The Cenozoic: the Age of Mammals AND Birds?

[Infinity Blade]

www.flickr.com/photos/daveynin/43496213244

Although this is an idea I've first heard of a while back (back when Duane Nash was running Antediluvian Salad), I've begun thinking about it again recently.

antediluviansalad.blogspot.com/2013_03_17_archive.html

^Here's an old blog post by Nash detailing this. His basic premises for why the Cenozoic is not just the Age of Mammals, but also the Age of Birds can be summarized as follows:

1.) In terms of species birds outnumber mammals about 2:1 (since then, a study has come out proposing that present day avian diversity is actually significantly underestimated, suggesting there may be ~18,000 species alive today; Barrowclough et al., 2016->).
2.) Birds are up there with mammals at the top of the highest terrestrial biomasses (humans and brown rats hold spots #1 and #2, with the domestic chicken at #3).
3.) Predatory birds play a profound role in controlling rodent populations (which contain the most present day mammal species out of any other order).
4.) Birds can/have occupied niches mammals fill (i.e. large land carnivore and herbivore miches), while mammals have failed to occupy some niches birds occupy.

I understand that calling a period, era, or age an "Age of *insert clade here*" doesn't truly give you a full picture of the world's diversity during that timespan (you could call the Cenozoic and Mesozoic plenty of other things too, other than the "Age of Mammals" or the "Age of Reptiles", respectively). At the same time, however, I'm sure these aforementioned labels are meant to convey which vertebrates "dominated". That is, which vertebrates occupied the majority of niches, including specialized ones, out of all the niches vertebrates at the time occupied.

So what do you think? Is the Cenozoic better thought of as the Age of Mammals and Birds or not? Anything else to consider?

[creature386]

The absence of pterosaurs certainly helps matters, so this isn't unsurprising.

It nonetheless isn't an easy question to answer. Evolution isn't goal oriented, so to one person, dominance can mean having lots of biomass or lots of species (in which case birds win). Another persons dominance, however, can mean having all of the heavy-hitters (whales, elephants, large carnivores, etc.). What I'm interested is, how did the situation look in the Mesozoic? If factors like biomass and biodiversity strongly favored over mammals back then, a case could be made that mammals benefited more from the extinction of the dinosaurs and the Cenozoic can thus be rightfully called their golden years. If, however, the situation was the same or even more in favor of the mammals back then, then the idea of an age of mammals and birds is more than justified.

[Infinity Blade]

I have my own opinion of what "dominance" should mean, but even there I have some uncertainties. That is, I don't think dominance should necessarily mean producing the largest fauna of the period: I consider birds occupying the lion's share of volant niches today to be dominance, for example. But if we establish that small species can be representative of dominance (and a lot of modern birds are small), where do we draw the line? Being a specialist? At something else? Squamates have been thriving throughout the Cenozoic with mostly small forms too, but no one considers the Cenozoic to be the Age of Squamates (this goes back to the point I made in the OP; "Age of *blank*" isn't the full picture).

So yeah, there's my critique of my own opinion. I still don't think dominance should mean "biggest taxa" (because well, small lifeforms are just as important to ecosystems as well), but I'm not 100% sure of what to think of my own idea of it.

As for your question, I don't know. I'm pretty sure it's a safe bet that mammalian biomass and biodiversity in the Mesozoic was nowhere near what it is now, but then again the same might be said for birds as well (pterosaurs, as you mentioned).

[Infinity Blade]

"Large, flightless birds are truly remarkable creatures, but the real success among birds belongs to the fliers. Even though few skeletal modifications occurred during the Cenozoic, a bewildering array of adaptive types arose. If number of species and habitats occupied is any measure of success, birds have certainly been at least as successful as mammals."
Historical Geology->

^I guess there's the species diversity perspective, but also the habitats occupied perspective.

Anything else to add?

[dinosauria101]

Been thinking about this for a while.

I suppose it would depend on whether you prefer mammals or birds. Both seem to work.