Dead ossicones, and other characters describing Palaeotraginae (Giraffidae; Mammalia) based on new material from Gansu, Central China

While the identity and validity of the extant families of ruminants are undoubted, there are significant problems with the determination of the interrelationships among the families, notably within the families of the Pecora, or horned ruminants. The morphological features used to construct ruminant phylogeny have been a source of controversy: many features used over the past century have been shown to be highly homoplastic and related to functional similarities. Ruminants evolved in the context of the later Cenozoic climatic changes, and many lineages adopted functional morphological adaptations related to feeding on more abrasive diets (resulting in the parallel evolution of a greater extent of loph development in the molars and, in some lineages, hypsodonty) and locomotion in open habitats (resulting in the parallel evolution of fused metapodials and reduction and/or loss of lateral digits). The fact that the molecular phylogeny shows a very different pattern from the currently accepted morphological one is of particular cause for concern, especially as molecular data are of no use for understanding the relationships of extinct lineages. Here we review the morphological data used in ruminant phylogenetics, and show even many of the less obviously functional features (e.g., number and position of the lacrimal orifices) are subject to homoplasy and variation, especially when fossil taxa are included. In addition, many morphological features treated as independent traits in phylogenetics are correlated (e.g., cranial morphology associated with hypsodonty). Some potentially reliable features are identified, but these do not help to sort out relationships within the Pecora. We advocate for the investigation into better morphological features, possibly derived from basicranial and ear region characters (although these features are not without their own issues of homoplasy), and for caution in character consideration in performing phylogenetic analyses

The earliest ossicone and post-cranial record of Giraffa

The oldest Giraffa material presently known consists of dental specimens. The oldest post-cranial Giraffa material belongs to the Plio-Pleistocene taxon Giraffa sivalensis, where the holotype is a third cervical vertebra. We describe three non-dental specimens from the Early Late Miocene of the Potwar Plateau, including an 8.1 million year old ossicone, 9.4 million year old astragalus, and 8.9 million year old metatarsal and refer them to Giraffa. The described ossicone exhibits remarkable similarities with the ossicones of a juvenile modern giraffe, including the distribution of secondary bone growth, posterior curvature, and concave pitted undersurface where the ossicone would attach to the skull. The astragalus has a notably flat grove of the trochlea, medial twisting between the trochlea and the head, and a square-shaped sustentacular facet, all of which characterize the astragalus of Giraffa camelopardalis. The newly described astragalus is narrow and rectangular, unlike the boxy shaped bone of the modern giraffe. The metatarsal is large in size and has a shallow central trough created by thin medial and lateral ridges, a feature unique to Giraffa and Sivatherium. Our described material introduce the earliest non-dental material of Giraffa, a genus whose extinct representation is otherwise dominated by teeth, and demonstrate that the genus has been morphologically consistent over 9 million years

Hypsodont Crowns as Additional Roots: A New Explanation for Hypsodonty

The hypsodont crown of Equus and of other hypsodont ungulates has two functions: It has an extra crown in the alveolus which erupts and becomes a functional crown that enables the horse to live longer and feed on abrasive foods and grit. The second functional aspect is that the crown, while it is in the alveolus, acts as a root to support high stress during mastication. In general, roots do not increase in size during evolution when the tooth crown increases. Delayed development of the true root is a heterochrony phenomenon and is possibly dynamically interactive with the forces applied on the crown. Thus, when the crown becomes worn, as in old age, the mastication forces acting on it are very strong. This is an interesting phenomenon and reinforces our hypothesis of the second functional difference that the young tooth's crown embedded in the alveolus acts as a supporting root. The Equus hypsodont tooth has been represented by a class I lever. That is, the fulcrum is in the middle: the effort is applied on one side of the fulcrum and the resistance (or load) on the other side, for example, as in a crowbar. As an individual Equus ages, the alveolar tooth height decreases. Data display an exponential increase in force generated as tooth height decreases. The elongation and closure of the root is delayed until the crown is almost entirely worn. When the crown becomes worn, the mastication forces acting on it are very strong. This is an interesting phenomenon and reinforces our hypothesis that the young tooth's crown, embedded in the alveolus, acts as a supporting root. This discovery is based on the observation that fossil ungulates most commonly die at an early age, leaving a substantial amount of crown unused. The unused crown is not likely a reserve tooth crown for a season of hardship because it is rare to find examples of such hardships in the fossil record

Astragalar Morphology of Selected Giraffidae.

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 Cervical Osteology of Okapia johnstoni and Giraffa camelopardalis.

Giraffidae is the only family of ruminants that is represented by two extant species; Okapia johnstoni and Giraffa camelopardalis. Of these taxa, O. johnstoni represents a typical short-necked ungulate, and G. camelopardalis exemplifies the most extreme cervical elongation seen in any ruminant. We utilize these two species to provide a comprehensive anatomic description of the cervical vertebrae. In addition, we compare the serial morphologic characteristics of the okapi and giraffe cervical vertebrae, and report on several osteologic differences seen between the two taxa. The giraffe neck appears to exhibit homogenization of C3-C7; the position of the dorsal tubercle, thickness of the cranial articular process, shape of the ventral vertebral body, and orientation of the ventral tubercle are constant throughout these vertebrae, whereas these features are serially variable in the okapi. We also report on several specializations of the giraffe C7, which we believe relates to an atypical cervico-thoracic junction, corresponding to the substantial neck lengthening. The morphologic differences exhibited between the okapi and giraffe cervical vertebrae have implications on the function of the necks relating to both fighting and feeding

First identification of Decennatherium Crusafont, 1952 (Mammalia, Ruminantia, Pecora) in the Siwaliks of Pakistan

Previously undescribed remains of a new large giraffid have been identified from the late Miocene Siwaliks Hills of the Potwar Plateau in Pakistan. This taxon is very intimately related to the late Miocene giraffid genus Decennatherium, previously only certainly identified in the Iberian Peninsula, and with some possible remains assigned to Decennatherium crusafonti from Aliäbäd (Iran). The new material collected in the Siwaliks Hills shows a high morphological similarity with the Spanish remains of the genus, especially the early Vallesian Decennatherium pachecoi. Two previously undescribed ossicone fragments from the same area are also described and identified as cf. Decennatherium. These findings represent the easternmost occurrence of the genus Decennatherium and show a late Miocene migration of the genus throughout the Iberian Peninsula and Southern Asia.M.R. acknowledges an FPI predoctoral grant (Spanish Government MINECO) as well as the EEBB-FPI grant program 2013, 2014 and 2015

Complete articulated necks of the giraffe and the okapi.

<p>(A) Lateral view of C1-T2 of <i>Giraffa camelopardalis</i> (AMNH 82001). (B) Lateral view of C1-T2 of <i>Okapia johnstoni</i> (NMNH 399337). The black line demarcates the actual length of the <i>O</i>. <i>johnstoni</i> neck in relation to that of <i>G</i>. <i>camelopardalis</i>. The scale bar corresponds to 200 mm.</p

Anatomic Terminology of the giraffe and okapi vertebrae.

<p>(A) Labeled C3 vertebra of <i>Okapia johnstoni</i> (AMNH 51197). (B) Labeled C3 vertebra of <i>Giraffa camelopardalis</i> (AMNH 82001). The anterior arch is drawn in green; <i>O</i>. <i>johnstoni</i> has a continuous arch, and <i>G</i>. <i>camelopardalis</i> has an interrupted arch. The post-tubercular ridge of <i>O</i>. <i>johnstoni</i> is drawn in blue. 1- cranial bulge, 2- cranial articular process, 3- ventral tubercle, 4- cranial opening of the foramen transversarium, 5- caudal opening of the foramen transversarium, 6- spinous process, 7- transverse process, 8- intertubercular plate, 9- dorsal tubercle, 9’-accessory dorsal tubercle, 10- caudal articular facet, 11- post-tubercular ridge, 12- ventral ridge, 13- pars interarticularis, 14- caudal extremity, 15- lamina. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136552#pone.0136552.ref018" target="_blank">18</a>].</p

Coefficient of variation of C3-C6 for eleven measurements in <i>G</i>. <i>camelopardalis</i> and <i>O</i>. <i>johnstoni</i>.

<p>Coefficient of variation of C3-C6 for eleven measurements in <i>G</i>. <i>camelopardalis</i> and <i>O</i>. <i>johnstoni</i>.</p

Ventral views of okapi and giraffe vertebrae showing morphologic characters.

<p>(A) Ventral view of <i>Okapia johnstoni</i> C5 vertebra. (B) Ventral view of <i>Okapia johnstoni</i> C6 vertebra. (C) Ventral view of <i>Okapia johnstoni</i> C7 vertebra. (D) Ventral view of <i>Giraffa camelopardalis</i> C5 vertebra. (E) Ventral view of <i>Giraffa camelopardalis</i> C6 vertebra. (F) Ventral view of <i>Giraffa camelopardalis</i> C7 vertebra. The shape of the ventral vertebral body and intertubercular plate is shown in blue, and the ventral ridge, when present, is drawn in green.</p