Let's talk about something near and dear to my heart - carnivores. Specifically, mammalian carnivores. These guys are my main field of study, and I realized that I haven't talked about them here, and a new paper in the Journal of Vertebrate Paleontology has given me that opportunity.
First, a point of clarification. "Carnivore" is an ecological classification, that is, those animals (and a few plants) that eat meat. "Carnivoran" is a taxonomic classification, meaning members of the mammalian order Carnivora. The latter includes most of the things you probably think of mammalian 'carnivores' - lions, wolves, bears, badgers, weasels, etc. It also includes many things that are not carnivorous, i.e., non-carnivorous carnivorans, like raccoons, pandas, and that most recent addition to the carnivoran order, the olinguito. There are also many carnivorous mammals that are not are not carnivorans - grasshopper mice eat a lot of insects and meat, so do some primates, like tarsiers and even chimps.
Within the order Carnivora there are two main groups - the cat-like forms, or 'feliforms', and the dog-like ones, or 'caniforms'. All modern carnivorans can fit into one of these two groups. The feliform families include cats
(big and small), hyaenas
(which surprises many people, who tend to think they're closer to dogs), and a few groups of lesser known small carnivorans, which include civets
(who might or might not live in manors), and the endemic carnivorans of Madagascar
(including my favorite carnivore of all time, the fossa
). Caniform families include dogs, wolves, and foxes (canids
, the aquatic carnivores
(seal, sea lions, and walruses), the red panda
(in its own family), skunks
, raccoons and their relatives
(like the newly found olinguito
) and the mustelids
- a particularly diverse family that includes weasels, badgers, wolverines, martens, and otters.
Some of my favorite carnivorans - (top) Cryptoprocta ferox
the fossa (bottom) the olinguito (Bassaricyon neblina
They are a particularly diverse group today, which makes them a model for studying evolutionary diversification. Their dietary range includes animals that only eat meat, like big cats (called hypercarnivores), insectivorous forms (including many small carnivores), omnivorous ones who eat a range of food, like coyotes, and a number of very specialized taxa, like otters who eat shellfish and pandas who eat leaves. They get around in a wide range of ways too. There are generalized animals that move around on the ground, like raccoons; tree-living animals, including martens; runners like wolves or cheetahs; semi-aquatic groups like otters, and the fully aquatic pinnipeds (seals and their relatives). They have the widest range of sizes of any mammalian family, from the tiny least weasel that weighs just 10's of grams (just a few ounces) to the gigantic elephant seals, which can weigh 1000's of kilograms (up to 8500 lbs).
The smallest (the least weasel, Mustela nivalis
) and largest (elephant seal, Mirounga sp.
) species in the order Carnivora.
Carnivorans weren't always so diverse in the past. The earliest carnivorans were relatively small, under 10kg (~20lbs.), and probably had omnivorous to carnivorous diets. This is what makes modern small carnivorans interesting to me - they are probably a good model for the earliest forms. Unfortunately, many of these extant small taxa aren't particularly well-known. They are often cryptic, and being small, they don't generate the excitement of the largest carnivorans, like lions, and tigers and bears (oh my!). This is a shame to me, as most modern carnivorans are small, but the big ones get all the press.
These oldest carnivoran taxa date to the beginning of a time period called the Eocene, around 55 million years ago. A recent paper in the Journal of Vertebrate Paleontology
by Floréal Solé and his colleagues described specimens of one of the earliest carnivoran species. The specimens come from Dormaal in Belgium, a site already known for yielding fossils from this interesting time. Many of the fossils there are fragmentary, but the new specimens include over 250 dental specimens, as well as a few ankle bones.
The species, Dormaalocyon latouri
, described in a new article in JVP.
The new specimens are interesting for a number of reasons. The ankle bones suggest that the animal was arboreal, that is, it climbed around in trees. It had been previously suggested that a large forest ran from modern-day Europe to North America. At the time, the two continents were linked via a land-bridge that spanned the North Atlantic. This wouldn't have been the kind of forest we would expect there now, with conifer trees and cold winters. The climate at the time was much hotter, actually the hottest it's been since the disappearance of the dinosaurs 65 million years ago. The new finds are from a time right after an event known as the Paleocene-Eocene Thermal Maximum (PETM)
. In and around this time, large, subtropical forests ranged far into northern latitudes. There are fossils of primates far into Canada, even as far north as Ellesmere Island. In addition, this subtropical forest would have extended across the north Atlantic land-bridge, allowing these early carnivorans to find their way between the continents.
Another interesting aspect is that the fossils are very old, right near the beginning of the Eocene. No higher carnivorans are known from before this time, an era known as the Paleocene, but this find implies there must be some out there. The new fossils are primitive, but certainly not the most primitive. The question then becomes, where are these earlier representatives? The answer, as is often the case, is probably Asia. There are early representatives of the group in both Europe and North America, and some of these show intriguing connections to early carnivorans known from China. Much of the fossil wealth of China is only beginning to uncovered, and there's a lot of land there to uncover, so perhaps the search for the earliest carnivorans will turn there next.
A time scale of the Cenozoic.