Data from: Testing a developmental model in the fossil record: molar proportions in South American ungulates

A developmental model, based upon murine rodents, has been proposed by Kavanagh et al. (2007) to explain lower molar proportions in mammals. We produce a clade-wide macroevolutionary test of the model using the dental evolutionary trends in a unique radiation of extinct mammals endemic to South America (“Meridiungulata”) that comprise a diverse array of molar morphologies. All of the South American ungulate groups examined follow the inhibitory cascade model with the exception of two groups: Interatheriidae (Notoungulata) and Astrapotheria. For most taxa studied, ratios between lower molar areas are greater than 1.0 indicating a weak inhibition by m1 on the subsequent molars in the tooth row, and a trend to greater absolute size of the posterior molars. Comparisons of mean ratios between clades indicate a significant phylogenetic signal can be detected, particularly between the two groups within Notoungulata: Typotheria and Toxodontia. Body mass estimates were found to be significantly correlated with both m3/m1 and m2/m1 ratios, suggesting that the larger body size achieved the weaker inhibition between the lower molars. Molar ratio patterns are examined and discussed in relation to the independent and numerous acquisitions of hyspodonty that are characteristic of dental evolution in ‘Meridiungulata’.Kavanagh等人（2007）提出了一种基于鼠科啮齿类（murine rodents）的发育模型，用以阐释哺乳动物的下臼齿比例格局。本研究以经历独特演化辐射的南美洲特有已灭绝哺乳动物类群"南蹄类（Meridiungulata）"的牙齿演化趋势为研究对象，对该模型开展了支系全域的宏观演化检验；该类群涵盖了多样的臼齿形态类型。本次研究涉及的所有南美洲有蹄类类群均符合抑制级联模型（inhibitory cascade model），仅除外两类：间齿兽科（Interatheriidae，隶属于南方有蹄目（Notoungulata））与闪兽目（Astrapotheria）。就多数研究类群而言，下臼齿面积比值均大于1.0，这表明第一下臼齿（m1）对齿列后续臼齿的抑制作用较弱，且后臼齿存在绝对尺寸增大的演化趋势。支系间平均比值的比较结果显示，可检测到显著的系统发育信号（phylogenetic signal），其中以南方有蹄目（Notoungulata）下的型兽亚目（Typotheria）与弓齿兽亚目（Toxodontia）两类群间的信号尤为显著。研究发现体重估算值与m3/m1、m2/m1比值均呈显著相关，提示类群体型越大，其下臼齿间的抑制作用越弱。本研究对臼齿比值格局进行了分析与讨论，并结合"南蹄类（Meridiungulata）"牙齿演化中多次独立起源的高冠齿（hypsodonty）特征展开了探讨。