Growth Pattern and Functional Morphology of the Cervical Vertebrae in the Gerenuk (Litocranius walleri): The Evolution of Neck Elongation in Antilopini (Bovidae, Artiodactyla)
Growth Pattern and Functional Morphology of the Cervical Vertebrae in the Gerenuk (Litocranius walleri): The Evolution of Neck Elongation in Antilopini (Bovidae, Artiodactyla)
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DOI：
10.1007/s10914-017-9396-7
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发表时间：
2019-06-01
影响因子：
1.9
通讯作者：
Endo，Hideki
中科院分区：
文献类型：
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作者：
Gunji，Megu;Endo，Hideki
长颈已经在几个不同的分类群中独立进化，但这种特征的进化过程尚未完全清楚。在这项研究中，我们研究了Antilopini部落(牛科，偶蹄目)颈部延长的骨骼机制。我们计算了该部落中颈部最长的Gerenuk(Litcranius Weller I)颈椎的生长模式，并与两个近缘物种的颈椎生长模式进行了比较。脊椎的生长速度在不同物种之间没有显著差异，这表明Gerenuk的长颈是胎儿或幼年阶段颈椎伸长的结果。Gerenuks的颈椎形态不同于亲缘关系较近、相对长颈的Dama瞪羚(Nanger Dama)，突起位于枢椎腹弓的背侧表面。这意味着Gerenuks具有发育良好的枢椎横向韧带，其功能是将枢椎的齿状突固定在枢椎上。我们还发现，寰椎位于Gerenuk的枢椎神经脊椎附近，这表明该物种的枢椎关节过度伸展在骨学上是有限的。当在高高的树叶上觅食时，Gerenuus以两足的姿势自由伸展和伸展脖子，而不移动整个身体。Gerenuk特有的这些形态特征增强了寰枢椎关节的刚性，并在这种独特的觅食行为中降低了关节半脱位的风险。
Long necks have evolved independently in several different taxa, but the processes underlying the evolution of this trait are not yet fully understood. In this study, we examined the skeletal mechanism underlying the neck elongation in the tribe Antilopini (Bovidae, Artiodactyla). We calculated the growth patterns of the cervical vertebrae in the gerenuk (Litocranius walleri), which possesses the longest neck in this tribe, and compared it with those in two related species. The growth rates of the vertebrae were not significantly different between species, suggesting that the long neck of the gerenuk has resulted from the elongation of the cervical vertebrae during the fetal or juvenile stage. The morphology of the cervical vertebrae of gerenuks differed from that of the closely related, relatively long-necked dama gazelle (Nanger dama), with protrusions occurring on the dorsal surface of the ventral arch of the atlas. This implies that gerenuks possess a well-developed transverse ligament of the atlas that functions to hold the dens of the axis against the atlas. We also found that the atlas lies in close proximity to the neural spine of the axis in the gerenuk, suggesting that hyperextension of the atlantoaxial joint is osteologically limited in this species. While foraging on high foliage, gerenuks flex and extend their necks freely in a bipedal posture without moving their entire body. These morphological characteristics peculiar to the gerenuk enhance the rigidity of the atlantoaxial joint and decrease the risk of subluxation of the joint during this unique foraging behavior.