Your Daily Fossil

Pachycrocuta - The Giant Hyena 

Mounted specimen from the Zhoukoudian Museum, Beijing. 

Reconstruction by Mauricio Antón

When: Pliocene to Pleistocene (~ 5 million to .5 million years ago)

Where: Europe, Asia, and Africa

What:Pachycrocutais a prehistoric member of the Hyaenidae. Today hyenas are restricted to Africa and western Asia, but their fossil record has revealed they were once much more wide spread. Pachycrocuta has been found in Africa and Asia, but most specimens have been found in Europe, with many localities in the Iberian Peninsula. The largest species was Pachycrocuta brevirostris, which stood over 3 and a half feet (~100 cm) at the shoulder and is estimated to have weighed over 400 lbs (190 kg). This makes it about the size of a modern lioness! Cave deposits in both Spain and China have revealed multiple almost complete skeletons, suggesting that these animals lived in packs and utilized these caves as their dens. 

As Pachycrocuta is even more heavyset and adapted for bone crunching than the living bone-crunching hyenas, it has been suggested that this fossil form was even more dependent on scavenging kills than living species. But there really is not much evidence to pack this up other than thought-experiments. As it appears that some large cat species were displaced when Pachycrocuta moved into their ranges, it is more likely it was a direct hunter that would take advantage of pre-killed remains when it could drive away other predators. Like 99% of carnivores today. The predator/scavenger divide is really not a fast or hard line at all. Even more evidence of hunting comes from the remains of interactions between Pachycrocuta and Homo errectus. These two species overlapped and bones of our poor relative have been found in Pachycrocuta dens in China! 

Hesperocyon - The First Dog

When: Eocene to Oligocene (~39 - 33 Million years ago)

Where: North America

What: Hesperocyon is the oldest known and one of the most primitive members of the canids. It was a relatively small form, at 2ft 8 inches (~80cm) long on average, with slender limbs.  This ‘first dog’ is not the ancestor of all living canids, as it falls into a group of dogs that is now totally extinct; the Hesperocyoninae.  However, this small lithe form is thought to strongly resemble the true common ancestor of all canids. It was capable of climbing trees, but was more at home on the ground, and was showing more adaptations for the ability to run quickly on the ground than its non crown carnivoran ancestors. The ability to run fast for long distances is called cursoriality, and this is the primary locomotion type of most living canids. 

The world that Hesperocyon lived in was a changing world. The lush sub-tropical forests of western North America that characterized the early Eocene period were quickly disappearing, as the world became cooler and drier. The fossil record shows many groups of mammals becoming more adapted to open spaces, losing their arboreal adaptations as the trees disappeared and the great plains of the Oligocene spread.  Groups that did not adapt to this new more open world vanished, such as most North American primates, like Notharctus,and a group of very arboreally adapted stem carnivoramorphans, exemplified by Vulpavus. The canid-line adapted very well to this new open world, with three distinct subgroups quickly popping up; the group that today’s fossil belongs to, the Hesperocyoninae, the Borophaginae (see Epicyon), and the Canidae; the group all modern species of dogs fall into. 

Reconstruction by Mauricio Antón

Vulpavus

Mounted specimen at the American Museum of Natural History, NYC

When: Early to Middle Eocene (50-46 million years ago)

Where: Best fossils from Western North America, some European material referred, but its very fragmentary.

What: Vulpavus is a basal relative of the order Carnivora. Living species in this order include dogs, cats, bears, seals, hyenas, civets, mongooses, and meerkats, to name but a few members of this diverse clade. As these animals are all in the same taxonomic group, they have a common ancestor. Vulpavus falls on the lineage before this common ancestor, thus it is equally closely related to all living carnivorans.  There are a slew of fossil taxa that fall outside of Carnivora, but are more closely related to this order than any other group, ranging from the early Paleocene to the late Eocene. Vulpavus is one of the most well studied, as complete skeletons have been known since the early 1900s.

Functional studies of Vulpavus show this animal was well adapted for an arboreal life style, climbing though the sub-tropical forests of ancient Wyoming. Previously it was thought this was the ancestral condition of Carnivora, and that later fossils that are less arboreal adapted reflected a ‘decent from the trees’ leading to  Carnivora. Current studies have shown instead that Vulpavus represents an early offshoot from this lineage, which became extremely well suited for life in the trees. Not only could it climb well, but its teeth were less blade-like than its relatives, as most fossils related to Carnivora were well adapted for eating meat. This meant that Vulpavus would have eaten much more plant material than its ancestors, which had a meat based diet much like most living carnivorans. The forests of Wyoming vanished in the mid-Eocene as the area became cooler and drier, and with this loss Vulpavus also became extinct.

I like to refer to this animal and its relatives outside Carnivora as kitty-dogs, as they are a mix of features from both dog-line and cat-line modern carnivorans.

Epicyon haydeni - the largest dog 

When: Mid to Late Miocene (~20 to 5 million years ago) 

Where: Throughout much of  North America, excepting northern Canada. 

What: Epicyon haydeni is the largest canid known. It is estimated to have weighed in at roughly 375 lbs (~170 kg).  Even though it was the size of a bear, it still retained the relatively long legs and resulting fast speed that characterizes dogs. These dogs were not just ‘scaled up’ wolves, they were much more solidly built in general and had teeth more adapted for bone crunching. While they were top predators, and perhaps hunted in packs, they were no doubt also scavengers - able to crush bone in order to eat what had been left behind by other hunters. 

Epicyon is a genus in the clade Borophaginae. This is one of the three major subclades of the dog family. The last common ancestor of the borophagines and the modern canines lived over 30 million years ago. While this subclade is characterized by large bone crushing dogs, it also contained dogs which more more resemble living forms such as the wolf. In the reconstruction image the large dog is Epicyon haydeni and the smaller is another member of the same genus.   On the whole, borophagines were more omnivorous than their canine relatives.