New palaeothentid marsupials (Paucituberculata) from the middle Miocene of Quebrada Honda, Bolivia, and their implications for the palaeoecology, decline and extinction of the Palaeothentoidea

Paucituberculatan marsupials, particularly members of the family Palaeothentidae, were important components of South American mammal communities during much of the Cenozoic. However, after the late early Miocene, palaeothentid remains are rare in the fossil record, and the group is last recorded at late middle Miocene sites in Colombia, Bolivia and possibly Argentina. Here, we describe new specimens of palaeothentids from one of these late middle Miocene sites, Quebrada Honda, Bolivia, which include: (1) the first described lower dentitions of Acdestis maddeni, which exhibit distinctive features such as a greatly elongated paracristid and a single-rooted m4; (2) the first described late middle Miocene palaeothentines, representing two new species of Palaeothentes, P. serratus sp. nov. and P. relictus sp. nov., distinguished from other species of Palaeothentes by the presence of an anterobasal cingulid and reduced anterior trigonid crest, among other features; and (3) remains of a third new species, Chimeralestes ambiguus gen. et sp. nov., distinguished from other palaeothentids by its combination of a labially positioned cristid obliqua, reduced m4, and sharply curved entocristid. Phylogenetic and palaeoecological analyses show that Quebrada Honda palaeothentids were taxonomically and morphologically diverse and likely spanned a wide range of ecological niches. Combined with the wide geographical distribution of palaeothentoids during the late middle Miocene, this suggests that the disappearance of these marsupials was preceded by an abrupt rather than gradual decline in taxonomic and ecological diversity as well as geographical range. http://zoobank.org/urn:lsid:zoobank.org:pub:DA7E10BA-7203-4F5A-A3AB-F0E7352B101C

少结牙目有袋类（Paucituberculatan marsupials），尤其是古袋貘科（Palaeothentidae）的成员，在新生代绝大多数时期都是南美哺乳动物群落的重要组成类群。然而，早中新世晚期之后，古袋貘科的化石记录变得极为稀少，该类群的最晚化石记录见于哥伦比亚、玻利维亚以及可能的阿根廷的中中新世晚期遗址。本文记述了采自上述中中新世晚期遗址之一——玻利维亚克布拉达本田（Quebrada Honda）的古袋貘科新标本，其包含三类新材料：（1）首次被记述的马登短吻袋貘（Acdestis maddeni）下颌齿列，该标本具有标志性特征：极度延长的下前尖脊（paracristid）以及单根的第四臼齿（m4）；（2）首次被记述的中中新世晚期古袋貘亚科类群，代表两个古袋貘属（Palaeothentes）新种：锯齿古袋貘（Palaeothentes serratus sp. nov.）与孑遗古袋貘（Palaeothentes relictus sp. nov.）；相较于其他古袋貘属物种，二者凭借前基部齿带（anterobasal cingulid）、退化的前三角脊（anterior trigonid crest）等多项特征得以区分；（3）第三新属新种——模糊奇袋貘（Chimeralestes ambiguus gen. et sp. nov.）的化石遗存，该类群与其他古袋貘科物种的鉴别特征组合包括：唇侧位的下后尖脊（cristid obliqua）、退化的第四臼齿以及显著弯曲的下内尖脊（entocristid）。系统发育与古生态分析显示，产自克布拉达本田（Quebrada Honda）的古袋貘科类群在分类学与形态学上均具有丰富多样性，且大概率占据了广泛的生态位空间。结合中中新世晚期古袋貘总科（palaeothentoids）广泛的地理分布，这一结果表明：这类有袋类的灭绝过程，其分类、生态多样性以及地理分布范围的衰减是突发性的，而非渐进式的。http://zoobank.org/urn:lsid:zoobank.org:pub:DA7E10BA-7203-4F5A-A3AB-F0E7352B101C