Collaborative Research: A Phylogeny of Placental Mammals based on Paleocene Taxa: Determining the Impact of the K-Pg Extinction on Mammalian Evolutionary History

合作研究：基于古新世类群的胎盘哺乳动物系统发育：确定 K-Pg 灭绝对哺乳动物进化史的影响

基本信息

批准号：
1654964
负责人：
Jan Janecka
金额：
$ 11.6万
依托单位：
Duquesne University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-07-01 至 2023-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1654964&HistoricalAwards=false
关键词：
Collaborative Research Phylogeny Placental Mammals

项目摘要

Sixty-six million years ago, an asteroid impact in the Gulf of Mexico profoundly changed life on Earth. In the following mass extinction event, non-avian dinosaurs, which had been the dominant terrestrial vertebrates, did not survive. One surviving group was the mammals; yet, they did more than just survive, they in turn became the dominant vertebrates in most ecosystems. However, the scientific community still does not understand how mammals flourished in the post-extinction world. Numerous mammalian fossils from the first few million years after the extinction event have been discovered, including the first large mammalian herbivores. However, it is unclear how these unusual fossils relate to mammals alive today - are they direct ancestors or merely distant cousins? This project will focus on this neglected fossil record from the first 12 million years after the asteroid impact, a time characterized by high global temperatures and brief episodes of rapid global warming. By understanding what these extinct mammals were, this project will explore the true role of this extinction event in the evolution of mammals, examining which kinds of mammals survived, and how and why they recovered and evolved in a very rapidly changing climate. Today, Earth is experiencing a modern-day extinction event, as environmental change and human actions are threatening many species. Although the current circumstances differ from those 66 million years ago, understanding the underlying biological processes acting in a post-extinction world will guide us in the future.Controversy surrounds the origin of placental mammals and the role of the Cretaceous-Paleogene (K-Pg) extinction event on their evolution, with evidence from morphology on the one hand and DNA on the other at odds. DNA-based studies argue for a Cretaceous placental origin, with the K-Pg event having little impact, whereas morphology-based studies argue for a Paleogene origin driven by the K-Pg event. Previous phylogenetic analyses of placentals have sampled heavily from older (Cretaceous) and younger (Eocene, 56 to 34 million years ago or earlier) taxa, but the sizable mammalian diversity from the Paleocene (66 to 54 million years ago) has been largely ignored. This project will correct this shortcoming by including most Paleocene lineages in a comprehensive phylogeny designed to directly address the controversy regarding the impact of the K-Pg event. Over 1,500 morphological characters, including some studied with computer tomography (CT), from 262 extinct and extant taxa will be combined with over 35,000 base pairs from 26 nuclear genes from extant mammals, and analyzed together using maximum parsimony, maximum likelihood, and Bayesian methodology. The reconstructed phylogenetic trees will be used to resolve the origin of Placentalia and diversification of major subclades using divergence time analyses, and to estimate body size and morphological character evolution rates using model-based techniques. The evolutionary and diversity rates will be compared to paleoecological data to assess the impact of early Paleogene climate variation on mammalian history.

6600万年前，对墨西哥湾的小行星影响深刻改变了地球上的生活。在接下来的大规模灭绝事件中，曾经是主要的陆生脊椎动物的非阿奇恐龙没有生存。一个幸存的群体是哺乳动物。然而，他们做的不仅仅是生存，反过来又成为大多数生态系统中的主要脊椎动物。但是，科学界仍然不了解哺乳动物在后灭绝世界中的繁荣。发现灭绝事件的头几百年以来，许多哺乳动物化石已经被发现，其中包括第一个大型哺乳动物食草动物。但是，目前尚不清楚这些不寻常的化石与今天活着的哺乳动物有何关系 - 它们是直接祖先还是远处的表亲？该项目将重点介绍这一被忽视的化石记录，从小行星影响后的头1200万年开始，这一时间为全球温度较高和快速全球变暖的短暂发作。通过了解这些灭绝的哺乳动物是什么，该项目将探讨这一灭绝事件在哺乳动物进化中的真正作用，检查哪些哺乳动物幸存下来，以及它们如何以及为什么在迅速变化的气候下恢复和演变。如今，随着环境变化和人类行动威胁着许多物种，地球正在经历现代灭绝事件。尽管目前的情况与6600万年前的情况有所不同，但了解在后灭绝世界中作用的潜在生物学过程将在未来引导我们。对比型围绕着胎盘哺乳动物的起源以及硬币 - 果仁（K-PG）灭绝事件的作用在其演变中，并在其一手和DNA上具有形态的证据。基于DNA的研究主张白垩纪胎盘起源，而K-PG事件的影响很小，而基于形态学的研究则主张由K-PG事件驱动的古近期起源。先前对胎盘的系统发育分析已经从较旧（白垩纪）和年轻（始新世，56至3400万年前）进行了大量取样，但是古代（66至5400万年前）的相当大的哺乳动物多样性在很大程度上被忽略了。该项目将通过在综合系统发育中包括大多数古新世谱系来纠正这一缺点，旨在直接解决有关K-PG事件影响的争议。超过1,500个形态特征，包括与计算机断层扫描（CT）一起研究的，来自262个灭绝和现存的分类单元将与来自现存哺乳动物的26个核基因的35,000多个碱基对结合在一起，并使用最大的副型，最大的副脉，最大似然和贝叶斯方法进行分析。重建的系统发育树将使用散布时间分析来解决胎盘的起源和主要子甲的多样化，并使用基于模型的技术估算身体大小和形态特征演化速率。将将进化率和多样性率与古生态数据进行比较，以评估早期古生气候变化对哺乳动物史的影响。