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 <i>Acdestis maddeni</i>, 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 <i>Palaeothentes</i>, <i>P. serratus</i> sp. nov. and <i>P. relictus</i> sp. nov., distinguished from other species of <i>Palaeothentes</i> by the presence of an anterobasal cingulid and reduced anterior trigonid crest, among other features; and (3) remains of a third new species, <i>Chimeralestes ambiguus</i> 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

贫齿有袋类（Paucituberculatan marsupials），尤其是古袋貘科（Palaeothentidae）的成员，在新生代的大部分时期都是南美哺乳动物群落的重要组成部分。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化石产地。本文记述了产自上述中中新世晚期化石产地之一——玻利维亚克布拉达洪达（Quebrada Honda）的古袋貘科新标本，其包含以下三类材料：（1）马登无齿袋兽（Acdestis maddeni）的首个被描述的下颌齿列，该标本具有显著特征：极度延长的下前嵴以及单根的第四下臼齿（m4）；（2）首个被描述的中中新世晚期古袋貘亚科（Palaeothentinae）材料，代表两个古袋貘属（Palaeothentes）新种：锯形古袋貘（P. serratus sp. nov.）与孑遗古袋貘（P. relictus sp. nov.），二者与其他古袋貘属物种的区别在于具有前基齿带（anterobasal cingulid）以及退化的前三角嵴等特征；（3）第三个新物种歧异嵌袋兽（Chimeralestes ambiguus gen. et sp. nov.）的化石，该物种与其他古袋貘科成员的区别在于兼具唇侧位置的下后嵴、退化的第四下臼齿以及强烈弯曲的下内嵴等特征。系统发育与古生态分析显示，克布拉达洪达的古袋貘科类群在分类学与形态学上均具有丰富的多样性，且大概率占据了广泛的生态位。结合中中新世晚期古袋貘类（palaeothentoids）广泛的地理分布，这一发现表明这类有袋类的灭绝，其前序的分类、生态多样性以及地理分布范围的衰退并非渐进式，而是骤然发生的。http://zoobank.org/urn:lsid:zoobank.org:pub:DA7E10BA-7203-4F5A-A3AB-F0E7352B101C