Denizens of Madrid’s Miocene woods: the red panda relatives
If we think of today’s red panda, our mind travels to the thick forests of the Eastern Himalayas ad South Western China, where this cute carnivore spends its days peacefully munching bamboo. But back in the Miocene, the fossil relatives of the red panda were not only much more widespread, ranging from North America to the Iberian peninsula, but they also were rather more diverse.
The living red panda, Ailurus fulgens, is the only surviving member of the family Ailuridae, and its dentition is quite specialized for the consumption of leaves, and especially those of the bamboo. Another specialization is the presence of a “false thumb” and enlarged bone in the wrist that it shares with the giant panda, and which both animals use as a help to handle bamboo shoots while feeding. But the earliest members of the family were generalist animals, with more primitive, all-purpose teeth, reflecting a more varied diet that included a lot of animal protein. Just like the living red panda, those early ailurids were smallish animals, not much larger than your average house cat. But during the Miocene, stem ailurids gave rise to a group of larger carnivores, actually rivalling a modern leopard in size: the Simocyonines.
One region of the world that has provided an unusually rich fossil record of the ailurids is, you guess it… Madrid! Here, in middle Miocene sediments in Madrid’s capital city, we have found remains of Magerictis imperialiensis, a small species still resembling the stem ailurids, and which combined the small body size of the red panda with a long, dog-like muzzle to house its primitive dentition.
But the most spectacular ailurid fossils from Madrid are those of the simocyonine Simocyon batalleri, from the Vallesian (late Miocene) site of Batallones-1.
With a shoulder height of 70 cm and a body weight of around 60 Kg, this animal was much larger than the red panda. Its dentition was well adapted for a varied diet of meat, carrion, invertebrates and even vegetable matter, and it would be a predator to reckon with if we could see it in the flesh. The problem is that it had to share the Batallones Miocene surroundings with a collection of truly fearsome competitors, from heavy bear-dogs to sabertooth cats.
In the face of such competition, discretion would be the best part of valour for Simocyon, and it would quickly climb up the nearest tree!. Its postcraneal skeleton reveals excellent arboreal abilities. In fact, it was probably one of the most refined climbers around, as revealed by the presence of a “false thumb”, an enlarged carpal bone that allowed Simocyon to grab thin branches with its forepaws and get a firm grip in the tree tops, probably beyond the reach of other carnivores such as the sabertooth cats. But the dexterous hands of Simocyon also would serve it to reach edible objects in the trees, including leaves, fruits and even bird’s eggs.
Here is a reconstruction of the skeleton of Simocyon batalleri (top), and a comparison between the bones in the palm of the hand of the giant panda (bottom left) and Simocyon (bottom right), with the radial sesamoid bone or “false thumb” marked in blue
The presence of the “false thumb” in this early relative of the red panda suggests that this feature of the ailurid hand did not originally evolve as an adaptation to feed on bamboo -in fact, the diet of Simocyon was much more like that of a dog than that of a panda!. All evidence suggests that the early ailurids developed a large radial sesamoid as an adaptation for proficient climbing, and only afterwards was this feature “recycled” by the later, more vegetarian red pandas, as an aid in handling bamboo. A nice example of evolution just “making do” with the available materials!