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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，一颗小行星撞击墨西哥湾，深刻地改变了地球上的生命。在接下来的大灭绝事件中，曾经占主导地位的陆生脊椎动物——非鸟类恐龙没有存活下来。一个幸存的群体是哺乳动物；然而，它们不仅仅是生存下来，它们反过来成为大多数生态系统中占主导地位的脊椎动物。然而，科学界仍然不明白哺乳动物是如何在灭绝后的世界里繁衍生息的。在大灭绝事件发生后的最初几百万年里发现了许多哺乳动物化石，包括第一批大型食草哺乳动物。然而，目前还不清楚这些不寻常的化石与今天活着的哺乳动物有什么关系——它们是直系祖先还是仅仅是远亲？该项目将重点关注小行星撞击后最初1200万年被忽视的化石记录，这一时期的特点是全球气温升高，全球迅速变暖的短暂时期。通过了解这些灭绝的哺乳动物是什么，这个项目将探索这次灭绝事件在哺乳动物进化中的真正作用，研究哪些哺乳动物幸存下来，以及它们如何以及为什么在快速变化的气候中恢复和进化。今天，由于环境变化和人类活动威胁到许多物种，地球正在经历一场现代灭绝事件。尽管目前的情况与6600万年前不同，但了解灭绝后世界的潜在生物过程将指导我们未来的研究。围绕胎盘哺乳动物的起源和白垩纪-古近纪（K-Pg）灭绝事件在其进化中的作用存在争议，一方面来自形态学的证据和另一方面来自DNA的证据存在分歧。基于dna的研究认为是白垩纪胎盘起源，K-Pg事件影响不大，而基于形态学的研究认为是由K-Pg事件驱动的古近纪起源。先前对胎盘的系统发育分析大量取样于较老的（白垩纪）和较年轻的（始新世，5600万至3400万年前或更早）分类群，但古新世（6600万至5400万年前）相当大的哺乳动物多样性在很大程度上被忽视了。该项目将通过将大多数古新世谱系包括在一个全面的系统发育中来纠正这一缺点，该系统发育旨在直接解决有关K-Pg事件影响的争议。来自262个已灭绝和现存分类群的1500多个形态学特征，包括一些用计算机断层扫描（CT）研究的特征，将与来自现存哺乳动物的26个核基因的35000多个碱基对相结合，并使用最大简约、最大似然和贝叶斯方法进行分析。重建的系统发育树将用于通过分化时间分析来解决胎盘的起源和主要亚支系的多样化，并使用基于模型的技术来估计体型和形态特征的进化率。将进化率和多样性率与古生态数据进行比较，以评估早古近纪气候变化对哺乳动物历史的影响。