Notoungulates are an extinct clade of South American mammals, comprising a large diversity of body sizes and skeletal morphologies, and including taxa with highly specialized dentitions. The evolutionary history of notoungulates is characterized by numerous dental convergences, such as continuous growth of both molars and incisors, which repeatedly occurred in late-diverging families to counter the effects of abrasion. The main goal of this study is to determine if the acquisition of high-crowned incisors in different notoungulate families was accompanied by significant and repeated changes in their enamel microstructure. More generally, it aims at identifying evolutionary patterns of incisor enamel microstructure in notoungulates. Fifty-eight samples of incisors encompassing 21 genera of notoungulates were sectioned to study the enamel microstructure using a scanning electron microscope. We showed that most Eocene taxa were characterized by an incisor schmelzmuster involving only radial enamel. Interestingly, derived schmelzmusters involving the presence of Hunter-Schreger bands (HSB) and of modified radial enamel occurred in all four late-diverging families, mostly in parallel with morphological specializations, such as crown height increase. Despite a high degree of homoplasy, some characters detected at different levels of enamel complexity (e.g., labial versus lingual sides, upper versus lower incisors) might also be useful for phylogenetic reconstructions. Comparisons with perissodactyls showed that notoungulates paralleled equids in some aspects related to abrasion resistance, in having evolved transverse to oblique HSB combined with modified radial enamel and high-crowned incisors.

中文翻译：

---

Notoungulata（胎盘，哺乳动物）中门牙釉质微结构多样性的进化和功能意义

Notoungulates 是南美哺乳动物的一个灭绝分支，包括大量不同的体型和骨骼形态，包括具有高度特化牙列的分类群。notoungulates 的进化史的特点是许多牙齿趋同，例如臼齿和门牙的持续生长，这在晚期分叉的家庭中反复发生，以对抗磨损的影响。本研究的主要目标是确定在不同的有蹄类动物家族中获得高冠门牙是否伴随着其釉质微观结构的显着和重复变化。更一般地说，它旨在确定无蹄类动物门牙釉质微结构的进化模式。对包含 21 个 notoungulates 属的门牙的 58 个样本进行切片，以使用扫描电子显微镜研究牙釉质微观结构。我们表明，大多数始新世分类群的特征是门牙 schmelzmuster 仅涉及径向牙釉质。有趣的是，涉及亨特-施雷格带 (HSB) 和改良径向牙釉质的衍生 schmelzmusters 发生在所有四个晚期发散家族中，大部分与形态特化平行，例如冠高增加。尽管高度同质性，但在不同程度的牙釉质复杂性（例如，唇侧与舌侧，上切牙与下切牙）中检测到的一些特征也可能对系统发育重建有用。