether these higher numbers are still considered valid. While the highest claimed running speeds credited to Pronghorn are likely to be too high, there’s no doubting the incredible stamina of these animals: their average speed exceeds that of any other terrestrial animal, including the cheetah.

A Pronghorn might be off the ground for distances of up to 8 m when running at full-tilt, and its hooves are heavily cushioned with cartilage. The question of why the Pronghorn is so fast when no modern American predator is anywhere near as speedy has often been asked and the favoured answer is predictable: we’ll get to that soon [illustration below from Casa Editrice AMZ's Animal Life in North America].

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The Pronghorn is an anatomical oddball and is among those animals sometimes described as having been ‘designed by committee’ (camels and therizinosaurs are among the others). As depicted in the self-explanatory cartoon below, it’s been said that its feet (which are fully didactyl, lacking dew hooves) recall those of giraffes, that the erectile hair patches on its rump resemble those of Antidorcas (the Springbok), and so on (I’ve lost the source for this illustration, but it’s from one of the Orbis World of Wildlife volumes, originally written by Felix Rodriguez de la Fuente).

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A key pronghorn character is the presence of paired, supraorbitally positioned frontal horns that are never shed. While the bony core is unforked, its keratinous covering is forked (in males) and is shed annually (we’ll be looking at this subject more later on).

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In males [like the one shown here, from wikipedia], the horns are longer than the ears and have obvious anterior prongs. The horns of females are typically shorter than the ears and are usually simple spikes without the prongs. As usual for horned mammals, however, lots of variation has been reported. Females with especially large horns, and females with no horns at all, are on record. Males also differ from females in having black patches on the face and neck, and in running with the nose tilted down towards the ground (as opposed to running with the head’s long-axis held parallel to the horizon: it would be interesting to know why this sexual dimorphism occurs). There’s loads of other weird stuff worth commenting on: intrauterine siblicide, shock-moulting, their reluctance to leap over obstacles, and their attraction to unfamiliar objects.

Five subspecies have been named: the large, widespread, ‘typical’ A. a. americana, the critically endangered A. a. peninsularis of Baja California (less than 200 persist), the endangered A. a. sonoriensis of north-west Mexico and southern Arizona, A. a. mexicana of Mexico and the south-western USA, and A. a. oregona of Oregon. The validity of some of these subspecies has been questioned, but some – like A. a. sonoriensis – have stood up to scrutiny (Paradiso & Nowak 1971).

As usual, introductions and relocations made by people have messed up the original distributions of these subspecies. The transplant of thousands of Pronghorns into New Mexico between 1936 and 1957, for example, means that any original subspecies boundaries there have become blurred (O’Gara 1978). People have also moved Pronghorns (possibly belonging to A. a. oregona) from Oregon to Washington, and animals from southern Arizona (where the endangered A. a. sonoriensis occurs) have had their numbers boosted by introduction from northern Arizona. For some stupid reason, 40 Montanan Pronghorns were introduced to Lanai in the Hawaiian Islands in 1959 (there’s a very sad story here; it ends with the last members of the herd dying out by the mid 1970s).

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Little known is that a second species of Pronghorn – A. anteflexa – was proposed by Gray (1856) for a pair of horns [shown above] shown to him by the Earl of Derby (their provenance was unknown). These horns were particularly long and the apex of each horn curved strongly forwards. However, horns of this sort seem to crop up as oddities within normal A. americana populations: very similar horns are seen in the captive individual shown below (from Los Angeles Zoo; photo by Chris Valle, from wikipedia).

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As is so often the case, the living Pronghorn is merely the surviving remnant of a much more diverse group, and some extinct pronghorns were spectacular and very unusual compared to Antilocapra (though.. don’t get me wrong, others were boring and mundane :) ).

It’s these many diverse fossil forms that we’ll be looking at next. To those of you already familiar with these animals: please try and refrain from spoiling the surprises for everyone else!

For more on artiodactyls at Tet Zoo, see…

Refs – –

Gray, J. E. 1856. Notice on the horns of an unrecorded species of pronghorn (Antilocapra), in the collection of the Derby Museum, Liverpool. The Annals & Magazine of Natural History 17 (2nd series), 424-426.

Kitchen, D. & Maher, C. R. 2001. Pronghorn. In Macdonald, D. (ed) The New Encyclopedia of Mammals. Oxford University Press, pp. 528-529.

Lindstedt SL, Hokanson JF, Wells DJ, Swain SD, Hoppeler H, & Navarro V (1991). Running energetics in the pronghorn antelope. Nature, 353 (6346), 748-50 PMID: 1944533

Nowak, R. M. 1999. Walker’s Mammals of the World, Sixth Edition, Volume II. The Johns Hopkins Univesity Press (Baltimore and London).

O’Gara, B. W. 1978. Antilocapra americana. Mammalian Species 90, 1-7.

Paradiso, J. L. & Nowak, R. M. 1971. Taxonomic status of the Sonoran pronghorn. Journal of Mammalogy 52, 855-858.

Comments

  1. #1 John Hutchinson
    July 20, 2010

    Great article as always.
    Sharp (1997 J Zool 241) provided the only accurate measurement of cheetah faster speeds in the literature at 29m/s; 64mph, but >70mph is not inconceivable. That’s about all that can be said for cheetah speeds (until RVC PhD student Penny Hudson publishes her work), but then we know more about them than about most species!

  2. #2 Stu of the Peak
    July 20, 2010

    Wonderful animals, excellent article.

    Just back from three weeks in the US, with a week in the Hell Creek and a few days in Yellowstone and mucho driving in between so saw quite a few pronghorns (along with lots of other wildlife and dead dinosaurs etc), especially on the prairie of the Dakotas. We tended to see them in small groups or occasionally singly (and at least one roadkill was identifiable as a pronghorn.

  3. #3 Luna_the_cat
    July 20, 2010

    I grew up with these guys — there was a herd whose main territory was just north of our place, and we encountered them a lot. [T]heir reluctance to leap over obstacles, and their attraction to unfamiliar objects — you’re not kidding; the unfortunates near us had their population kept quite artificially small due to their tendency to hang themselves up on barbed-wire fences that they could have easily leapt over, and their unfortunate attraction to bright orange bicycle warning flags (the boy to the east of us used to poach them; he’d stick one of those flags out in the middle of the field, set up a blind, wait until they came right up to stare at the flag like silly sheep, and then shoot a couple. The f***ing bastard finally shot twelve out of 14 of them one year, and the remaining two left or were killed elsewhere.)

    I have to admit, I don’t know anything about other, extinct species.

    I’m really looking forward to the rest of this series.

  4. #4 Caterina
    July 20, 2010

    @Luna_the_cat: Why didn’t you shoot the kid? Sounds like he’s the type to shoot wolves from airplanes, and I’d like to see all of them on the ice being shot at from planes!

  5. #5 Luna_the_cat
    July 20, 2010

    @Caterina — in all honesty, I didn’t shoot the kid because he was a better shot than I was. I might well have missed, and he’d have shot back.

    I did consider ambush a couple of times.

    The thing which really galled me, then and now, was that he wasn’t even hunting for meat. He just liked killing things. On the couple of times our family tried complaining to the sheriff (yes, Western towns still have sheriffs), though, nothing happened; he wasn’t interested in doing anything about it — to much trouble to take over something that didn’t matter.

  6. #6 J. S. Lopes
    July 20, 2010

    I wonder how so many Artiodactyles developped horns, but no Perissodactyle. Even among Artiodactyles, only Ruminantia and the putative tylopod Protoceratidae have horned members: no Suiform, no Camelid/Oreodontid, no Ancodonta. Why? Because proto-ruminants were headbutters?

  7. #7 Hai~Ren
    July 20, 2010

    J.S. Lopes: I don’t know if you would consider the warts seen on pigs as horn-like structures. And the Miocene suid Kubanochoerus (unicorn-pig!) did possess horns…

  8. #8 ObSciGuy
    July 20, 2010

    “…shock-moulting, their reluctance to leap over obstacles, and their attraction to unfamiliar objects.”

    So true – I once helped wildlife officials capture a number of Pronghorn for relocation, and I was surprised at how short the fenced was! Shock molting was restricted to a few patches on most but not all few individuals, if I remember correctly.

    I have a photo and a few more details in this blog post if anyone’s interested (scroll down to “Quick Story”).

  9. #9 J. S. Lopes
    July 20, 2010

    uh, Kubanochoerus… I forgot it! Anyway, it had a single frontal horn, different from the most common double, lateral, cranial horns of artiodactyles (and the multiple too). It seems to be a different structure, more alike to nasal centred horns of rhinoceroses.

  10. #10 Andreas Johansson
    July 20, 2010

    I wonder how so many Artiodactyles developped horns, but no Perissodactyle

    Brontotheres would be horned perissodactyls.

  11. #11 Boesse
    July 20, 2010

    My Fiancee and her father go out hunting for these guys in eastern Montana; a lot of people don’t like the way they taste, but man – there’s nothing like antelope steaks and antelope jerky. “Speedgoat” is a pretty commonly heard term in southwestern and eastern Montana, in the MSU vicinity.

    WRT their tendency to avoid jumping over obstacles, they will have certain places they remember where they can crawl under fences (or through gaps in broken fences, more rarely). Last summer while I was TAing the Montana S.U. field geology course, we were driving up a dirt road near Dillon, MT, and saw a male that hadn’t crawled under the fence yet and was stuck between the two fences on either side of the road; he was so panicked, he tore off in the direction we were coming from. We passed him at about 30 mph, and he must’ve passed us at a higher speed than that; all I remember is a blur, and how cool the sound was of his hooves striking the ground.

    Oh, and for anyone who’s been “chirped” at by Pronghorns – they make the strangest vocalization I’ve heard of any mammal (at least, relative to what you’d expect). Picture someone mooing into one of those wooden toy train whistles.

  12. #12 CS Shelton
    July 20, 2010

    Lay commenters like myself might be confused by the definition of horn y’all are using. Rhinoceros sure looks like it has a horn. Perissodactyls these days consist of tapirs, horses, and rhinos (as far as I know), so one out of three extant clades having prominent horns ain’t shabby numbers. Unless you’re defining horn in a way I don’t get.
    Off the top of my head, a few entire artiodactyl branches lack horns – whippomorphs and tylopods, and suines depending on your definition again. And all my info comes from reading a single Dougal Dixon book a year ago, so feel free to slap me around.

  13. #13 Frank
    July 20, 2010

    “World of Wildlife volumes, originally written by Felix Rodriguez de la Fuente”

    This book is wonderful! The best book about wildlife I ever read. Of course this statement doesn’t have a lot of weight given that I’m Brazilian, and good books about nature are incredibly difficult to find here. Take this book, for example, it was published here in the sixties, never to be published again.

    It is wonderful because, unlike other books that I’ve seen, it doesn’t divide animals by clade, but by region and biome. It first introduces an habitat, explaining what it takes to live there, and then talks about the animals who inhabit that area. Most books that I’ve read only show a list of closely related animals, and give their characteristics in a vacuum.

  14. #14 Kelly Clowers
    July 20, 2010

    Very cool, I love pronghorns, since I am from Montana (although not the part were pronghorns live). I can’t wait for part 2!

  15. #15 anthrosciguy
    July 20, 2010

    We’ve seen a lot of pronghorns in the years we’ve RVed around the west, in many states. Last year we had a male pronghorn run alongside us for about a mile, doing between 35-40 mph. He had a fence beside him which was probably why he didn’t turn right and run from us (I’ve read that they don’t/can’t jump fences and instead crawl under them, but I’ve never seen that behavior despite trying), but he didn’t seem to be having the least bit of difficulty maintaining that speed. After a while though I worried he might be frantic about us so I sped up, although there really wasn’t any sign of it. It is hard to definitively record the speed of an animal like that, especially over a distance, since they’re running over much rougher ground than you’d be likely to drive, and getting them to whatever their top speed is… well, how do you do that?

    There’s been some interesting work done with pronghorns trained to run on treadmills. Searching for “pronghorn” and “treadmill” will turn some of these up; here’s an article about one of those studies:
    http://discovermagazine.com/1992/dec/thepronghornspro172

  16. #16 John Conway
    July 20, 2010

    Speedgoat is the best name for any animal, ever.

  17. #17 Lar
    July 20, 2010

    I was once served pronghorn pate by Valerius Geist, made from a pronghorn he’d shot himself. Pretty good, as I recall. Gave me some artiodactylous cred as well, or so I thought.

    The “chirping” sound (# 11) – is that what you’d call it? Never could describe it myself, although I’ve heard it a lot – anyone doing herpetological field work in the shortgrass prairie is irresistably attractive to pronghorns.

  18. #18 Nathan Myers
    July 20, 2010

    What John Conway said.

  19. #19 Anonymous
    July 20, 2010

    “Lay commenters like myself might be confused by the definition of horn y’all are using. Rhinoceros sure looks like it has a horn.”

    Rhinoceroses do have horn-like structures on their head, but these are technically not horns because they are made of compressed cartilage. True horns are defined as protruding cranial structures supported in some way by spikes of bone and are never entirely shed (hence why deer antlers are not horns either). Among modern species, true horns occur in bovids and pronghorns, as well as some extinct lineages of artiodactyls. Brontotheres are the only perrisodactyls which have true horns.

    The “inability to jump” problem is a big deal out west. Many pronghorn herds, despite doing well during the summer, are now having trouble moving to greener pastures during the winter because their migration is barred by cattle fences. If they can, they will climb under it, but they normally cannot jump over such obstacles.

    “To those of you already familiar with these animals: please try and refrain from spoiling the surprises for everyone else!”

    You mean we can’t talk about Ram…OHDEARGOD (dragged off to be eaten by azdarchids).

  20. #20 Sven DiMilo
    July 20, 2010

    There’s some cool physiology underlying that speed and stamina…part 3?

  21. #21 Abyssal
    July 20, 2010

    Could ceratopsians have had forked hornsheathes too?

  22. #22 Joseph
    July 20, 2010

    Saw these guys at Richmond Zoo. I’m from England, so I’d never seen them before. Thought they had such a wonderfully odd face…

  23. #23 Zach Miller
    July 20, 2010

    I thought rhino horns were composed largely of keratin, not cartilage? I’ve been wrong before.

    I wouldn’t be surprised if ceratopsians exhibited a LOT of individual variation in terms of horn sheaths or horn curvature or number of horns or number of epocciptals or whatever else. They readily transform from one species to another in very short periods of geologic time, so I’d think that strong background variation in the genetic pool would contribute to such quick transformations.

  24. #24 deang
    July 20, 2010

    I see small herds of these out in west Texas near Big Bend National Park. One of my favorite mammals. And yes I do know about the extinct ones, but I won’t say anything.

  25. #25 Anonymous
    July 20, 2010

    Whoops, meant to say keratin. Mistyped cartilage there.

  26. #26 David Houston
    July 20, 2010

    Woohoo! Pronghorns. Such cool animals.

    I don’t know how fast Cheetahs run, but Al Oeming had an anecdote about taking his cheetahs out running and getting pulled over by the cops for speeding… Cop didn’t believe his story – until the cats showed up…

    @Lar. Cool. You’ve met Valerius Geist? neat. let alone being served game he himself shot. Wow.

  27. #27 CS Shelton
    July 20, 2010

    Thanks for the information, y’all. Abyssal – I read some cats think the pachycephalosaur dome was a core for an unknown horny surface. What would that look like? …

  28. #28 Coturnix
    July 20, 2010

    So, what do you think of the hypothesis that the speed was an adaptation to fast predators who are now extinct, with no selective pressure for reduced speed since then? As in:

    Byers JA, 1997. American pronghorn: social adaptations and the ghosts of predators past. Chicago: University of Chicago Press.

  29. #29 Noni Mausa
    July 21, 2010

    “…their reluctance to leap over obstacles…”

    Which explains a story a friend told me a few years ago.

    They were driving out west (North Dakota?) and were being paced by a pronghorn. When they came to a fence, instead of jumping over as my friends had expected, the pronghorn dropped to the ground and slid UNDER the fence, then popped up still running on the other side.

    Noni

  30. #30 Mike from Ottawa
    July 21, 2010

    The Pronghorn is an anatomical oddball and is among those animals sometimes described as having been ‘designed by committee’ (camels and therizinosaurs are among the others).

    Let’s face it, the therizinosaurs weren’t just designed by a committee, they were designed by a committee on LSD.

    I only found out a few days ago that pronghorns aren’t actually antelopes and here’s Darren taking them on. That’s luck.

  31. #31 Darren Naish
    July 21, 2010

    Coturnix (comment 28): we’ll get to that :)

  32. #32 Zach Miller
    July 21, 2010

    @CS Shelton: It would look ridiculous.

  33. #33 CS Shelton
    July 21, 2010

    I’m sure it would. There’s a highly improbable illustration in my little Dougal Dixon book “The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures” on page 358. If it was true, I imagine it wouldn’t be shaped like that… But I don’t know what it would look like.

  34. #34 Zach Miller
    July 21, 2010

    LOL. That’s the picture that popped to mind when you asked the question!

  35. #35 Lars
    July 21, 2010

    @ David Houston

    Yes, I used to know Val Geist – worked for him for a while on an Elk study. Very nice fellow.

    Funny to hear of Al Oeming. My ex worked for him for a while, back in the late 70s, I think. The Golden Cat tried to drag her in through the food slot one day, and that was that.

    You must be an Albertan.

  36. #36 kris
    July 21, 2010

    , 40 Montanan Pronghorns were introduced to Lanai in the Hawaiian Islands in 1959 (there’s a very sad story here; it ends with the last members of the herd dying out by the mid 1970s).

    is there any more to the sad story? can we hear it please?

  37. #37 doug l
    July 21, 2010

    Some of the historic descriptions I’d read of the herds of pronghorns in the Great Basin and how they were eradicated (they ate the grass that the introduced cattle would need) are almost beyond belief, with thousands and thousands killed from large herds, collected and set fire in large trenches. The photos looked to be from the 20s.
    I’d also read descriptions of people witnessing stampedes of pronhorn that would thunderpast and delay cars for a half hour; one of the last great aggregation of grazing animals in the US, if not THE last.
    I’d heard from a naturalist that the pronghorn were well adapted to the Great Basin and its distinct pattern in landscape and that they used their speed, endurance and incredible ability to detect distant rain to run to the location of the rain (within a 40 mile range) and be able to exploit the surface water which lasts typically only a few hours, and the immediate following flush of desert plants that follow periodic rainfall.

  38. #38 ech
    July 21, 2010

    “their average speed exceeds that of any other terrestrial animal” – you mean over a ~10 minute period, right? I doubt they have a higher average speed than dogs, horses, or even humans over a several hour period.

  39. #39 CS Shelton
    July 21, 2010

    That’s not what it sounds like to me, ech. 40 mph for a half hour is pretty damn good endurance. I imagine if they slowed down a bit, paced themselves, they could put the species you mentioned to shame. Maybe not dogs though – I hear wolves are legendary trekkers. Got any specific info?

  40. #40 Daniel Fosha
    July 22, 2010

    You glossed over the bigger story. 40 – 50 million down to .5 to 1 million today. Substantial recovery? That’s 1% – 2.5% of the original population remaining. Here’s a question then: Is the antelope functionally extinct?

    Plenty out there for hunters and tourists to play with, but its embarrassing what we call recovery these days. Take what you can get I suppose.

  41. #41 David Houston
    July 22, 2010

    @Lar
    Saskatchewanian. Born and raised in Saskatoon, expat in the States, now. Oeming was giving a talk for the Saskatchewan Natural History Society, probably about ’70. And, yes, if ‘Houston’ rings a bell, that’s my dad (birds, not mammals)

  42. #42 William Miller
    July 22, 2010

    @Daniel Fosha: “Here’s a question then: Is the antelope functionally extinct?”

    I’d say definitely not — it still is numerous enough in the proper habitat to play its ecological role; that habitat is just rarer (with conversion of land to human uses). Pronghorn are not that rare; you can see them pretty reliably on long drives through the appropriate habitat — there’s just less of that habitat. If the open prairies returned (say, if farming shifted from the Great Plains to somewhere else, rather as it’s shifted away from the Eastern US in the past century) I’m sure their numbers would increase again.

  43. #43 doug l
    July 22, 2010

    I wonder whether the reported abundance of pronghorns in the 1850s was a result of the native people being reduced early due to european introduced disease and the slaughter of predators, like wolves, that came along with early european settlers.

  44. #44 Dartian
    July 24, 2010

    Darren:

    I’ve lost the source for this illustration, but it’s from one of the Orbis World of Wildlife volumes, originally written by Felix Rodriguez de la Fuente

    I second Frank’s praise for that book series; it really was an epic work by the late great Felix Rodriguez de la Fuente, the ‘Spanish David Attenborough’. It had several neat, innovative illustrations, by different artists, of the same kind as that pronghorn picture. (Speaking of that picture, by the way; notice the shape of the horns of the ibex in the upper left corner. It’s clearly meant to be a Spanish ibex Capra pyrenaica.)

    Finally, a pronghorn trivia question. Which Academy Award-winning movie includes footage of pronghorns?

  45. #45 Cameron
    July 24, 2010

    Dartian:

    I recall Llewelyn hunting speedgoats at the beginning of No Country for Old Men.

  46. #46 Dartian
    July 24, 2010

    Cameron:

    I recall Llewelyn hunting speedgoats at the beginning of No Country for Old Men.

    You recall correctly.

  47. #47 cfrost
    July 24, 2010

    There is a bronze statue of a pronghorn outside the Wasco County courthouse in the town of The Dalles, Oregon dedicated to the people who resisted the shenanigans of the followers of Bhagwan Shree Rajneesh who took over the town of Antelope in the 1980’s and then tried to gain further political power in the county by means of the interesting strategy of giving the voters diarrhea.

    http://www.flickr.com/photos/pirateyjoe/3284974175/

    http://www.flickr.com/photos/pirateyjoe/3285789518/in/set-72157616008380099/

  48. #48 Dale Hoyt
    July 25, 2010

    In SW Kansas I saw Pronghorns startled by my car approaching them apparently run directly through barbed wire fencing. When I stopped to investigate I discovered that the lower two strands of wire were separated by a distance of about 3 feet. The animals were running toward this gap and tucking up their forelimbs under their chest and leaping between the strands. They looked as though they hardly broke stride when passing through the fencing. It seems as thought the ranchers in the area are very accommodating — at least the ones that fence off the range bordering the highway I was on.

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