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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 animals and plants of the Oligocene rainforest at Riversleigh (as envisioned by an artist)
Occasionally in the geological past, extraordinary circumstances resulted in the near-perfect preservation of an entire ecosystem. These astonishing fossil beds are known as Lagerstätten (one of the first such finds was in Germany) and they provide one of the best sources of information about life on this planet. A particularly rich Lagerstätten is located in the arid scrubland of Riversleigh in northwest Queensland, Australia: there fossils from the Oligocene and Miocene epochs are preserved in uncompressed limestone (which allows paleontologists to recover 3 dimensional skeletal remains). During the late Oligocene, Riversleigh was a lush and vibrant rainforest filled with an incredible profusion of bizarre life forms. When the Oligocene ended, the region dried into grasslands (and the climate continued to dry out further in subsequent epochs until the present, when the area is a near desert).
The giant carnivorous platypus (Obdurodon tharalkooschild)
All of this is backstory to a remarkable recent discovery. This week paleontologists studying the bats, snakes, and strange tropical marsupials of Riversleigh made an unexpected discovery–a giant hunting platypus twice the size of the living species. This big predator, Obdurodon tharalkooschild, was a formidable meter long (3 foot) creature with sharp teeth for grabbing crayfish, amphibians, aquatic reptiles, and fish. The newly discovered platypus lived in the long-lost rainforests of Queensland. It was a generalist with a much larger diet than the somewhat specialized modern platypus.
No, it wasn’t THAT big…
Monotremes (platypuses & the more recently evolved echidnas) are an extremely ancient branch of mammalian life which date back at least to the Jurassic–and more likely to the Triassic epoch or earlier. Platypuses are believed to have evolved in what is now South America and then spread to Antarctica and finally to Australia. The amazing giant hunting platypus indicates that there were hitherto unexpected branches of platypus evolution. I wonder if Obdurodon tharalkooschild was toxic (like the modern platypus). I also wonder what strange monotreme fossils lie beneath the ancient ice of Antarctica.
A human (black), an African Elephant (gray), a Mastodon (french blue) and a Paraceratherium (sky blue)
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.
Artist’s Conception of Paraceratheriums Migrating (from asecic.org)
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.
Fossil Paraceratherium skeleton in a museum
The Eocene (Illustration by Bob Hynes for the Smithsonian Institution)
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.
A Global Map of the Early Eocene (map by Dr. Ron Blakey)
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.
Titanboa with Ancient Crocodilian (painting by Jason Bourque)
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.
Phenacodus, a goat-sized grazer of the Eocene era (painting by Heinrich Harder)
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.
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
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