Fisher Rebecca E, Scott Kathleen M, Naples Virginia L
Department of Basic Medical Sciences, University of Arizona, College of Medicine-Phoenix, Arizona 85004-2230, USA.
Anat Rec (Hoboken). 2007 Jun;290(6):673-93. doi: 10.1002/ar.20531.
Based on morphological analyses, hippos have traditionally been classified as Suiformes, along with pigs and peccaries. However, molecular data indicate hippos and cetaceans are sister taxa (see review in Uhen, 2007, this issue). This study analyzes soft tissue characters of the pygmy hippo forelimb to elucidate the functional anatomy and evolutionary relationships of hippos within Artiodactyla. Two specimens from the National Zoological Park in Washington, D.C. were dissected, revealing several adaptations to an aquatic lifestyle. However, these adaptations differ functionally from most aquatic mammals as hippos walk along river or lake bottoms, rather than swim. Several findings highlight a robust mechanism for propelling the trunk forward through the water. For example, mm. pectoralis superficialis and profundus demonstrate broad sites of origin, while the long flexor tendons serve each of the digits, reflecting the fact that all toes are weight-bearing. Pygmy hippos also have eight mm. interossei and a well-developed m. lumbricalis IV. Retention of intrinsic adductors functions to prevent splaying of the toes, an advantageous arrangement in an animal walking on muddy substrates. Published descriptions indicate common hippos share all of these features. Hippo and ruminant forelimbs share several traits; however, hippos are unique among artiodactyls in retaining several primitive muscles (e.g., mm. palmaris longus and flexor digitorum brevis). These findings are consistent with the hypothesis that hippos diverged from other Artiodactyla early in the history of this group. Additional analyses of hindlimb and axial muscles may help determine whether this trajectory was closely allied to that of Cetacea.
基于形态学分析，传统上河马与猪和西猯一同被归类为猪形亚目。然而，分子数据表明河马和鲸类是姐妹分类单元（见乌亨，2007年，本期综述）。本研究分析了倭河马前肢的软组织特征，以阐明河马在偶蹄目动物中的功能解剖结构和进化关系。对来自华盛顿特区国家动物园的两个标本进行了解剖，揭示了一些对水生生活方式的适应性特征。然而，这些适应性特征在功能上与大多数水生哺乳动物不同，因为河马是沿着河流或湖泊底部行走，而不是游泳。一些发现突出了一种强大的机制，可推动身体在水中向前移动。例如，胸浅肌和胸深肌显示出广泛的起始部位，而长屈肌腱为每个趾提供服务，这反映出所有脚趾都承重的事实。倭河马还有八块骨间肌和一块发育良好的第四蚓状肌。保留内在内收肌的功能是为了防止脚趾张开，这对于在泥泞底物上行走的动物来说是一种有利的结构。已发表的描述表明普通河马具有所有这些特征。河马和反刍动物的前肢有几个共同特征；然而，河马在偶蹄目动物中是独特的，因为它们保留了几块原始肌肉（例如掌长肌和趾短屈肌）。这些发现与河马在偶蹄目动物历史早期就与其他动物分化的假设一致。对后肢和轴向肌肉的进一步分析可能有助于确定这种进化轨迹是否与鲸类密切相关。
