Alvaro Kedding/© AMNH
Alvaro Kedding/© AMNH
Alvaro Kedding/© AMNH These smaller animals were important parts of their ecosystems and give insights to the ancestry of important living groups, including our own. However, our knowledge of them is very incomplete, because their tiny fossils are hard to find and difficult to study.
In this SciCafe, the Museum’s Macaulay Curator of Dinosaur Paleobiology Roger Benson discusses his use of cutting-edge 3D-scanning techniques, including CT scanning and synchrotron tomography, to provide remarkable visualizations of some of the smallest Jurassic vertebrates.
[MUSEUM HALL NOISE]
[Museum visitors walk around two large dinosaur skeleton mounts of hadrosaurs, or duck-billed dinosaurs.]
ROGER BENSON (Macaulay Curator, Division of Paleontology): So some of the biggest dinosaurs were really big. And paleontologists have noticed this a long time ago,
[Two paleontologists, talking to each other, stand next to a huge dinosaur bone, as tall as each of the paleontologists.]
BENSON: –and asked a lot of questions about how it is that they got so big. But what is often overlooked–
[BENSON appears on screen, speaking to the camera.]
BENSON: –is even the smallest dinosaurs were not really that small compared to many vertebrates alive today.
[A magnifying glass in a Museum display focuses on a small fossil dinosaur skull.]
BENSON: We’ve occasionally found some pretty small dinosaurs,
[Some small model dinosaurs, based on the small skull, look up with huge eyes. Above them is a model of the grown adult dinosaur of the same species.]
BENSON: –but they all turn out to be babies.
[BENSON reappears, speaking to the camera.]
[MUSIC]
BENSON: So if I found a mouse-sized dinosaur, I would be so surprised and excited.
[The logo for the American Museum of Natural History appears over footage of dinosaur collections. A title appears: “Where Are All the Tiny Dinosaurs? With Paleontologist Roger Benson”.]
[BENSON reappears on screen, sitting in a room full of dinosaur bones and speaking to the camera.]
BENSON: Hi, I’m Roger Benson,
[Text appears in the lower left hand of the screen: “Roger Benson, Macaulay Curator, Division of Paleontology”]
BENSON: –and I’m the Macaulay Curator of dinosaur paleobiology at the American Museum of Natural History. Now, I’m here in the big bone room, which is a storeroom where we keep hundreds of giant dinosaur bones from the late Jurassic. But I’m also interested to study the fossils of much smaller animals like this one.
[BENSON holds up a palm-sized chunk of rock, where small ridges of black fossil bone are just barely visible on the surface.]
BENSON: Often, because it’s much easier to find the fossils of large animals,
[Panning around the fossil collections, a person walks up a set up steps to get to a higher shelf. The bones on the shelves are all almost human-sized.]
BENSON: –they’re just easier to see because their bones are large, we end up studying as paleontologists some of the biggest animals that lived, and that includes giant dinosaurs.
[Quick nature shots of some small animals: a squirrel, a salamander, a bumblebee, and a lizard.]
BENSON: But small animals are important today. They make up almost all species on Earth. And the same was true in the past.
[BENSON reappears on screen, speaking to the camera.]
BENSON: So if we really want to understand ecosystems of the past, and where the diversity of animals that we see today came from, so its evolutionary origins, then we need to know much more about small-bodied animals. Over the last 10 years, I’ve particularly spent a lot of time in the middle Jurassic of Scotland,
[A car drives through a winding road in the Scottish countryside.]
BENSON: –in places where we don’t really find many dinosaur bones,
[Photos of BENSON on the rocky Scottish coast, looking at rocks.]
BENSON: –but we find the bones of much smaller animals.
[BENSON reappears on screen, speaking to the camera.]
BENSON: When we’re looking for small animals we get our faces right up close to the rock,
[A photo of BENSON crouched in a rocky hillside looking at a tiny fossil.]
BENSON: –and we’re looking for tiny, tiny bones that we just couldn’t see if we weren’t crawling around on our hands and knees.
[BENSON reappears on screen, speaking to the camera.]
BENSON: We go through a lot of trousers this way.
[Closeup shots of small dark fossil bits poking out of pale rock faces, some with a penny next to them for scale.]
BENSON: And these are fossils whose bones are so small that it’s physically difficult for us to extract them from the rock. And we’re really able to explore these fossils,
[BENSON brings a wrapped fossil specimen to the chamber of a CT scanner.]
BENSON: and understand their importance just thanks to new technology like CT scanning. So the CT scanning allows us–
[BENSON reappears on screen speaking to the camera, holding up a palm-sized chunk of rock.]
BENSON: –to look inside of a rock like this that we haven’t physically extracted the bones,
[BENSON in front of a computer screen looking at CT scanning results.]
BENSON: –but we can digitally peel away the layers of rock. And study the anatomy of the animal inside,
[Black and white videos from CT scans being moved through layer-by-layer, with fossil bone appearing as white in a gray matrix.]
BENSON: –and then understand its importance for evolutionary history.
[BENSON reappears on screen, speaking to the camera.]
BENSON: So in the big bone room I am surrounded by the bones of some of the biggest dinosaurs that ever lived.
[A giant long-necked Barosaurus towers over the Museum’s main rotunda.]
BENSON: And those are the giant, long-necked sauropod dinosaurs,
[The Museum’s Apatosaurus fossils on display in the dinosaur halls.
BENSON: –that commonly weighed around 40 tons.
[The Museum’s Patagotitan cast, a titanosaur, leans its head out of a massive doorway.]
BENSON: And the biggest ones, animals like Patagotitan or Argentinasaurus, could have weighed 60-70 tons.
[BENSON reappears on screen.]
BENSON: Now, that is much bigger than the largest land mammals today.
[Nature footage of African elephants roaming the grasslands.]
BENSON: So the biggest elephants might weigh up to eight tons. And that’s about one tenth of the size of the largest dinosaurs.
[A fossil cast of an Archaeopteryx specimen with wing-like arms, splayed out in rock.]
BENSON: The smallest dinosaurs include–
[A piece of paleoart showing a black, bird-like Microraptor. Text reads: “Microraptor.”]
BENSON: –small predators like Microraptor,
[A photo of a Fruitadens model, which is a small dinosaur that looks almost like a hadrosaur, with long quills or feathers on its back.]
BENSON: but also small herbivores like the ornithischian bird-hipped dinosaur, Fruitadens. And these animals weighed,
[Another small dinosaur specimen, bird-like and flattened on a rock. Text label reads: “1 lb (0.5 kg)”.]
BENSON: –at their smallest, about half a kilo, or one pound. That’s about the size of a big rabbit.
[BENSON reappears on screen speaking to the camera.]
BENSON: Now half a kilo seems small to us. It’s about half the weight of a typical bag of flour.
[Another small bird-like dinosaur fossil.]
BENSON: But actually, this is big compared to many living groups.
[Nature footage of a rabbit eating some green grass.]
BENSON: So a mammal that weighs half a kilo is in the 75th percentile of mammal body masses.
[A chipmunk scratches itself with its hind legs and eats a seed.]
BENSON: So three quarters of mammals are smaller than that.
[A small yellow bird pokes its way through pink cherry blossoms.]
BENSON: And nine tenths, or 90% of living bird species are smaller than that.
[A lizard leaps to catch a tiny insect.]
BENSON: Almost all lizard species are smaller than this as well,
[A frog lurks below a lily pad.]
BENSON: and the same is true for amphibians.
[BENSON reappears on screen speaking to the camera.]
BENSON: So it seems remarkable that the smallest dinosaurs were actually quite big animals compared to many other species on earth today, but also in the past. Now, you may be thinking, but hang on a second, I know there are tiny birds like hummingbirds that weigh just a few grams, and you keep telling me that birds are dinosaurs.
[A hummingbird drinks from a bird feeder. Two goldfinches eat seeds from a bird feeder.]
BENSON: So how is it that birds are able to be tiny when other dinosaurs weren’t?
[The modern-day birds swipe to the right. Different bird fossils, looking in many ways similar to previous dinosaur fossils seen in this video, appear.]
BENSON: In the early Cretaceous, about 120 million years ago, we see the first rich fossil records of early birds
[BENSON reappears on screen speaking to the camera.]
BENSON: and then in the blink of a geological eye, suddenly birds are small,
[A fossil bird appears. Text reads: “Rapaxavis panni, 10-20 grams”]
BENSON: –smaller than any other dinosaur that ever lived.
[Another fossil bird appears. Text reads: “Cathayornis yandica, 20-30 grams”]
BENSON: And this is really a biological enigma,
[Another fossil bird appears. Text reads: “Cruralispennia, 10-20 grams”]
BENSON: –not only that birds were able to do something that’s unique among dinosaurs,
[A modern-day bird hops on a tree branch before flying away. Text reads: “Poecile palustris, 10-12 grams”]
BENSON: –but also that it seems to happen so quickly and so early in bird evolution.
[BENSON reappears on screen.]
BENSON: So we have this unusual situation where the ancestors of dinosaurs could be tiny. The living descendants of dinosaurs, the birds, they’re able to be tiny. But dinosaurs themselves seemed to be forbidden from being tiny. And we don’t really understand that. But it seems really important that we should if we really want to understand dinosaurs and their biology.
[BENSON digs for fossils in the field, talking with other paleontologist and sweeping away dust from rock.]
BENSON: One of those reasons is, maybe we just didn’t find the fossils. Now, that could happen because, firstly, it’s hard to find small things,
[Someone holds up a very tiny fragment of bone, embedded in a sugar-cube-sized piece of rock.]
BENSON: –because they're small. It’s hard for us to see them in the first place.
[BENSON continues to dig for fossils and looks at a small piece of rock.]
BENSON: But it could also happen because small animals have more fragile bones
[BENSON crouches in the Museum’s paleontological collections, looking at a tray of tiny fossils.]
BENSON: –that preserve less readily. So their fossils don’t occur in the first place.
[BENSON reappears on screen speaking to the camera.]
BENSON: Now, both of these explanations are unlikely, because dinosaurs lived alongside much smaller animals
[Hands hold up a small fossil lizard skull, complete with tiny teeth, no bigger than a golf ball.]
BENSON: –including lizards and mammals and amphibians,
[A tiny pterosaur fossil comes into focus.]
BENSON: and we frequently find the skeleton of these small animals
[Camera pans up from a label that reads “Unidentified lizards” to rows and rows of tiny ice-cube sized boxes containing tiny fossils.]
BENSON: –that lived alongside the dinosaurs.
[BENSON reappears on screen.]
BENSON: So it seems very likely that genuinely tiny, mouse-sized dinosaurs just didn’t exist in the first place.
[BENSON opens a cabinet in the Museum’s fossil dinosaur collections space.]
BENSON: So we need to look for biological explanations. So what is it about dinosaurs,
[Camera sweeps across the huge body of a titanosaur on display.]
BENSON: –that meant that they just couldn’t get so small? So perhaps it’s possible that dinosaurs,
[A display fossil of an Allosaurus leans over its prey.]
BENSON: –with their reptile like methods of getting food,
[A bird-like fossil Archaeopteryx.]
BENSON: but their somewhat mammal and bird-like hot body temperatures,
[Camera pans up to the huge, long neck of an Apatosaurus.]
BENSON: –were somehow physiologically and biologically unique in a way that forbid them from having small adult body sizes.
[BENSON reappears on screen speaking to the camera.]
BENSON: Now, this is something we can try and model mathematically, and confusingly, it doesn’t really provide a good explanation. It could explain why dinosaurs might be slightly larger than other animals,
[An illustration showing silhouettes of a Microraptor and a Fruitadens dinosaur. Text reads “500g” on each of them, and above them text reads “The smallest dinosaurs.”]
BENSON: but it doesn’t explain the fact that in general even the smallest dinosaurs are much larger,
[A square draws itself around the silhouettes of three tiny animals barely visible below the two dinosaur silhouettes. Text next to the square reads “1-2g”]
BENSON: you know, 100 times larger than
[We zoom into the square and see a small shrew silhouette, hummingbird silhouette, and tiny lizard silhouette. Text reads within each, respectively: “2g, 2g, 0.5g.” Text above reads: “The smallest birds, mammals, and reptiles.”]
BENSON: –the smallest birds, the smallest mammals, and the smallest lizards.
[BENSON reappears on screen, speaking to the camera.]
BENSON: So we have a lot more work to do to really understand this enigmatic feature of dinosaur biology.
[BENSON stands in the fossil collections, looking at a drawer that has been pulled out. Credits roll.]