Desmostylians

Let’s look back through the mists of time to peak at one of the most mysterious and perplexing of mammals, the desmostylians, the only extinct order of marine mammals (although in dark moments I worry that more are soon to follow). Desmostylians were large quadrupeds adapted to life in the water. They had short tails and mighty limbs. Because of this morphology, taxonomists initially thought that they were cousins of proboscideans and sirenians (elephants and manatees), but the fact that their remains have only been found far from Africa (the origin point of elephants, mammoths, mastodons, and manatees & sea cows) along with perplexingly alien traits has caused a rethink of that hypothesis.

(Art by Ray Troll fror SMU)

Extant between the late Oligocene and late Miocene, the desmostylians had powerful tusklike cylindrical teeth and dense heavy bones. The smallest (and oldest) were peccary sized creatures whereas the largest grew to the size of medium whales. It seems like desmostylians lived in littoral parts of the ocean—near coasts and shores where they used their pillar like teeth to graze great kelp forests. They scraped or rasped up the kelp and sucked it down their voracious vacuum maws like spaghetti! It must have been an astonishing sight! My favorite marine paleoartist, Ray Troll has made exquisite pictures of these majestic creatures which help us to visualize them. I really hope they looked this funny and friendly (if they were anything like herbivorous manatees, they probably did!).

(Art by Ray Troll, courtesy SMU)

Speaking of manatees, the gentle sirenians had a hand (or flipper?) in the demise of the poor desmostylians. The dugongs and manatees would never fight anyone or even protect themselves with force—they simply outcompeted the less nimble desmostylians for resources, although one wonders if climate-change and the continuing evolution of different coastal sea plants might also have helped do in the great desmostylians.

The Hyrax

Yesterday, if you read the post concerning pikas, you probably found yourself wondering why pikas are found throughout the highlands of North America, Europe, and Asia but do not dwell in the rocky scree of Africa and the Middle East.  As it turns out, another animal grazes the arid mountain lands in those areas.  Although superficially this furry herbivore seems to share many features with the pika, it is a very different sort of creature with an entirely different (and rather grand) history.

A Rock Hyrax near Capetown, South Africa

I’m writing about the hyrax, a tiny tusked grazing creature with certain anachronistic features of earlier mammals (such as an unique dentition and poorly developed internal temperature regulation ).  Hyraxes are the only living members of the family Procaviidae, itself the only extant family of the order Hyracoidea.  Hyracoids are rare and unusual today, found only in niche ecosystems, but 40 million years ago they were among the dominant grazers in Africa.  We’ll get back to the paleontological history of the hyrax family at the end of the article, but for now here’s an overview of the living hyraxes.

Hyraxes (photo by Vladimir Danilov)

Found in rocky and mountainous area of the Sahara and the Middle East, hyraxes are equipped with sweat glands on the tough rubbery pads of their feet.  This helps them keep cool and gives them traction on the steep cliffs where they dwell.  Additionally they have sophisticated kidneys which help minimize water consumption in their arid rocky homes.  Among the small mammals, Hyraxes, uniquely, possess multi-chambered stomachs capable of digesting plant materials and fibers.  Their complicated digestive apparatus makes use of numerous symbiotic bacteria to absorb the nutrients out of the coarse shrubs and weeds they eat.  Unlike cows and other artiodactyl ruminants, hydraxes do not chew a cud–however their aggressive tusk gnashing was mistaken for cud-chewing by biblical law-givers so um, I guess they are (incorrectly) not kosher according to Deuteronomy.

A Family of Rock Hyraxes (Procavia capensis)

Hyraxes are small animals but they have long lives, elaborate social networks, and surprisingly capacious memories (at least according to zoologists and neurophysiologists).  I have watched them at the Bronx zoo where they live in an enclosure filled with baboons and ibexes: it is intriguing to see how their miniature society copes with these large aggressive neighbors.  The hyrax colony has all sorts of rules and communication protocols dealing with sentries, foragers, and communal huddling for warmth.  Their elaborate social behavior (quite lacking in yesterday’s pikas and tomorrow’s groundhogs) makes sense when one looks at their relatives.

A Painting of Arsinotheriums by Heinrich Harder

As I noted above the Hyracoids were a very diverse and widespread taxonomic order in Africa during the Eocene and Oligocene epochs (55 to 34 million years ago). To quote the McGraw-Hill Encyclopedia of Science and Technology,  “the early hyracoids ranged from animals as small as rabbits to ones as large as modern Sumatran rhinoceroses. The fossil skeletons of the early hyracoids indicate that some species were active runners and leapers, while others were heavy, piglike quadrupeds.”  In fact these hyracoids, or their immediate ancestors, seem to have been the basal group (which is to say the progenitors) of the paenungulates.  DNA sequencing and the fossil record both give compelling evidence for this relationship.  This means that the long ago ancestors of the hyraxes–which looked much like today’s hyraxes–were also the grandfather species for the mighty proboscideans—the towering mammoths, the mighty gomphotheres, the mastodons, and the ingenious elephants.  Not only that, the early hydracods were also ancestors to the desmostylians, the embrithopods (like the pictured Arsinoitherium), and the gentle sirenians such as dugongs and manatees.  When you look at a hyrax you are not looking a tusked groundhog, but at a sophisticated social animal with some giant successful cousins.

A (Proboscidean-centric) Portion of the Paenungulata Clade