Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA.
Biol Lett. 2011 Dec 23;7(6):925-8. doi: 10.1098/rsbl.2011.0470. Epub 2011 Jul 13.
Modern debate regarding the extinction of non-avian dinosaurs was ignited by the publication of the Cretaceous-Tertiary (K-T) asteroid impact theory and has seen 30 years of dispute over the position of the stratigraphically youngest in situ dinosaur. A zone devoid of dinosaur fossils reported from the last 3 m of the Upper Cretaceous, coined the '3 m gap', has helped drive controversy. Here, we report the discovery of the stratigraphically youngest in situ dinosaur specimen: a ceratopsian brow horn found in a poorly rooted, silty, mudstone floodplain deposit located no more than 13 cm below the palynologically defined boundary. The K-T boundary is identified using three criteria: (i) decrease in Cretaceous palynomorphs without subsequent recovery, (ii) the existence of a 'fern spike', and (iii) correlation to a nearby stratigraphic section where primary extraterrestrial impact markers are present (e.g. iridium anomaly, spherules, shocked quartz). The in situ specimen demonstrates that a gap devoid of non-avian dinosaur fossils does not exist and is inconsistent with the hypothesis that non-avian dinosaurs were extinct prior to the K-T boundary impact event.
现代关于非鸟类恐龙灭绝的争论是由白垩纪-第三纪（K-T）小行星撞击理论的发表引发的，这场争论已经持续了 30 年，争论的焦点是地层中最年轻的恐龙化石的位置。在白垩纪末期，报道了一个没有恐龙化石的区域，被称为“3 米空白”，这一现象加剧了争议。在这里，我们报告了发现了地层中最年轻的恐龙化石标本：一个角龙的眉骨化石，它位于一个根系不发达的粉砂质泥岩漫滩沉积物中，距离孢粉学定义的边界不超过 13 厘米。K-T 边界是通过三个标准来确定的：（i）白垩纪孢粉类生物数量减少，且没有后续恢复，（ii）存在“蕨类 spike”，以及（iii）与附近的地层剖面相关，该剖面存在主要的天外撞击标记（如铱异常、球粒、冲击石英）。该原位标本表明，不存在没有非鸟类恐龙化石的空白区域，这与非鸟类恐龙在 K-T 边界撞击事件之前就已经灭绝的假说不一致。
