If small feathered non-avian dinosaurs had survived, I suspect we would call all of them “birds” (or by whatever word we called modern birds), even the ones that didn’t fly. “Animals with feathers” is a pretty natural group when contrasted with those that don’t have them. We had no problem calling ostriches and penguins “birds” even when we didn’t know they belonged to the same clade.
After all, we lumped crocodilians, turtles, snakes, and lizards as “reptiles,” even though they are pretty dissimilar and don’t belong to the same clade (at least, if birds are excluded).
I agree–just like we have to include “egg-laying” as a possible trait of mammals since we still have monotremes around. If the monotremes hadn’t made it, the definition of “mammal” would have been different.
Cladistically, the definition of a what is known as a “crown group” (all living forms in a group) may be different from what is known as the “stem group” (extinct ancestral group). Modern birds are easy to define on a number of characters. If you go back to the Cretaceous, you have to rely on highly technical characteristics of the skeleton to distinguish them from bird-like dinosaurs. Likewise, for modern mammals we can rely on hair and mammary glands to define them. In fossil forms, they are arbitrarily defined on details of the jaw articulation.
My guess would be that large sauropods would have emitted proportionally less methane than an equal biomass of ungulates. First, the ungulates would be individually much smaller and because of this would have had a higher metabolism and energy requirements, requiring them to process more food. Second, large sauropods may have been passive homeotherms, relying on their vast size to maintain their body temperature, again reducing their relative energy requirements.
Doesn’t sauropods’ efficiency mean more biomass of herbivores per biomass of vegetation? And so a greater overall conversion rate of plant carbon into methane compared to ungulates.
That doesn’t follow. Greater efficiency means greater conversion of plant carbon into animal tissue. Methane is a bacterial waste product and represents an energy loss to the animal.
If sauropods used the same fermentation system as ruminants, I think they would produce a similar amount of methane per amount of plant biomass processed, since this is dependent on bacterial processes. (However, kangaroos depend on a different kind of bacteria for fermentation which produces 80% less methane than that of cows. We can’t really know the rate of methane production in sauropods without knowing what system they used.)
But, still, the overall conversion rate of plant carbon into methane is going to be proportional to the total animal biomass. While the amount of methane emitted per ton of sauropod is going to be less than the amount per ton of ungulate, because there’s more tons of sauropod, there’ll be more total methane collectively emitted by the sauropods.
No. The amount of methane depends on the amount of plant material consumed, not the amount of animal biomass it supports. 1000 tons of plant material may support 100 tons of sauropods or 50 tons of ungulates, but its still going to produce the same amount of methane when fermented.*
*Of course, all other things being equal. We don’t know the productivity or digestibility of Mesozoic plants compared to grasses, for example.
Hmm. I see the dependence on the amount of vegetation consumed, but doesn’t the animal consuming it determine how much is converted into animal vs converted into methane vs ejected out the rear end?
And there’s also a temporal component. Which goes through the 1000 tons of plants faster: the 100 tons of sauropods or the 50 tons of ungulates?
(By the way, thanks for humoring me along this tangent.)
No. As I’ve already said, the methane is not a product of the animal, it’s a product of the bacteria in its gut. Assuming ungulates and sauropods used the same kinds of bacteria for fermentation (and that’s a big assumption), the same amount of plant material should produce the same amount of methane.
Again, that’s going to be determined by the bacteria rather than the kind of animal. There’s no point in an animal eating faster than the bacteria can ferment what it eats.
Think of fermenting alcohol. The rate of production of alcohol is going to depend more on the kind of yeast and amount of sugar rather than the size of the container you’re fermenting it in.*
*I recognize that the size of the vat could have some effect on the rate of fermentation, but I’m talking about general principles here rather than details.
True, but there is still a fair question to ask why these feathered dinosaurs survived and those feathered dinosaurs didn’t, regardless of how those divisions occurred. In other words, we could still sensibly ask the same question, we just might have different answers because the dividing lines are in different places.
We’re basically looking at the traits that differed and then trying to back-explain why those differences had different outcomes.
And the answer may be “no particular reason.” A viable population of species a might have just happened to be in a sufficiently sheltered spot after the impact and species b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, and z didn’t. And it could have just as easily have been one of the other species, or have been none at all.
Right. It’s easy to explain why certain groups were all killed off - basically everything large - than which groups survived among the rest.
Some birds survived because they were small and could fly. But it’s important to emphasize that nearly all birds became extinct as well, as well as all other small flying vertebrates. Being small and capable of flight didn’t save the pterosaurs or enantiornitine birds. As mentioned above, only four clades of birds appear to have survived the extinction event, which means as few as four species may have survived. (It was probably somewhat more, but quite possibly more than 95% of bird species existing at the time were killed off.) And evidence suggests that 93% of all mammals were killed off. Even among the groups that survived which species did so was largely a lottery.
And even among those few lucky species (however many of them there were), probably most of the individuals died off, too. It could be that, of all of the myriad birds of thousands of different species who could have been over the lake (and away from the fires) at the moment, it just happened to be those particular ones who actually were.
