Dromomerycids: discuss

You don't hear much about dromomerycids these days, it's always protoceratids hogging all the limelight. Here's one of the more obscure forms, the derived cranioceratin dromomerycine Procranioceras skinneri from the Miocene of the USA (originally named as a member of the speciose genus Cranioceras).


All dromomerycids are North American and they were mostly a Miocene event, petering out after the Middle Miocene and disappearing during the Early Pliocene (Janis & Manning 1998, Semprebon et al. 2004). They resembled various bovids and deer in proportions and probably lifestyle: some seem to have been bushbuck-like browsers, others have been likened to ecotone-dwelling reedbucks, while the last of them, Yumaceras, was a giant of over 380 kg. Cranial projections were the norm. The aletomerycines had supraorbital horns (apparently larger in males than females) and sabre teeth (again, apparently only in males), while the dromomerycines had both supraorbital horns and a weird dorsal projection on the occiput. This was largest in cranioceratins like Pediomeryx and Cranioceras.

So much more could be said... antorbital vacuities, sexual dimorphism, the function and loss of those sabre teeth... but this was meant to be a 'picture of the day'. Thanks to Markus Bühler once again!

Finally: against my better judgement, I've written up some thoughts on Quick & Ruben's new paper about the absence of an avian-like respiratory system in non-avian dinosaurs. It's coming next.

Refs - -

Janis, C. M. & Manning, E. 1998. Dromomerycidae. 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. 477-490.

Semprebon, G., Janis, C. & Solounias, N. 2004. The diets of the Dromomerycidae (Mammalia: Artiodactyla) and their response to Miocene vegetational change. Journal of Vertebrate Paleontology 24, 427-444.


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So, Darren, I want to ask you more about horns of mammals. I'd like to know more about untypical cases of horn formation at mammals of non-horned groups of today. Yes, I know about horned rodent Epigaulus, horned hog Kubanochoerus and so on. I'd like to know more about first steps of horn formation and the structures of this kind at modern mammals. Yes, I'd like to try to predict the formation of horns at future animals.

By Pavel I. Volkov (not verified) on 16 Jul 2009 #permalink

Next to the exhibited skull was a portrait of a living Cranioceras, and it was shown with very tiny antlers at the end of the bony horns. I have never seen any other reconstruction which shows this miniature antlers. Are they just fictive or are they actually known from the fossil record? I looked a bit like a very beefed up version of a muntjak.By the way, this skull can be seen like many other great fossils and animals in the Museum of Natural History Berlin.

The WP entry on Dromomerycidae suggests that chevrotains may be living dromomerycids. Is this plausible?

By Andreas Johansson (not verified) on 16 Jul 2009 #permalink

Cool! :-)

By Michael Ogden … (not verified) on 16 Jul 2009 #permalink


Were the dromomerycids the only artiodactyls that you know of that had that those dorsal projections? Was it common in Dromomerycids? I know ampelomeryx had some funky growth as well...

By Sebastian Marquez (not verified) on 16 Jul 2009 #permalink

Unusual relatives of the camels were the Protoceratidea with bony structures appearing in some unexpected places.
Too bad we can`t bring these species back to life thru Genetic engineering

By Bob Michaels (not verified) on 16 Jul 2009 #permalink

Thanks for comments. Did it have a tall neck? Nope, that weird occipital process must have projected out the back of the head as a curving, blade-like pseudo-horn. I think the surface texture suggests a covering of skin rather than horn, though this doesn't seem to have been the case for the supraorbital horns. Re: horn formation in mammals (comment 2) - that's a rather complicated area that I can't do justice here and now, sorry.

With regard to reconstructions that show little deciduous tips to the horns (comment 3), this comes from a reconstruction in Frick (1937): Janis & Manning say that there's no evidence for it. Are chevrotains living dromomerycids? (comment 4). That's the first I've heard of this and I'd be interested to know if it's been formally supported anywhere: dromomerycids have usually been regarded as close to giraffids or cervids, with more recent work supported an affinity with palaeomerycids and deer within Cervoidea.

That's all, gotta go...

Ref - -

Frick, C. 1937. Horned ruminants of North America. Bulletin of the American Museum of Natural History 69, 1-669.

Wow, that's really weird. It's supraorbital horns and general skull shape remind me of antilocaprids.

Since you mentioned it was something you could expand on, I just wanted to let you know that I would be thrilled if you talked about antorbital vacuities. Those things have puzzled me for a long time and I've had trouble finding any in depth explanations for them anywhere.

about loss of those sabre teeth...
Sexually dimorphic suggests they were used in male-male combat in rutting season. Obvious thought is that they were given up when better weapons (horns) became available. Is the Dromo record good enough to test that? (Does it show big canines in early species with small horns and canines reduced in what seem to be later members of same lineage with bigger horns?)
I had the impression-- based on VERY superficial reading-- that something like this was plausible for deer: antlerless deer (and near-dear like Muntjacs) have big canines but the deer with biggest antlers don't. Is this right?
... It wouldn't account for Hoplitomeryx, but that animal is SERIOUSLY odd!
(Thanks, Darren, for another Mammal post!)

By Allen Hazen (not verified) on 16 Jul 2009 #permalink

Allen, that's my impression too - in general, large canines in ruminants seem to be negatively correlated with large cranial appendages (which is a tossy way of saying "horns"). The interesting case for me is Hydropotes, the Chinese water deer, which appears likely to have descended from antlered ancestors (it's the sister taxon to Capreolus among living deer) and regained large canines as it lost the antlers.

I believe the over-armoured condition of Hoplitomeryx has been suggested as a defense against aerial predators, but I don't know that I'm convinced.

Gilbert, C., A. Ropiquet & A. Hassanin. 2006. Mitochondrial and nuclear phylogenies of Cervidae (Mammalia, Ruminantia): systematics, morphology, and biogeography. Molecular Phylogenetics and Evolution 40 (1): 101-117.

It's interesting that there have been fossil ruminants - such as Cranioceras and its kin with three 'horns', and Hoplitomeryx with five (IIRC) - that had an uneven number of prominent cranial appendages. Most extant ruminant taxa have either one pair* of horns/antlers (the four-horned antelope Tetracerus quadricornis has two pairs of horns) or none at all. It's also unusual with noticeable asymmetry in horn size or shape; among extant ruminants, there's nothing quite like the functionally almost one-horned bovid Tsaidamotherium from the Miocene of Asia. Yet another reminder of how the extant fauna offers just a tiny glimpse into the diversity of extinct taxa...

* Giraffa is sort of an exception - apart from its two 'regular' horns it may have one or three extra horn-like protuberances on its head.


Hydropotes, the Chinese water deer, [...] [i]s the sister taxon to Capreolus among living deer

Really? I could be wrong but I think there was another recent molecular study that found Alces to be the sister taxon of Capreolus. (Don't remember if that study included Hydropotes; I don't have my references available at the moment so I can't look this up until later.)

Folks, you are wonderful!

I saw deer phylogeny and didn't thought about re-evolving tusks of Hydropotes.

This Tsaidamotherium is not, by any chance, known from one abnormal specimen?

Chris: Thanks for that information. I had been under the impression that Hydropotes is a basal cervid. But if those molecular data are correct, then not only is the Chinese water deer secondarily antler-less but it's also a member of the 'American' clade of deer (the odocoileines), despite its geographical distribution.

Jerzy: As I said, I'm a bit reference-challenged at the moment. But if memory serves me right (and somebody please correct me if I'm wrong), Tsaidamotherium is known from several specimens and its horn arrangement apparently was indeed as it is reconstructed in the illustration I linked to.

Well, the geographic distribution of Hydropotes is not a problem. Capreolus is Eurasian too, while Alces and Rangifer are Holarctic. The strictly American deer form a clade that these other taxa don't belong to.

Re: "Finally: against my better judgement, I've written up some thoughts on Quick & Ruben's new paper about the absence of an avian-like respiratory system in non-avian dinosaurs. It's coming next."

I look toward to reading it. Please put a link to the paper and hope it will be in PLos or Acta so we can not have to pay for it. Thanks.

Re: asymmetry
O.k., Tsaidamotherium. There was also a tiny (hare-sized?) critter whose name I can't recall: the AMNH in New York displays a skeleton, mount6ed as if leaping to escape from a very large ?? Amphicyonid ??, the two skeletons mounted over a cast of tracks showing such pursuits did occur.

Any more?

There's a minor asymmetry in Rangifer (reindeer/caribou): one, but only one, antler developes a brow tine that extends forward over the snout and expands to something that looks like (and may be) a snow scraper. For any asymmetric species known from an adequate number of specimens we can ask: is the "handedness" of the asymmetry uniform or variable. (In Rangifer, some individuals are "right-scrapered" and some "left-scrapered.") In the illustration of Tsaidamotherium Dartian linked to, it looks as if all three individuals have large right horns...

By Allen Hazen (not verified) on 19 Jul 2009 #permalink

Allen: you're thinking of the Miocene merycodontine pronghorn Ramoceros. There are several species (Frick even named subspecies for one of them), and individuals in a species are not consistent - some have longer horns on the left and others on the right. I must do a post about asymmetry in tetrapods some time.

Many of these early Miocene small ruminants, particularly merycodontine antilocaprids and aletomerycine palaeomerycids (the now generally accepted name for dromomerycids) are a mess systematically, and need a lot of work. Hopefully some student there with a good month or more at the AMNH might give it a start.
I've recently did a little work on merycodontines (PaleoBios current issue) and aletomerycines (JVP in press), and would love to assist anyone that wants to give it a try.