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The largest land animal alive today is the mighty African elephant, however even the largest adult bull elephants were dwarfed by the largest land mammal ever to exist. The giant herbivore Paraceratherium stood 5.5 metres (18 ft) tall at the shoulder. When standing upright the creature’s head (which was approximately the same size as character actor Danny Devito) was about 8 metres (26 ft) above the ground. Although debate continues about how much the beast weighed, reasonable estimates suggest it could have massed from 15 to 20 metric tons which means that the animals were as large as mid-sized sauropod dinosaurs from the previous era. Partial skeletons of Paraceratherium were discovered by different scientists at different times–which has confusingly resulted in three different names for the genus: 1) Paraceratherium which means”near horn animal” in Greek; 2) Indricotherium which was derived from a mythical Russian progenitor-monster called the Indrik-Beast; and 3) Baluchitherium which means “Baluchistan beast”, in honor of Baluchistan, an arid portion of the Iranian plateau, where a fossil specimen was unearthed. Paleontologists prefer to call the genus “Paraceratherium,” however, thanks to TV specials and museum shows the name “Indricotherium” remains popular with the public.
Paraceratheriums were perissodactyls. The giant creatures were most closely related to the living rhinoceroses (although they shared ancestors with tapirs and horses as well). Paraceratherium’s immense size allowed it to eat the branches and leaves of large trees. They ranged across what is now Central Asia across Iran, India, Pakistan, Mongolia, Kazakhstan, and China. The various species of Paraceratherium had long graceful necks somewhat like that of Okapis. Additionally they possessed nimble elongated upper lips with which to strip leaves off of branches. These lips were no quite trunks but probably resembled the long grasping snout/lips of tapirs. Although Paraceratherium was closely related to rhinoceroses, they lacked the rhino’s characteristic horns—their giant size meant they did not need them. The genus originated in the Eocene and flourished during the Oligocene—a golden age of perissodatyls. However as the global cooling became more pronounced in the late Oligocene, the great creatures gradually vanished.
The Eocene epoch (which lasted from 56 million ago to 34 million years ago) was hot! Temperate forests ran all the way to the poles. Steamy tropical jungles grew in the latitude where Maine is now and the equatorial regions of earth were (probably) sweltering. Tropical reefs formed in the coastal waters around a heavily forested and ice-free Antarctica. Since there was not year-round ice at each pole, the sea levels were much higher.
The Eocene was a time when most of the contemporary mammalian orders first appeared. The earliest artiodactyls, perissodactyls, rodents, bats, probiscideans, sirenians, and primates all originated during this time. Of course mammals were not the only story: the Eocene was also a time of great diversification for birds and many familiar orders of avians developed then. Reptiles begin to put the setbacks which marked the end of the Cretaceous behind them and several giant new species emerged including an immense tropical ur-python and a host of crocodiles and turtles. It is harrowing to think that the first wee dawn horses and cute little early atiodactyls were forced to contend with a 13 meter long super snakes and giant crocodilians (which flourished in the great hot swamps of Alaska), but such is the case.
The high temperatures of the Eocene are perplexing to scientists. By contrast, the temperatures of the Paleocene (which was the first era of the Cenezoic and had directly preceded the Eocene) were much more temperate. In fact the temperature spike of 56 million years ago seems to have ended the Paleocene and brought about the diversification of Eocene life. The rapid warming is known as the Palaeocene-Eocene thermal maximum and scientists have been vigorously debating what caused the climate change. An immense amount of carbon seems to have entered the atmosphere at this time, which in turn led to greenhouse warming. It remains controversial as to how such a large quantity of carbon got into the atmosphere. Comet/meteorite impact, massive peat fires, and volcanic activity have been suggested as triggers, however supporting evidence is lacking. The release of globally significant quantities of hydrocarbons–which had been trapped in undersea clathrates seems like a more feasible hypothesis, as does the idea that the earth’s orbit brought the planet closer to the sun for a time.
The end of the Eocene was also linked to the carbon cycle. Reduced carbon dioxide in the atmosphere seems to have led to global cooling and newly evolved varieties of grasses began to invade large swaths of the world. Additionally two massive meteor strikes in Siberia and Maryland combined with substantial volcanic activity to finish off the long hot summer. But during the Oligocene, the era which followed the Eocene, the world was a much more familiar place inhabited by orders of animals which are still here with us today (or are us–since primates first evolved during the Eocene).
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.
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.
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.
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.
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.