Ever since the discovery of Macrauchenia patachonica by Charles Darwin in 1834, the affinities of litopterns—a group of extinct South American Native Ungulates (SANUs)—have been elusive. In particular, the interfamilial relationships and timing of the familial diversification within the order Litopterna have not been addressed with adequate taxon and character sampling, and modern phylogenetic methods. We address these issues using a new morphological matrix of 703 dental and mandibular characters, scored for the earliest litopterns alongside early SANUs of other orders (Astrapotheria, Notoungulata, Pyrotheria, and Xenungulata). We also included members of families that have been often included within Litopterna, such as Didolodontidae, Protolipternidae, Indaleciidae, and Notonychopidae, the last two sometimes grouped in the order Notopterna. We conducted maximum parsimony and undated and tip-dated Bayesian phylogenetic analyses. Our results indicate that (1) didolodontids, protolipternids, and kollpaniines should be considered early SANUs, but not particularly closely related to any order, (2) Indaleciidae and Notonychopidae usually form a monophyletic group (Notopterna), and (3) Litopterna is a monophyletic unit composed of four families [Adianthidae, Anisolambdidae (subfamilies Anisolambdinae and Sparnotheriodontinae), Macraucheniidae, Proterotheriidae], and tentatively the notoptern families Indaleciidae and Notonychopidae with a probable origin ~64.0 Mya in the Early Palaeocene.

中文翻译：

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Litopterna（哺乳纲：胎盘纲）和“古老”南美有蹄类动物基于牙列的新系统发育


自从查尔斯·达尔文 (Charles Darwin) 于 1834 年发现 Macrauchenia patachonica 以来，与已灭绝的南美原住有蹄类动物 (SANU) 的陆足鸟 (Macrauchenia patachonica) 的亲缘关系一直难以捉摸。特别是，Litopterna目内的科间关系和科多样化的时间尚未通过足够的分类单元和性状采样以及现代系统发育方法得到解决。我们使用包含 703 个牙齿和下颌特征的新形态矩阵来解决这些问题，该矩阵对最早的白齿兽以及其他目（Astrapotheria、Notoungulata、Pyrotheria 和 Xenungulata）的早期 SANU 进行了评分。我们还包括了经常被纳入 Litopterna 的科的成员，例如 Didolodontidae、Protolipternidae、Indaleciidae 和 Notonychopidae，后两个有时被归为 Notopterna 目。我们进行了最大简约性以及未注明日期和最新日期的贝叶斯系统发育分析。我们的结果表明（1）didolodontids、protolipternids 和 kollpaniines 应被视为早期 SANU，但与任何目都没有特别密切的关系，（2）Indaleciidae 和 Notonychopidae 通常形成单系群（Notopterna），（3）Litopterna 是由四个科 [Adianthidae、Anisolambdidae（亚科 Anisolambdinae 和 Sparnotheriodontinae）、Macraucheniidae、Proterotheriidae] 和暂定的 notoptern 科 Indaleciidae 和 Notonychopidae 组成的单系单位，可能起源于古新世早期~64.0 Mya。