The Evolution of Reptiles

The Evolution of Reptiles — page 5 — MASS EXTINCTION At the end of the Cretaceous all of the nonavian dinosaurs went extinct The avian dinosaurs continued to evolve into birds The dinosaurs weren't the only reptiles to be hit hard by this extinction event So were two groups of ocean predators mosasaurs and plesiosaurs Scientists don't agree on what caused this global extinction but they do know that it was something that changed the environment causing greenhouse gases to rise and temperatures around the world to heat up Some scientists believe this was caused by an asteroid striking Earth and throwing dust and dirt into the air Others believe debris was thrown into the air when volcanoes erupted Whatever the cause plants that needed a lot of sunlight died out Animals that ate these plants also died as did animals that preyed on them This mass extinction meant that other plants and animals had the opportunity to fill those niches leading to the evolution of many new species This period is sometimes known as the End Cretaceous Extinction or the Cretaceous Paleogene Extinction because the extinctions came between the Cretaceous and Paleogene 66-23 MYA periods period 145-66 MYA just before the majority of dinosaurs became extinct It was approximately the length of a school bus and weighed about as much as an African elephant Scientists know that it wasn't fully grown because its leg bones had not fully fused a process in which bones in a young animal grow together as the animal ages Its discovery was vitally important because very few fossils from the Cretaceous have been found in Africa It is difficult to find fossils in Africa because so much of the land is covered in vegetation Sallam and his crew made their find in the desert where the soil and rocks are visible Because so few African fossils have been found all discoveries like Sallam's are important This one is key because it also refutes a theory about the isolation of African dinosaurs

The Evolution of Reptiles — page 6 — Three hundred MYA Earth's landmasses formed a single supercontinent Pangaea During the Cretaceous this supercontinent divided into Gondwana which included Africa and Laurasia which included Europe Because of this split many scientists believed that by the late Cretaceous dinosaurs in Africa were isolated from those in Europe Yet M. shahinae more closely resembled its European relatives than it resembled the sauropods of southern Africa Africa was not as isolated as scientists had thought For Dr. Sallam and his team M. shahinae is only the beginning to understanding African dinosaurs The paleontologists hope to make another find Where they found the huge herbivore they also hope to find the carnivore GONDWANA Three hundred MYA the continents as seen on Earth today did not exist Instead there was one large landmass known by scientists as Pangaea pictured Scientists believe that this supercontinent sat on several tectonic plates or slabs of rock that make up the surface of the planet As these tectonic plates shifted Pangaea split and by 200 MYA there were two continents Gondwana contained what are now South America Africa Australia and Antarctica Laurasia included modern North America Europe and Asia The tectonic plates continued to shift and landmasses moved The continents have been in their modern positions for less than 65 million years

The Evolution of Reptiles — page 7 — that preyed on it There are many gaps in what scientists know about ancient reptiles so every piece of information brings them closer to understanding how reptiles evolved EVOLUTION When scientists speak of evolution they are talking about the physical changes that take place in species over time These changes don't mean a group of animals is getting better but they don't mean that the group is getting worse either They simply mean that a plant or animal JEAN BAPTISTE species is changing LAMARCK In 1809 Jean Baptiste Lamarck published his The first scientist who published an theory that individual animals could acquire explanation of evolution was the French a trait and pass it down to their offspring He naturalist Jean Baptiste Lamarck in 1809 but it pointed out that giraffes reach up to feed on tree leaves Lamarck believed that all of wasn't until 1859 that an accurate description the stretching actually made their necks of the process was released English naturalist and limbs longer When these giraffes had offspring they passed down these long necks Charles Darwin wrote a book called on the and long legs It didn't take long for other Origin of Species by Means of Natural Selection scientists to disprove this theory It was clear that a person who has strong arms from hard work does not automatically have a child with strong arms

The Evolution of Reptiles — page 8 — In this book Darwin put forward the idea that nature and survival were the forces through which evolutionary change occurred Darwin observed that a species could have a number of diverse traits Because of these traits some animals would have an improved chance of survival They might be better runners or might be better able to blend with the landscape than others Because they survived longer they would have more offspring Many of these offspring would inherit the beneficial traits survive longer reproduce more and pass the traits on again to their own offspring Generation by generation the positive traits would be present in more individuals and the less beneficial traits would slowly disappear as animals with those traits failed to reproduce in large numbers As certain traits became more common and others less common the species evolved But Darwin did not understand how evolution occurred A key piece to this puzzle emerged in 1866 when scientist Gregor Mendel published some important rules of heredity Mendel noted that a tall pea plant bred with a short pea plant produced tall offspring When he bred two of these offspring three fourths of the resulting plants would be tall and one fourth would be short Mendel realized that each plant inherited traits from both parents with certain traits known as dominant traits expressed most often In pea plants tallness is dominant over shortness Scientists today know that change also occurs

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