Pelvic limb and tail musculature of the red kangaroo ( Macropus rufus )

Most members of the marsupial mammalian family Macropodidae move around in their environments using a bipedal form of hopping and are instantly recognizable by their elongated lower limbs and long, robust, nonprehensile tails. Paleontologists rely on anatomical descriptions of living species to make inferences about locomotor evolution and how anatomical specializations in kangaroos vary with body size. Even though the locomotor anatomy of the smaller eastern grey kangaroo ( Macropus giganteus ) is well documented, a review of the literature demonstrates a near absence of documentation of the musculoskeletal anatomy of the red kangaroo ( Macropus rufus ), the largest living marsupial. To fill this gap in knowledge, this work describes the musculoskeletal anatomy of the pelvic limb and tail of the red kangaroo and documents anatomical differences from the eastern grey kangaroo and other large terrestrial marsupials. We performed two complete pelvic limb and tail dissections on two lightly embalmed red kangaroos: one male adult obtained from Grant's Farm nature park (St. Louis, MO), and one juvenile male obtained from Louisiana State University School of Veterinary Medicine. Anatomical features and attachments of all muscles were recorded and photographed during the dissection; skeletal remains were macerated and cleaned after dissection by a dermestid beetle colony. Our studies of the pelvic and tail musculature of red kangaroos demonstrated differences between eastern grey and red kangaroos in attachments for two specific muscles of the proximal pelvic limb: The attachments of the ischiofemoralis in the red kangaroo differ in that this muscle's proximal and distal attachments form broad aponeuroses, as opposed to narrower tendinous attachments in the eastern kangaroo. The small lateral rotators of the hip (obturator internus, obturator externus, piriformis, and the two gemellus muscles) in the red kangaroo are more distinct from one another, and the distal attachment of the piriformis is distal to the greater trochanter of the femur instead of medial to it, as described in the literature for the eastern grey kangaroo. Additionally, prominent muscle bellies for three muscles originating in the distal pelvic limb and attaching to the pes are nonexistent or inconsistent with the literature: the extensor digiti II and III longus, peroneus digiti IV, and peroneus digiti V are not found in either red kangaroo specimen, even though they've been described for the eastern red kangaroo. Ultimately, more specimens are necessary to verify these differences and address inconsistencies in the literature before we can make any inferences about how these differences may subtly affect locomotion in these closely related taxa. Support or Funding Information This research was supported by Indiana University School of Medicine. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .