Abstract: The carnivoran family Hyaenidae has an evolutionary history stretching ~20 Ma, with high generic diversity in the fossil record and a paucity of living species. Their ecological diversity peaked during the late Miocene, when multiple sympatric species made up a major component of the carnivoran guild in many fossil faunas. Here one group of late Miocene hyaenids and their sister family Percrocutidae, from the Linxia Basin of northwestern China, was studied using geometric morphometrics analysis of cranial shape. The morphology of Ictitherium and Hyaenictitherium was shown to be intermediate between those of living spotted hyena Crocuta and canidsCanis and Lycaon. The larger Dinocrocuta and Adcrocuta overlap extensively in morphology with extant Crocuta. Juvenile Dinocrocuta and Crocuta are more similar to each other in cranial morphology than either is to adult individuals of their species. Furthermore, adult Hyaenictitherium andIctitherium fall within the range of variation of extant juvenile Crocuta. These findings indicate that Crocuta and Dinocrocuta not only converge on robust adult cranial morphology, but may also share similar ontogenetic trajectories; the prolonged period of ontogeny in Crocuta required for developing the robust morphology may also be true for Dinocrocuta. The ictithere-like morphology of juvenile Crocuta suggests that adult cranial shape of the extant hyaenid is obtained via continued allometric growth from, and beyond, the ictithere bauplan.

摘要： 本文采用几何形态测量的方法对产自和政地区的鬣狗科Hyaenictitherium, Ictitherium, Adcrocuta和旁鬣狗科Dinocrocuta的材料进行研究，分析了这4个属保存完好的头骨标本的侧面形态。与东非大草原现生食肉动物的头骨整体形态分布的比较和分析表明，和政的鼬鬣狗(Ictitherium)和鬣型鼬鬣狗(Hyaenictitherium)的头骨形状分布介于现生斑鬣狗(Crocutacrocuta)、犬科猎狗(Lycaon pictus)和金豺(Canis aureus)之间，为二者似豺生态形态的解释提供了几何形态测量证据。再者，上述两属化石鬣狗的形状分布与现生斑鬣狗的幼年个体形状重叠，表明现生斑鬣狗头骨的发育机制可能是在鼬鬣狗祖先类型的异速生长规律基础上的持续发育，进而演化出现有的粗壮形态。此外，巨鬣狗(Dinocrocuta)和副鬣狗(Adcrocuta)的头骨形状与现生的斑鬣狗在几何形态测量空间内有普遍重叠的现象，指示了这些异时出现的种类具有相似的生态形态，因而可能占据相近的生态位。结果还显示巨鬣狗和斑鬣狗的幼年个体形状相近，以及两者从幼年到成年发育的形状变化过程也具有相似的规律。因而，巨鬣狗和斑鬣狗之间的趋同演化不仅表现在成年头骨的粗壮程度上，而且在幼年发育模式中也存在平行演化现象。现生发育学与行为生态学已经证实，相对其他大型食肉动物，现生斑鬣狗发育粗壮头骨形态的机制不是以增速生长，而是以延长发育期来实现的。由此推断，巨鬣狗的发育期有可能和现生鬣狗相当(35个月)，也可能由于具有相对粗壮和巨大的头骨形态，其发育期会延长些。当然，这个新解释仍需要更多的化石数据和发育研究来证实。