Tetrapod Zoology

In the previous article we looked at the discovery of the Red panda Ailurus fulgens, and also at some aspects of its biology and distribution. There's so much I didn't cover: Red panda physiology is bizarrely interesting, for example. In this article we're going to look at the Red panda's fossil relatives. As I implied in the last article, the Red panda's friends and relations once roamed far and wide. And remember that the term 'panda' belongs to the Red panda and its kin, not to the giant pandas (which are bears, and not close kin of pandas proper). The Red panda and its close relatives belong to a group that we'll be calling the ailurines, and they belong within a more inclusive group which we'll be calling the ailurids...

The first fossil panda to be reported came from... England. In 1888, William Boyd Dawkins described Ailurus anglicus from the Pliocene Red Crag of Suffolk. The Red Crag has a pretty neat fossil mammal fauna: it's also yielded the European puma Puma pardoides, which you'll recall from the European jaguars and pumas article. The jaw fragment described by Dawkins (1888) was about a third bigger in its dimensions than the corresponding part of the A. fulgens jaw, so he described A. anglicus as a 'larger and more powerful animal' than the living species. In 1899, Max Schlosser described a fossil panda skull from Romania, and decided that it was different enough from A. fulgens to deserve its own genus, and the name Parailurus was born. A. anglicus was also referred to this genus. European fossils belonging to Parailurus were later reported from Slovakia and Germany too.

American pandas

In 1977, Parailurus was reported from North America: Tedford & Gustafson (1977) reported a Parailurus tooth from the Pliocene Ringold Formation of Washington. Sasagawa et al. (2003) later reported Parailurus from the Pliocene Ushigakubi Formation of Japan and Sotnikova (2008) has just described a new species (P. baikalicus) from the Pliocene of Transbaikalia (Russia). Members of this genus seem to have had a wide Holarctic distribution, inhabiting western North America, Asia and Europe at least. Cladistic analysis suggests that Parailurus and Ailurus are sister-taxa (Wallace & Wang 2004), though the possibility that an Asian species of Parailurus gave rise to Ailurus has been suggested at times [adjacent image shows ailurine phylogeny from Wallace & Wang (2004)].

We now know that a second, more primitive ailurine lineage also inhabited North America, thanks to the recent description by Wallace & Wang (2004) of Pristinailurus bristoli from the Upper Miocene/lower Pliocene Gray Fossil Site in Tennessee [life restoration of this species, by Steven Wallace, is shown at the very top]. Wallace & Wang (2004) suggested that this species be known as Bristol's Appalachian panda (the 'Bristol's' refers to Larry Bristol, the finder of the holotype). Originally described from teeth, breaking news for 2008 is that the Gray Fossil site has recently yielded a complete Pristinailurus skull [shown in image below] as well as a reasonable amount of postcranial material. This hasn't yet been published, but you can read about it (and see many images) here. Phylogenetic analysis of tooth characters indicates that Pristinailurus is outside of the ailurine clade that includes Ailurus and Parailurus (Wallace & Wang 2004).

There's no evidence for bamboo at the Gray Fossil Site, raising the question of what Pristinailurus ate. Wallace & Wang (2004) noted that river cane Arundinaria - a member of the bamboo family - is present in Tennessee today, and they suggested that it or a close relative may have been more widespread when Pristinailurus was alive. They also note however that this panda would have had to have gone without bamboo during part of its evolution (during the migration from Eurasia into North America, for example... assuming that that is what it did).

Another fossil ailurine is known from Europe: Magerictis imperialensis, from the Lower Miocene of Spain. It's only known from a single molar unfortunately: this shows that it had a specialized dentition like that of Ailurus and probably had a similar lifestyle. If so, it shows that herbivorous ailurines (and, by inference, their sister-taxon... on which, read on) had evolved not longer after the appearance of the very earliest ailurids in the Late Oligocene.

The simocyonines

So that's the ailurines. Recent discoveries have shown that a long-controversial group of fossil carnivorans, the simocyonines, are also close relatives of Ailurus and should be regarded as part of the same little group, Ailuridae. Originally described in the 1850s and classified alongside a motley assortment of animals now regarded as ursids, canids and mustelids, simocyonines were later identified as part of Canidae, Mustelidae, or Procyonidae, or as relatives of the bear-dogs, or amphicyonids (see Wang 1997 for a review). A list of cranial characters shared with Ailurus allowed Wang (1997) to demonstrate their ailurid identity however. Among these characters are a very strongly arched zygomatic arch, a long external auditory meatus, an erect or anteriorly inclined coronoid process, a particularly big second upper molar, and grooves on the lateral sides of the canines (argh! More mammals with grooved canines!). We currently know of three simocyonine genera (Alopecocyon from Europe, Actiocyon from North America and Simocyon from Europe, Asia and North America), most of which are Middle or Upper Miocene [Chinese Simocyon skull shown in adjacent image].

Unlike ailurines, simocyonines have highly reduced anterior premolars, posterior molars specialized for crushing, and carnassials clearly suited for shearing. These features indicate that, in contrast to ailurines, simocyonines were hypercarnivores and not omnivores or herbivores (Wang 1997, Peigné et al. 2005). Amphictis from the Late Oligocene and Early Miocene of Eurasia, identified by some as an ailurid more basal than both simocyonines and ailurines, also seems to have been hypercarnivorous, so this was always certainly the primitive state for ailurids.

The big crushing posterior premolars of simocyonines have led some authors to suggest that these animals were ecologically equivalent to the bone-crushing borophagine canids (though note that only a few borophagines were like this and, as usual, the group included more diversity than what we're typically exposed to) (e.g. Baskin 1998). Given that simocyonines were clearly good climbers however (read on), they can't have been that much like borophagines. It's possible that they grabbed carcasses or bits of carcasses and then carried them off into trees, but it's also possible that, rather than being crushers of big bones, they used those big posterior premolars to mash up mid-sized prey, bones and all (Peigné et al. 2005).

Long lumbar vertebrae with pointed neural spines and elongate transverse processes show that simocyonines had powerful back muscles which would have provided them with a bounding gait similar to that seen in living mustelids. Puma-sized Simocyon - the best known simocyonine - was surprisingly large for this sort of gait, however, and it's likely that it was built this way because it was a climber rather than a runner. Indeed this is supported by the rest of its skeleton: its shoulders recall those of climbing procyonids like kinkajous (and those of bears, which can also climb), and its forelimbs were flexible and capable of rotation (in cursorial carnivorans, the forelimbs tend to be capable of very little rotation). A new piece of evidence provides further evidence for climbing abilities in simocyonines [adjacent life restoration of Simocyon by Mauricio Antón].

The panda's thumb all over again

Like giant pandas, ailurines possess a 'false thumb': a structure that projects from the wrist (it's actually a radial sesamoid) and is used in gripping the plant stems that the panda then feeds from. The sesamoid was recently described as a rod-like bone lacking a bony articulation with any of the other bones of the hand (Endo et al. 2001), and it has usually been imagined as a specialization for herbivory convergent with that of giant pandas. New data on A. fulgens, however, has demonstrated that the sesamoid is subrectangular (rather than rod-like) with a cartilaginous cap (Antón et al. 2006), and it definitely does have a bony contact with other bones (specifically with the scapholunar).

Furthermore, the discovery of a false thumb in a simocyonine has indicated that this structure did not evolve for use in herbivory given that simocyonines weren't herbivores that wanted to hold on to bamboo stems (so far as we know): Salesa et al. (2006b, 2008) therefore argued that the false thumb evolved early on in carnivorous ailurids as an aid for an arboreal lifestyle, allowing these climbing animals to better grasp small branches, and was later exapted in Ailurus and its close relatives for use in manipulating plant stems. Some simocyonines (like the Spanish species Simocyon battaleri) lived alongside large cats like Paramachairodus and might only have escaped from such animals by retreating to thin branches where the cat was unable to follow (Salesa et al. 2006b, 2008). It has also been suggested that S. battaleri might have eaten from carcasses cached in trees by Paramachairodus [adjacent image shows hand skeletons of Giant panda (on left) compared with that of S. battaleri. 'rs' = radial sesamoid].

Incidentally, we all know that Giant pandas Ailuropoda have 'false thumbs'. But, like Ailurus among the ailurids, we now know that Ailuropoda isn't unique among the ursids in this respect, as the Spectacled bear Tremarctos ornatus also has a very similar large radial sesamoid. Given this phylogenetic distribution it was recently suggested that enlarged radial sesamoids were primitive for ursids but that, while giant pandas and spectacled bears retained them, other ursids reduced them (Salesa et al. 2006a). This discovery (which has been mostly overlooked) is a big deal as it shows that the false thumb of the Giant panda is - like that of the Red panda - apparently inherited from less specialised ancestors, and did not originally evolve for an unusual bamboo-eating lifestyle.

An enduring question about ailurines and simocyonines has been how they're related to other carnivorans, and several different views have been promoted based on different lines of morphological and genetic evidence. I've now written way too much and need to wrap up quickly here, so all I will say is that genetic work on the living Red panda indicates that it and its relative are not procyonids (the group that includes raccoons and coatis), they instead seem to be the most basal branch of the carnivoran clade that includes bears, mustelids and procyonids (Flynn et al. 2000), or the most basal branch of Musteloidea, the clade that includes mustelids and procyonids (Flynn et al. 2005) [adjacent skull reconstruction and life restoration of Simocyon by Mauricio Antón, and from Peigné et al. 2005]

For previous Tet Zoo articles on members of the bear-mustelid-procyonid carnivoran clade (Ursida or Arctoidea or whatever), see the Erongo carcass article, the one on islands of otters and strange foxes, and part II of the Velvet Claw homage. Ailurines and simocyonines have both been in the news in recent years, and quite a few people have written about them. The Voltage Gate covered pandas several times, Carl Zimmer wrote about Simocyon back in 2005, and Nimravid recently wrote about simocyonines here. Roberts & Gittleman (1984) - the classic and most useful reference on the living Red panda - is available for free here, Flynn et al.'s 'Whence the Red panda' can be obtained free here, and Peigné et al.'s 2005 paper on Simocyon can be downloaded for free here.

Refs - -

Antón, M., Salesa, M. J., Pastor, J. F., Peigné, S. & Morales, J. 2006. Implications of the functional anatomy of the hand and forearm of Ailurus fulgens (Carnivora, Ailuridae) for the evolution of the 'false-thumb' in pandas. Journal of Anatomy 209, 757-764.

Baskin, J. A. 1998. Procyonidae. In Janis, C. M., Scott, K. M. & Jacobs, L. L. (eds) Evolution of Tertiary Mammals of North America. Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Cambridge University Press, pp. 144-151.

Dawkins, W. B. 1888. On Ailurus anglicus, a new carnivore from the Red Crag. Quarterly Journal of the Geological Society, London 44, 228-231.

Endo, H., Sasaki, M., Kogiku, H., Yamamoto, M. & Arishma, K. 2001. Radial sesamoid bone as part of the manipulation system in the lesser panda (Ailurus fulgens). Annals of Anatomy 198, 181-184.

Flynn, J.J., Nedball, M. A., Dragoo, J. W. & Honeycutt, R. L. 2000. Whence the red panda? Molecular Phylogenetics and Evolution 17, 190-199.

- ., Finarelli, J. A., Zehr, S., Hsu, J. & Nedbal, M. A. 2005. Molecular phylogeny of the Carnivora (Mammalia): assessing the impact of increased sampling on resolving enigmatic relationships. Systematic Biology 54, 317-337.

Peigné, S., Salesa, M. J., Antón, M. & Morales, J. 2005. Ailurid carnivoran mammal Simocyon from the late Miocene of Spain and the systematics of the genus. Acta Palaeontologica Polonica 50, 219-238.

Salesa, M. J., Siliceo, G., Antón, M., Abella, J., Montoya, P. & Morales, J. 2006a. Anatomy of the "false thumb" of Tremarctos ornatus (Carnivora, Ursidae, Tremarctinae): phylogenetic and functional implications. Estudios Geologicos 62, 389-394.

- ., Antón, M., Peigné, S. & Morales, J. 2006b. Evidence of a false thumb in a fossil carnivore clarifies the evolution of pandas. Proceedings of the National Academy of Sciences 103, 379-382.

- ., Antón, M., Peigné, S. & Morales, J. 2008. Functional anatomy and biomechanics of the postcranial skeleton of Simocyon batalleri (Viret, 1929) (Carnivora, Ailuridae) from the Late Miocene of Spain. Zoological Journal of the Linnean Society 152, 593-621.

Sasagawa, I., Takahashi, K., Sakumoto, T., Nagamori, H., Yabe, H. & Kobayashi, I. 2003. Discovery of the extinct red panda Parailurus (Mammalia, Carnivora) in Japan. Journal of Vertebrate Paleontology 23, 895-900.

Sotnikova, M. V. 2008. A new species of lesser panda Parailurus (Mammalia, Carnivora) from the Pliocene of Transbaikalia (Russia) and some aspects of ailurine phylogeny. Paleontological Journal 42, 90-99.

Tedford, R. H. & Gustafson, E. P. 1977. First North American record of the extinct panda Parailurus. Nature 265, 621-623.

- . & Harington, C. R. 2003. An Arctic mammal fauna from the Early Pliocene of North America. Nature 425, 388-390.

Wang, X. 1997. New cranial material of Simocyon from China, and its implications for phylogenetic relationship to the red panda (Ailurus). Journal of Vertebrate Paleontology 17, 184-198.