The extinction of the dinosaurs

Abstract

Non-avian dinosaurs went extinct 66 million years ago, geologically coincident with the impact of a large bolide (comet or asteroid) during an interval of massive volcanic eruptions and changes in temperature and sea level. There has long been fervent debate about how these events affected dinosaurs. We review a wealth of new data accumulated over the past two decades, provide updated and novel analyses of long-term dinosaur diversity trends during the latest Cretaceous, and discuss an emerging consensus on the extinction's tempo and causes. Little support exists for a global, long-term decline across non-avian dinosaur diversity prior to their extinction at the end of the Cretaceous. However, restructuring of latest Cretaceous dinosaur faunas in North America led to reduced diversity of large-bodied herbivores, perhaps making communities more susceptible to cascading extinctions. The abruptness of the dinosaur extinction suggests a key role for the bolide impact, although the coarseness of the fossil record makes testing the effects of Deccan volcanism difficult.

Dinosaurs in decline tens of millions of years before their final extinction

“…Our results showing high levels of speciation in hadrosauriforms and ceratopsids, although consistent with previous findings (8), seem to contradict more recent work that suggests that these groups underwent a decline in morphological diversity during the last two stages of the Cretaceous of North America (13,26). These dinosaur species are morphologically and ecologically (at least at the family level) conserved (27), with most of the derived characteristics concentrated in their crania (24).…”

“…To accurately identify causal mechanisms of Mesozoic dinosaurian demise, we recommend that future studies focus on a longer time period than just the last 10-20 My of the Cretaceous (4,13,42,43). In addition, our results highlight the importance of considering the expected increase in species number as clades expand and accounting for shared ancestry using phylogenetic approaches.…”

“…dinosaurs | evolution | speciation | phylogeny | Bayesian methods N onavian dinosaurs met their demise suddenly, coincident with the Chicxulub impact in Mexico around 66 Mya; however, whether there was any long-term trend toward declining diversity leading to the Cretaceous-Paleogene (K-Pg) boundary has been controversial and debated for decades (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). This longstanding dispute has been prolonged partly because of differences in fossil datasets from different parts of the world and difficulties in rock dating but most importantly, methodological weaknesses-previous attempts have been nonphylogenetic, and analyses were conducted on simple time-binned tabulated data, resulting in a lack of statistical rigor (phylogenetic and temporal nonindependence have not been considered), and did not truly investigate evolutionary dynamics, such as speciation and extinction rates.…”

Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development

“…These results may have implications for nonavian dinosaur extinction. The end of the Cretaceous was marked by extreme catastrophe and rapid climatic change, resulting in a resourcelimited environment (82). Growth-curve analyses suggest dinosaurs and basal birds were endothermic (83) or mesothermic (84) [i.e., considerably more energetically wasteful than ectothermic amphibians and reptiles (85)] but required a year or more to reach somatic and sexual maturity (35,83).…”

New tyrannosaur from the mid-Cretaceous of Uzbekistan clarifies evolution of giant body sizes and advanced senses in tyrant dinosaurs

“…These multiton, ecologically dominant latest Cretaceous species (tyrannosaurids) evolved from an ancestral lineage of basal tyrannosauroids, which originated more than 100 million years before T. rex but for most of their history remained second-tier predators, rarely with a mass exceeding that of a horse (2)(3)(4). The ascent of tyrannosaurs from these early species to the latest Cretaceous giants was one of the seminal events in dinosaur evolution, establishing the final dinosaurdominated faunas that flourished before the end-Cretaceous mass extinction (5).…”