Eocene Diatryma Gastornis Moertherium Barylambda Uintatherium Eobasileus Andrewsarchus Brontotherium

The name Eocene means the "dawn of recent life" Originally the Eocene was the first epoch of the Cenozoic, but then the Paleocene was erected as an earlier epoch. The Early Eocene is much warmer, the entire planet is experiencing a greenhouse state. Life during the Eocene was pretty similar to that of the Paleocene, a warm tropic world, high sea-levels and island continents, invertebrates and plants similar to those today, while mammals continue to evolve and diversify along many lines.

In the Late Paleocene and the Eocene there is Gastornis pariensis (Gaston's bird"). It is based on fragmentary early finds in Europe. A faulty reconstruction delayed recognition of the relationship to the North American Diatryma. They may be the same animal or at least very close relations. If so this would indicate continued contact between North America and Europe. From Europe is Eohippus ( Dawn Horse) or Hyracotherium (mole beast) a palaeothere.Once thought to be an early horse it had 4 hoofed toes on the front feet and 3 hoofed toes on each hind foot. It had a long skull with 44 long-crowned teeth designed to browse on leaves and shoots.

A Uintatherium surveys his surroundings before moving on toward the flood plain. It is a vegetarian and usually travels alone or in small groups.

Riff's Lost World JA RU Uintatherium. Custom diorama submitted by Riff Smith photo by Bob.

Uintatheres( Dinocerata ) were ancient, distant cousin of horses, elephants and whales. They first appeared near the end of the Paleocene and became extinct by the end of the Eocene. They left no descendents and their relationship to earlier forms are still debated. They may be related to Toxodonts and Liptoterns of South America. Uintatherium was 10 -15 feet long and lived in North America and Asia. It was the largest plant eater of its time.

Eobasileus cornuta (horned dawn king) had 6 bony knobs on its face. The rhino sized Eobasileus had saber canines and lived in the late Eocene. It was closely related to Uintatherium but a distinct animal.

PlayVision Eobasileus from the small mammal series and Diatryma by Panini.

There were no mammalian carnivores for the first part of the Paleocene. The mesonychids were the first mammalian meat eaters and flourished until the Oligocene when creodonts and true carnivores replaced them. Most mesonychids were the size and shape of large wolves or bears, although some were as small as foxes. Members of this group had a heavy robust skull armed with sharp canine teeth and huge round-cusped molar teeth, suitable not only for eating meat but also for crushing bone. The body was also very wolf like, with a long tail and limbs. Like many modern carnivores, mesonychids walked on the tips of their long toes, rather than flat-footed. Despite all these carnivorous adaptations, however, mesonychids were derived from hoofed mammals. The proof is in their toes, which had hooves rather than claws. By the Middle Eocene (approximately 50 to 47 million years ago), the mesonychids had declined rapidly in North America and Eurasia, where once they had dominated. The reasons for this decline are unclear. This period was a time of major climatic change, with global cooling and drying that destroyed the dense forests where mesonychids once had ruled. With the coming of open habitats, prey species became faster and more agile. Large, clumsy predators like mesonychids might have had difficulty finding cover to ambush their prey. In addition, some paleontologists speculate that mesonychids were less efficient at eating meat than creodonts or carnivores, since the blunt, rounded cusps of mesonychids molars never developed the specialized, scissor like shearing edges found in more specialized carnivorous mammals. For whatever reasons, in the late Middle Eocene the mesonychids were very rare. They disappeared from North America at the end of the Middle Eocene (approximately 37 million years ago) and from Asia in the Late Eocene (about 34 million years ago).

One branch may have survived to this day in the oceans: the whales. Molecular biologists link them generally to the even-toed ungulates like Hippos, but many paleontologists favor a descent from the Mesonychia. The most primitive whales from early Eocene coastal deposits in Asia show some striking similarities to mesonychids. It seems likely that is is a case of convergent evolution.

Andrewsarchus the last of the Asian mesonychids was a truly spectacular beast . Only one specimen of this animal is known, but it is a skull almost a meter long, more than twice the size of any bear that has ever lived. If the rest of the animal were also bear like, it would have been about four meters long, two meters high at the shoulder, and weighed almost four times as much as the largest known bear.

The mesonychid carnivore Andrewsarchus seeks shelter in the woods. It is a fierce animal up to 13 feet long and it is primarily a scavenger but it will attack larger animals.

Riff's Lost World Starlux Andrewsarchus. Custom diorama submitted by Riff Smith photo by Bob.

Brontotherium was 8 ft high at the shoulder and lived in North America. Recently Brontotherium fossils have been redated from the Oligocene to the Late Eocene. Like many Eocene browsers they were not able to adapt fast enough the spread of the grasslands at the end of the Eocene.

Brontotherium from Ral Partha metal figure line and Nabisco premiums.

Arsinoitherium lived in small groups and would have been in the water most of the time like modern Hippos. It couldn't straighten its legs, suggesting they were better for wading and swimming than for walking. The large pair of horns that male Arsinoitherium possessed were found to contain blood vessels which indicate that the horns could have been covered by skin, much like the small ossicones found on the head of the modern day giraffe.
Photo and custom figure from Fred Hinojosa.

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At the beginning of the Paleozoic giant birds like Diatryma are found in Europe, North America, Africa, South America and Australia. Only Asia which was cut off from Europe by an inland sea has no giant birds. The land bridge between North America and Asia was covered in ice. In Asia there are no giant birds and mammalian predators evolve. At the end of the period the climate changes creodonts are able spread to North America, Europe and Africa. The big birds are still found in South America and Australia but die out everywhere else. It is implied that the mammals replaced birds which weren't adaptable. In South America the phorasracids linger until the last ice ages when South America is connected to North America by a land bridge. Initially they do very well spreading north but die with the last of the mega fauna. Creodonts are replaced by modern carnivores. The large browsers and avian predators die out at the end of the Eocene. Many have no close living relatives. The end of the Mesozoic open up new niches for the placental to diversify into to. The most successful families of animals all die out and are not related to modern families. Being first may not be that important.