Weekly Spotlight: Capricamelus

28 02 2010

NOTE: Hat tip to my regular reader Doug for the idea and most of the information I’ve obtained (Dr. Donald Prothero is also deserving of many thanks in this department). For those interested, Doug has recently joined the blogosphere, having launched what promises to be a most interesting publication: “A Central Coast Paleontologist: The Chronicle Of An Epic Quest Interspersed With Paleontology, Geology, And Maybe An Occasional Rant From An Aspiring Fossil Hunter”. Don’t take my word for it, check it out!

Good tidings and well-wishes and sorry for the extended posting delay (college has been quite trying of late!).

Anyone familiar with this humble blog is doubtlessly aware of my undying love for animals which we tend to instinctively identify as a recognisable species only to discover that they’re actually much more akin to an entirely different group, an adoration which is by no stretch of the imagination exclusive to yours truly. Few examples of this amazing evolutionary situation are as head-turning as that of Capricamelus gettyi, a camel that for all the world looks like a goat.

Camelids are a surprisingly diverse lot, but can nevertheless be osteologically united chiefly by the following characteristics:

-They lack any sort of ornamental headgear, such as horns, antlers, or ossicones.

-They possess a well-developed sagittal crest.

-They sport a distinct ‘hook’ on their mandibles.

-Their cheek teeth are selenodont.

-They have upper and lower incisors, both of which are medium-sized and hooked.

-Their necks are notoriously elongate and, in some cases, closely resemble those of giraffids. The anterior neural spines are low and long.

-The radius and ulna are co-ossified (‘united’).

-The fibula is incredibly slight, having been reduced to a spine fused to the proximial end of the tibia.

-The 3rd and 4th medapodials are fused proximially, but this connection terminates further down the limb in question.

-Perhaps most significantly, camelids are the only fully digitigrate modern ungulates; in fact, many can even utilize plantigrade locomotion. This is primarily due to their long, thick, padded toes and large toenails.

Camelid evolution has been studied for decades, as partially evidenced by this 1920 illustration.

The evolution of camels and their relatives is a complex and fascinating tale, one which I feel Ian Lange has nicely summarized in the following excerpt from his book “Ice Age Mammals Of North America: A Guide To The Big, The Hairy, And The Bizarre” (NOTE: this volume was written for a general audience and consequently isn’t nearly as technical as most of those I’ve quoted):

“This group of Old and New world grazing animals with big lips, big soft eyes, and unmistakable figures has its roots in the late Eocene time, about 40 million years ago, in North America… By Oligocene time, 37 million to 24 million years ago, the sheep-sized Probrotherium had evolved. It had two toes and lived in open woodlands in what today is South Dakota. During the Miocene epoch, 24 to 5 million years ago, camels increased in size, with their legs and necks lengthening. By approximately 5 million years ago, in early Pliocene time, some early camels were huge. Camels also lived in South America then and had reached the old world by way of the Bearing Isthmus, which connected Alaska with eastern Siberia. Llamas, close relatives to camels, arose in North America in late Tertiary time and subsequently spread into South America…

Camels roamed North and South America, Asia, Africa, and Europe, and llamas ranged widely in North and South America by late Pliocene time, 3 million and 2 million years ago…For unknown reasons, the apparently plentiful camels and llamas became extinct in North America at the end of the Pleistocene epoch, about 10,000 years ago. Camels also died out in South America at this time.”

Capricamelus itself is a member of the Stenomylinae superfamily, which, according to Donald Prothero and Robert J. Emry’s “The Terrestrial Eocene-Oligocene Transition In North America”,

“Since the Stenomylini appear suddenly in the late Arikareean with all their bizarre specializations, several authors… postulated that they diverged very early in camel evolution, possibly as early as the Eocene…[It’s been] pointed out that Stenomylus, Pseudolabis, and Miotylopus (and Capricamelus, though this genus was discovered after the book’s publication) share the derived character of weak or absent mesostyle. In addition to this feature, the peculiar maxillary fossa, the precocious elongation and hypsodonty of the teeth, and the posterior extension of the premaxilliary are all good synapomorphies which corroborate this hypothesis of relationships…

The expanded taxon Stenomylinae is an important, previously unrecognized monophyletic group that was the dominant group of camels during the Whitneyan and Arikareean.”

More specifically, Capricamelus was a member of the Miolabinae, a subfamily which also contains the genera Miolabis, Nothotylopus, and Paramiolabis.

Right then, having sufficiently dawdled, its high time to cover this week’s beastie itself. Capricamelus hails from the  Tecopa Lake Basin, which lies just south of Death Valley, California and sports Late Pliocene rock.  As indicated by the above illustration and the opening paragraph of this post, this animal essentially posessed identical limb proportions to those of a modern Oreamnos mountain goat. Consequently, despite being of the same general size as Lama guanicoe, it’s neck was some 25% shorter. Interestingly, despite the overwhelming aforementioned tendency for camelids to harbor partially-fused metapodials, this isn’t the case in Capricamelus, which sports no osteological junction of any kind in this area. This primitive characteristic strongly suggests that the lineage which produced these ‘goat-camels’ likely diverged from other miolabines approximately 17 million years ago, presumably from an ancestral Stenomylus-like genus. However, despite this rudimentary anatomical feature, Capricamelus was a fairly advanced animal, as evidenced by its elongated rostrum and powerful dental battery.

It’s also worth mentioning that Capricamelus may not have been an evolutionary anomaly, despite the fact that the fossil record has provided us with very few comparable organisms. This assertion may be cited as a fairly logical one on the basis of the fact that this creature’s exquisite adaptations for low-gear locomotion is entirely consistent with the location of its original discovery (which, by the way, consisted of at least fifteen individuals hailing from various age groups), a semiarid area surrounded by mountains: a geological setting which seldom produces a reliable source of fossils remains. Hence, it’s entirely possible that this animal and its kin may have persisted for millions of years whilst eluding the ultimate fate of being preserved for posterity. Only time and further research will confirm or deny this suggestion.

May the fossil record continue to enchant us all!

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4 responses

1 03 2010
Donald Prothero

Kudos on the nice writeup! Just one thing: Lange doesn’t seem to have much first-hand experience with camel paleontology. Protylopus was thought to be a camel a century ago, but it has been in its own family, the Oromerycidae, since at least 1955. Oromerycids are sister-taxa to Camelidae, and look much like the most primitive camels (except in key details), but they are NOT camels. See my chapters on both topics in the 1998 Janis et al. volume.

1 03 2010
tanystropheus

Many thanks for the heads-up, Dr. Prothero! I’ve updated the post accordingly. As for Ian Lange, I believe he earns a living as a geologist who considers himself to be a paleo enthusiast. His book is rather good, though he obviously commits the occasional factual error.

1 03 2010
accpaleo

Thanks for the very kind plug at the top.

“evolutionary anomaly”? I never thought of that. I always thought of it as a wonderful example of convergent evolution.

2 03 2010
tanystropheus

That’s my view as well. By ‘evolutionary anomaly’, I was simply referring to way in which some people may percieve this unusual genus.

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