Late Cretaceous diversification of herbivores

[Halichoeres]

An analysis of jaw and tooth morphology of herbivores throughout the Cretaceous finds that there was a burst of "disparification," which means greater morphological differences among taxa, toward the end of the Cretaceous. That might suggest that the K-Pg extinction truncated a wild radiation of ornithischians (although sauropods weren't enjoying this same increase in diversity).


The left part of this just estimates the morphological diversity of various clades for the entirety of the Cretaceous.
The right side shows different intervals of the Cretaceous (oldest on the bottom) and highlights in red all the clades that were at that moment expanding in morphospace (morphological diversity, you can think of this as which clades were evolving new shapes of jaws and teeth). There's an awful lot of red in the Santonian and Campanian.

Open access: https://www.cambridge.org/core/services/aop-cambridge-core/content/view/E5FDBA59F1F5AE1CAC396777CA9088B4/S009483731800026Xa_hi.pdf/_div_class__title__Multifaceted_disparity_approach_reveals_dinosaur_herbivory_flourished_before_the_end-Cretaceous_mass_extinction__div_.pdf

[Newt]

Interesting. I wonder how much of this disparification was driven by changes in plant ecology, and how much by niche partitioning in well-filled ecosystems? The late Cretaceous may be the longest interval in the entire Phanerozoic without a major terrestrial extinction event, so maybe the low-hanging fruit of oral morphospace had already been plucked and necessity mothered innovation.


It does seem a little apples to oranges to compare oral anatomy diversification in ornithischians versus sauropods, as sauropods are (a) largely committed to postoral processing and (b) notorious for lack of skull preservation.


I guess I should read the paper before commenting... [size=78%]  [/size]

[Halichoeres]

Interesting. I wonder how much of this disparification was driven by changes in plant ecology, and how much by niche partitioning in well-filled ecosystems? The late Cretaceous may be the longest interval in the entire Phanerozoic without a major terrestrial extinction event, so maybe the low-hanging fruit of oral morphospace had already been plucked and necessity mothered innovation.


It does seem a little apples to oranges to compare oral anatomy diversification in ornithischians versus sauropods, as sauropods are (a) largely committed to postoral processing and (b) notorious for lack of skull preservation.


I guess I should read the paper before commenting... [size=78%]  [/size]

I mean, honestly, in the PCO plot the sauropodomorphs seem to occupy a pretty large volume of morphospace. But they don't particularly expand toward the end of the Cretaceous, which I think jibes with what we know about diminishing taxonomic diversity of sauropods in the latest Cretaceous.

Plant ecology vs. niche partitioning is a super interesting question in light of the long stable Cretaceous. I don't know the answer but yeah, really interesting question. I think it's interesting too that they found this just in jaw/tooth morphology, so there's probably a very minor effect of sexual selection, which I think is otherwise a pretty good hypothesis to explain some of the cranial morphology of hadrosaurs, ceratopsians, and pachycephalosaurs.