Kim Sora L, Thewissen J G M, Churchill Morgan M, Suydam Robert S, Ketten Darlene R, Clementz Mark T
Department of Geology and Geophysics, University of Wyoming, 1000 East University Avenue 3006, Laramie, Wyoming 82071; 2Department of Anatomy and Neurobiology, Northeast Ohio Medical University, Rootstown, Ohio 44272; 3Program in Ecology, University of Wyoming, 1000 East University Avenue 3622, Laramie, Wyoming 82071; 4Department of Wildlife Management, North Slope Borough, Barrow, Alaska 99753; 5Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543; and Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts 02114.
Physiol Biochem Zool. 2014 Jul-Aug;87(4):576-84. doi: 10.1086/676309. Epub 2014 Jun 3.
Abstract Cetaceans are obligate aquatic mammals derived from terrestrial artiodactyls. The defining characteristic of cetaceans is a thick and dense lip (pachyosteosclerotic involucrum) of an ear bone (the tympanic). This unique feature is absent in modern terrestrial artiodactyls and is suggested to be important in underwater hearing. Here, we investigate the mineralogical and biochemical properties of the involucrum, as these may hold clues to the aquatic adaptations of cetaceans. We compared bioapatites (enamel, dentine, cementum, and skeletal bone) of cetaceans with those of terrestrial artiodactyls and pachyosteosclerotic ribs of manatees (Sirenia). We investigated organic, carbonate, and mineral composition as well as crystal size and crystallinity index. In all studied variables, bioapatites of the cetacean involucrum were intermediate in composition and structure between those of tooth enamel on the one hand and those of dentine, cementum, and skeletal bone on the other. We also studied the amino acid composition of the cetacean involucrum relative to that of other skeletal bone. The central involucrum had low glycine and hydroxyproline concentrations but high concentrations of nonessential amino acids, unlike most bone samples but similar to the tympanic of hippos and the (pachyosteosclerotic) ribs of manatees. These amino acid results are evidence of rapid bone development. We hypothesize that the mineralogical and amino acid composition of cetacean bullae differs from that of other bone because of (1) functional modifications for underwater sound reception and (2) structural adaptations related to rapid ossification.
摘要 鲸目动物是源自陆地偶蹄目的水生哺乳动物。鲸目动物的一个关键特征是耳骨（鼓骨）上有一层厚而致密的唇状结构（厚骨硬化性骨膜）。现代陆地偶蹄目动物没有这一独特特征，而该特征被认为在水下听觉中很重要。在此，我们研究了这层骨膜的矿物学和生化特性，因为这些特性可能为鲸目动物的水生适应性提供线索。我们将鲸目动物的生物磷灰石（牙釉质、牙本质、牙骨质和骨骼）与陆地偶蹄目动物以及海牛（海牛目）的厚骨硬化性肋骨进行了比较。我们研究了其有机成分、碳酸盐和矿物成分以及晶体大小和结晶度指数。在所有研究变量中，鲸目动物骨膜的生物磷灰石在组成和结构上一方面介于牙釉质和另一方面介于牙本质、牙骨质及骨骼之间。我们还研究了鲸目动物骨膜相对于其他骨骼的氨基酸组成。与大多数骨样本不同，但与河马的鼓骨和海牛的（厚骨硬化性）肋骨相似，中央骨膜的甘氨酸和羟脯氨酸浓度较低，但非必需氨基酸浓度较高。这些氨基酸结果证明了骨骼的快速发育。我们推测，鲸目动物大泡骨的矿物学和氨基酸组成与其他骨骼不同，原因在于：（1）对水下声音接收的功能适应性；（2）与快速骨化相关的结构适应性。
