The phylogeny of the red panda (Ailurus fulgens): evidence from the hindlimb

Abstract

The red panda (Ailurus fulgens) is an endangered carnivore living in the temperate forests of the Himalayas and southern China. The phylogeny of the red panda has been the subject of much debate. Morphological and molecular studies have supported a wide range of possible relationships, including close ties to procyonids, ursids, mustelids, and mephitids. This study provides additional morphological data, including muscle maps, for Ailurus. The hindlimbs of four cadavers from the National Zoological Park were dissected. Red pandas retain a number of muscles lost in other carnivore groups, including muscles and tendons related to their robust and weight-bearing hallux. Three features, including a single-bellied m. sartorius, a proximal insertion for m. abductor digiti V, and an absent m. articularis coxae, are found in all terrestrial arctoids, including Ailurus. In addition, red pandas are similar to ursids and canids in lacking a caudal belly of m. semitendinosus, while they resemble procyonids and mustelids in the degree of fusion observed between mm. gluteus medius and piriformis. Furthermore, Ailurus and procyonids are characterized by numerous subdivisions within the adductor compartment, while red pandas and raccoons share a variable m. semimembranosus, composed of one, two, or three bellies. Lastly, a deep plantar muscle inserting onto the metatarsophalangeal joint of the hallux is described for Ailurus. This muscle has not been previously described and is given the name m. flexor hallucis profundus. Additional dissections of the forelimb and axial musculature of red pandas may shed further light on the phylogeny of this species. In addition, the muscle maps presented here offer a valuable resource for interpreting the functional anatomy of fossil ailurids.

Fig. 1

Lateral view of the gluteal region and thigh in Ailurus.

Fig. 2

Pelvis muscle maps for Ailurus. (A) dorsal, (B) ventral, (C) lateral views.

Fig. 3

Femur muscle maps for Ailurus. (A) caudal, (B) cranial, (C) medial, (D) lateral views.

Fig. 4

Deep view of the gluteal region in Ailurus.

Fig. 5

Tibia and fibula muscle maps for Ailurus. (A) caudal, (B) cranial, (C) medial, (D) lateral views.

Fig. 6

Medial view of the thigh in Ailurus.

Fig. 7

Medial view of the leg and pes in Ailurus.

Fig. 8

Lateral view of the leg and pes in Ailurus.

Fig. 9

Pes muscle maps for Ailurus. (A) plantar, (B) dorsal views.

Fig. 10

Plantar views of the pes in Ailurus. (A) superficial, (B) intermediate, (C) intermediate with m. quadratus plantae removed, (D) deep views.

Fig. 11

Dorsal view of the pes in Ailurus.

Fig. 12

(A) M. flexor hallucis profundus in Ailurus. (B) Histological slide (10×) demonstrating the muscle tissue present in this structure.