Astragalar Morphology of Selected Giraffidae

Abstract

The artiodactyl astragalus has been modified to exhibit two trochleae, creating a double pullied structure allowing for significant dorso-plantar motion, and limited mediolateral motion. The astragalus structure is partly influenced by environmental substrates, and correspondingly, morphometric studies can yield paleohabitat information. The present study establishes terminology and describes detailed morphological features on giraffid astragali. Each giraffid astragalus exhibits a unique combination of anatomical characteristics. The giraffid astragalar morphologies reinforce previously established phylogenetic relationships. We find that the enlargement of the navicular head is a feature shared by all giraffids, and that the primitive giraffids possess exceptionally tall astragalar heads in relation to the total astragalar height. The sivatheres and the okapi share a reduced notch on the lateral edge of the astragalus. We find that Samotherium is more primitive in astragalar morphologies than Palaeotragus, which is reinforced by tooth characteristics and ossicone position. Diagnostic anatomical characters on the astragalus allow for giraffid species identifications and a better understanding of Giraffidae.

The earliest ossicone and post-cranial record of Giraffa

“…However, in our study we are not addressing paleoecological implications of the single astragalus. Anatomical features of the giraffid astragalus do allow for the diagnosis and identification of species based on unique combinations of characteristics [ 19 ]. The Giraffa sp.…”

“…The Giraffa sp. specimen is different from the modern giraffe, Sivatherium , Helladotherium , Honanotherium , and Bohlinia , in which the astragalus is boxy and wide [ 19 ]. We believe this wider-than-long shape relates to the large body size of these giraffids, and that a relatively wider astragalus can better accommodate substantial body weight.…”

“…See Solounias and Danowitz (2016) for a complete astragalar description and measurements of Giraffa camelopardalis and other giraffids [ 19 ].…”

Fossil Giraffidae (Mammalia, Artiodactyla) from the late Miocene of Thermopigi (Macedonia, Greece)

“…Nevertheless, there are distinct morphological differences on the limb bones of both taxa. Detailed descriptions of characters of post-cranial elements of both H. duvernoyi and S. major, were given by Kostopoulos (2009), Ríos et al (2016), and Solounias and Danowitz (2016b).…”

Is the Astragalar Index a Valid Character for the Study of Giraffid Phylogeny?

“…The Giraffidae is a relict family with only two extant genera: Giraffa [1] and Okapia [2] in the past was more abundant and diversified, with more than 40 taxa spanning the past 20 million years (since the beginning of the early Miocene) [3][4][5][6]. Nevertheless, until recently only a few studies approached the description of their phylogenetic relationships [4,5], due to the lack of appropriate materials to build a solid character matrix and the scarcity of complete fossil giraffid skulls as well as the high intra-and interspecific variability of most of giraffid teeth [7,4] the postcranial skeleton has probed key to giraffid identification [6,[8][9][10].…”