Sunday, April 24, 2016

[PaleoEcology / Paleontology • 2016] Dental Disparity and Ecological Stability in Bird-like Dinosaurs Prior to the End-Cretaceous Mass Extinction


A small feathered dinosaur swoops down on an unsuspecting lizard while a bird hunts for seeds in this reconstructed slice of life in Alberta 66 million years ago. A new theory suggests that a seed diet helped birds survive the mass extinction event that wiped out all other dinosaurs.
illustration: Danielle DUFAULT

Highlights
• Tooth shape disparity in small maniraptoran dinosaurs is examined in the Cretaceous
• Results show stability and sudden extinction in this guild at the end of the Cretaceous
• Groups are mostly static in shape space except for larger size in the early Maastrichtian
• Evolution of an edentulous beak and granivory may have been key to the survival of birds

Summary
The causes, rate, and selectivity of the end-Cretaceous mass extinction continue to be highly debated. Extinction patterns in small, feathered maniraptoran dinosaurs (including birds) are important for understanding extant biodiversity and present an enigma considering the survival of crown group birds (Neornithes) and the extinction of their close kin across the end-Cretaceous boundary. Because of the patchy Cretaceous fossil record of small maniraptorans, this important transition has not been closely examined in this group. Here, we test the hypothesis that morphological disparity in bird-like dinosaurs was decreasing leading up to the end-Cretaceous mass extinction, as has been hypothesized in some dinosaurs. To test this, we examined tooth morphology, an ecological indicator in fossil reptiles, from over 3,100 maniraptoran teeth from four groups (Troodontidae, Dromaeosauridae, Richardoestesia, and cf. Aves) across the last 18 million years of the Cretaceous. We demonstrate that tooth disparity, a proxy for variation in feeding ecology, shows no significant decline leading up to the extinction event within any of the groups. Tooth morphospace occupation also remains static over this time interval except for increased size during the early Maastrichtian. Our data provide strong support that extinction within this group occurred suddenly after a prolonged period of ecological stability. To explain this sudden extinction of toothed maniraptorans and the survival of Neornithes, we propose that diet may have been an extinction filter and suggest that granivory associated with an edentulous beak was a key ecological trait in the survival of some lineages.


Figure 2: Tooth Disparity Through Time – A plot of tooth disparity (shape variation) thought the last 20 million years of the Cretaceous from the four groups of bird-like dinosaurs analyzed in this study.

A small feathered dinosaur swoops down on an unsuspecting lizard while a bird hunts for seeds in this reconstructed slice of life in Alberta 66 million years ago. A new theory suggests that a seed diet helped birds survive the mass extinction event that wiped out all other dinosaurs.
illustration: Danielle DUFAULT

Derek W. Larson, Caleb M. Brown and David C. Evans. 2016. Dental Disparity and Ecological Stability in Bird-like Dinosaurs Prior to the End-Cretaceous Mass Extinction. Current Biology.  DOI:  10.1016/j.cub.2016.03.039

Fossil teeth suggest that seeds saved bird ancestors from extinction http://esciencenews.com/node/1250215
Why did birds live while dinosaurs died? It’s a seedy story, researchers say /via @globeandmail http://www.theglobeandmail.com/technology/science/why-did-birds-live-while-dinosaurs-died-its-a-seedy-story-researcherssay/article29705574
Fossil teeth suggest that seeds saved bird ancestors from extinction https://www.sciencedaily.com/releases/2016/04/160421133639.htm

1 comment:

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