At least in the case of mammal groups above the species level, the relationships are faily well understood by this point, thanks to the advance in molecular and genetic studies over the last couple of decades. Disputes are more likely to arise when we question how broadly we should define a particular group, and what taxonomic level it might have. (The latter, of course, are entirely artificial; the cat family is provably a 'real' thing, but the fact that we call it a 'family' rather than giving it some other rank is essentially arbitrary).
This becomes a much bigger issue when we look at animals we know only from fossils. For one thing, we will have fewer, and generally less complete, specimens to examine. Furthermore, unless they are really recent, genetic analysis is out of the question. But, on top of all of that, when we travel back in time, lines become inherently blurred. There's always going to be the question of where exactly the 'not yet X' becomes 'X', even if we had perfect information about them. Which we don't.
Bovines are considered a subfamily within the larger cattle family, which also includes antelopes, sheep, and goats. I've previously looked at the various living bovine species in a series on this blog, and there, I noted that there are three main branches within the subfamily. The two most important of these today are the bovins (cattle, bison, buffalo, yak, etc.) and the tragelaphins (spiral-horned antelopes), with the first of those being characterised, among other features, by a particular heavy build.
It is now generally agreed that the bovins evolved around the end of the Miocene from animals currently placed in the third 'tribe' of living bovines: the boselaphins. These are represented today by just two species, the nilgai and the four-horned antelope but, obviously, neither of these are the actual ancestor of cows and bison. Indeed, the use of the term 'boselaphin' to describe these putative ancestors is really just one of convenience. It's almost certain that that isn't literally what they were, just that they happened to look similar, and we haven't got a better word for them.
Either way, we can ask the question of when the whatever-they-were turned into bovins as we understand them. And any answer to that question is going to be messy. In the case of Europe, for example, there has been considerable debate as to when bovins first reached the continent, driven largely by the relevant fossils being too rare and incomplete for it to be apparent whether they actually are early bovins, or late survivors of their ancestors.
At least, until recently.
Camps del Ninots is a fossil site in northeastern Spain, just south of Girona. It was formed by a volcanic eruption that occurred when rising lava hit a layer of deep groundwater. The resulting explosion of steam and molten rock blasted a hole in the ground 1 km (1,000 yards) across that was partially filled with water to form a lake. Sediment built up at the bottom of the lake with just the right anoxic environment to preserve animals that ended up there as unusually complete and well-preserved fossils - a lagerstatte.
The latest dating places the rock strata that now lie where the lake once was as having been laid down during the early Pliocene, about 4.4. million years ago. We have been excavating the site for over 20 years now, uncovering all sorts of vertebrate fossils, including fish and frogs as well as land animals. Among the large land mammals, three species stand out: a rhinoceros, a tapir, and, of more relevance to today's post, a bovine.
The fossils in question were assigned to the relatively obscure genus Alephis. This is otherwise known mainly from southern France, northern Italy, and elsewhere in Spain, with possible fragmentary remains from Greece and Slovakia and even some from southern England. Historically, both this and its close relative Parabos, lie at the heart of the question of where the line between bovins and early 'boselaphins' should be drawn.
About a month ago, a study was published examining the fossils of at least 14 individuals, some of them remarkably complete and well-articulated. As always, we can never say that this is the last word on the matter, not least because answers to these sorts of questions will always come down, at least in part, to personal interpretation. But we can certainly say that it tells us something.
Perhaps the first finding of significance is that the researchers believe that the species in question doesn't belong to Alephis at all, but to Parabos. This was first defined in 1929, to include two known fossil species that had previously been placed with blackbucks, in what is now the gazelle subfamily. With at least five species already known, Parabos lived in much the same geographical area as Alephis, with fossils known from southern Spain across Europe to as far east as Moldova and Turkey.
The fossils reveal a heavily built, antelope-like animal with slightly curved horns facing backwards on its head, giving it an appearance similar to that of the living anoa, or dwarf buffalo, of Sulawesi. However, it was quite a lot larger than those are, with an estimated average body mass of 420 kg (925 lbs), similar to, say, a female red deer or elk. This would, in fact, have made it the largest known European "antelope" of its day, and perhaps of the entire Pliocene. The average weight, however, conceals a degree of variation, suggesting that males may have been larger than females, although not to the extent seen in living species of bovin today.
Features of the horns, along with other aspects of the skeleton, indicate that the animal did not fit neatly within either the modern bovins or the early European 'boselaphins' such as Tragoportax. In fact, it had some unique features in common with both, suggesting an intermediate form. The authors of the study prefer the idea that it is closer to the bovins, partly because of its relatively large size, and partly because female Tragoportax were hornless, which none of these animals are. Still, they concede that it could also be a case of parallel evolution among the last gasp of a separate lineage. It's likely, here, among the fuzzy lines between groups (one of which is long extinct), that future debates will end up being focused.
The climate in Spain at the time the animal lived was warm temperate to subtropical and relatively humid. The lake within which the fossils were found is known to have been surrounded by broad-leaved woodland and small streams, with conifers on the higher slopes. This fits with the sort of habitat that the 'boselaphins' are thought to have favoured, rather than the more open, grassy plains preferred by the likes of living bison. However, here again, the teeth of this species of Parabos suggest a somewhat mixed diet, not as browse-based as its putative ancestors, but not yet as heavy on grass as bovins would later be.
The shape of the animal also fits with a forested environment, since it doesn't look to have been capable of fast running. For defence, it may have partly relied on its large size for the time, and the females having horns would doubtless have helped, too.
These are not the ancestors of today's European bovins, since undoubted 'true' bovins, such as Ugandax, already lived in Africa at the time, where they appear to have evolved partly in response to the expansion of local grasslands. But they could be the first example to enter the continent, some early offshoot coming across, likely via Asia, and thriving in a habitat just a little too damp and heavily wooded for their larger, more modern-looking kin. But, equally, they could be examples of local forest animals developing larger size and bovin-like features in an attempt to survive as the climate changed towards something that would, in the longer run, favour aurochs and European bison.
The answer as to which remains, as it so often does, fuzzy.
[Picture by Leonardo Sorbelli, available under CC-BY-4.0, cropped from the original.]
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