The earliest ossicone and post-cranial record of Giraffa

Reproductive endocrinology, morphological traits, and sexual selection in a population of wild South African giraffes

Sex steroids are pervasive in mammals and evolutionarily conserved, but differences in the nuances of endocrine profiles characterize distinct species. Two sex steroids, testosterone and progesterone, feature prominently in the life history of mammalian taxa, but neither one has been analyzed from wild giraffes. Our study was designed to address this gap in knowledge by examining how these sex steroids are related to biological features and giraffe life history. We conducted the research at Rooipoort Nature Reserve a 44,000 ha private nature reserve in South Africa on a population of South African giraffes (Giraffa camelopardalis giraffa). Eleven adult giraffe cows and seven adult bulls were immobilized and various biological samples and morphological measurements were obtained. We analyzed both testosterone and progesterone using Ultra High Performance Liquid Chromotography - Tandem Mass Spectrometry (UHPLC-MS/MS). We found that non-pregnant females had lower progesterone concentrations than pregnant females and that those in the last trimester of pregnancy showed a slight drop in progesterone, as well as an increase in testosterone. Among males, chronological age was correlated with testicle size, testosterone concentrations, and ossicone volume. We propose that the progesterone decline functions partly to accelerate resumption of ovulation because giraffes become pregnant while lactating, and that the testosterone elevation provides an endocrine mileu for female defense of neonatal calves, given that lion predation is a major threat to calf survival. We suggest that male reproductive strategies are mediated by the age-related impacts of testosterone on growth in both body mass and ossicone volume as a consequence of sexual selection. We conclude by noting that the robust and solid ossicones of male giraffes function in mate competition as wedges that are used to topple opponents by raising their legs and placing them in an off-balanced position that can seriously injure them when falling to the ground.

Preliminary ontogeny of the giraffe neck

The giraffe juvenile has different proportions of head to neck from the adult. The head just about doubles in size from the juvenile to adult, whereas the neck increases almost 4.5× (roughly four times) in length. The T1 posterior dorsal vertebral width of the newborn is clearly wider than in the adult where it is narrow. In the okapi, the dorsal vertebral width is narrow in both juvenile and adult. The giraffe neck changes in ontogeny anisometrically. In the okapi the changes are more isometric. The giraffe juvenile vertebrae are shorter and do not have fused the cranial epiphyseal plates. That facilitates anterior elongation-growth. The ventral tubercles are undeveloped. The juvenile T1 is wide caudally unlike the adult. This may be a similarity to a gelocid (Gelocidae) ancestor of the giraffe.

Unexpected cranial sexual dimorphism in the tragulid Dorcatherium naui based on material from the middle to late Miocene localities of Eppelsheim and Hammerschmiede (Germany)

Tragulids, chevrotains or mouse deer, were common faunal elements during the Miocene. During that time, Dorcatherium was the most abundant genus, with D. naui being the first described species. Besides their abundance, until recently only very limited cranial material was available for investigation. Here we present a redescription of the first complete skull of D. naui from the middle to late Miocene locality of Eppelsheim, Germany, based on micro-computed tomography. Furthermore, we present a description and comparison of two additional, new skulls of D. naui from the late Miocene hominid locality Hammerschmiede, Germany. Within Dorcatherium, so far, only three other complete skulls are known, all belonging to D. crassum. A comparison between the three skulls of D. naui and the already known skulls of D. crassum shows that these two species differ in morphological features of the skull, such as laterally facing orbitae, separation of supraorbital foramen from supraorbital groove by a bony bridge, well-developed parietal plateau, prominent nuchal tubercle, less-developed nuchal crests, and the presence of an occipital crest. Moreover, two different osteological morphotypes are present in the skulls of D. naui that can be interpreted as a previously unknown sexual dimorphism. Very similar features are observed in D. crassum, which can be likewise related to the same dimorphism. However, males of D. naui differ from males of D. crassum by the presence of frontoparietal bulges, which were probably used for sexual display and during male-male combats in males of D. naui. For the first time, sexual dimorphism in Dorcatherium is described based on skull characteristics, which are, so far, unknown from any other fossil or extant tragulid.

Formation, structure, and function of extra-skeletal bones in mammals

This review describes the formation, structure, and function of bony compartments in antlers, horns, ossicones, osteoderm and the os penis/os clitoris (collectively referred to herein as AHOOO structures) in extant mammals. AHOOOs are extra-skeletal bones that originate from subcutaneous (dermal) tissues in a wide variety of mammals, and this review elaborates on the co-development of the bone and skin in these structures. During foetal stages, primordial cells for the bony compartments arise in subcutaneous tissues. The epithelial-mesenchymal transition is assumed to play a key role in the differentiation of bone, cartilage, skin and other tissues in AHOOO structures. AHOOO ossification takes place after skeletal bone formation, and may depend on sexual maturity. Skin keratinization occurs in tandem with ossification and may be under the control of androgens. Both endochondral and intramembranous ossification participate in bony compartment formation. There is variation in gradients of density in different AHOOO structures. These gradients, which vary according to function and species, primarily reduce mechanical stress. Anchorage of AHOOOs to their surrounding tissues fortifies these structures and is accomplished by bone-bone fusion and Sharpey fibres. The presence of the integument is essential for the protection and function of the bony compartments. Three major functions can be attributed to AHOOOs: mechanical, visual, and thermoregulatory. This review provides the first extensive comparative description of the skeletal and integumentary systems of AHOOOs in a variety of mammals.