Tetrapod Zoology

Here’s a photo Matt Wedel took in the Raymond Alf Museum in Claremont, California. The lined-up skulls belong (I think) to Megacerops, the large to very large Late Eocene brontothere previously known as Brontotherium. Like most other brontotheriine brontotheres it has reduced, globular upper incisors and is very wide at the back of the skull. The upper incisors were in fact so small that they might have been virtually useless, and these animals probably relied on a prehensile lip to gather food. Must stop there – want to start talking about horns and evidence for intraspecific combat, but this is a ‘picture of the day’ and I don’t have time.

By the way, I’m not really sure what ‘Freddie’ is. It looks like a rhino, possibly a hyracodontid. Does anyone know?

I’m not entirely sure why they decided to give the specimens pet names, but I will admit that it’s amusing.

Comments

#1 kelebek
March 26, 2009

ilginnççç…

[from Darren: banning this spammer's email address has not prevented him/her from posting to the site every day. From now on I will let the comments appear, but will delete the url every time. Pointless, but, like I said, banning them hasn't worked.]
#2 Metalraptor
March 26, 2009

Excellent picture Darren. I love mammals of the Oligocene/Miocene (and to some extent the latest Eocene as well). I heard Dixon suggest in his book “World Encyclopedia of Dinosaurs & Prehistoric Creatures” that Uintatherium had a similar predicament with the incisors, and may have used a prehensile tongue to gather food. If so, would these strange adaptations possibly have contributed to the downfall of these wonderous beasts? At first, these animals did well, but then the group started to go downhill as they developed more complex and specialized feeding apparatuses.

“Freddie” does indeed look somewhat like a hyracodont rhino, but I cannot tell for sure, the picture I have gotten from the blog is too small. What is sad is that we really need a guide to pre-ice age North American cenozoic life. North America had such interesting creatures, including oreodonts (my favorite), protoceratids, bone-crusher dogs, etc., but no one pays any attention to them. Its always hominid or monkey this, basal proboscidean that, and even the South American mammals get more attention as a whole than our Cenozoic does. To add insult to injury, the last definitive guide on these wonderous mammals was published…in 1918.
#3 Hai~Ren
March 26, 2009

Annoying little bastards, aren’t they? I absolutely loathe spammers. Does ScienceBlogs allow its users to ban particular IP addresses?

Interesting intra-specific variation in the shape of the horns. Is Megacerops known to be sexually dimorphic? I’m kind of reminded of the sexually dimorphic Embolotherium that appeared in Walking With Prehistoric Beasts.
#4 Darren Naish
March 26, 2009

On spammers…

Annoying little bastards, aren’t they? I absolutely loathe spammers. Does ScienceBlogs allow its users to ban particular IP addresses?

The Sb platform lets you ban individual email addresses. With this spammer, I have banned them about ten times, yet still their comments come through. And this is not because they use a different address each time. Weird. I really should stop caring.

On Cenozoic mammals: I’ve been saying for ages that I plan to cover such things as oreodonts, borophagines, dinoceratans and chalicotheres. I will eventually, I promise. It’s just there are so many other tetrapods that keep getting in the way.

On brontotheres specifically, yes, derived brontotheriine brontotheres – the ‘eubrontotheres’ of some authors – males have larger horns than females. So we might be seeing sexual dimorphs in the photo above. Canine size is also dimorphic in the group. And I’ve just realised that ‘Freddie’ might be a brontothere too, possibly one of the Middle Eocene taxa like Metatelmatherium.
#5 Dartian
March 26, 2009

Darren:

And I’ve just realised that ‘Freddie’ might be a brontothere too, possibly one of the Middle Eocene taxa like Metatelmatherium.

Small, early titanothere would be my (non-expert) guess too. Aren’t hyracodontid skulls typically slightly more gracile than that creature’s skull?

Megacerops, the large to very large Late Eocene brontothere previously known as Brontotherium.

I’m still in denial over this particular name change. I loved the name Brontotherium and the story behind it (the Sioux discovering titanothere fossils and calling them ‘thunder beasts’, etc.). I fully agree with the principle of applying the rules of priority in biological nomenclature, but still… *Sigh*
#6 Darren Naish
March 26, 2009

Dartian says…

Aren’t hyracodontid skulls typically slightly more gracile than that creature’s skull?

I suppose they’re not as deep above the orbits. But they can still look pretty chunky: google Hyracodon.
#7 Dartian
March 26, 2009

Darren:

But they can still look pretty chunky: google Hyracodon.

I did, but in the hyracodont skull images I found (for example this), the nasal bone seems to be smaller than that of ‘Freddie’. On the other hand, the early titanothere skulls illustrated in Stanley (1974:449) have larger nasal bones (Stanley’s paper, alas, had the only even halfway useful illustrations I could find).

Reference:

Stanley, S.M. 1974. Relative growth of the titanothere horn: a new approach to an old problem. Evolution 28, 447-457.
#8 Darren Naish
March 26, 2009

Dartian: agreed. I’m going for Metatelmatherium as the most likely bet, but Palaeosyops, Telmatherium and Sthenodectes might be possible. Dammit, need an expert
#9 Mike Keesey
March 26, 2009

… Megacerops, the large to very large Late Eocene brontothere previously known as Brontotherium.

That’s it, all names starting with Bronto- are cursed. Brontops, you’re next.
#10 Darren Naish
March 26, 2009

Indeed. I guess people need to make some new ones. Hint hint.
#11 Andreas Johansson
March 26, 2009

Brontoscorpio still lives, doesn’t it?
#12 Thomas R. Holtz, Jr.
March 26, 2009

Brontops is gone, too. It also got absorbed by Megacerops, apparently in:
Mihlbachler, M. C., S. G. Lucas, and R. J. Emry. 2004. The holotype specimen of Menodus giganteus, and the “insoluble” problem of Chadronian brontothere taxonomy. In Lucas, S. G., K. E. Zeigler, and P. E. Kondrashov, editors. Paleogene mammals. New Mexico Museum of Natural History and Science Bulletin 26:129–135.
#13 Darren Naish
March 26, 2009

Yes, Mihlbacher’s work has shown that Brontops species are either synonymous with Megacerops coloradensis [previous Tet Zoo comment here], or are nomina dubia. I haven’t seen Mihlbacher et al. (2004), cited above, but am going from the review provided by Janis et al. (2008).

Ref – -

Janis, C. M., Hulbert, R. C. & Mihlbachler, M. C. 2008. Addendum. In Janis, C. M., Gunnell, G. F. & Uhen, M. D. (eds). Evolution of Tertiary Mammals of North America, Vol. 2. Cambridge University Press (Cambridge), pp. 645-693.
#14 Nathan Myers
March 26, 2009

Common names are immune. It may not be Brontotherium any more, but they can still be brontotheres. And, they are! Likewise brontosaur, for all of Diplodocidae.
#15 Raymond Minton
March 26, 2009

I have a soft spot for these elephantine brutes, maybe because they’re flamboyant and unlike anything found in the modern world. It’s interesting that, though these are seemingly formidable animals, in important ways these creatures didn’t change (their teeth stayed virtually the same, even when they grew huge) and were apparently unable to adapt, while their contemporaries and relatives, the horses, changed profoundly and are still thriving today.
#16 Zach Miller
March 26, 2009

I just answered my own question with Wikipedia, but it doesn’t hurt to get the opinions of experts: What are the closely living or fossil relatives of brontotheres? And what was the Walking with Beasts brontothere with the scoop-horn?
#17 Mo Hassan
March 26, 2009

The “scoop-horn” was Embolotherium.

I agree with whoever has said Hyracodon for Freddie’s identity. That’s what I thought when I first saw it.

I’m quite annoyed that this spammer is Turkish. It’s obviously a robot though, no need to call it “him” or “her”!
#18 Christopher Taylor
March 26, 2009

What are the closely living or fossil relatives of brontotheres?

The most commonly reported view has placed brontotheres closer to horses than rhinos and tapirs (e.g. Froehlich, 1999), but there have been dissenters (e.g. Hooker & Dashzeveg, 2004, placed brontotheres outside the perissodactyl crown group entirely). I get the impression that brontotheres in phylogenetic analyses have an annoying tendency to be pogo-taxa – that is, they bounce madly all over the place with no obvious sort of pattern.

Froehlich, D. J. 1999. Phylogenetic systematics of basal perissodactyls. Journal of Vertebrate Paleontology 19 (1): 140-159.

Hooker, J. J., & D. Dashzeveg. 2004. The origin of chalicotheres (Perissodactyla, Mammalia). Palaeontology 47 (6): 1363-1386.
#19 Christopher Taylor
March 26, 2009

And what was the Walking with Beasts brontothere with the scoop-horn?

Forget Walking with Beasts… what were the incredibly late-surviving brontotheres that got labelled “rhinos” on Ice Age?
#20 Andy
March 26, 2009

[from Darren: sorry, delayed by spam-filter.]

Wow, I wasn’t expecting to see this on Tetrapod Zoology! I’m curator at the Raymond M. Alf Museum of Paleontology, home of Freddie and friends. “Freddie” is a Paleosyops from the Bridger Formation of Wyoming. . .as for the exact identifications on the brontotheres, I don’t recall offhand (I’m at home right now). And the origin of the names with the skulls. . .that’s an interesting story. The specimens were discovered by high school students from The Webb School of California (now The Webb Schools) on summer collecting trips with Ray Alf. Students who found a specimen were allowed to “name” it. The names have been left with the specimens in honor of the discoverers, and as a nod to Ray (who gave an extremely engaging and dramatic tour of the museum). For those who haven’t heard of him, Ray Alf was a remarkable and inspirational high school teacher who built this museum from the ground up. . .to this day, high school students (along with museum director Don Lofgren and I) are actively engaged in the collection, preparation, curation, and research of specimens from the western United States. Notable alumni include Malcolm McKenna, S. David Webb, Dan Fisher, and many more. . .(Kitt Clark, a co-author on the recent Permian extinction paper in Geology, is also a recent alum). If you live in southern California and like fossils, the Alf Museum is certainly worth a visit!
#21 William Miller
March 27, 2009

Alright, I promise that if I ever get to name a taxon (yeah, right), I’ll use Bronto- in the name if it is at all appropriate. (Even if it was discovered on a thundery day, or in a state known for its thunderstorms…)
#22 Dartian
March 27, 2009

Andreas:

Brontoscorpio still lives, doesn’t it?

No, it became extinct in the Silurian.

(Sorry, couldn’t resist…)
#23 Metalraptor
March 27, 2009

“What are the closely living or fossil relatives of brontotheres?”

Brontotheres are classified in most family trees as hippomorphs, cousins of paleotheres and horses. Once you get past the other hippomorphs, the closest cousins of the brontotheres are the other perrisodactyls, the chalicotheres, rhinos, and tapirs (which all form the clade Ceratomorpha). After that, I would think the phenacodonts would be the next closest relationship. Once classified as “condylarths”, phenacodonts have been attributed as a family of mammals ancestral to the Perissodactyla.

So, its a Paleosyops. Interesting. I have not seen a lot of the earlier brontotheres, mostly looking at the latest members of the family, Brontops/Megacerops. Though it is interesting how rather than showing Osborn’s now debunked idea of orthogenesis, there were many types of brontotheres running around in the Eocene; horse-like species, small, fleet-footed forms, and even semi-aquatic varieties.
#24 Andy
March 27, 2009

An alum of Webb Schools provided some more background on the skull “Betsy” – “she” was the first of the series found and named in 1947 by Malcolm McKenna, and was prepared by William Otto at CalTech.
#25 David Marjanović
March 27, 2009

From now on I will let the comments appear, but will delete the url every time.

PZ said it’s now very easy to delete an entire comment.

I heard Dixon suggest in his book “World Encyclopedia of Dinosaurs & Prehistoric Creatures” that Uintatherium had a similar predicament with the incisors, and may have used a prehensile tongue to gather food. If so, would these strange adaptations possibly have contributed to the downfall of these wonderous beasts? At first, these animals did well, but then the group started to go downhill as they developed more complex and specialized feeding apparatuses.

Both ruminants and camels lack upper incisors entirely. They have a horny ridge instead, which they use (together with the lower incisors) to rip off plants.

I’m still in denial over this particular name change.

Megacerops doesn’t happen to be a nomen oblitum, does it?

If not, someone should perhaps write a petition to the ICZN…

What are the closely living or fossil relatives of brontotheres?

An SVP meeting abstract from last year says bronto- and chalicotheres are sister-groups, and together they form the sister-group of the crown-group of Perissodactyla.

BTW, I don’t think it has ever been seriously tested whether (some or all) phenacodontids and perissodactyls really are sister-groups. Surprises like that happen; at the SVP meeting last year there was a talk about placental phylogeny that failed to find “miacids” and “viverravids” as carnivoromorphs, for example.
#26 David Marjanović
March 27, 2009

It’s interesting that, though these are seemingly formidable animals, in important ways these creatures didn’t change (their teeth stayed virtually the same, even when they grew huge) and were apparently unable to adapt, while their contemporaries and relatives, the horses, changed profoundly and are still thriving today.

Well, something drastic seems to have happened at the Eocene-Oligocene boundary…

Also, only some of the horses changed profoundly, and only very few of those are still alive.
#27 Allen Hazen
March 28, 2009

The Ungulate– not just the Perissodactyl– family tree is a mess. With Perissodactyls, the Horses and Paleotheres go together, as do the Tapirs and Rhinoceroses. Then there are the Brontotheres, and then there are the Chalicotheres: so, four big groups of Perissodactyl. How to group the four seems to be … I’ve seen numerous different topologies proposed: not all the possible ones (there are 12 fully dichotomized topologies for 4 clades), but about as many as I’ve seen articles.

As for who the nearest outgroup to the Perissodactyls is… Phenacodus and company were favorites for a long time, and are still in the running… but some studies have shown them to be closer to Afrotheria. Then there is Radinskya, whose palate and upper molars struck some as more Perissodacttyl-like than those of Phenacodonts, though others think it was a Phenacolophid: Phenacolophids being widely thought of as close to Proboscideans, and so (I assume) Afrotheres. As far as I know, Radinskya is known only from the type specimen…

Among LIVING taxa, one molecular study produced what has to be one of the coolest names yet: it found a clade of bats, Carnivorans (to whom Pangolins seem to be closely related) and Perissodactyls, which the authors dubbed “Pegasoferae”: “ferae” for the Carnivorans, and “Pegaso” for the bats and horses!

Nor is it much better looking for relatives of Artiodactyls. The favorite there has been some long-legged version of the Arctocyonid Chriacus (the unfortunate complication being that standard-issue Chriacus seem to have been arboreal and very un-artiodactyl-like in locomotor specialization). On the other hand, an Asian Paleocene mammal (described from two partial dentaries and some teeth, which may have been from one individual) called Ganungulatum has been alleged similar to basal Artiodactyls, and also compared to Mioclaenids. (Ganungulatum is described in a 2007 paper in by Schiebout et al. in “Vertebrata Palasiatica”: Googling the genus name will get links leading to a pdf.)
#28 David Marjanović
March 28, 2009

The Ungulate– not just the Perissodactyl– family tree is a mess.

Quite so. For example, there is no monophyletic Ungulata. Even Perissodactyla and Artiodactyla are not sister-groups – not even when only extant taxa are considered.

Phenacodus and company were favorites for a long time, and are still in the running… but some studies have shown them to be closer to Afrotheria.

(Yes, but that’s suspect for a number of reasons.)

Phenacolophids being widely thought of as close to Proboscideans

What?

Anyway, a great big morphological placental phylogeny was presented at the SVP meeting last year. It will make everyone equally unhappy, I think.
#29 Allen Hazen
March 29, 2009

David Marjanovic–
I know there is no monophyletic Ungulata: I should have said “the whole orchard of Ungulate family trees”? Or, more precisely, “The Perissodactyl tree is a mess, the Artiodactyl tree is a mess, and the South American….”
(Grin!)

Could you give me some references– if there is enough in print to give references too! — on doubts about the placement of Phenacodus? I’m a non-specialist (but with access to a university library), and I’m trying to educate myself on these matters.

As for Phenacolophids… I ***was*** sure (but your response makes me doubt) that Phenacolophids had been associated with Arsinoitheres, and Arsinoitheres seem to be associated with Proboscideans… and the neck bone am connected to the head bone….
#30 David Marjanović
March 29, 2009

I’ll try to look for references, but probably not soon.

(Of course, one of the reasons why it’s suspect is simply biogeography, but that’s not a terribly strong argument by itself.)

The arsinoithere-tethythere association appears to hold so far.
#31 Allen Hazen
March 30, 2009

David Marjanovic–
Thanks!
As for biogeography… I would certainly take it as a reason for being at least a bit sceptical of a Phenacodont-Tethythere link, but since people have tried to link Sengis with North American Hyopsodontids, I suppose one ***could*** say that all biogeographical bets are off!
Arsinoitheres are known from Turkey, aren’t they? And Phenacolophids are Asian. So if either or both are linked closely to Tethytheres, fairly early “Afrotherians” were on the wrong side of the Tethys.
#32 Allen Hazen
March 31, 2009

Just to substantiate my claim that LOTS of topologies have been proposed for Perissodactyl relationships…
Kenneth Rose, in his “The Beginings of the Age of Mammals”(*) mentions about ten studies, between the 1960s and the early 2000s. For the four groups E (Equoidea= horses and Paleotheres), C (Chalicotheres), R (Tapiroidea, including Rhinoceroses) and B (topic of this post) they seem(**) to have proposed two fully resolved trees,
(E,B),(C,R)) and
(B,(C,(H,R)),
two trichotomies
((E,B),C,R) and
((C,B),H,R),
and the fully unresolved “taxonomic grass”. The one study (by Holbrook) he illustrates with a cladogram came up with even worse grass: Perissodactyls showing a basal hexachotomy of the four groups mentioned plus two “orphan” genera, Homogalax and Cardiolophus.

Some people apparently believe in another family (= clade, sometimes given the Linnean rank of family and sometimes not), the Isectolophidae. Holbrook’s study, however, rejects this: some “Isectolophids” are the two orphan genera from his tree, others (Isectolophus) are deemed Tapiroids, but basal to the Tapir/Rhinoceros split.

It gets worse. One of our four groups may not be as firm in its constitution as we hoped. Paleotheres are supposed to be a group close to the horses, but apparently there is some controversy as to whether some Paleotheres shouldn’t be reclassified as… Isectolophids.

And assignment of various Eocene genera to our bigger groups is often uncertain.

Bottom line: Brontotheres were Perissodactyls, but they weren’t horses or tapirs or rhinoceroses, and anything beyond that is still up in the air.

–
(*) Johns Hopkins University Press, some time since the turn of the millennium. Think of it as a sequel to Kielan-Jaworowska, Cifelli and Liu’s “Mammals from the Dinosaur Age” taking the story up to the mid-Tertiary… except that the fossil record of even EARLY-Tertiary mammals is so much more complete than that of Mesozoic that coverage can’t be as comprehensive.
(**) “Seem” because he gives only brief verbal descriptions of the different hypotheses, and a few are not completely clear.
#33 David Marjanović
March 31, 2009

since people have tried to link Sengis with North American Hyopsodontids, I suppose one ***could*** say that all biogeographical bets are off!

Well, yes, except that the link between macroscelideans and “hyopsodontids” has already been questioned, I think in an SVP abstract or two from last year.

That arsinoithere from Turkey, isn’t it Oligocene?
#34 Dartian
March 31, 2009

Allen:

Arsinoitheres are known from Turkey, aren’t they? And Phenacolophids are Asian.

According to Gheerbrant et al. (2005), the order* Embrithopoda consists of three families: “Phenacolophidae” (known from China & Mongolia), Paleoamasiidae (Turkey & Romania), and Arsinoitheriidae (Africa).

* Sorry, David!

David:

That arsinoithere from Turkey, isn’t it Oligocene?

According to the same source, Paleoamasiidae is Eocene.

Reference:

Gheerbrant, E., Domning, D. & Tassy, P. 2005. Paenungulata (Sirenia, Proboscidea, Hyracoidea, and relatives). In Rose, K.D. & Archibald, J.D. (eds.), The Rise of Placental Mammals: Origins and Relationships of the Major Extant Clades, Johns Hopkins University Press, Baltimore, pp. 84-105.
#35 Allen Hazen
March 31, 2009

Thank you, Dartian!

I couldn’t remember where I’d read about Phenacolophids & co, but it was probably the Gheerbrandt et al. chapter you refer to.

Rose and Archibald seem to have made a policy decision with regard to “The Rise of Placental Mammals”: one chapter would be devoted to molecular stuff, and otherwise contributors would be asked to concentrate on morphological evidence: as I recall, a number of the phylogenies proposed looked questionable in the light of molecular studies.

That and the absence of a chapter on South American weirdness were my main complaints about what I generally thought was a lovely book!
#36 Allen Hazen
March 31, 2009

David Marjanovic–
Yes, I thought the “hyopsodontid(*)”/macroscelidean link was, umm, not very well established (the original evidence was on the order of “Look at this “hyopsodontid” tibia-fibula and see how much it looks like the one from extant Rhynchocyon” as I recall): I just cited it as a precedent for a biogeographically, umm, surprising hypothesis about relations between Afrotheres and Laurasian fossil taxa.

Suppose we assume, for the sake of argument, that the molecular mafia are RIGHT, and that Afrotheria is a genuine monophyletic clade. It doesn’t NECESSARILY follow that Afrotheria originated in Africa deep in the Cretaceous, or that it was exclusively African until the Eocene. So biogeographical incongruity is maybe grounds for scepticism about a link between, say, Phenacodontidae and Paenungulata, but it isn’t conclusive against it. I have the feeling we are in agreement about this?

(*) I note your quotes (scare-quotes?): the “hyopsodontid” in question was, i.i.r.c., an Apheliscine. And the monophyly of “Hyopsodontidae” seems to be very much in doubt….
#37 Graham King
April 4, 2009

Allen Hazen wrote:

as I recall, a number of the phylogenies proposed looked questionable in the light of molecular studies

As a curious onlooker, non-specialist…
Do molecular studies look only at proteins (etc) specified by expressed genes? I ask, because it occurs to me that some relevant proteins might well be absent from some relative species yet be coded-for in their DNA that’s not expressed (genes switched-off… maybe later to be switched on again, in their descendants). Or, alternative duplicated gene versions could be switched in/out of use in lineages.

Thus any phylogeny not taking these possibilities into account (not checking genotype as well as phenotype), could get screwed up.

Or is that all well-understood and made part of each molecular study? Are the molecules compared ones whose genes always are straightforwardly expressed, not thusly tinkered with?
#38 Graham King
April 4, 2009

I wrote

As a curious onlooker, non-specialist…

To clarify, that refers to myself, not Allen!
#39 Tim Morris
October 11, 2009

I think I just had an “embolism”…

This is some funny schizzle.