With the return of roaring, moving dinosaurs to the Academy’s Special Exhibits Gallery, you might be wondering how we know what we know about dinosaur movement. To answer this seemingly simple question, we must consider the complex ways that animal locomotion has changed over time.
Many backboned animals alive today are quite different from the animals from which they evolved, yet they still share many features with their ancestors. Over generations, populations of living things have changed and adapted to their surroundings, applying the most useful attributes of their predecessors and relatives and leaving behind the less useful traits.
Below, Academy Dinosaur Hall Coordinator and paleo-artist Jason Poole demonstrates through illustrations how the movements of backboned animals, including dinosaurs, have developed and adapted over time. From fish in and out of water to reptiles, T. rex, and mammals of the land and sea, animals across time have been making the most of what they inherited as they strive to survive in their surroundings.
[color-box color=”green”]Our Cast
The characters that we’ve chosen to focus on epitomize various inherited motions that evolved over tens of millions of years. Evolution is a branching process that generates diversity, creating a tree of related species that often share distant common ancestors. These species may not be direct descendants of each other, yet their methods of locomotion demonstrate their shared ancestry.[/color-box]
Our story begins and ends in the water, home to all life billions of years ago. Originating about 530 million years ago during the Cambrian explosion, primitive fish were the earliest vertebrates. Over time, they have developed useful methods of locomotion to propel themselves through the water.
If you’ve ever watched fish swim, you have probably seen them use an undulating motion, with their whole bodies or parts of their bodies moving rhythmically from side to side. Some fish combine this undulating motion with an oscillating movement of their fins, waving them back and forth at regular intervals. These motions work in cooperation with their long, narrow shape, allowing fish to save energy as they cut through the water.
At least 365 million years ago during the Devonian Era, some creatures began to spend time on land. These animals used the side-to-side body motion seen in fish as they developed features necessary for terrestrial life. Leading up to the first land animals is Tiktaalik roseae, a 375-million-year-old lobe-finned fish discovered by a team of scientists including Academy paleontologist Ted Daeschler. Tiktaalik looks like a cross between primitive fish and the first four-legged animals (tetrapods). With scales, a flat head, a neck, and fins that enclosed a shoulder, elbow, and wrist, Tiktaalik is the first creature in the fossil record to show some of the specialized features that we see in amphibians.
Unlike fish fins, Tiktaalik’s fins supported its body as it moved around in shallow streams, ponds, and mudflats, possibly in an effort to avoid large predators living in deeper waters. Tiktaalik had a sprawled posture, with its fin-legs projecting down and to the sides. Its body undulated in a fish-like, side-to-side motion, but it had developed limbs to carry this movement onto land. Eventually, this motion would be passed on to lizards, snakes, crocodiles, and other tetrapods.
With the transition of fish relatives onto land, vertebrates brought the side-to-side motion common in the
water to terrestrial living. Reptiles such as crocodiles and alligators, for example, move themselves through water by undulating their tails from side to side. Their undulating spines coordinate the movements of the four legs propelling them on land. Like many reptiles, they also walk in a sprawled posture similar to Tiktaalik’s.
Today’s scientists and engineers use computer models to better understand dinosaur movements. These models look closely at dinosaur anatomy alongside the motions of live creatures to recreate the way dinosaurs may have moved. Even with plentiful skeletal fossils, dinosaur trackways (sets of footprints), and advanced computer modeling, scientists still have questions about dinosaur anatomy and movement. Still, we can begin to imagine what it might have been like to walk among the dinosaurs.
Dinosaurs are descendants of the sprawling Archosaurs, a group that includes ancestors of crocodiles. These animals moved with their legs under their bodies to save energy. With their back legs under their bodies, some dinosaurs’ front “hands” were free for digging, grasping, catching prey, and eating. Dinosaurs maintained a wave-like motion in their movements, but instead of the smooth side-to-side wiggle often seen in fish, dinosaurs integrated up and down motions into their walking and running gaits.
One area where the fish-like, side-to-side motion did appear as in dinosaurs’ tails. Scientists know that tail motion was restricted laterally because they have identified ossified (strengthened) tendons that prevented up and down movement. Hadrosaurs, Stegosaurs, and even the famous T. rex waved their tails from side to side, which may have supported and balanced their movement.
Just as dinosaurs benefited from moving their legs underneath their bodies, land mammals living long after the dinosaurs continued to perfect this motion. If you watch your pet dog or a zoo mammal move, you can see that their hips swing forward as they take a step. This swinging allows their hind feet to move in their intended direction before they hit the ground.
Over time, mammals’ spines developed an up-and-down bowing motion that enabled them to experiment with a wide range of directional motion in their backs. This additional flexibility in their spines allows animals that walk on all fours to attain faster bursts of speed to capture or avoid prey.
A lineage of hooved mammals that shared similarities with today’s hippopotami took this inherited up-and-down spinal motion of four-legged land mammals back into the water. Modern whales are relatives of these creatures. If you watch a YouTube video of whales moving through water, you can see that their backs bow up and down as their streamlined bodies glide through the water.
A version of this article originally appeared in the summer 2016 issue of Academy Frontiers.
[color-box color=”green”]Want to learn more about dinosaur movement? Check out our newest special exhibit, Dinosaurs Unearthed, in the Special Exhibits Gallery! Back by popular demand—roaring, moving, life-size animatronic dinosaurs invade the Academy for a multi-sensory experience for the whole family. State-of-the-art and scientifically accurate—down to the feathers on T. rex—Dinosaurs Unearthed features more than a dozen realistic, full-bodied dinosaurs, as well as skeletons, fossil casts of skulls, claws, and horns, real specimens of mosasaur and Spinosaurus teeth, an Oviraptor egg, and the ever-popular coprolite (dino poop).
Visitors will experience brand-new interactives, such as a multi-touch table and a scale that tells you how you measure up to different dinosaurs. A Dino Detective touch-screen quiz, chances to control dinosaur movements, and other activities encourage exciting hands-on exploration. Learn more and buy tickets today![/color-box]