Phylogenetics and Systematics

The systematic classification of the Giant Panda Ailuropoda melanoleuca has been the subject of much debate. In the past, scientists have alternately placed the panda in the raccoon family PROCYONIDAE (Cockrum, 1962; Raven, 1936), in the bear family URSIDAE (Davis, 1964, Wozencraft, 1989a; Wozencraft 1989b), or even in it’s own family AILURIPODIDAE (Hunt, 1974; Corbet and Hill, 1986). It appears that the traditional use of gross anatomical features in determining systematic relationships has resulted in conflicting hypothesis about the panda’s origin (Schaller, 1985). This is due in part to the adaptive physiological differences between pandas and both raccoons and bears.

The Giant Panda is bearlike in appearance. It has a stocky, lumbering build with a large head and short tail. It’s limbs are plantigrade, each terminating in five toes with non-retractile claws. It has a typically ursid dentition (I3/3 C1/1 P4/4 M2/3 = 42), though highly modified for its specialized diet of bamboo (Schaller, 1985). Like raccoons and their relatives, the Giant Panda may have a reduction of the first lower premolar. Additionally, the panda and procyonids share such anatomical features as inflated auditory bullae and a shortened rostrum (Cockrum, 1962). However, unlike both procyonids and ursids, the panda features a sixth digit, known as the pseudothumb. With this, the panda is better able to grasp and manipulate bamboo. Furthermore, the panda has a distinctly catlike feature, the rhinarium, or nose pad (Davis 1973).

Modern phylogenetics frequently incorporates molecular data as well as morphological characters when attempting to sort out the relationship among taxa. In one study, Sarich (1976) demonstrated that the albumin and transferrin blood proteins of the panda are more genetically similar to those of the ursids than of the procyonids. Another study based on an analysis of blood serum even suggested a procyonid ancestor for bears (Seal et al. 1970). While such a result may add an interesting dimension to the classification debate, it should be noted that such an ursid-procyonid relationship is not supported by the fossil record (Schaller, 1985). In fact, it is speculated that the panda may have a North American ancestor in Indarctos species, which lived in the Miocene with procyonid ancestors Bassariscus, Edaphocyon and Procyon (Martin, 1989).

The most recent attempts to clarify the relationship among pandas, bears and raccoons use mitochondrial DNA sequence evolution to identify the phylogeny of these groups. Zhang and Ryder (1993) used cytochrome b and RNA genes to determine that the Giant Panda is indeed most closely related to other bear species. Additionally, their study indicates that the kinkajou lineage, a branch of the procyonids, has evolved faster than any of the arctoid lineages. It is interesting to note that this study indicates that the Giant Panda represents the first outgroup to all arctoids, and this result is corroborated in further studies (Zhang and Ryder, 1994).

In summary, it is clear that various approaches to determining the phylogeny of the Giant Panda have produced a variety of results. The majority of fossil, anatomical and molecular evidence suggests that pandas are members of the bear family, with raccoons and their relatives as the arctoid next-of-kin.

Bibliography:

Cockrum, E. (1962) Introduction to Mammalogy. Ronald Press, New York.

Corbet, G. and J. Hill. (1980) A World List of mammalian Species. Cornell University Press, Ithaca.

Davis, D. (1973). Pandas. Curtis Books, New York

Hunt, R. (1974) The Auditory Bullae in Carnivora: An Anatomical Basis for Reappraisal of Carnivore Evolution. J. Morphol. 143:21-76.

Martin, L. (1989) Fossil History of Terrestrial Carnivora. In Carnivore Behavior, Ecology and Evolution (Vol 1). J.L. Gittleman, editor. Cornell University Press, Ithaca.

Raven, H. (1936) Notes on the Anatomy of the Viscera of the Giant Panda (Ailuropoda melanoleuca). Am. Mus. Nov. 877:1-23.

Sarich, V. (1976) Transferrin. In “Chi-Chi”, the Giant Panda Ailuropoda melanoleuca at the London Zoo 1958-1972: A Scientific Study. Trans. Zool. Soc. London 33:77-171.

Schaller, G. (1985). The Giant Pandas of Wolong. University of Chicago Press, Chicago.

Seal, U., N. Phillips and A. Erickson. (1970) Carnivora Systematics: Immunological Relationships of Bear Serum Albumins. Comp. Biochem. Physiol. 31:799-811.

Wozencraft, W. (1989a) The Phylogeny of the Recent Carnivora. In Carnivore Behavior, Ecology and Evolution (Vol. 1). J. L. Gittleman, editor. Cornell University Press, Ithaca.

Wozencraft, W. (1989b) Classification of the Recent Carnivora. In Carnivore Behavior, Ecology and Evolution (Vol. 1). J.L. Gittleman, editor. Cornell University Press, Ithaca.

Zhang, Y. and O. Ryder. (1993) Mitochondrial DNA sequence evolution in the Arctoidea. Proc. Natl. Acad. Sci. USA 90:9557-9561.

Zhang, Y. and O. Ryder. (1994) Phylogenic relationships of bears (the URSIDAE) inferred from mitochondrial DNA sequences. Molec. Phylo. Evol. 3:351-359.