Creodonts were a category of carnivorous mammals that are now
extinct. The last of them died out in the Pliocene (7-2 million years
ago). Creodonts were not the ancestors of today's mammalian
carnivores. The Miacids were the prehistoric mammals from which dogs,
wolves, foxes, cats, hyenas, etc. are descended. Modern carnivores'
carnassial teeth (ones for shearing and cutting) are the upper fourth
molars. The carnassial teeth of Creodonts were the upper first molars.
Creodonts were wide ranging carnivores. Fossils of them have been
found in North America, Asia, Europe, and Africa.
Paleontologists have divided the Creodont family into these three
groups:
Hyaenodonts - Dog-like Creodonts
Oxyaenids - Cat-like Creodonts
Limnocyonids - These had long skulls and narrow snouts.

I shall now discuss some genera of these groups. First I will
mention Hyaenodon. The largest species of this genus was Hyaenodon
gigas. It was about 9 feet long and weighed around 230 kg. Hyaenodon
gigas was a ferocious predator that lived on the plains of Central
Asia (for example, in Mongolia). Paleontologists believe that it was
likely a nocturnal hunter (i.e. hunted mainly at night) and traveled
in packs. This animal was capable of killing the giant pigs, such as
Dinohyus and Entelodon. Hyaenodon gigas died out around 25 million
years ago, which in the early Miocene period. Megistotherium was a
large Hyaenodont with a skull about 3 feet long. Fossils of it have
been found in northern Africa, especially in Libya and Egypt.
Hyaenodon horridus lived during the Oligocene (38-26 million years
ago) and was a fast and formidable hunter. Fossils of it have been
found in the western part of the U.S.
Pterodon was a genus of Hyaenodonts. Fossils of it have been dug
up in Europe and Egypt. For example, Pterodon remains have been found
in the Fayyum deposits of Egypt.
With regard to the Oxyaenid family of Creodonts, most of them
were cat-like. However, there were some exceptions, such as
Sarkastodon. It was bear-like and was about 10 feet long. Sarkastodon
lived in Central Asia. Fossils of it have been found in Mongolia.
Lymnocyonids do not seem to have been as common as the other two
families of Ceodonts. One species was called Limnocyon verus. Another
was Limnonocyon potens. Fossils of Limnocyonids have been found in
Wyoming and several other western states of the U.S. In terms of
their bones, there is a strong humeral shaft. This indicates that
they were specialists in digging and preyed on burrowing animals.
The questions has been asked: Why did Creodonts die out?
Paleontologists have formulated these theories:

(1) Competition from Miacid carnivores

(2) Herbivorous animals (i.e. potential prey) becoming faster and
being able to more easily outrun the Creodonts. Creodonts were
apparently not all that quick.

Some paleontologists think that it may have been a combination of
these two factors. And it is possible that there were reasons that we
do not know about yet.

Neal Robbins