Osteological comparisons of appendicular skeletons: a case study on Patagonian huemul deer and its implications for conservation

Abstract

Early explorers described huemul (Hippocamelus bisulcus) as stocky, massive and short-legged deer of mountains, comparing them to ibex (Cabra ibex), chamois (Rupicapra rupicapra), mountain sheep (Ovis canadensis) and mountain goats (Oreamnos americanus). Subsequent key paleontological work also claimed that huemul are mountain deer. However, all these comparisons of huemul to other ungulates were done without any supporting data. These historic events lead to: (i) the continued prevailing claim that huemul are mountain deer; and (ii) that their natural range is the Andean mountains, as evidenced by the current distribution. We found that early writings about huemul generally reported their rareness, disappearance or near extinction. References to stocky and short-legged huemul were casual remarks made about deer found mainly in refuge areas. Paleontological comparisons were based on a new fossil labelled as mountain deer which, however, has been shown to be a construct and declared a ‘nomen nudum’. Behaviour like the aggressive horseshoe stance and thick long hair dissimulate stockiness by distorting body shape. Comparing leg morphometrics of huemul and 12 other ungulates revealed that huemul cannot be associated with rock climbing species. Intraspecific proportional leg length is not static and is influenced by ecogeography, nutrition, physiology and factors affecting exercise. Thus, climate, altitudinal hypoxia and locomotor pattern employed according to terrain, predation and forage affect the appendicular skeleton. Nutritional deficiencies occurring in Andean mountains are notorious for affecting bone development, causing osteopathology and altering body shape. Frequent underdeveloped huemul antlers and high incidence of osteopathology support the effect from mineral deficiencies. Skeletal proportions are affected by numerous factors, causing large intraspecific variation. Relative metapodial length varies up to 70% in better studied cervids, and populations from different environments can be clearly distinguished. Huemul morphology does not overlap with rock climbing species previously considered analogous, but falls within the range of other cervids. We caution against the rigid application of modern huemul occurrences in interpreting past habitat use. The few historic extra-Andean accounts cannot be considered abnormal outliers. Huemul ecology must be interpreted in terms of first principles rather than applying direct analogues from the present. This allows us to begin to use the past to understand the present instead of repeating the fallacy of imposing the present on the past. Current efforts to recover remaining huemul are distinctly based on the assumption that huemul foremost belong in rugged mountains, because of their supposed special adaptions and resemblance to stereotype ungulates, also erroneously believed to only occur in rugged mountains elsewhere. We conclude that the present empirical comparisons support many other lines of evidence that huemul existed in treeless habitat and colonised Andean forests and higher altitudes secondarily. Habitat breath of huemul is thus more like that found in other closely related Odocoilines, promising tremendous new opportunities for recovery efforts.