Data from: Ancient DNA from the extinct South American giant glyptodont Doedicurus sp. (Xenarthra: Glyptodontidae) reveals that glyptodonts evolved from Eocene armadillos

Glyptodonts were giant (up to ~2,400 kg), heavily armoured relatives of living armadillos, which became extinct during the Late Pleistocene/early Holocene alongside much of the South American megafauna. Although glyptodonts were an important component of Cenozoic South American faunas, their early evolution and phylogenetic affinities within the order Cingulata (armoured New World placental mammals) remain controversial. In the present study we used hybridisation enrichment and high-throughput sequencing to obtain a partial mitochondrial genome from Doedicurus sp., the largest (1.5m tall, and 4m long) and one of the last surviving glyptodonts. Our molecular phylogenetic analyses revealed that glyptodonts fall within the diversity of living armadillos. Reanalysis of morphological data using a molecular “backbone constraint” revealed several morphological characters that supported a close relationship between glyptodonts and the tiny extant fairy armadillos (Chlamyphorinae). This is surprising as these taxa are among the most derived cingulates: glyptodonts were generally large-bodied and heavily armoured, while the fairy armadillos are tiny (~9-17 cm) and adapted for burrowing. Calibration of our phylogeny with the first appearance of glyptodonts in the Eocene resulted in a more precise timeline for xenarthran evolution. The osteological novelties of glyptodonts and their specialisation for grazing appear to have evolved rapidly during the Late Eocene to Early Miocene, coincident with global temperature decreases and a shift from wet closed forest towards drier open woodland and grassland across much of South America. This environmental change may have driven the evolution of glyptodonts, culminating in the bizarre giant forms of the Pleistocene.

雕齿兽（Glyptodonts）是一类体型庞大（体重可达约2400千克）、身披厚重装甲的现生犰狳近亲，在更新世晚期/全新世早期（Late Pleistocene/early Holocene）与绝大多数南美巨型动物群一同灭绝。尽管雕齿兽是新生代（Cenozoic）南美动物群的重要组成部分，但它们的早期演化历程以及在有甲目（Cingulata，带装甲的新大陆胎盘类哺乳动物）中的系统发育亲缘关系仍存在较大争议。本研究通过杂交富集与高通量测序技术，从雕齿兽属（Doedicurus sp.）——该类群体型最大（高1.5米、长4米）且为最后残存的雕齿兽类群之一——中获取了部分线粒体基因组（mitochondrial genome）。我们的分子系统发育分析结果显示，雕齿兽类群嵌套于现生犰狳的物种多样性谱系之内。借助分子"骨架约束"对形态学数据进行再分析后，我们发现了多个支持雕齿兽与现存小型倭犰狳（Chlamyphorinae，倭犰狳亚科）存在紧密亲缘关系的形态学特征。这一结论颇令人意外，因为该类群属于演化特化程度最高的有甲目类群之一：雕齿兽普遍体型硕大、装甲厚重，而倭犰狳体型微小（体长约9至17厘米）且适应穴居生活。以雕齿兽在始新世（Eocene）的首现记录作为系统发育时间校准点，我们的系统发育树为异关节总目（Xenarthra）的演化提供了更为精准的时间框架。雕齿兽的骨骼形态革新特征及其对放牧习性的特化，似乎在始新世晚期至中新世（Early Miocene）早期快速演化，这一演化时段与全球气温下降、南美大部分区域从湿润密闭森林向干燥开阔林地与草原转变的地质事件高度同步。这类环境变化或许推动了雕齿兽的演化历程，最终演化出更新世时期外形怪异的巨型类群。