It is widely held that the dinosaurs were driven to near extinction because of the Chicxulub asteroid collision with the Earth about 65 million years ago (MA). Without doubt, dinosaur diversity in the fossil record after the collision was at most a percent of what it was prior to the collision. But whether the collision was the principal cause of the extinction is more difficult to assess. In Did the Chicxulub Impact Cause the K-T Extinction? I compute and compare models of the time series of the number of genera of the Dinosauria and the Mollusca in the period 230 MA – 50 MA. The models are agnostic about whether specific events occurred, and in this sense do not require Chicxulub to explain the Dinosaurian diversity collapse. There is at least one apparently non-asteroidal genera-extinction rate in the Dinosauria fossil record (at 112 MA) whose relative magnitude is comparable to that which occurred at ~65.5 MA. The Dinosauria genus-diversity collapse at 65.5 MA, therefore, could be explained if a (relative) extinction rate comparable to that at ~112 MA were in progress and few new Dinosauria genera were being created past 65.5 MA.
This paper was last updated on 4 February 2019/0808 US Central Time.
It has recently been argued that, based on a maximum parsimony analysis of a broad set of oviraptorosaur, archaeopterygid, and basal deinonychosaur morphological data, Archaeopteryx is not on the main line of avian evolution, and instead is more similar in general morphology to the oviraptorosaurs than to the archaeopterygids and basal deinonychosaurs. In Archaeopteryx: oviraptorosaur or archaeopterygid/deinonychosaur? I argue that a variable-character-coding-based Bayesian phylogenetic analysis does not sustain this view.
This paper was last updated on 9 February 2019/0954 US Central Time.
This page was last updated on 9 February 2019 at 1007 US Central Time