Scientists uncover clues about how dinosaurs roamed Earth

Analysis by Dr. Karen Shaw Becker

dinosaur migration

Story at-a-glance -

  • University of Tokyo researchers tracked species from millions of years ago, using fossils to learn more about ancient migration routes, how species interacted and how land masses may have moved
  • The study involved a unique collection of data from evolutionary studies, locations of fossil dig sites and ages of fossils and used computer simulations to determine the most likely routes of migration used by ancient species that roamed the Earth 145 million to 66 million years ago
  • Nonavian dinosaurs were divided into two groups, one that lived in the Northern Hemisphere and one that lived in the Southern Hemisphere
  • While these groups of dinosaurs could travel between Europe and Africa during the Early Cretaceous period (145 million to 100 million years ago), they became isolated in the Late Cretaceous period (100 million to 66 million years ago)
  • Three supercontinents existed in the Early Cretaceous period — North America-Europe-Asia, South America-Africa and Antarctica-India-Australia
  • Things began to change by the Late Cretaceous period, however, with only the North America-Europe-Asia supercontinent remaining

Biogeography is the study of the geographic distribution of plants and animals.1 The present-day distribution of plants and animals provide many insights into the history of landmasses and their climates, but researchers are also interested in studying extinct species, including dinosaurs.

University of Tokyo researchers, in particular, tracked species from millions of years ago, using fossils to learn more about ancient migration routes, how species interacted and how land masses may have moved. In a study published in Systematic Biology,2 a biogeographical network analysis is used to convert "evolutionary relationships into geographical relationships." As a University of Tokyo news release reported:3

"For example, cats and dogs are more closely related to each other than to kangaroos. Therefore, a geographical barrier must have separated the ancestors of kangaroos from the ancestors of cats and dogs well before cats and dogs became separate species."

Insights into how dinosaurs roamed the Earth

The study involved a unique collection of data from evolutionary studies, locations of fossil dig sites and ages of fossils and used computer simulations to determine the most likely routes of migration used by ancient species that roamed the Earth 145 million to 66 million years ago.

"If we find fossils on different continents from closely related species, then we can guess that at some point there must have been a connection between those continents," study author Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo, said in the news release. Some intriguing findings were uncovered, including:4

  • Nonavian dinosaurs were divided into two groups, one that lived in the Northern Hemisphere and one that lived in the Southern Hemisphere
  • While these groups of dinosaurs could travel between Europe and Africa during the Early Cretaceous period (145 million to 100 million years ago), they became isolated in the Late Cretaceous period (100 million to 66 million years ago)
  • Three supercontinents existed in the Early Cretaceous period — North America-Europe-Asia, South America-Africa, and Antarctica-India-Australia

Things began to change by the Late Cretaceous period, however, with only the North America-Europe-Asia supercontinent remaining. The other supercontinents separated into the continents as they are today, although they were still in different locations. Kubo added, "During the Late Cretaceous period, high sea levels meant that Europe was a series of isolated islands. It makes sense that nonavian dinosaur species differentiated between Africa and Europe during that time."5

Fossilized footprints suggest some dinosaurs moved quickly

Images of dinosaurs often depict them as slow and plodding, but separate research by Kubo and colleagues called this into question. By studying the fossilized footprints of Marasuchus, an ancient Dinosauriforme, or ancestor of dinosaurs, that lived during the Triassic Period and measured only about half a meter in length (1.6 feet), they found that it likely walked on two feet with an average stride of 1.15 meters (3.7 feet).6

"Given how high their hips stood, they probably walked very quickly," Kubo told Nikkei Asian Review.7 On the other hand, Archosaurs, ancestors of crocodiles, were about 2 to 3 meters (6.5 to 9.8 feet) in length but walked with an average stride of just 0.77 meter (2.5 feet), a short stride that suggests a slower, clumsier gait. "The fact that Dinosauriformes could walk fast is probably one reason they flourished instead of becoming extinct," Kubo said.8

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Ancient migration patterns may be responsible for horses as we know them today

Learning seemingly small details about ancient animals can uncover major clues about how they became the animals we know and love today. Horses are a prime example. One study, published in the journal Science,9 created an evolutionary tree of 131 extinct horse species and seven still living today.

While it was expected that significant changes in teeth and body size — larger body size would help the animals transition from forests to grasslands — would be seen during periods of rapid diversification, the rates of change were similar to periods with low diversification.

In fact, body size evolution remained fairly consistent during times of low and high speciation (or the formation of new species), but periods with high speciation actually were associated with lower rates of teeth changes. Instead, it's thought that external environmental factors and patterns of migration may have been the driving forces behind the rapid diversification into new horse species.

Interestingly, ancient horses had multiple toes — four, then three and most species eventually lost their side toes and ended up with one single large hoof. Early forest-dwelling horses also had shorter legs than later, grassland-dwelling species. The longer legs helped the horses to run faster, a useful ability when you live out in the open plains.

Dinosaurs used temporary land bridges to migrate

Getting back to dinosaur migration, it's believed that as the supercontinent Pangaea split up, dinosaurs migrated into other areas of the world, likely via temporary land bridges that appeared due to changes in sea levels.10 Study author Alex Dunhill, Ph.D., from the School of Earth and Environment at the University of Leeds, said in a news release:11

"Such massive structures — spanning, for example, from Indo-Madagascar to Australia — may be hard to imagine. But over the timescales that we are talking about, which is in the order of tens of millions of years, it is perfectly feasible that plate tectonic activity gave rise to the right conditions for such land bridges to form."

The featured study also pointed to changing sea levels as crucial in dinosaur migration and differentiation. "During the Late Cretaceous period, high sea levels meant that Europe was a series of isolated islands. It makes sense that nonavian dinosaur species differentiated between Africa and Europe during that time," Kubo said.12

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