The Rise and Fall of the Protoceratidae

The artiodactyls are arguably the most successful order of large land mammals (as long as we don’t mention a dominant lone species of large aggressive primates). Just perusing a list of artiodactyl names reveals how universal and important they are: goats, pigs, cows, giraffes, hippos, sheep, Protoceratidae… wait. What? Among the familiar families of artiodactyls there is an unfamiliar name—an entire vast lineage of hoofed animals completely gone forever. These were the Protoceratidae, hooved animals analogous to their cousins the deer, giraffes, and the camels. The Protoceratidae ranged across North America from the Eocene through the late Pliocene (46 million to 5 million years ago). For 41 million years great herds of these animals grazed the Rocky Mountains, the Great Plains, Appalachia, and Mexico (although the Laramide orogeny was still ongoing as they evolved, and the Great Plains were at first a great forest).

Protoceratidae had complex stomachs for breaking down grasses and other tough vegetation which they grazed upon. Initially the protoceratids were tiny like the smallest deer, but as time progressed some grew to the size of elk. Although the bones in their legs were somewhat different from deer and camels they would have looked similar at a distance…except for a stand-out feature. Male Protoceratidae had a rostral bone—a powerful y-shaped spar of bone jutting from their nose.   It is believed that this was a sexual display, meant to impress female Protoceratidae and for sparring with other males for territory and mates (although anybody who has ever been jabbed in the face with a sharpened bone by an elk-size animal would probably testify that the rostral bone could be used defensively).  The protoceratids also had a pair of more conventional horns on either side of their head like deer and cattle.

Synthetoceras tricornatus

I wish I could show you more of this extinct family. They lived for a long time and took many shapes and appearances as they spread across the continent into many different niches. A species of particular note was Synthetoceras tricornatus, which was the largest of the protoceratids and which was endemic to most of the continent during the Miocene. Look at how lovely they are. I am ready to move to Texas and start a ranch for them—if they weren’t all dead.

Protoceras

So, what killed off the Protoceratids after 40 million years of success? It seems like they were outcompeted by other, more familiar forms of artiodactyls which developed as the Cenezoic wore on (and which were better suited to vast tracts of grassland—which came to dominate the landscape as the forests died back). The last protoceratid, the Kyptoceras, lived in semi-tropical forests of Florida during the Miocene. Perhaps it was like the Saola, an ever-dwindling wraith that lived deep in the rainforest and was seldom seen until one day it was gone completely. It is an appropriately melancholy picture of the last descendant of a once-great house.

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Musk Deer

Musk Deer

Continuing our series of posts about saber toothed mammals we come to a second family of living creatures.  Half way between the primitive chevrotains (mouse deer) and the familiar true deer (cervids) are the Moschidae, a family of small artiodactyls consisting of one genus with several similar species.  The musk deer are small delicate grazers which live in the forested mountains or alpine scrubland of Asia.  Musk deer weigh between 7 and 17 kilograms (15 and 37 lb) depending on gender, age, and species. Unlike true deer, the little creatures lack antlers, but male musk deer make up for this absence with a pair of elongated canine teeth which they use to fight for breeding rights.

Alpine Musk Deer (Moschus chrysogaster)

Like true deer, musk deer eat the tender shoots of trees and grasses, as well as berries, lichens, and mosses.  Females live in small territories of approximately 100 to 200 acres.  The territory of a dominant male will overlap several of the females’ territories.  Female musk deer give birth to a single fawn.  Musk deer are nocturnal or crepuscular.  They use their acute hearing and excellent sense of smell to flee from predators at the slightest hint of danger.

The skull of a male Siberian Musk Deer (Moschus moschiferus)

Male adult musk deer have a musk pouch located between their genitals and their umbilicus which they use to attract mates.  Unfortunately for the little saber toothed deer this pouch also attracts human hunters.  For centuries (or longer) musk has been a prized luxury good, so much so that, at times, prices have soared to $45,000/kg on the black market. The musk is said to have an incredibly complex aroma but the main notes are earthy, woody, and “animalic” (i.e. fecal).  Dried musk grain must be substantially tinctured with alcohol before it produces a perfume which is pleasant to humans.  The resultant substance however served as a mainstay of the perfume industry and as a cure-all nostrum in ayurvedic medicine until the creation of synthetic musk.  Poor musk deer from several species were nearly wiped out because of whatever mysterious power their sexual marking fluid has on humankind.

The Dwarf Musk Deer (Moschus berezovskii)

The Long Summer of the Eocene

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).