The "terrible lizards" are even older than we'd thought. Here's how scientists figured that out.
Dinosaurs, it turns out, may be even older than we'd thought. A new paper, published today in the journal Biology Letters, pushes dinosaurs' lineage back 10 million to 15 million years earlier than we'd previously known, dating them back into the Middle Triassic age. (Previously, the oldest known dinosaur came from the same area in present-day Argentina -- from rock sediments figured to be about 230 million years old.)
As lead researcher Sterling Nesbitt told Live Science, "This is our best evidence of a Middle Triassic dinosaur."
The discovery hinges on a set of bones that were unearthed in Tanzania in the 1930s: a humerus (upper-arm) bone and six vertebrae. (This kind of partial evidence is common when it comes to ancient fossil records: The full skeletons we're familiar with from museums, Nesbitt points out, are rare paleontological luxuries.) The species those bones belonged to is named Nyasasaurus parringtoni, and it lived, the paper reports, sometime between between 240 million and 245 million years ago -- a time when Earth's continents were still fused together in the unified landmass known today as "Pangaea." (Tanzania would have been the southern tip of that mass.)
The dating discovery answers -- or, at least, makes strides toward in answering -- questions that have long been a matter of debate among paleontologists. How old, exactly, are dinosaurs? Since the mid-19th century, scientists have been suggesting that dinosaurs existed in the Middle Triassic (the oldest dinosaur fossils fit into the Late Triassic period). But that theory has been based on fragmentary evidence: literal fragments of bone, but also fossilized footprints. And pedal prints are fairly unreliable when it comes to offering hard data about the creatures that made them: There are lots of animals, and they make lots of similar prints -- particularly over the course of millions of years of Earth-roaming.
Bones, however, are much more conclusive when it comes to the insights they offer about their owners. Even a partial skeleton can contain a wealth of data. Nyasasaurus parringtoni likely stood upright, T-Rex-style, and measured somewhere between 7 and 10 feet in length (3 feet at the hip). It likely had a long neck and tail, and would have been about the size of a large Labrador retriever. Though the animal's overall mass is tougher to determine, it likely weighed somewhere between 45 and 135 pounds. If the creature is not the earliest dinosaur, Nesbitt said, "then it is the closest relative found so far."
But then: How do you actually tell the world, "here is the earliest dinosaur -- or dinosaur-like creature -- we know of"? How do you make that determination in the first place?
The first challenge for Nesbitt and his team was to determine whether the bones in question actually belonged to an early dinosaur. The team used our existing knowledge of dinos -- the fact, say, that the beasts tended to grow quickly -- and applied that to the clues provided by the bones. In this case, a cross-section of the humerus bone suggested the haphazard growth of tissue, which is a sign of rapid growth in the animal the bone belonged to. Dino-y? Check.
Furthermore, "we can tell from the bone tissues that Nyasasaurus had a lot of bone cells and blood vessels," study co-author Sarah Werning, a UC Berkeley researcher who did the study's bone analysis, said in a statment. "In living animals, we only see this many bone cells and blood vessels in animals that grow quickly, like some mammals or birds."
The team also considered the way the bones would have interacted with the musculature of the animal in question. In this case, the humerus displayed an enlarged crest -- an enlarged area, that is, where the animal's arm muscles would have attached to its shoulder muscles. And early dinosaurs are, per Nesbitt, the only animals known to exhibit that particular feature. Dino-y? Check again.
Once the team was reasonably convinced that the bones in question belonged to a dinosaur-like creature, the members moved on to the matter of dating. For that, they analyzed the fossils' surroundings, aging the layer of rock where the fossil was found and, for comparison, the layers both above and below it. They also compared the fossils with similar remains found worldwide. Dino-y, but old? Check. And check.
So. Based on all that, we now have a new, tentative timeline for dinosaurs' stay on Earth. And we have, too, a new sense of how dinosaurs evolved into the "terrible lizards" that live in our minds and our culture today. Dinos developed slowly. They eased into their power, starting small and growing -- and growing and growing -- as Earth evolved with them. The newest paleontological discovery offers a new way to understand an old insight: that dinosaurs' domination of the terrestrial world was as gradual as it was finite.