Dear 100 Hour Board,
The question: If dinosaurs were somehow brought back to life and reintroduced into the wild (as invasive species, essentially), what kind of effects would this have on the world's ecosystems? If a detailed answer is impossible, I can completely understand.
The reason I'm asking: I had a dream last night in which my dad and I were trying to figure out what had been eating our chickens, and by looking at a footprint in the mud we saw that it must have been a dinosaur. The dinosaur had apparently eaten my sister, too, which I viewed as a minor detail. I then dreamed that I woke up and decided to ask this question to the Board. And there you have it.
So really, I ought to sign this question as
-the subconscious of yayfulness
Dear subconscious c/o conscious,
Trick question! There is already a living clade of dinosaurs–saurischian theropods–integrated into nearly every ecosystem. Class Aves. We like to call them "birds." But, because the subconscious doesn't usually clarify meaning according to scientific standards of taxonomy, I'll examine your premise based on a few assumptions. Assumption 1: you mean currently extinct dinosaurs coming alive again. Assumption 2: you mean large dinosaurs, based on the fact that one is apparently large enough to eat family members and chickens, you probably aren't overly-concerned with the ramifications of re-introducing chicken-sized beasts like Compsognathus.
To successfully become a full-blown, sister-stomping, invasive species, dinosaurs would have to meet a couple biological requirements.
1. Could dinosaurs from ≥65 million years ago survive in today's climate at all?
Do you remember why dinosaurs went extinct in the first place? Although the mass extinction was mainly due to giant things smashing into the earth and thus destroying food chains from the bottom up, dinosaur extinction was probably also part of a more gradual climactic transition into a colder, more mammalian earth. As you can see if you look at climate change during the Phanerozoic, it is much cooler (5-10 degrees Celsius) on average today than it was during much of the Mesozoic and especially the Cretaceous. How do we know it's colder now? Because there is absolutely no evidence of any kind of polar ice or glaciation during the Cretaceous, and evaporite deposits (which occur at hot and dry extremes) peaked during the Triassic and Jurassic periods.
So I imagine dinosaurs might have problems like this today:
Save a dinosaur. Support global warming.
It's not just temperature that's changed in the last tens to hundreds of millions of years. Oxygen levels in the atmosphere also tend to fluctuate. Triassic and Jurassic dinos are used to greater or about equal levels of oxygen we enjoy today, but Cretaceous lizards might be gasping for breath a little. However, I don't think that oxygen availability (which changes more radically at different altitudes than between the Mesozoic era and now) is a big deal.
However, Triassic lizards would be more comfortable with cold temperature extremes, as most of the land mass they lived on had huge temperature variation due to the distance from the center of the supercontinent to the sea. Many dinosaurs that lived in temperate or tropical forest during the Mesozoic might find a home in the tropical forests of today.
2. Given that some species are able to hack it in our Cenozoic climate, could any of them prosper enough to outcompete native wildlife and become invasive?
From the Forest Service: Often, invasive species owe their success in colonizing new ecosystems to one or more of the following characteristics:
- They tolerate a variety of habitat conditions: as I said above, dinosaurs can tolerate a variety of habitat conditions with the probable exception of extremely cold ones they've never encountered. Triassic dinos especially are used to drastic fluctuations in surface temperature. Because fossils are limited to areas where bones could be fossilized properly (often swampy conditions) and estimations of climate from millions of years ago are difficult to pin down exactly, our knowledge of what kind of habitat conditions different dinosaur species would tolerate are educated guesses at best.
- They grow and reproduce rapidly: again, we don't know all the specifics about dinosaur family planning, but it's highly probable based on nest evidence that dinosaurs grow and reproduce about as rapidly as crocodiles, laying a clutch of eggs each year. There is circumstantial evidence that some dinosaurs like Maiasaura provided some parental protection to their young, reducing the mortality rate. Their reproduction rate would be much slower than small mammals, but compared to current large herbivores and apex predators, their reproduction would be comparatively rapid.
- They compete aggressively for resources (like food, water, and nesting sites): partially-healed toothmarks caused by dinosaurs being found on dinosaur bone fossils, evidence of cannibalism, as well as the fact that they were the dominant life form for hundreds of millions of years strongly suggest that when it came to resource allocation, dinosaurs were fierce competitors.
- They lack natural enemies or pests in the new ecosystem: leaving the human propensity of shooting large, scary things aside, this seems to be obviously the case. Whatever ate non-avian dinosaurs will have been very hungry, not to mention dead, for at least 65 million years. However, dinosaurs can still eat dinosaurs as they used to do, and I'm sure crocodiles wouldn't mind resuming their old dinosaur-chomping ecological role.
Overall, I think that if humans gave dinosaurs a sporting chance, they might be pretty good at outcompeting some native wildlife and being invasive species.
3. So, ultimately, what would the impact on ecosystems be?
Let me map it out for you!
First, coastlines would warp slightly and all islands smaller than Jamaica would vanish into the sea. (Just kidding! Those changes are purely the effect of my questionable hand-cartography skills.)
Second, this map is based on a magical even distribution of dinosaurs, instead of a mass release into the wild at a certain location. As we know, dinosaurs would avoid extreme northern and southern latitudes. (Well, not avoid, technically, it would be a more "go there and die and fail to be a significant presence there" type phenomenon.) In the yellow areas, desert-adapted dinosaurs would thrive, especially Triassic species adjusted to cold night temperature swings. Dinosaurs like Coelophysis, Dilophosaurus, and Spinosaurus would compete with local predators. With reptilian water-tight skins, dinosaurs may be able to outcompete some mammals during extreme conditions. In the green areas, many Cretaceous and Jurassic dinosaurs would enjoy the tropical and subtropical forest conditions they are adjusted to. More temperate areas of forest, like that in the Appalachians and many parts of Asia, would be less-hospitable but probably still sustain species like Eoraptor, Staurikosaurus, Iguanodon, Allosaurus, Elaphrosaurus, Torrosaurus, and Parasauropholus. Large species tromping through forests cause interesting effects on local vegetation, both because of their sheer size and stomping action, but also because of their voracious plant-eating. An example of this we see today is the impact of reintroduced elephants on trees. In the orange area, dinosaurs like Gallimimus, Chindesaurus, Struthomimus, and that raptor with a really un-scary name, Bambiraptor, used to semi-arid savannah conditions would become invasive. Large to mid-size predator dinosaurs like Spinosaurus and Utahraptor would compete with current apex predators, perhaps hastening the extinction of the cheetah as its niche is taken over by raptors and its currently existing genetic doom plays out more rapidly than anticipated. As much as I love the cheetah, I have to admit it would be pretty funny to read the conservation news headline "UTAHRAPTOR HASTENS DEMISE OF THE CHEETAH." In the purple striped areas, an interesting ecological melee between crocodilians and dinosaurs would play out. Alligators and crocodiles would prey on baby dinosaurs, dinosaurs would prey on them, and they would both compete for similar prey. Over thousands of years, a directional selection towards ginormous crocodiles could occur, until dinosaurs would reach their former stalemate with animals the size of sarcosuchus.
Overall, I don't think dinosaurs would exclude, outcompete, or cause the extinction of many mammal species, which are better-adapted for today's planet currently. I think the main impact would be on forests, crocodiles, and also current apex (top of the food chain) predators. Many large dinosaurs were the apex predators of their day, and current apex predators like the leopard or the dingo would be hard-pressed to try and attack a full-grown Tyrannosaurus. Perhaps, among many mammalian predators, there would be a behavioral and ecological shift towards scavenging, to avoid such direct competition with gigantic dinosaurs. Or perhaps the giant dinosaurs never take over at all due to ecological reasons I haven't even considered.
Or maybe–just maybe–current apex predators and dinosaur apex predators form an unholy alliance???
Just kidding. That's at least three levels of impossible beyond what I'm even considering here.
Despite the ability of some BYU professors to pick up a tiny skull fragment and just from that identify a species of dinosaur, there's so little we can guess accurately to the point of knowing for certain about dinosaur ecology and the conditions of the world they lived in. Luckily, we will never have the opportunity to see this answer proved wrong.
4. But what do you think would actually happen if some mad scientists unleashed breeding pairs of large dinosaurs upon the world?
The scientists would get in BIG TROUBLE, we'd recapture or shoot all the dinosaurs, and resume our daily lives with maybe a couple people trampled on but ultimately no ecosystem-wide impacts. Then, many, many movies would be made about the incident. Schemes almost as crazy (see: the Pleistocene rewilding project) have been flatly rejected in the past. And this one has the unfortunate problem of being completely impossible. Ah, well, one can dream.