Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Barcelona, Catalunya, Spain.
PLoS One. 2013 Jul 25;8(7):e70743. doi: 10.1371/journal.pone.0070743. Print 2013.
In mammals that grow up more slowly and live longer, replacement teeth tend to appear earlier in sequence than in fast growing mammals. This trend, known as 'Schultz's Rule', is a useful tool for inferring life histories of fossil taxa. Deviations from this rule, however, suggest that in addition to the pace of life history, ecological factors may also drive dental ontogeny. Myotragus balearicus is an extinct insular caprine that has been proved to be an excellent test case to correlate morphological traits with life history. Here we show that Myotragus balearicus exhibits a slow signature of dental eruption sequence that is in agreement with the exceptionally slow life history of this species, thus conforming to 'Schultz's Rule'. However, our results also show an acceleration of the absolute pace of development of the permanent incisors in relation to that of the posterior teeth. The rodent-like incisors of Myotragus balearicus erupted early not only in relative but also in absolute terms (chronological age), suggesting that feeding characteristics also plays an important role in dental ontogeny. This is in agreement with ecological hypotheses based on primates. Our study documents a decoupling of the pace of development of teeth in mammals that is triggered by different selection pressures on dental ontogeny. Moreover, we show that Myotragus kopperi from the early Pleistocene (a direct ancestor of the late Pleistocene-Holocene M. balearicus) follows the pattern of first incisor replacement known in living bovids. Hence, the advance in the eruption sequence of the first incisors occurs along the Myotragus evolutionary lineage over a period of about 2.5 Myr. To our knowledge, this is the first fossil evidence of an advance of the emergence of the permanent first incisor along an anagenetic mammalian lineage.
在生长缓慢、寿命较长的哺乳动物中，替换牙的出现顺序往往比生长迅速的哺乳动物更早。这种趋势被称为“舒尔茨法则”，是推断化石类群生活史的有用工具。然而，对这一法则的偏离表明，除了生活史的节奏外，生态因素也可能驱动牙齿的个体发生。Myotragus balearicus 是一种已灭绝的岛屿山羊，已被证明是将形态特征与生活史相关联的绝佳案例。在这里，我们表明 Myotragus balearicus 表现出缓慢的牙齿萌出序列特征，这与该物种异常缓慢的生活史一致，因此符合“舒尔茨法则”。然而，我们的结果还显示，与后牙相比，永久门齿的绝对发育速度加快。Myotragus balearicus 的类似啮齿动物的门齿不仅在相对意义上（相对年龄）而且在绝对意义上（chronological age）早萌出，这表明摄食特征在牙齿个体发生中也起着重要作用。这与基于灵长类动物的生态假设一致。我们的研究记录了哺乳动物牙齿发育速度的解耦，这是由牙齿个体发生的不同选择压力引起的。此外，我们表明，来自早更新世的 Myotragus kopperi（晚更新世-全新世 M. balearicus 的直接祖先）遵循生活牛科动物中已知的第一门齿替换模式。因此，第一门齿萌出序列的提前发生是在大约 250 万年的 Myotragus 进化支系中发生的。据我们所知，这是第一个关于永久第一门齿沿着有丝分裂哺乳动物谱系提前出现的化石证据。
