Adaptive Radiation in Mammals

Adaptive Radiation in Mammals

By: Kevin Alcala

Cambrian Explosion

• This was a short period of time in which the number of groups of organisms on Earth rapidly increased
• Most major animal groups appeared for the first time around 545 million years ago
• There was especially an expansion of complex, multi-cellular organisms
• This went against Darwin's belief that populations evolved gradually; therefore, many scientists are skeptical that this diversification happened so rapidly

Conclusion

Mid-Jurassic Era

• When new niches become available, new species will form in order to fill these niches
• Adaptive radiation involves the diversification of species occurring much more rapidly than under normal conditions
• Many scientists still have their doubts since adaptive radiation, in some cases, conflicts with Darwin's beliefs
• However, while many of Darwin's beliefs are still used today, we are continuing to expand on them as time goes on and we learn more
• Future studies on adaptive radiation will help us to better understand whether events such as the Cambrian Explosion are really plausible

How does adaptive radiation occur?

• When environmental changes cause mass extinctions, this opens up new ecological niches for the survivors
• With these new niches available, the survivors experience evolution and form new species that fill these niches
• A few organisms make their way to new, often distant areas
• New areas bring new environmental challenges, and new species began to form that will each take on a new niche

• Recent studies have suggested that mammals may have experienced adaptive radiation sometime in the Jurassic Era, which is earlier than we had previously thought
• Mammals in the early-mid Jurassic Era underwent changes in structure over many generations and were a key component of the origin of crown-group mammals
• This was likely connected to the acquisition of the dentition, middle-ear, and shoulder girdle
• It is still up for debate what exactly caused this period of adaptive radiation, but many believe that can be attributed to the breakup of Pangea

Introduction

• "The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges"
• In other words, many new species form due to the new availability of niches
• Shows a spike in graphs depicting diversity of species
• Often occurs after a period of mass extinction

Breakup of the Continents

• The diversification of mammals can be greatly attributed to the separation of the continents
• Pangea split due to the movement of Earth's tectonic plates beginning about 200 million years ago, and the continents have been drifting apart since then
• South America and Australia were especially isolated from the other continents during the Tertiary Period and marsupials thrived there
• Meanwhile, placental mammals expanded in diversity on other continents

Cenozoic Era

• When the dinosaurs became extinct due to extreme environmental changes approximately 65 mya, the mammals had the opportunity to become the dominant terrestrial creatures on Earth
• In only 10 million years, approximately 130 genera and 400 species evolved
• Whales became the first fully aquatic mammals
• Bats became the first flying mammals
• The evolution of primates and rodents exploded
• New environmental habitats and food sources were what allowed mammals to thrive
• For example, new forests appeared that were ideal for primates who swung from tree to tree