Structure of white rhinoceros (Ceratotherium simum) horn investigated by X-ray computed tomography and histology with implications for growth and external form

Abstract

The nasal and frontal horns of two individuals of Ceratotherium simum were examined by x-ray computed tomography (CT scanning), gross observation of sectioned horn, and light microscopy of histological sections of the horn tissue. CT scans of both sets of horns reveal a periodic banding pattern that is evident upon gross observation of sections as darker bands of tissue. The overlap of these bands in both histological and CT slices suggests the presence of both a photoabsorbent component (melanin) and a radiodense component (calcium phosphate salts, most likely hydroxyapatite or octocalcium phosphate). The distribution of these two components in the horns is hypothesized to contribute to the differential wear patterns that produce the characteristic sweeping conical shape of rhinoceros horn from what otherwise (in the absence of wear and UV exposure) would be cylindrical blocks of constantly growing cornified papillary epidermis. Although extant rhinocerotids are unique in possessing a massive entirely keratinous horn that approximates the functions of keratin-and-bone horns such as those of bovid artiodactyls, the tissue structures that make up the horn are strikingly convergent with other examples of papillary cornified epidermis found in horses, artiodactyls, cetaceans, and birds.

A Comparative Study of Some Morphological and Microscopic Identifying Features of Genuine Rhino (Rhinoceros unicornis) Horns and Fake Horns

“…Similarly, the density of fake horn ranged from 0.42 to 2.24 g/cm 3 with the average value of 1.21 g/cm 3 ± 0.34. Most of the rhino horn samples (89%) had a density between 0.5 to 1.0 g/cm 3 . But the majority of the fake horns (58%) had a density between 1.0-1.5 g/cm 3 .…”

“…The density of rhino horn ranged from 0.465 to 6.047 g/cm 3 with the average value of 0.794 g/cm 3 ± 0.22. Similarly, the density of fake horn ranged from 0.42 to 2.24 g/cm 3 with the average value of 1.21 g/cm 3 ± 0.34.…”

“…The observed morphological parameters in genuine rhino horns were color, surface texture, basal elevation, frontal groove, light penetration capability at the basal margin, straight height (cm), outside curve length (cm), basal circumference (cm), mass (g) and density (g/ cm 3 ). Likewise, the studied parameters in fake horns were mass (g), straight height (cm) and basal circumference (cm).…”

“…Most of the rhino horn samples (89%) had a density between 0.5 to 1.0 g/cm 3 . But the majority of the fake horns (58%) had a density between 1.0-1.5 g/cm 3 . The proportional density of rhino horn and fake horn depicted in the Figure 7 indicate that there is a cluster of rhino horn density with higher frequency compared to disperse density of fake horn.…”

“…Rhino horn lacks a bony core and is anchored to the dermis covering the frontal and nasal bones [2]. The chief non-keratinous components of the rhino horn are calcium and melanin which make the horn more resistant to physical wear and breakdown [2,3]. Rhino horn seemed to be world's most valuable substance and thus its illicit trade has been steadily increasing with different purposes of ritual, medicinal and recreational activities.…”