Sunday 12 May 2024

Before Cats Could Purr

Although the differences are obvious when we can see the spots or stripes on their fur, the various species of cat are often very similar in form, and it can be hard to tell them apart based on the skeleton alone. For this reason, through much of the 20th century, all of the "purring cats" except the cheetah were placed in the single genus Felis. That's not the case today, when we distinguish genera not only for the larger purring cats, such as pumas and lynxes, but others that modern genetic evidence tells us are distinct, such as the group that includes the ocelot.

Given this, it's hardly surprising that the same should go for fossil species, too. It may well be that if we had genetic evidence on those, or could even just see their coat colour, we would be more willing to distinguish them but, when all you have is an often fragmentary skeleton, there isn't much to go on.

In the 19th century, however, things were different, with the trend at the time being to differentiate species based on relatively minor characters. Indeed, all of those additional genera into which we divide the 20th-century conception of Felis today were first named in the 19th (or, in the case of Lynx, 18th) century before being merged back again. Even so, because of the limitations of the fossil record, relatively few extinct genera of non-sabretooth cat were named prior to the fashion changing again in the late 1990s.

The oldest surviving such name is Pseudaelurus, first applied to a partial jawbone that had originally been described (as a species of Felis) by Henri de Blainville in 1843. The genus name, coined by Paul Gervais in 1850 translates as "false cat" and referred to a cougar-sized animal with features that indicated it was more primitive than those in any living genus. The original specimen was French, but it was later joined two other species (again, both originally placed in Felis), one from Austria, and one from North America.

So where does this "new" genus fit within the cat family? The cat family, in the current scheme, consists of three subfamilies. The "purring cats" are those that can, well, purr. It includes all of the small living species, as well as cheetahs, puma/cougar/mountain lions, servals, and the various kinds of lynx/bobcat. More technically, these are the feline cats, as distinct from the pantherine, or "roaring cats". This subfamily contains all of the other living big cats: lions, tigers, leopards, and jaguars. 

The remaining subfamily, the machairodontines, are the sabretooth cats, which are, of course, all extinct. These are by no means the ancestors of living cats, with the last ones, belonging to the famous Smilodon genus, dying out as recently as 12,000 BC at the end of the Last Ice Age. While physical differences in the skeleton also set them apart, some of the last sabretooths are also recent enough for us to extract DNA from their fossils, confirming that they formed a separate lineage that diverged from the other cats before the two living subfamilies diverged from one another - that is to say, a housecat is more closely related to a tiger than it is to a sabretooth, and the sabretooths left no living descendants.

With Pseudaelurus, we have no way analysing the DNA, because they are far too old, living only during the Miocene epoch between about 20 and 8 million years ago. This is long enough ago that they could potentially be the ancestors of one or more of the three subfamilies or perhaps be placed as the most primitive members of one of them. In the 1970s, researchers took a look at the canine teeth of Pseudaelurus, and concluded that, while they certainly weren't "sabres" they were significantly flattened compared with what we'd expect to see in non-sabretooth cats. More recent studies, using a wider range of features have confirmed this; Pseudaelurus is related to the sabretooths, potentially even including their ancestor.

But there is a problem here. That's because, as originally Pseudaelurus basically consists of those fossil cats that lack more modern features. Defining something on the basis of what it doesn't have, rather than what it does, is fraught with difficulty and, at least today, is frowned upon. The question naturally arises that, since there are multiple species of Pseudaelurus, can we be certain that they are all closely related, if we can't point to some specific feature that they all share (beyond being cats)?

In short, no.

In fact, it is now generally agreed that Pseudaelurus, as it was defined at the beginning of the last century, consists of a group of primitive cats that are not each others' closest relatives. More significantly, the various species recognised at the time don't all fit in the same part of the cat family tree. We now talk of these animals as being "Pseudaelurus-grade" meaning that they represent a snapshot in time before modern felid features had fully evolved, but are united by no more than that. In a sense, they are all the same height up the family tree, but they aren't all in the same branch. 

This requires us to dismantle the genus as it was conceived of a hundred years ago, creating new genera for those species whose branches we can identify. Although other species have been added since, it turns out that these map to the three species we knew about as of 1900.

Pseudaelurus-grade cats in blue

De Blainville's original French specimen from 1843 gets to keep the original name, since that was the one Gervais had used when he created the genus in the first place. This is now P. quadridentatus, and it so happens that this is the one whose analysis had revealed the link to the sabretooths. So it still gets to stay in that branch, alongside some newer specimens discovered elsewhere in Eurasia, with some as far afield as China.

The position of the North American specimens less clear. As early as 1929, Hungarian palaeontologist Miklós Kretzoi placed all of these in a new genus he named Hyperailurictis. Nobody, however, seems to have paid any attention to this until as recently as 2010, when the genus was resurrected. It, too, may be related to sabretooths but perhaps not as closely as Pseudaelurus, and it was probably the first cat to enter North America, at the end of the "Cat Gap" 18 million years ago.

This leaves the Austrian specimen and more recent examples that appear closely related to it. Kretzoi had also recognised the distinct nature of these in 1929, placing them in the genus Styriofelis, which was also resurrected in 2010. This does not have the flattened canine teeth of Pseudaelurus proper and every indication is that it belongs to the non-sabretooth lineage, although it probably lived before the roaring and purring cats separated from each other, and thus belongs to neither subfamily. 

We don't however, have the relevant bones from the throat to determine whether it could roar, purr, or neither - although the last of those would seem the most likely.

By the time that Styriofelis was restored as a genus, others had been named that also belong, more or less, to the Pseudaelurus-grade, including some from Africa, and we do know of some more recent forms that we can in either the purring or roaring cats with some confidence. Now we have another.

Coming from a roughly 16 million-year-old deposit on the edge of the Madrid urban area, Magerifelis peignei ("Peigné's Madrid cat") was identified from one half of a jawbone. That may not sound like much, but it had almost all of the teeth still attached, and if there is one thing that mammalian palaeontologists love when it comes to fossils, it's a good look at the teeth. 

These show several features that link the animal with the Pseudaelurus-grade, such as the fact that there is still a tiny second molar tooth, something living cats lack. Despite this, there are just enough advanced traits in the other teeth that the discoverers think it is more likely to be placed as a very early branch within the purring cats - the true felines. This seems to be a little shaky, not least given how much of the animal we have and how old it is in comparison with known felines, so it's also possible that it groups with Styriofelis. Either way, there is enough to tell us a little about how this early non-sabretooth may have lived.

Judging from the size of the teeth, and assuming typical feline body proportions, the authors used an established mathematical formula to estimate the body weight of the living animal as 7.6 kg (16 lbs 8 oz.), about the same as a female bobcat. However, the jaw is larger and heavier than we would expect for the size of the teeth, so the assumption about typical body proportions might not be correct in this case. Without the relevant parts, there's no way to be sure, but it could be that this was a comparatively powerful and muscular animal, larger than the formula would suggest - say, the size of a Eurasian lynx.

That strong jaw, however, also shows the point where the jaw muscles would have been attached in life, and these are also larger than we would expect, suggesting an animal with a powerful bite. If that's the case then, while the animal's main food would probably have been mice, squirrels, and birds, it should also have been able take down prey that the similarly-sized bobcat would baulk at. Possibilities known to have lived in the area include the small musk deer Micromeryx and other horned ruminants not closely related to living animals that would have been about the size of a large hare or jackrabbit. 

They would hardly have been the dominant predators of their day, since, among others, the leopard-sized false sabretooth Sansanosmilus lived in the area but a heavyset bobcat-sized animal stalking through the woodlands would still have been a significant part of the local ecology.

[Picture by Roger Witter, in the public domain. Cladogram adapted from Salesa et al. 2023 and Piras et al. 2013.]

No comments:

Post a Comment