As highlighted in the present study, however, this potential adaptive elongation of the neck occurred within the context of several evolutionary constraints. If such a microevolutionary scenario holds true, where a series of adaptive morphological changes occurred in response to climatic and vegetative variation during the Miocene, then individual cervical vertebral lengths and entire vertebral column lengths for fossil species in the Palaeotraginae should gradually adopt extant giraffe-like proportions.
The lengthening of the cervical region between P. In the present study we demonstrated that the giraffe neck length is unique, both quantitatively and qualitatively. Our analysis of the fossil record suggests that the evolution of the long neck in the Palaeotraginae occurred between roughly 14 and 12 Mya in the species linking P.
A punctuated event occurring over such a brief period of geological time could be essentially invisible in the fossil record. Given that we are most likely to be discussing an increase in total length of the cervical vertebrae of approximately mm between P. Recent observations on the development of the skeletal system may lend support to this line of reasoning.
The boundaries between the various vertebral regions are marked by the anterior expressional limits of specific Hox genes Krumlauf, It is possible to imagine a situation during the presomitic stage in giraffe development the embryo would have a crown-rump length of around 1 cm , where the cervical—thoracic border, delineated by the expression of specific Hox genes, becomes located in a position slightly more caudal in the overall presomitic mesoderm to that seen in other ungulates.
This may result from an underexpression of the specific cervical—thoracic border Hox gene markers, or may result from an alteration in the upstream regulators of Hox genes Krumlauf, , causing this presomitic border to move to a location that is more caudal in comparison with the antero-posterior location of the cervical—thoracic border in the presomitic mesoderm found in other ungulates.
Subsequent somitogenesis would more than likely occur through more or less normal processes, as evidenced by the existence of seven cervical vertebrae in the giraffe, the standard ungulate appearance of the remaining giraffe vertebrae, and the typical location of the fore- and hindlimbs in relation to the vertebral regions Krumlauf, Given that this proposed type of change would occur during embryonic development, at the presomitic stage, the actual dimensions of the potential caudal shift in the cervical—thoracic border may only be in the millimetre or less range.
If such a qualitative change in the pattern of gene expression were to occur, and lead to the genesis of a longer neck, it is then likely that this type of change would have passed rapidly through palaeotragine populations between 14 and 12 Mya. Although the influence of toxins like CTs on gene expression patterns needs further investigation, such a scenario could be a source for rapid change in the length of the cervical vertebral region in the palaeotragines. The present study has demonstrated that the evolution of the elongated giraffe neck is unique among the ungulates.
Moreover, the manner in which the cervical vertebrae scale in comparison with other ungulate species indicates a qualitative change in neck development and evolution see above. If one imagines an interpolated line through the data obtained for C2—C5 for these two members of the Camelidae given that more data would be required to confirm this imagined line , this line falls almost parallel with, but above that, of the other ungulates.
This, in contrast with the scaling seen in the developmental series of giraffe where the regression slope is steeper than that of the other ungulates, indicates a change in quantity, and not quality, in these two members of the Camelidae.
Thus, although the neck is longer, this increase in length may be associated with a quantitative change in the Camelidae, as opposed to both a quantitative and qualitative change in the Giraffidae. Further studies on other species of Camelidae e. Although not specifically examined in the present study, another long-necked ungulate, the gerenuk Litocranius walleri , may show yet another independent evolution of the lengthening of the neck.
Thus, within the ungulates, there are possibly three independent evolutionary occurrences of cervical elongation, and it would be of great interest to investigate these further. This variance in the manner of evolution of long necks indicates interesting aspects in terms of the patterns of gene expression and gradients in the presomitic and somitic mesoderm, as within the giraffe and Tanystropheus type of long neck with limited cervical vertebrae , changes in the pattern of Hox genes in the presomitic mesoderm would allow for a greater proportion of the presomitic mesoderm to become cervical, with the additional possibility of pulses of the fibroblast growth factor FGF signalling inhibitor SU in the somitic mesoderm allowing for larger somite size Slack, In the long neck with many cervical vertebrae, changes in the presomitic mesoderm, creating a larger cervical region, as well as a potential increase in the expression of FGF in the somitic mesoderm, may lead to increased somite numbers, and hence to more cervical vertebrae Slack, Potentially, studies of the molecular development of mice with long tails, some with extra caudal vertebrae and others with longer caudal vertebrae Rutledge et al.
The current study raises a number of issues, not only about the giraffe, but also about other ungulates and the evolution of long necks in general. The current state of knowledge on both the fossil record and sources of influence on developing embryos does not allow for either a gradualistic microevolutionary or punctuated interpretation of the evolution of the elongated giraffe neck to be supported over the other, but does suggest many ways forward to resolve the manner in which the length of the giraffe neck was attained.
Increased research of both the paleobiology and developmental biology of the giraffe, and other ungulate species, will ultimately resolve the questions surrounding the evolution of long necks in the giraffe. Determining the manner in which the giraffe neck evolved is an important theoretical and practical issue for evolutionary biology, as it has been demonstrated in this study that many constraints play important roles in both evolutionary scenarios.
It will also be important to further examine the evolution of neck length in the Camelidae and other potentially long-necked ungulates, such as the gerenuk, as it appears that the mechanisms through which lengthening of the neck was attained in these species may differ, both quantitatively and qualitatively, in comparison with the giraffe.
These independent evolutions, and potentially differing mechanisms, of evolving a long neck in ungulates, may be directly contrasted with those seen in extant birds, such as the Ratites, as the birds do not have the same phylogenetic constraint on the number of cervical vertebrae Galis, Such a comparative approach makes the giraffe neck, and indeed the other long-necked species, heuristically useful models in understanding evolutionary mechanisms, and the balance between phylogenetic and developmental constraints, structural laws of form, and adaptive pressures that drive the evolution of all biological structures Gould, We would also like to thank Teresa Kearney at the Department of Mammals, Transvaal Museum, Pretoria, South Africa for access to giraffe, okapi, and springbok specimens.
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Giraffa camelopardalis. Transactions of the Royal Society of Southern Africa 58 : 51 — The genetics of these species indicate that they are as different from each other as a polar bear and a grizzly bear. To help wild giraffe populations, the Zoo partners with Dr. Specifically, the Zoo provides GCF with support for population surveys, education efforts, and research on giraffe ecology, genetics, and conservation.
Currently, GCF is working with local governments in East Africa to increase giraffe conservation efforts. They are also conducting research and monitoring the population on Northern giraffe subspecies in Uganda, as well as studying a skin disease in giraffe that currently has no known cause.
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Make a Donation. View Zoos. Home Blog Truth or Tall Tale? Little known facts about giraffe in the wild. Giraffe have more neck bones than a human. I do NOT recommend trying this at home… Giraffe tongues are like opossum tails.
Male and female giraffe are impossible to tell apart. The Cleveland Metroparks Zoo is helping to secure a future for giraffe. You can help protect wild giraffe too. Share This Page Copy. Benefits Admits two named adults in the same household and their children or grandchildren 18 years and under limit six Two free guests every visit Free gift. Benefits Admits two named adults in the same household and their children or grandchildren 18 years and under limit six One free guest every visit Free gift.
Purchase Family Membership Renew Gift. The extremely elongated neck of the giraffe results from the disproportionate lengthening of the cervical vertebrae and not by the addition of more vertebrae. The elongation of the neck takes place largely after birth. How many bones are there in a giraffe's neck? Biology Animals Invertebrates vs. Linica Uday. Oct 6, A giraffe may have a tall neck but it still has 7 bones like humans and all other mammals.
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