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| Chasmaporthetes |
Four living species isn't very many for a family of mammals but, like many other such small groups, there is a long fossil history that includes a great many extinct forms. These varied in form even more than the living species do. At one extreme are animals larger and stronger even than the living spotted hyena, while at the other (all living very early on) are small tree-climbing animals that looked more like civets.
Somewhere in between are the "running hyenas".
The best-known of these is Chasmaporthetes, which lived across Africa and much of the Northern Hemisphere from around 5 to 0.8 million years ago. We know from its remains that it had large fles-cutting teeth and limbs adapted for chasing down prey; it may not have had the speed of a cheetah, but it was likely a good deal stronger and may have hunted in a similar manner.
Two other genera are typically grouped with it, on the assumption that they had a similar lifestyle. However, we have far fewer remains for either of them, especially when it comes to the limb bones. Their teeth and jaws were at least similar to those of Chasmaporthetes, hence the assumed similar lifestyle, but it's hard to prove. Of the two, Lycaena is the earlier, but Hyaenictis is perhaps the least known.
Hyaenictis was first described by French palaeontologist Albert Gaudry in 1861, from a fossil unearthed at Pikermi, just outside Athens. It was almost a hundred years before remains attributable to the genus were discovered anywhere else, and most such sites have only been identified in the last 20 years.
We currently know of at least three species, which may have differed from one another as much as say, lions do from tigers or coyotes from wolves. H. graeca is the original named by Gaudry, and known only from Greece, where it lived around 7 million years ago, towards the end of the Miocene. The other two definitive species include a 9-million-year-old form from Spain, and a 5-million-year-old one from South Africa and Kenya. Fossils that are harder to place and that may or may not belong to the known species have been found at other sites, mostly in Kenya, although there is also a possible example from Ethiopia.
With so few limb and body bones, the question of Hyaenictis's running ability remains unresolved. However, there have been considerable advances in our knowledge and in statistical and measurement techniques over the decades since many of the existing fossils were last described. Last year, researchers published a detailed re-examination of most of the known fossils, along with six newly discovered ones from Greece, aiming to see if there was anything new this could tell us about the creature they once belonged to.
Because all we have are partial skulls and jawbones, a large part of the resulting paper consists of a detailed discussion of the precise shape of the teeth. Much is made, for example, of the absence of a metaconid on the m1, and there's a line about the imbrication of the dp3... the sort of thing that mammal palaeontologists spend a lot of time talking about, but that would require a large chunk of this post to explain, and that's unlikely to make an interesting read if I did.
The upshot of a lot of this, however, is that Hyaenictis shows an intermediate development between the tooth form of the older Lycaena and the later Chasmaporthetes. This doesn't prove that each directly evolved into the other in a chain since there may, of course, be other forms we don't know about, but it does show a general evolutionary trend within the group towards a more specialised animal. Presumably, this would also be reflected in aspects of their lifestyle, since Lycaena's own ancestors were probably more like jackals than the fast-running pursuit predators that survived into the Ice Ages.
However, one of the reasons that the study of tooth shapes is so key to mammalian palaeontology is that they can tell us a lot about what the animal in question ate. In the case of hyenas, a key adaptation is the presence of teeth towards the back of the jaw that are large enough and strong enough to crack bone. The relevant teeth are modified in Hyaenictis, being considerably more robust than those in, say, lions, but not quite as much as in the living hyenas. For example, they don't have quite as wide a base - making them better for piercing than crushing - and the microscopic structure of their enamel indicates that it wasn't as strong and resilient as we might expect.
The authors conclude that Hyaenictis could crush bones, cracking them open to get at the marrow as a living hyena would. But, equally, this can't have been as common and effective a habit as it is in the modern animals, and Hyaenictis therefore probably ate a higher proportion of soft meat, wasting less time on getting at hard-to-reach nutrition.
Another source of evidence comes from looking at the sites where the fossils were discovered. From other studies, for example, we know that, at the time Hyaenictis lived there, the area around Athens was a warm savannah landscape, dominated by grass but with patches of trees. The sites at which the Spanish species were found were more heavily wooded, consisting of subtropical forest. The pattern is repeated at the sites in Africa, with woodland of various kinds predominating wherever Hyaenictis was found.
That's interesting, because, if it really was a fast-chasing animal, we'd expect a more open environment. Cheetahs don't live in jungles, but out on the plains where whatever they are chasing has limited opportunities for escape, and the predator doesn't have to keep swerving to avoid trees or heavy undergrowth. The only limb bones we do have for Hyaenictis come from a juvenile in South Africa; they look to be more suited for speed than strength, but that may just be because it was young and slender, saying little about the adult form.
On the other hand, the authors point out that wolves are pursuit predators, and they often live in woodland. Perhaps Hyaenictis may not have been as pure a chasing animal as cheetahs, or as we have good reason to suppose the later Chasmaporthetes was, but that doesn't mean that it wasn't at least developing in that direction.
They also raise the point that Hyaenictis is relatively rare, with far fewer fossils (especially adults) from the sites where it is known than for the larger, more muscular, hyena Adcrocuta. This raises a possibility that has previously been considered for sabretooth cats: where more than one form of a generally similar predators live in the same area, they will inevitably compete. Living spotted hyenas will chase off leopards and cheetahs from their kills given half a chance, and lions will do the same to them, so Adcrocuta might have competed with Hyaenictis.
If that's right, the smaller running hyenas might have been forced into the woodlands because the larger ones drove them away from where they would prefer to be. It's hard to know whether this was true, and it depends in part on where Adcrocuta itself wanted to hunt, but it's a distinct possibility. At a time when many kinds of hyena lived in the same area, they couldn't all have been winners.
[Photo by Jonathon Chen, from Wikimedia Commons.]
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