I said in the previous pronghorn article that the modern pronghorn - Antilocapra americana - is but the tip of the phylogenetic iceberg, if you will; the only surviving member of a group that was previously far more diverse [the adjacent photo (from wikipedia) shows Ramoceros osborni. Yes, it really looked like that, read on].
As we'll see here, fossil pronghorns encompassed a reasonable amount of diversity: there were kinds with deer-like pseudo-antlers as well as others that superficially resembled living African antelopes like kudu or nyala, there were tiny dwarf forms, and there were also some real oddballs, unlike anything before or since. All of this is very well known among palaeomammalogists, but as usual the information isn't widely available outside of the technical literature. My aim here is to provide a very brief, introductory review to fossil pronghorns: for in-depth treatments, the reader is directed to Janis & Manning (1997), Heffelfinger et al. (2004) and Davis (2007).
Pronghorns (or antilocaprids) are an entirely North American group: for reasons that aren't clear, they never invaded South America when the Panamanian land-bridge formed, nor did they migrate into Asia (so far as we know). It might be that the general restriction of pronghorns to relatively arid habitats slowed or prevented their spread, but this doesn't explain everything. During most of the Miocene, several pronghorn taxa were contemporaneous: this was true during the Middle Miocene when woodlands were widespread, but the largest radiation of the group coincided with the spread of savannah habitats in the Late Miocene. During the late Hemphillian (Late Miocene), as many as seven pronghorn genera were contemporaneous (some of which contained several species), all of which were derived antilocaprine forms, often with complex horns [pronghorn phylogeny below, showing some of the main characters, from Janis & Manning (1998)].
'Merycodontines': moose-like palmation and crazy asymmetry
Several pronghorn taxa that are mostly restricted to the Early and Middle Miocene have historically been grouped together as the merycodontines. These lack the derived characters that unite the antilocaprine pronghorns, and are generally small pronghorns with branched, sometimes antler-like, horns in the males (females were hornless: a fact suggesting more solitary, more territorial habits than those of later, antilocaprine pronghorns). It's generally agreed that 'Merycodontinae' is paraphyletic (Janis & Manning 1997), though note that (so far as I know), no detailed, comprehensive phylogenetic analysis of Antilocapridae has ever been carried out... I mean, other than Janis & Manning (1997). McKenna & Bell (1997) recognised a merycodontine group, but used the name Cosorycinae (named by Cope in 1887, it has priority over Merycodontinae Matthew, 1904).
Among the 'merycodontines' is Merriamoceros coronatus from the late Early Miocene and early Middle Miocene of California, Nevada, Nebraska and Montana [shown here; from Heffelfinger et al. (2004)]. Its short horns terminate in an elongate platform formed of many short, finger-like tines: a palmate morphology superficially resembling that of moose.
One of the most unusual pronghorns - in fact, one of the most unusual artiodactyls - also belongs to this region of the cladogram: Ramoceros from the Middle and early Late Miocene. Several species (and even subspecies) have been named, and a second 'genus' - Paramoceros - is nowadays included by most authors within Ramoceros. The main horn shaft is long, and three tines are present near the tip, forming a deer-like pseudo-antler [skull of R. ramosus, in posterior view, shown below]. Oh, and - - one horn (it might be either the left or the right) is about twice the length of the other one. If the asymmetry was variable intraspecifically (and, so far as I can, it is), does this mean that 'left handers' (viz, those with a long horn on the left) could only fight with 'right handers (viz, those with a long horn on the right), or what? I haven't ever seen a discussion of this in the literature, but that doesn't mean it doesn't exist.
The surface texture of 'merycodontine' horns suggests that they were skin-covered, rather than sheathed in horn.
Antilocaprine pronghorns: some bovid-like
The majority of pronghorns belong to Antilocaprinae, a clade characterised by a more posteriorly positioned orbit, reduction of the anterior tine on the horn and enlarged auditory bullae. The metapodials of antilocaprine are more elongate than those of other pronghorns, they all seem to have lacked the side toes that were present in more basal forms, and their premolars are proportionally larger and more molariform (all pronghorns have high-crowned teeth; evidence from tooth wear indicates that Miocene species relied more on grass than does the living species (Semprebon & Rivals 2007). It might seem paradoxical that, while the living species has the highest-crowned teeth of any pronghorn, only 12% or so of its diet is composed of grass. However, it's been argued (e.g., Janis 1995) that it's the soil and grit ingested with leaves - and not necessarily the abrasiveness of the leaves themselves - that controls hypsodonty in herbivorous mammals. It may therefore be that Antilocapra inhabits 'dustier' habitats than its fossil relatives).
Most antilocaprine lineages possessed branched horns where a prominent anterior tine gave the bony horn-core a forked appearance: however, the anterior tine was reduced or lost in some lineages and they then evolved long horns resembling those of gazelles or spiral-horned antelope. In Proantilocapra platycornea [shown here, from Barbour & Schultz (1934)], the anterior tine was absent and the horns were short, laterally compressed and with rounded tips. As suggested by its name, Proantilocapra was originally interpreted as close to the ancestry of Antilocapra (Barbour & Schultz 1934). The affinities of Antilocapra seem to lie elsewhere, however (Texoceros from the Late Miocene may be the closest extinct relative of Antilocapra).
The anterior tine was also lost in Osbornoceros osborni from the Late Miocene of New Mexico and Texas: this taxon possessed slender, posterolaterally twisted horns that look much like those of some gazelles or the Nyala Tragelaphus angasii [adjacent life restoration of O. osborni by Nobu Tamura, from wikipedia. The fossils only have a single horn-core, so I'm presuming that the artist has reconstructed hypothetical horny prongs by analogy with extant Antilocapra: read on].
Four-horned and six-horned antilocaprines
In some members of the antilocaprine clade Stockoceratini, the main shaft of the horn became reduced until it was virtually absent while, at the same time, the tines became enlarged. The result is that these pronghorns must have looked as if they had four (e.g., Hayoceros and Stockoceros) or even six (e.g., Hexameryx) horns, all emerging supraorbitally in a cluster. Webb's (1973) reconstruction of Hexameryx simpsoni from the Pliocene of Florida is shown below. In the fossils of these animals, the horn tips have a different, smoother surface than the horn bases, suggesting that skin clothed the horn base and that keratin sheaths were restricted to the tips.
These enlarged tines are typically cylindrical in cross-section, but can be blade-like. To make things even weirder, in some stockoceratins (e.g., Hexobelomeryx), two of the three enlarged tines are so closely aligned that they must have been united in a single keratin sheath, though this was presumably forked like the underlying bone. Worth noting here (again) is the fact that Antilocapra has unbranched bony horn-cores but a branching keratin sheath: could the unbranched horn-cores of fossil pronghorns have supported branched keratin sheaths? We really don't know, and this possibility means that the reconstructions you see here - like Webb's rendition of Hexameryx - may well be conservative.
Another particularly remarkable group of pronghorns are the ilingoceratins (their formal name is Ilingoceratini). As in Proantilocapra and Osbornoceros, the tines became reduced in this group, and in the most 'extreme' ilingoceratins the main shaft of the horn twists laterally. This is most prominently developed in Ilingoceros [shown here, from Heffelfinger et al. (2004)] where two spiral ridges extend along the length of each horn such that they resemble the spiralling horns of kudus and other such antelopes. On naming I. alexandrae (two species of Ilingoceros are currently recognised), Merriam (1909) originally considered it to be what we would today call a tragelaphine bovid (the group that includes nyalas, kudus and elands). He later realised that it was an antilocaprid thanks to its high-crowned teeth and other features. The horns in at least some Ilingoceros specimens have forked tips, but the forks here don't seem to be homologous to the tines present elsewhere among pronghorns.
I said earlier that some extinct pronghorns were tiny. Capromeryx of the Pliocene and Pleistocene - again, several species are known, and subspecies have even been named for some of them - first appears in the fossil record as an animal similar in size to the living Pronghorn (or, about 85% of it anyway). It then seems to have undergone a dwarfing trend, such that a species from the Late Pleistocene (namely C. minor, originally described from Rancho La Brea) was less than 60 cm tall at the shoulder [in the painting below - by Carl Buell, used with permission - Capromeryx runs past the legs of the giant camel Titanotylopus]. It might be presumed that these tiny pronghorns were secretive animals that lived like modern dik-diks or dwarf antelopes, and were not denizens of open-habitats like their larger cousins. But their remains are in fact found in what were once grassland habitats, albeit in places where there were clumps of trees.
And so ends our brief look at the diversity of fossil pronghorns. I hope you enjoyed it! More on pronghorns later - there is still much to look at.
For the previous article on pronghorns see...
And for previous Tet Zoo articles on artiodactyls see...
- Welcome.... to the world of sheep
- Return.... to the world of sheep
- Tet Zoo picture of the day # 23 (entelodonts)
- Traumatic anal intercourse with a pig
- It's such a load of bull
- Duiker, rhymes with biker
- Sable antelopes and the miseducation of youth
- Giant killer pigs from hell
- The plasticity of deer
- Over 400 new mammal species have been named since 1993
- Stuffed megamammal week, day 1: Khama
- Stuffed megamammal week, day 2: Eland
- Stuffed megamammal week, day 3: Okapi
- Great Asian cattle
- Dromomerycids: discuss
- Death by lightning for giraffes, elephants, sheep and cows
- A close-up look at a Hairy babirusa (includes links to many other babirusa articles)
- Testing the flotation dynamics and swimming abilities of giraffes by way of computational analysis (includes links to other giraffe articles)
- A new angle for hippos (includes links to other hippo articles)
- A 'consensus cladogram' for artiodactyls
Refs - -
Barbour, E. H. & Schultz, C. B. 1934. A new antilocaprid and a new cervid from the late Tertiary of Nebraska. American Museum Novitates 734, 1-4.
Davis, E. B. 2007. Family Antilocapridae. In Prothero, D. R. & Foss, S. E. (ed) Evolution of Artiodactyls. Johns Hopkins University Press, pp. 227-240.
Heffelfinger, J. R., O'Gara, B. W., Janis, C. M. & Babb, R. 2004. A bestiary of ancestral antilocaprids. Proceedings of the 20th Biennial Pronghorn Workshop 20, 87-111.
Janis, C. M. 1995. Correlations between craniodental morphology and feeding behavior in ungulates: reciprocal illumination between living and fossil taxa. In Thomason, J. (ed) Functional Morphology in Vertebrate Paleontology. Cambridge University Press, pp. 76-98.
- . & Manning, E. 1998. Antilocapridae. In Janis, C. M., Scott, K. M. & Jacobs, L. L. (eds) Evolution of Tertiary Mammals of North America. Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Cambridge University Press, pp. 491-507.
McKenna, M. C. & Bell, S. K. 1997. Classification of Mammals: Above the Species Level. Columbia University Press (New York).
Merriam, J. C. 1909. The occurrence of strepsicerine antelopes in the Tertiary of northwestern Nevada. University of California Publications, Bulletin of the Department of Geology 5, 319-330.
Semprebon, G. M. & Rivals, F. 2007. Was grass more prevalent in the pronghorn past? An assessment of the dietary adaptations of Miocene to Recent Antilocapridae (Mammalia: Artiodactyla). Palaeogeography, Palaeoclimatology, Palaeoecology 253, 332-347.
Webb, S. (1973). Pliocene Pronghorns of Florida Journal of Mammalogy, 54 (1) DOI: 10.2307/1378880
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Very interesting! I was not aware of that antilocaprid diversity.
"for reasons that aren't clear, they never invaded South America when the Panamanian land-bridge formed, nor did they migrate into Asia."
Maybe there was a really short fence? :)
Wow. Those are some funky horns. Does anyone have any ideas as to how those horns were used? Some of them seem to have some specific function. Beyond the usual decorative/demonstration of fitness/sexual dimorphism roles.
"for reasons that aren't clear, they never invaded South America when the Panamanian land-bridge formed, nor did they migrate into Asia."
POst-Eocene migrations to Asia were through temperate or glacial terrains, and antilocapras probably remained nested in warmer, southern regions, like tayassuids and geomyids. Analogously to these New World endemic taxa, there's a lot of mammals that has never gone out of Old World, like suids, viverrids, hyenines hyenids, antilopes, rhinocerotine rhinoceroses, true buffaloes, etc.
Panamanian land-brigde probably was covered by tropical forest, so preventing many animals from savannah or drier places to reach the south, like bisons, caprines, lions, running hyenas and teleoceratine rhinoceroses, for example.
But - recall that different groups of organisms tell different 'stories' on what the Panamanian landbridge was like. Neotropical rattlesnakes, for example, are animals of open, seasonally dry habitats and avoid forests, but they simply must have moved across the land-bridge from Mexico, and now occur as far south as Argentina. Their phylogeography therefore supports the idea that the land-bridge (and, incidentally, part of Amazonia) was dominated by plains and other dry habitats. This sparked an interesting debate in the literature. See below.
Also - lions made it across the land-bridge: recall that they're known from as far south as Peru.
Gosling, W. D. & Bush, M. B. 2005. A biogeographic comment on: WÃ¼ster et al. (2005) Tracing an invasion: landbridges, refugia, and the phylogeography of the Neotropical rattlesnake (Serpentes: Viperidae: Crotalus durissus). Molecular Ecology 14, 3615-3617.
WÃ¼ster, W., Ferguson, J. E., Quijada-MascareÃ±as, A., Pook, C. E., SalamÃ£o, M. da G. & Thorpe, R. S. 2005. Tracing an invasion: landbridges, refugia, and the phylogeography of the Neotropical rattlesnake (Serpentes: Viperidae: Crotalus durissus). Molecular Ecology 14, 1095-1108.
- ., Ferguson, J. E., Quijada-MascareÃ±as, A., Pook, C. E., SalamÃ£o, M. da G. & Thorpe, R. S. 2005. No rattlesnakes in the rainforests: reply to Gosling and Bush. Molecular Ecology 14, 3619-3621.
So, Darren, thoughts as to whether or not the Pronghorn is the last of its line or just going through a species-wise bottleneck before founding a new diversity?
For mammals that never seem to left the North American continent, it's a wonder how antilocaprids are a sister kin to either giraffids or to the rest of the pecorans, since (as far as I'm aware of) first appear in the fossil record from the Old World. Possibly the ancestral pecoran first appear in North America and went back and forth between North America and Eurasia many times and evolve into the extant pecorans today (after all we seen it happen with equids, caninids and camelids).
Not Darren, but if I had to guess, I'd guess the latter. The current single genera and species of pronghorn isn't really a normal thing for the family, as even during the Pleistocene there were several different genera of pronghorn. Hayoceras was around for most of the period, and little Capromeryx and its kin survived right up into the Rancholabrean (using NALMA periods here) before getting wiped out with the Pleistocene megafauna.
In addition, the current species of pronghorn is by no means endangered. The recovery of the pronghorn is one of conservation's success stories, with the species recovering to the point where it has become a pest in some western states (e.g., Wyoming). The pronghorn was also doing well pre-European settlement, ranging across large areas of midwestern North America in large numbers. Minus a little problem with fences (which is actually being fixed in some areas), the pronghorn seems very likely to survive.
And, assuming the pronghorn survives, its only competitors on the plains would be deer (and maybe large cattle species if they survive). Pronghorn have the advantage over deer in that they don't lose their cranial...things at some point during the year, meaning that they aren't defenseless for part of the year (and some studies in antelope have shown that many open-plains dwelling species do better if horns are maintained as much as possible in the species) and they don't have to waste a whole bunch of energy every year just to regrow their horns (which can take a lot out of deer). Plus the females have cranial...doodads (not as elaborate as the males, but still) unlike all other deer except caribou, which also helps out in open-environment spcies.
"During the late Hemphillian (Late Miocene), as many as seven pronghorn genera were contemporaneous"
The same story as the horses.
I wish there was some kind of time-machine.
I never understood why some creatures managed to get to SA and Asia and others don't.
Lions, Homotherium, different kinds of canidae, the imposing "Dog-faced Bear", horses, camels, deer etc all managed to cross the boundary but why bison and Pronghorns didn't make it is an complete enigma.
The Bering bride was maybe too cold but the Panaman bridge was (partly) open and warm.
To be honest. It doesn't really make sense.
I like a good mystery.
I think the condition of being "by no means endangered" must always be considered a) relative and b) provisional, here in the Anthropocene. Who knows whether humans will allow them to survive even one more megayear?
It might be presumed that these tiny pronghorns were secretive animals that lived like modern dik-diks or dwarf antelopes, and were not denizens of open-habitats like their larger cousins. But their remains are in fact found in what were once grassland habitats, albeit in places where there were clumps of trees.
For an animal only 60 cm tall, a grassland may well have provided sufficient cover, especially if they lived in something like the tallgrass prairie that characterized much of central North American plains until recently. The four current indicator species of that biome (Schizachyrium scoparium, Little Bluestem; Panicum virgatum, Switchgrass; Sorghastrum nutans, Indiangrass; and Andropogon gerardii, Big Bluestem) range from 92 to 183 cm in height today and may well have grown even taller under different climatic and soil conditions. My guess, though, is that the tiny antilocaprids probably preferred high visibility lands, and if they were as fast as or faster than today's pronghorns, they may have had few worries about predation.
@CM Koseman- LOL. That, sir, is comedy gold. Or at least bronze. @Wilbert- I confess, I don't like a good mystery. I'm excited by them, but easily frustrated too. Like PZ's lament about fossils (http://scienceblogs.com/pharyngula/2010/07/an_unpaleontological_lament_…), there are some things we'll never know and that hacks me off. Childish, for sure.
@Anonymous- I temper your optimism. Just because a species recovers numbers doesn't mean they can easily recover their genetic diversity. The current population is probably more prone to extinction than the last time the numbers were this high because individuals are more similar to each other - something (a disease, whatever) that kills one is more likely to be able to kill all of the others. Fortunately, they were never as rare as right whales were, or california condors are. Maybe they'll be fine.
#6: Radiations from species not adapted to urban existence seem unlikely as long as humans persist. Still, pervasive fencing makes population islands easy to maintain, and drift can do the rest.
#8: How do you fix the fence problem? Will they use a stile, or must you leave a space to squirm under? Don't the ... cranial appurtenances ... get hung up?
For why they never made it to South America, I'm going with the "low fence" hypothesis. Has anybody established the precise fence height that 50% of speedgoats won't jump? Seems lke a good senior thesis for a zoology student.
Just hypothesizing here. Bison were very recent additions to the North American fauna. Given time, perhaps they would've have made it over to South America. But, instead manifest destiny happened.
I had seen that image of the mounted Ramoceros before. But I had no idea that asymmetry was the norm. That's really cool.
Darren, do any of the later Antilocaprids show any signs of being non-cursorial? I'm assuming that at least some of the Miocene forms were. I'm just wondering if, after the faunal turnover at the Hemphillian/Blancan boundary, Pronghorns were restricted to more open terrain. Have there been Plio-Pleistocene fossils found east of the Mississippi?
Awesome post Darren!
I am a HUGE fan of odd early North American ruminants such as antilocaprids and aletomerycine and dromomerycine palaeomerycids, these posts are great reviews! I hope to see some more on other ruminants such as Floridameryx - truly a sign that North America has a very different past.
I just thought that I would add a brief comment ont he antiquity of the antilocaprids, as they seem to appear in North America in the Latest Arikareeean, contrary to the notion that they can be used to help indicate the Hemingfordian (see Beatty and Martin 2009 - PaleoBios:
I'm glad to see Edward Davis's 2009 chapter being used, it was a huge help and a major step in clearing up a long history of screwy taxonomy.
How many specimens of these asymetric creature are known? Because asymetry in antlers occurs quitte frequently in normal deer, too. S
Will pronghorn go extinct or diversify again into many species? I think it is impossible to tell. I read long ago, that somebody compared lots of Paleozoic lineages of inverts and found no relation whatsoever between number of taxa and extinction. So, it is as likely that the animal group will decrease and rebound as will decrease and go extinct. I read it long ago, and would be quite interested if somebody can dug the original reference.
re the lion occurrence in Peru;the lion fossils from Talara may not be lion but rather a very large Jaguar.
I saw a while ago on someones website which I irritatingly can't track down now that they had got DNA from the felid material from Talara and it was Jaguar.
Also Barnett et. al.'s 2010 paper on Lion phylogeny has a map showing the distribution of the american lion stopping in Central America.
This is probably the wrong post for this comment (presumably the next one will get back to the 'cheetah hypothesis'), but the speedgoats' speediness (and endurance, and fence-shyness) seem so extreme they might be sexually selected traits rather than the result of a predator-prey arms race. What's the breeding system like? - are long chases (and convention that leaping obstacles is just not done) involved in courtship?
The pronghorn's speed and stamina is extreme compared to anything else currently living in North America but not quite so extreme when compared to some cursorial ungulates of similar size living in Asia and Africa.
Similar feats of speed and endurance have been attributed to Saiga, Springbok, Blackbuck, and various Gazelles (both Gazella and Procapra).
These also would have been subject to predation by cheetah. Saiga are currently outside the range of cheetah and can outrun all their predators easily except humans on motorcycles (unfortunately).
At their lowest point, pronghorn numbers were about 20,000. Its not much, but its something that other recovering species like bald eagles would kill for.
From what I've heard, there are several groups trying to open up migration passages for pronghorn, and in areas with barbed wire replace the lowest-most wire with one that is barbed free. While they cannot jump, pronghorn will try to squirm under fences if they can to get across.
That's Shelton, Anonnyomymius. For rillz.
I was going to mention the wilderness corridor projects, but they won't do much for the vast tracts of land carved into cow food. Assuming they get off the ground at all (more difficult here than in Canada), which would be amazing.
Man, I'm just a total buzzkill. But seriously, pronghorn look to be in good shape, if famous naturalists are making them into steaks.
Scanlon- That is a hilarious but intriguing notion.
Probably the best that could be done for the speedgoat's recovery would be to breed and release a variant willing to jump fences. The trait should spread like wildfire.
Lions in S. America... the following paper states that new work (by Seymour) reveals Peruvian fossil 'lions' to be giant jaguars. Didn't know this until now, thanks LeeB.
Yamaguchi, N., Cooper, A., Werdelin, L. & Mcdonald, D. W. 2004. Evolution of the mane and group-living in the lion (Panthera leo): a review. Journal of Zoology 263, 329-342.
Pronghorns and fences: they will run, at full speed, under a fence (as stated up-thread), but obviously only if they can fit under it. Land-owners have therefore been encouraged to remove the bottom wires from fences in some areas.
I've downloaded Yamaguchi PDF, and there it's stated:
" Whatever the taxonomic details, lions expanded their
range further to Mexico and even as far south as Peru
(Hemmer, 1974; Martin & Klein, 1984), although the
Peruvian âlionsâ may have been huge jaguars (Seymour,
Were oldest Pecorans from North America? I think an Asian origin is more likely, with successive Transberigian waves to America.
However, Southern North American/Central American records are extremely poor, and we can't tell if a Southern refuge would be the craddle of many NA taxa.
I've heard in a couple places that pronghorn are able to pronk, which if true means they have some jumping ability. Anyone know if this is true?
but the site I remembered and finally found was http://
This site is no longer available but if you look it up on the internet wayback machine you can find it.
At the bottom of the site it discusses the Talara cats and how the big cat from there is a Jaguar and not a Lion.
Some think that the American "lion" is more closely related to the jaguar anyway... much like how the American "cheetah" could be the puma's closest known relative.
are springboks related to pronghorns?
what is springbok's ancestor?
I know they do, but the DNA work consistently shows that it is a lion, as is the cave lion.
They're more closely related to cattle than to pronghorns. They're bovids, not antilocaprids. You're looking at convergence between Old World and North American ruminants.
I didn't know that. (Just a few months ago, there was a JVP paper that argued against it being a lion.) Reference, please!
the reference is Barnett et al.(too many authors to list)
Phylogeography of lions(Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversity.
Molecular Ecology (2009)18, 1668-1677.
This is available online as a pdf.
If anyone wants a pdf copy of the lion paper- without library access- they can get it here.
The Christiansen+Harris paper that turns atrox into a jaguar (CRANIOMANDIBULAR MORPHOLOGY AND PHYLOGENETIC AFFINITIES OF PANTHERA ATROX: IMPLICATIONS FOR THE EVOLUTION AND PALEOBIOLOGY OF THE LION LINEAGE) has a few flaws, as I see it. When looking at the relationship of atrox it seems incredible not to include spelaea in your analyses. The DNA shows that spelaea and leo are sister groups, and atrox is an offshoot of spelaea. The Christiansen paper doesnt have any spelaea for comparison.
Ouch. How did I miss that?
Thanks for the link.
The earliest pronghorns were highly cursorial in comparison with most pecorans (but note at least some merycodontids retained side toes on the front legs -- later pronghorns were even more cursorial).
The notion that they evolved somehow to outrun the American cheetah flies in the face of the evidence that their high degree of cursoriality well predates this. Morphological "cursorial adaptations" are likely related to stamina/efficiency, not just running from those big bad predators (but they would certainly have been preadapted to avoid cursorial predators)
It is a bit of a mystery why they don't get out of North America. However, they are rare as fossils in Central America (as opposed to other savanna-type ungulates such as horses). Sometimes it's just the stochastic nature of the world, maybe no functional explanation, just happenstance.
Seasonal retention vs. loss of cranial appendages relates to mode of development of same, no reason to think that pronghorn are superior or inferior to deer here.
I see no reason to imagine that pronghorn can't pronk or jump -- this seems like some sort of urban myth to me. If deer can do this, why not pronghorn?--- this certainly isn't related to any difference in anatomy. Also, their diet is completely different to both deer and bison (low level open habitat mixed feeders, vs. browser or grazer, not to mention that they're much more hypsodont than deer and way smaller than bison, so not in the same niche as either). Extant pronghorns have extremely large hearts and lungs ---- may well be more "cursorial" (in terms of exercise physiology) than any Old World bovid.
No evidence at all for pronghorns going back and forward between N America and the Old World. Whoever they're related to (molecular and morphological data in conflict here) they're clearly a radiation from a single immigration in the early Miocene.
Also, PLEASE guys, the singular of genera is genus (even if I did fail Latin O level)
In the good old days, someone would herd 500 pronghorns all the way down to Panama (maybe using trained cheetah). Then people (and the cheetah) there would eat them. And the books would say
"Pronghorns don't get out of North America. Those that try, get eaten. They're smarter than that."
And we'd have an answer. Nowadays there are thousands of reasons not to try that. That's how we end up with virtual giraffes swimming in virtual water.
On a more serious note, this post has pointed me towards some awesome papers on phylogeny, (paleo)ecology/ecophysiology, modelling and evolution. Many by or citing C. Janis above (hi!).
The huge hypsodonty has also been attributed to the "retention of hypsodonty from ancestors with more abrasive diets", which is weird considering the higher current degree. But then, this is an animal that seems very specialized for stuff that simply isn't there...
Haven't seen any attempt to correlate the speed with avian predators so far, is that too dumb to ask about? :)
And I just wanted to mention "Chame, M. 2003. Terrestrial Mammal Feces: a Morphometric Summary and Description". TetZoo material right there.
I think the key words in that passage are 'there were clumps of trees'. These tiny antilocaprids were comparable in size to the largest leporids. And as hares and jackrabbits demonstrate, it is possible to be a medium-sized, non-burrowing, effectively defenceless herbivorous mammal and still be able to live in predominantly open habitats, as long as there is at least some cover available.
From a paleontologist's point of view, what, precisely, is a 'cursorial adaptation'? For example, would you consider Lepus to be cursorial?
Well, even adult pronghorns are sometimes killed by golden eagles Aquila chrysaetos (e.g., Deblinger & Alldredge, 1996), so it is certainly at least possible that predation by raptorial birds has been, and is, a non-trivial evolutionary selection factor for small- and medium-sized antilocaprids. But I'm not aware of any systematic studies dealing with this question.
Deblinger, R.D. & Alldredge, A.W. 1996. Golden eagle predation on pronghorns in Wyoming's Great Divide Basin. Journal of Raptor Research 30, 157-159.