When dinosaurs first appeared 238 million years ago, our planet looked very different than today. All seven continents were joined as one giant landmass. Pangea, as scientists named the behemoth, was located at the equator, so it was very warm.
Dinosaurs Around the World, on view through Jan. 20, 2019, nicely illustrates this concept that many of us learned in elementary school — and promptly forgot. If the dinosaurs also had been part of the curriculum — as they are the highlight of the exhibition — more of us may have remembered.
Curious about the dinosaur-climate-and-plate-tectonics connection, we asked Academy paleontologist and geologist Ted Daeschler to explain some of the changes the planet went through that led to dinosaurs popping up on every continent. Daeschler, PhD, is associate curator of vertebrate zoology at the Academy and a professor in Drexel’s Department of Biodiversity, Earth and Environmental Science.
About 150 million years ago after South America and its adjoining continents split from its northern land mass, the southern dinosaurs began evolving independently from the northern dinosaurs.
Are the continents still drifting apart from one another today?
Ted: Yes, the continents are certainly still on the move today. The breakup of Pangea began as rifting and the formation of new ocean basins that separated continents. But when one area opens, another closes, and the mountains of the Mediterranean region and the Himalayas are the result of collisions since Pangea began to break up.
During the time of the dinosaurs, Antarctica was not a frozen continent like it is today. There were forests of ginkgoes and ferns!
How can that be?
Ted: The Antarctic continent has not always been over the South Pole, and the Earth’s climate certainly changes over geological time. Fossil beds that are now part of the mostly glacial-covered Antarctic landmass were formed when conditions were very different than today. I recently returned from exploration for 390-million-year-old fossil fish in Antarctica. The strata we examined were formed in subtropical stream systems that were teaming with life in the distant past.
When Africa was still part of the Pangea giant land mass, its dinosaurs were similar to those all over the world. About 150 million years ago, Africa began to separate from the rest of Pangea and the African dinosaurs that developed during this period were some of the largest and meanest to ever walk the Earth.
Why did those dinos get so large, compared to dinosaurs of other continents?
Ted: There are many factors that may have led to the large size of some dinosaurs. One is the “arms race” between predator and prey species. Over evolutionary time (millions of years), natural selection for large-bodied predators would have created conditions where there was also selection for larger-bodied prey species. Additionally, large body size may have been more optimal for maintaining metabolic rates of some dinosaurs.
North America was once flooded by a shallow sea that divided it into two or three landmasses during part of the Age of Dinosaurs. The seas were filled with giant lizards (mosasaurs), monstrous sea turtles and long-necked plesiosaurs.
We are experiencing extreme weather patterns with large-scale flooding, sea level rise and coastal devastation. Could North America revert to a shallow sea again in time?
Ted: Yes, the surface of the earth is constantly changing, and there is no doubt that low-lying parts of North America would become inundated if sea levels were to rise significantly. Sea level change is a typical part of geological change, but it usually happens over a much longer period of time than the rate of change that we see today.
Dinosaurs endured for about 175 million years, through climate changes and continental changes, until the last non-avian dinosaurs disappeared about 66 million years ago when an asteroid struck the planet. Avian dinosaurs, A.K.A. birds, still live on every continent.
What does this tell us today as we are in the midst of the first human-caused mass species extinction and climate change?
Ted: I’m fond of pointing out that the one constant we can count on is change. Geological and biological change have always happened and will continue to happen. But human impacts on earth systems have superseded the natural rates of change and sometimes significantly sped up those rates. It is the increased rate of climate and environmental change that makes it difficult for plants and animals to adapt to new conditions.
You can learn more about these issues by visiting Dinosaurs Around the World, on view through Jan. 20.
By Carolyn Belardo with Ted Daeschler