Chewing, dental morphology and wear in tapirs (Tapirus spp.) and a comparison of free-ranging and captive specimens

Abstract

Feeding practice in herbivorous mammals can impact their dental wear, due to excessive or irregular abrasion. Previous studies indicated that browsing species display more wear when kept in zoos compared to natural habitats. Comparable analyses in tapirs do not exist, as their dental anatomy and chewing kinematics are assumed to prevent the use of macroscopic wear proxies such as mesowear. We aimed at describing tapir chewing, dental anatomy and wear, to develop a system allowing comparison of free-ranging and captive specimens even in the absence of known age. Video analyses suggest that in contrast to other perissodactyls, tapirs have an orthal (and no lateral) chewing movement. Analysing cheek teeth from 74 museum specimens, we quantified dental anatomy, determined the sequence of dental wear along the tooth row, and established several morphometric measures of wear. In doing so, we showcase that tapir maxillary teeth distinctively change their morphology during wear, developing a height differential between less worn buccal and more worn lingual cusps, and that quantitative wear corresponds to the eruption sequence. We demonstrate that mesowear scoring shows a stable signal during initial wear stages but results in a rather high mesowear score compared to other browsing herbivores. Zoo specimens had lesser or equal mesowear scores as specimens from the wild; additionally, for the same level of third molar wear, premolars and other molars of zoo specimens showed similar or less wear compared specimens from the wild. While this might be due to the traditional use of non-roughage diet items in zoo tapirs, these results indicate that in contrast to the situation in other browsers, excessive tooth wear appears to be no relevant concern in ex situ tapir management.

Dental wear proxy correlation in a long-term feeding experiment on sheep ( Ovis aries )

“…The exact cause and the duration of the process leading to the mesowear signal are still under debate [24]. A major assumption of the mesowear method is that its signal is not affected by individual age in a relevant way, at least within a certain range of ages [25] or macroscopic wear stages [5,26]. However, it also assumes that differences in mesowear can reflect changes between diets occurring over unknown periods of time.…”

“…8-13, 2]. Alternatively, in a less quantitative way, an individual's tooth wear stage-and thus its age-can be estimated by comparing its occlusal surface to a logical sequence of wear stages collected for the same species, often represented schematically [3][4][5][6]. Mesowear is a proxy recording tooth morphology on the macroscopic level, using the cusp's shape and occlusal relief as a proxy for wear [7,8].…”

“…Regardless of whether macroscopic descriptions of wear are performed in descriptive or quantitative terms, the concept of change over time may be implicit because the tooth's native state is typically present in the mind of the investigator as either unworn tooth height measurements or occlusal surface descriptions (e.g. [5]). With regard to microwear and DMTA, the native, unworn tooth is the implicit default state; nevertheless, the unworn surface does not need to be completely smooth, it can be morphologically structured due to its composition (enamel crystallite orientation, Hunter-Schreger bands, dentine tubuli, protein matrices) [19,20].…”

Avoiding the lockdown: Morphological facilitation of transversal chewing movements in mammals

“…The possibly most evident impairment of a transversal jaw movement is by interlocking canines (and neighboring incisors) that overlap the opposite jaw and thus prevent transverse (latero-medial or propalinal) jaw deflection (Figure 2). This arrangement is, for example, observed in peccaries and tapirs, which therefore have a primarily orthal chewing movement (Harris, 1975;Herring, 1972;Hohl et al, 2020;Kiltie, 1981). Kiltie (1981) considered this constraint an actual advantage for peccaries that prevented a dislocation of the jaw when biting on extremely hard seeds and nuts.…”