Osteopathology in Rhinocerotidae from 50 Million Years to the Present

Abstract

Individual elements of many extinct and extant North American rhinocerotids display osteopathologies, particularly exostoses, abnormal textures, and joint margin porosity, that are commonly associated with localized bone trauma. When we evaluated six extinct rhinocerotid species spanning 50 million years (Ma), we found the incidence of osteopathology increases from 28% of all elements of Eocene Hyrachyus eximius to 65–80% of all elements in more derived species. The only extant species in this study, Diceros bicornis, displayed less osteopathologies (50%) than the more derived extinct taxa. To get a finer-grained picture, we scored each fossil for seven pathological indicators on a scale of 1–4. We estimated the average mass of each taxon using M1-3 length and compared mass to average pathological score for each category. We found that with increasing mass, osteopathology also significantly increases. We then ran a phylogenetically-controlled regression analysis using a time-calibrated phylogeny of our study taxa. Mass estimates were found to significantly covary with abnormal foramen shape and abnormal bone textures. This pattern in osteopathological expression may reflect a part of the complex system of adaptations in the Rhinocerotidae over millions of years, where increased mass, cursoriality, and/or increased life span are selected for, to the detriment of long-term bone health. This work has important implications for the future health of hoofed animals and humans alike.

Peer Review #2 of "Foot pressure distribution in White Rhinoceroses (Ceratotherium simum) during walking (v0.2)"

“…Surprisingly, limb osteopathologies have remained common in rhinocerotid species across their evolution but increasing with estimated body mass. This is consistent with tradeoffs and compromises between large size, cursorial/mediportal morphology or athletic capacity, and limb health (Stilson et al, 2016).…”

“…While in captivity, they may develop foot disorders, in particular chronic foot diseases, osteoarthritis, bone remodelling, osteitis-osteomyelitis, pododermatitis, abscesses, and fractures (Galateanu et al, 2013;Jacobsen, 2002;Regnault et al, 2013;von Houwald and Flach, 1998) that compromise animal welfare or even cause mortality due to being painful, progressive and often untreatable. Even in wild rhinoceroses, there are reports of serious foot disease (Zainuddin et al, 1990), and a high incidence of osteopathology appears to be an ancestral evolutionary trait for the lineage, which may complicate efforts to improve the welfare of rhinoceroses (Stilson et al, 2016). To date, most focus on appendicular pathologies in extant rhinoceroses have been on the feet, but the latter study's finding that pathologies have been equally prevalent across the limbs throughout the ~50 million year history of Rhinocerotidae raises questions of whether more proximal limb pathologies remain common but overlooked in captive rhinoceroses.…”

“…Over millions of years of evolution, the feet of rhinoceroses have had to change with other alterations of limb morphology, locomotor behaviour, body size, habitat and more (e.g. Prothero, 2005;Stilson et al, 2016). Extant rhinoceroses include the second largest (after elephants) extant terrestrial mammals, with body masses in the White rhinoceros reaching up to 3600 kg (Groves, 1972;Hillman-Smith et al, 1986;Owen-Smith, 1992).…”

Skeletal pathology and variable anatomy in elephant feet assessed using computed tomography

“…But animal models show that enthesopathy can also occur without tendon microtears or inflammation and may be an adaptive response to loading (Benjamin, Rufai & Ralphs, 2000). Remodelling and enthesopathy are both frequently observed in rhinos and thought to reflect tissue loading (Regnault et al, 2013; Galateanu et al, 2013; Stilson, Hopkins & Davis, 2016). The linear appearance and the location of soft tissue mineralisation in our elephants suggest that the digital flexor tendons are the affected structures.…”

Peer Review #3 of "Interspecific variation in the limb long bones among modern rhinoceroses—extent and drivers (v0.1)"

“…Manuscript to be reviewed morphological and biomechanical criteria defining graviportality (Coombs, 1978;Langman et al, 1995). However, the peculiar morphology of hippos (barrel-like body and shortened limbs) linked to semi-aquatic habits (Mazza, 2014) has been considered alternately as mediportal (Coombs, 1978;Ross, 1984) or graviportal (Alexander & Pond, 1992;Carrano, 1999;MacFadden, 2005;Stilson, Hopkins & Davis, 2016). The graviportal condition in rhinoceroses is surely the least consensual: Gregory (1912) and Osborn (1929) considered rhinos as mediportal whereas later works assigned them a graviportal condition (Prothero and Sereno, 1982;Eisenmann and Guérin, 1984).…”