Chrysochloris sp. (Mammalia: Chrysochloridae), or the Cape golden mole, is an enigmatic insectivorous mammal from sub-Saharan Africa. Chrysochloridae is comprised of at least 18 species spanning 7 genera (Nowak, 1991), but may include as many as 21 species (Bronner and Perrin, 2001). The fossil record of the group extends to the late Eocene (around 40 million years ago) and the fossils are very similar in morphology to Recent species.
Golden moles are traditionally members of Insectivora, a group of placental mammals including true moles, shrews, and hedgehogs, and golden moles resemble the European mole (Talpa) superficially in overall skeletal structure. Although golden moles classically are considered insectivorans, their peculiarities have been known for a long time and Chrysochloridae may not belong within Insectivora (see Broom, 1916). The systematic affinities of golden moles, as well as a number of other placental mammals, were turned on their head by the results of recent molecular studies which separate chrysochlorids from most other insectivorans and group Chrysochloridae with Tenrecidae (tenrecs, which are often included in Insectivora as well), Tubulidentata (aardvarks), Macroscelidea (elephant shrews), Hyracoidea (hyraxes), Proboscidea (elephants), and Sirenia (sea cows) in a clade referred to as Afrotheria (e.g., Springer et al, 1997; Stanhope et al. 1998).
Chrysochlorids are excellent burrowers, a behavior that is reflected in their cranial and postcranial skeletons. The cranial bones of chrysochlorids fuse early in life, and the skull is wedge-shaped to move loose soil as the animal burrows.
The eyes of chrysochlorids are vestigial and skinned over, and the optic nerve is degenerate. Chrysochlorids lack pinnae (ear flaps), and the external ear opening is covered by dense fur.
The forelimbs are not rotated outward, as is the case with Talpa, but rather situated in a position similar to most other mammals with the palms of the front appendages facing ventrally. The fifth digit is lost on the manus, and the second and third digits possess enlarged claws used to loosen sediment. The enlarged olecranon process on the ulna of Chrysochloris provides an attachment surface for robust muscles used while digging. A leathery pad at the tip of the golden mole snout, coupled with muscular shoulders, is used to pack loose sediment into the walls of the burrow. Desert dwelling golden moles will move through sandy substrate in dorso-ventral undulations, much like the swimming movements of marine mammals (see Wake, 1993).
Because the eyes of chrysochlorids are reduced, golden moles depend on their sense of hearing. In several chrysochlorid species, including those in the genus Chrysochloris, the malleus is greatly enlarged to aid in the detection of subterranean vibrations (Cooper, 1928; von Mayer et al., 1995; Mason, 2003).
Golden moles burrow both deep and shallow, and they often use burrows built by rodents. Some species will cohabitate with rodents in the same burrow system (Bronner and Perrin, 2001). Chrysochlorids forage as they burrow, and their diet consists mostly of invertebrates, although a few species are known to eat legless lizards and other small vertebrates (Nowak, 1991).
Chrysochlorids have high thermal conductance but a rather low metabolic rate. They have low body temperatures in the thermal neutral zone relative to other similarly sized mammals, and all species enter into torpor during cold periods. Golden moles do not thermoregulate while resting, a behavior which greatly reduces the amount of energy expended (Bronner and Perrin, 2001).
About the Species
This specimen was collected from the forest near New Beni, East Congo on 24 October 1926 by the Chapin, Sage and Mathews expedition. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Mr. Ted Macrini of the Department of Geological Sciences, The University of Texas at Austin. Funding for scanning was provided by a National Science Foundation Dissertation Improvement Grant (DEB-0309369) to Mr. Macrini. Funding for image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.
About this Specimen
The whole specimen was scanned by Matthew Colbert on 22 October 2003 along the coronal axis for a total of 976 slices. Each slice is 0.0997 mm thick, with an interslice spacing of 0.0997 mm and a field of reconstruction of 47.5 mm. The right forelimb was rendered using slices 228-438 from the full body scan.
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Broom, R. 1916. On the structure of the skull in Chrysochloris. Proceedings of the Zoological Society of London 32:449-459.
Cooper, C.F. 1928. On the ear region of certain of the Chrysochloridae.
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(Chrysochloridae). Journal of Zoology 260:405-413.
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Chrysochloris stuhlmanni on the Animal Diversity Web (University of Michigan Museum of Zoology)
Chrysochloris visagiei on animalinfo.org
Chrysochloris asiatica on ecotravel.co.za