Billet Guillaume, Martin Thomas
Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Nussallee 8, 53115 Bonn, Germany.
Naturwissenschaften. 2011 Jun;98(6):509-17. doi: 10.1007/s00114-011-0795-y. Epub 2011 Apr 15.
The fossil South American ungulates are of great interest relative to the new phylogenetic framework elaborated for living placental mammals. In particular, studies on these endemic taxa can allow for testing congruence between southern placental phylogeny and plate tectonics, beyond what has already been suggested in the Atlantogenata hypothesis based on extant afrotherians and xenarthrans. The presence of delayed dental eruption relative to skull growth is one feature characterizing the extant afrotherians and possibly the xenarthrans. Late dental eruption has been mentioned previously in South American notoungulates, thus suggesting possible resemblance with afrotherians and perhaps xenarthrans. We provide here a detailed study of the dental eruption pattern relative to the skull growth in the notoungulates. In contrast to previous statements, our results demonstrate that there is currently no evidence for an afrotherian-like delayed dental eruption in this group. For now, the inferred absence of a delayed dental eruption in notoungulates does not support atlantogenatan/afrotherian affinities for the Notoungulata, but other atlantogenatan/afrotherian characteristics remain to be explored in more detail in this group and other South American ungulates.
相对于为现存有胎盘哺乳动物构建的新系统发育框架而言，南美洲的有蹄类化石极具研究价值。特别是，对这些特有类群的研究能够检验南半球胎盘类系统发育与板块构造之间的一致性，这超越了基于现存非洲兽类和贫齿类动物的大西洋兽类假说中已提出的内容。相对于头骨生长而言，牙齿萌出延迟是现存非洲兽类以及可能还有贫齿类动物的一个特征。此前在南美洲的南方有蹄目中曾提到过牙齿萌出较晚的情况，这表明它们可能与非洲兽类以及或许还有贫齿类动物存在相似之处。我们在此对南方有蹄目动物中牙齿萌出模式相对于头骨生长的情况进行了详细研究。与之前的说法相反，我们的研究结果表明，目前尚无证据表明该类群存在类似非洲兽类的牙齿萌出延迟现象。就目前而言，推断南方有蹄目动物不存在牙齿萌出延迟现象，并不支持南方有蹄目与大西洋兽类/非洲兽类之间的亲缘关系，但该类群以及其他南美洲有蹄类动物中其他的大西洋兽类/非洲兽类特征仍有待更深入地探究。
