The completed display on the 4th floor of AMNH. (Image copyright AMNH, credit: D. Finnin)
And paleontologists didn’t even need to find another fossil to figure it out. A new paper out in Biology Letters by Graeme Lloyd from Macquarie University and coauthors uses probability to rewrite the evolutionary history of the dinosaurs.
Paleontologists have started using new methods to figure out relationships between extinct animals and the timing of their evolutionary splits. In this case, these methods involve a combination of probability and fossil occurrence data. Combining the ages of fossil animals in a probabilistic framework can provide valuable information about rates of evolution and help determine with greater accuracy when key splits occurred.
But why can’t paleontologists just use fossil evidence? Why do they need more complicated probabilistic models to figure out what is going on with evolutionary history? “Fossil evidence will always underestimate the true divergence time,” Lloyd says. This basically means that the probability that the first appearance of a fossil in the fossil record is its “true” first appearance is so minute, it must be taken as a minimum age. “Paleontologists have (I think) clung to their precision over their accuracy. We have given distributions of ages for each divergence and thus captured uncertainty in our divergences for the first time.”
Lloyd was looking to create timescales of evolutionary transitions in dinosaurs and birds, specifically examining when the dinosaurs first came into being, and also when bird relatives first took flight. They created a new family tree of dinosaurs using 1,000 species, which is the largest ever, to test for answers to these questions.
Figure from the Biology Letters article showcasing the probability distribution of the origins of... [+]
They found that the origin of dinosaurs was most likely as far back as 250 million years ago during the Early Triassic—but there is a small probability they evolved even earlier at the end of the Permian. This is older than is previously thought, and also means that if the group really did evolve at the end of the Permian, they survived the greatest mass extinction event of all time at the Permo-Triassic boundary. Flight is estimated to have evolved during the late Middle to early Late Jurassic, which only slightly predates the earliest fossil of a putative bird that likely flew called Aurornis, so this result agrees with fossil findings.
