Sustained miniaturization, here defined as a drop in body size of at least two orders of magnitude from ancestors to descendants, is a widespread and important phenomenon in animals,1-3 but among dinosaurs, miniaturization occurred only rarely, once in the lineage leading to birds and once in the Alvarezsauroidea,1,3-5 one of the most bizarre theropod groups.1,5-7 Miniaturization and powered flight are intimately linked in avialan theropods,3,5,6,8-11 but the causes and patterns of body size reduction are less clear in the non-volant Alvarezsauroidea.1,5,6,12,13 Here, we present results from analyses on a comprehensive dataset, which not only includes new data from early-branching alvarezsauroids but also considers the ontogenetic effect based on histological data. Our analyses show that alvarezsauroid body mass underwent rapid miniaturization from around 110 to 85 mya and that there was a phylogenetic radiation of small-sized alvarezsauroids in the Late Cretaceous. Our analyses also indicate that growth strategies were highly variable among alvarezsauroids, with significant differences among extremely small taxa. The suggested alvarezsauroid miniaturization and associated phylogenetic radiation are coincident with the emergence of ants and termites, and combining previous functional morphological data, our study suggests that alvarezsauroid miniaturization might have been driven by ecological changes during the Cretaceous Terrestrial Revolution, more specifically by a shift to the myrmecophagous ecological niche.
|Number of pages||2|
|Early online date||30 Jun 2021|
|Publication status||Published - 23 Aug 2021|
Bibliographical noteFunding Information:
We thank Ding Xiaoqing for preparing specimens, Zhang Shukang for guidance in manufacturing histological slices, and Fenglu Han for suggestions on an early version of the manuscript. We thank Gregory Erickson and Sterling Nesbitt for providing essential osteohistological figures of Shuvuuia deserti and Albinykus baatar and Sungjin Lee and Jorge Meso for providing measurement data. We thank Martin Sander for discussions on osteohistology, Benjamin Moon for discussions on phylogenetic macroevolution, and Chenyang Cai and Yuming Liu for discussions on dinosaur-insect coevolution. We thank three anonymous reviewers for their careful work and thoughtful suggestions that have helped improve our paper substantially. This study was supported by the National Natural Science Foundation of China ( 41688103 and 41120124002 ) to X.X.; Newton Advanced Fellowships of Royal Society ( NA160290 ) and National Natural Science Foundation of China ( 42072008 ) to Q.Z.; National Research Foundation grants AOP 118794 , AOP 98800 , and IRG 95449 to J.N.C.; the US National Science Foundation ( EAR 0310217 ) to J.M.C.; and the Middlemiss Fund of the Geologists’ Association to Z.Q.
© 2021 Elsevier Inc.