Giraffa camelopardalis, KNM OM, 2269

Rios, M, Danowitz, M & Solounias, N, 2016, First comprehensive morphological analysis on the metapodials of Giraffidae, Palaeontologia Electronica 410 (10453), pp. 1-39 : 35-36

Giraffa camelopardalis limb proportions may represent the existence multiple species or subspecies, consistent with genetic studies ( Brown et al., 2007; Fennessy et al., 2016). This variability may also represent a higher degree of sexual dimorphism, where the wide range includes the smaller sized females mixed with the larger males in our dataset.

Giraffa camelopardalis exhibits extreme cervical elongation that exceeds that of most living and extinct ruminants, therefore providing substantial weight on the anterior portion of the body ( Danowitz and Solounias, 2015). The G. camelopardalis metapodials, however, are slender, and studies show that the humerus is the only appendicular bone that becomes more robust with regard to body mass and bone length ( van Sittert et al., 2015), suggesting a different functional adaptation to increasingly high loads in the giraffe. In fact, the decreased vertical angle of the giraffe metacarpus seems to act as a possible adaptation to the biomechanical demands imposed upon it by its slen- der shape ( van Schalkwyk, 2006).

There currently exist several cladistic analyses on Giraffidae , which are based on cranial and post cranial morphologies ( Hamilton, 1978; Geraads, 1986; Solounias, 2007). Using these previously established relationships, our metapodial morphologies in question do not clearly fit on the evolutionary framework. For example, the depth of the central trough, which is a feature that clearly separates the giraffids, does not correlate with the relationships between the described taxa. We find that the combination of limb morphologies is variable among species, and that closely related taxa do not share many limb features with one another. Recent research on the cervical anatomy and evolution of Giraffidae demonstrated that neck elongation and secondary shortening clearly fits on the backdrop of an evolutionary scheme; the primitive giraffids exhibit generally elongated vertebrae, the sivatheres possess features representing neck shortening, the palaeotragines display vertebrae with cranial elongation, and the two species of Giraffa exhibit vertebrae that are elongated cranially and caudally ( Danowitz et al., 2015b). In addition, morphological studies on the neck of Samotherium show that the cervical features are intermediate between those of the giraffe and the okapi, which reflects its phylogenic position between the two extant taxa ( Danowitz et al., 2015a). Skull features classically demonstrate phylogenetic patterns, as do neck morphologies; metapodials are apparently more complex and do not clearly fit the established relationships. The observed complexity of the metapodial anatomy may suggest that closely related species have specialized in locomotory factors independently of their origin within Giraffidae .

As there is no evidence for dwarfism in giraffids so far, length categories can be useful to identify and compare genera. In addition, the absolute length of the metapodials provides information about the neck elongation state, especially in the cases were the elongation is very high like in Bohlinia attica and Giraffa camelopardalis , as it would not be possible for a short-necked animal to drink with such long limbs when they reach their adult size ( Solounias, 2007; Danowitz et al., 2015b). We find that plotting the length versus proximal transverse diameter gives an idea of relative slenderness of the limbs, and provides better separation between individual giraffids. Sivatherium giganteum exhibits the stockiest limbs, and Bohlinia attica and Giraffa camelopardalis possess long and slender metapodials ( Figures 20 , 23 ). Interestingly, the dimensions of Samotherium major match closely to those seen in the majority of the sivatheres, including Helladotherium duvernoyi, Bramatherium megacephalum , and Birgerbohlinia schaubi . The absolute length, slenderness, RI, and morphological features together allow for better separation of giraffid genera and can facilitate future phylogenetic analyses.

Figures

FIGURE 20. Dispersion plot with the absolute metacarpal length of the Giraffidae analyzed. TABLE 3. Descriptive parameters of the metacarpal length of the Giraffidae (Max., maximum; Min., minimum; SD, standard deviation; Ntotal, total sample size).

FIGURE 23. Dispersion plot with the absolute metatarsal length of the Giraffidae analyzed.