The next time you wake up with sore hips or an aching back, you may want to thank your ancestors. No, not your grandmother or even your great-great-great grandfather. The ancestors in question lived millions of years ago—they were the first hominins, and they evolved a little trait called bipedalism. Previously, our earliest ancestors used quadrupedal strategies to get around. Bipedalism has been advantageous—it’s efficient, and frees up our hands for carrying important things as we move (like holding a cellphone while we walk). Yet, it also has its drawbacks.
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“Bipedalism eventually causes our hips and our backs to get all screwed up,” says Dr. Gavin Svenson, Director of Research & Collections and Curator of Invertebrate Zoology at the Cleveland Museum of Natural History. “That’s ancestry. We can’t escape that. We inherited what we inherited.”
All organisms undergo (or have undergone, in the case of the extinct) evolution, from microscopic viruses to the tiniest insects to prolific fungi to dinosaurs and everything in between. Humans aren’t the only ones managing evolution’s effects. There is no such thing as “perfect” when it comes to evolution. That’s because it’s not a purposeful process. Some traits simply benefit the organism while others might disadvantage it depending on what the organism is experiencing in life. Over time and generations, advantageous traits tend to be inherited while disadvantageous traits tend to die out—a process called natural selection.
Through natural selection, generations of organisms undergo rigorous, high-stakes trial and error. Ultimately, this process results in evolutionary change, often recorded through speciation (that is, the development of a brand-new species) or extinction. All of this happens gradually, on an incredibly lengthy timescale. Traits are passed from generation to generation, so it’s often difficult to see the changes in action. That’s why some scientists use the fossil record to gain a better understanding of evolutionary history.
When scientists look to the fossil record, they find widespread evolutionary change beginning in the Paleozoic Period. But another, later event set the stage for further significant evolutionary changes—a large continental split that happened about 200 million years ago. What was once Earth’s sole supercontinent—Pangea—gradually divided into two over a period of several million years. We call the resulting northernmost landmass Laurasia, and the southern zone Gondwana. This continental isolation produced some unique and bizarre animals that distinctly illustrate a mode of evolution called divergence.
“Divergent evolution happens when taxa, or animals, that have a common ancestor end up living in different environments with different modes of life, which then evolve different traits,” says Amanda McGee, Head of Collections and Collections Manager of Vertebrate Paleontology at the Museum.
Divergence explains why Late Cretaceous dinosaurs from Gondwana, such as Giganotosaurus, are so much bigger than northern dinosaurs of the same period, like Tyrannosaurus rex. Their differing forms and adaptations likely resulted from the changing paleolandscape caused by continental drift.
Over the next several million years, the supercontinent Gondwana broke into the southern continents we know today—South America, Africa, Australia, Antarctica, and the southeastern reaches of Asia, including India. As these now isolated continents shifted (due to tectonic movement) and developed distinct climates of their own, the Gondwanan dinosaurs continued to evolve.
African dinosaurs, like the Ouranosaurus, developed sail-like appendages, theorized to have been display structures or humps for the storage of fat. The even further isolated African island of Madagascar produced dinosaurs that had curious diets, like Masiakasaurus, one of the only dinosaurs showing concrete evidence of cannibalism. And dinosaurs from South America were extraordinarily large, as was the approximately 38-metric-ton Futalognkosaurus (for comparison, modern-day elephants weigh about 4 metric tons).
We know that each of these species evolved traits suited for specific niches that emerged as a result of different environmental pressures in their respective regions. But our understanding of these dinosaurs often comes from incomplete fossil specimens, and, in many cases, a species might only be known from a single or even partial fossil. This limited sample size can cause issues when we attempt to draw larger conclusions about the evolution of these species.
“In the fossil record, each specimen is a snapshot in time, but the fossils that you’re comparing are not all on the same page in that book. They are potentially tens or hundreds of thousands, or even millions, of years apart,” explains Lee Hall, Preparator for the Museum’s Department of Vertebrate Paleontology. “The resolution of the fossil record is notoriously poor for much of it.”
This poor resolution often leaves scientists at an impasse. They are faced with gaps in the evolutionary tree that make it difficult to draw any conclusions about when, where, or why certain characteristics emerged. In some cases, scientists turn to living specimens to gain a better understanding of how organisms evolve. They find that the best living examples to study in real time are things that have short life cycles and reproduce quickly, such as insects.
Many of the Museum’s researchers are interested in learning about insect evolution. Dr. Svenson is one such entomologist. He studies the evolutionary relationships of praying mantises, using genetics to determine how specific traits emerged. When we trace these modern-day species through evolutionary history, we see patterns of trait evolution that are driven by the continental shifts of the Late Cretaceous, similar to the case of Gondwanan dinosaurs. But the mode of evolution is different from the divergence we saw in dinosaurs.
“Gondwana was the geographic origin of modern-form mantises,” says Dr. Svenson. “That’s where you get mantises that evolved to appear like tree bark or sticks or dead leaves or flowers or even grass. And the coolest thing about it was that this pattern happened repeatedly in each continent because the major lineages were established before Gondwana broke apart. The specializations to mimic all sorts of different plant features took place within each continent, a pattern called convergent evolution.”
“Convergent evolution is where you have animals of different ancestry evolving to have similar body forms because they’re living in a similar environment,” explains McGee. For example, the dead leaf mantises of South America (Acanthops) and the unrelated dead leaf mantises of Southern Asia (Deroplatys) both evolved traits that helped them blend in with the dried, crumpled leaves in their respective environments.
To better understand how these traits emerge, we can create phylogenetic trees. These models use genetic and morphological information to estimate relationships among different species, even if they weren’t living in the same place at the same time. We can also use this information to narrow down specific events on the timeline that catalyzed evolution. Dr. Nicole Gunter, entomologist and Associate Curator of Invertebrate Zoology at the Museum, took this approach with dung beetles.
“Some researchers think that because almost all dung beetles feed on mammal dung, they must have evolved with mammals,” explains Dr. Gunter. This would have happened about 50 million years ago, during the Cenozoic Era. But she had a hunch this wasn’t the case, and when she looked at dung beetles’ DNA and created phylogenetic trees, the hypothesis just didn’t hold. The timing of dung beetles’ evolution aligned more closely with the emergence of angiosperms, or flowering plants.
“The results support the older Cretaceous age of dung beetles,” she says, referring to the period of time occurring over 110 million years ago. “This is in line with the fragmentation of Gondwana and long before the major mammal diversification.”
Keying in on genetically passed traits can also help determine what sets one species apart from another. This is what Dr. Andy Jones, the Museum’s William A. and Nancy R. Klamm Chair and Curator of Ornithology, was interested in learning when he studied a bird called the Island Thrush, found on dozens of islands across Southeast Asia. Speculating that plumage differences might tell us how the different island populations are related to each other, he compared these variations to the birds’ DNA patterns. He wondered if, perhaps, this species may be several different species living under the same name.
“It’s a really complicated colonization pattern. I thought, well, maybe the plumage tells us something about this,” says Dr. Jones. “I looked at the genetics and the coloration—they don’t match up at all. So, the plumage is actually pretty worthless for telling us how the different populations are related to each other. The similar coloration in populations separated by thousands of miles and several million years of evolution are likely due to convergence. The deep genetic differences between islands were a surprise. I think there’s a case to be made that Island Thrush is 30 or 40 different species <…> but we still don’t know the full story.”
With the help of this type of research, scientists have now built the scaffolding, or basic structure, we need to understand evolutionary relationships. But there’s still a lot to be learned. As more and more advanced technology emerges, scientists may finally have the right tools to better understand the evolutionary history of organisms like the Island Thrush. Much like the process of evolution, the theory itself is continuously evolving as scientists unlock new ways to study these phenomena.
This dedicated effort to understand evolution isn’t just for the sake of knowledge—there are vital, real-world applications for the research. For example, understanding how a species has evolved can help with conservation prioritization.
“At least in the U.S. under the Endangered Species Act, we don’t give as much recognition to sub-species. They get some protection, but it’s not quite the same. People care more about rare species, more than they do about a rare, local variation of something,” says Dr. Jones. Dr. Svenson echoes this sentiment.
“If you don’t understand what that whole picture looks like, you don’t have a chance at ensuring its stability, and that’s pretty much everything for us,” says Dr. Svenson. “And then there’s the real-world applications of this research aimed at understanding how nature has done it. I like bio-inspired design—biomimicry—too. Why spend all this time and expense engineering something that nature has already done for millions and millions and millions of years, and it works really well?”
Unfortunately, when circumstances arise that are far beyond a species’ normal living conditions, evolution just doesn’t have time to catch up. That’s when we lose these marvels of nature to extinction. This happened to the breathtaking giants of Gondwana when the asteroid hit the Yucatan Peninsula. And countless other species have experienced similar events throughout Earth’s history. It is simply the natural course of life.
Luckily, we can still witness some of these wonders firsthand in museums. The Cleveland Museum of Natural History’s permanent collections, in-house-produced exhibits like Dung Beetles!, and traveling exhibits like Ultimate Dinosaurs are here to give you the opportunity to see nature’s most impressive works of engineering firsthand.
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