Abstract:
Giraffa sivalensis occurred during the Plio-Pleistocene period and probably represents
the terminal species of the genus in Southern Asia. The holotype is an almost
perfectly preserved cervical vertebra of disputed anatomical location. Although
there is also uncertainty regarding this animal’s size, other specimens that have been
assigned to this species include fragments of two humeri, a radius, metacarpi and
teeth. Here we estimate neck length, leg length and body mass using interspecific
and, unusually, ontogenetic allometry of extant giraffe skeletal parameters. The
appropriateness of each equation to estimate body mass was evaluated by calculating
the prediction error incurred in both extant giraffes (G. camelopardalis) and okapis
(Okapia johnstoni). It followed that the equations with the lowest prediction error
in both species were considered robust enough to use in G. sivalensis. The size of
G. sivalensis, based on the holotype, is proposed as 400 kg (range 228 kg–575 kg),
with a neck length of approximately 147 cm and a height of 390 cm. The molar
lengths of tooth specimens considered agree with this size estimate. The humerus was
the most appropriate long bone to establish body mass, which estimates a heavier
animal of ca 790 kg. The discrepancy with the vertebral body weight estimate might
indicate sexual dimorphism. Radial and metacarpal specimens estimate G. sivalensis
to be as heavy as extant giraffes. This may indicate that the radius and metacarpus are
unsuitable for body mass predictions in Giraffa spp. Alternatively, certain long bones
may have belonged to another long legged giraffid that occurred during the same
period and locality as G. sivalensis. We have concluded that if sexual dimorphism
was present then males would have been about twice the size of females. If sexual
dimorphism was not present and all bones were correctly attributed to this species,
then G. sivalensis had a slender neck with a relatively stocky body.
