Crocodiles were the dominant land animals before dinosaurs, exhibiting immense diversity in size, shape, diet, and behavior.
Crocodiles evolved to become marine creatures resembling whales, while others adapted to various land environments.
Crocodiles miraculously survived two major mass extinctions and re-diversified, competing with mammals and adapting to changing climates.
Deep dives
Evolution of Crocodiles
Crocodiles, the ancestors of today's alligators and crocodiles, were the dominant land animals before the rise of dinosaurs. During the prehistoric periods such as the Triassic and Jurassic, crocodiles exhibited immense diversity in size, shape, diet, and behavior. They ranged from giant crocs as long as buses to crocs with hooves, spikes, and even the ability to walk on two legs. These crocs were more diverse and dominant than dinosaurs during this time. They occupied different ecological niches and had a greater variety of diets and behaviors.
Transition to the Water and Marine Adaptations
In the Jurassic period, crocodiles started to venture into water more extensively. They became semi-aquatic, moving between land and water, and eventually some crocs became fully adapted to aquatic life. These marine crocs, known as metriorhynchids, transformed their limbs into flippers, lost their dermal armor, and gave live birth in the water. They resembled whales and other marine creatures. Meanwhile, other crocs remained on land, adapting to different environments like semi-arid regions and even the Arctic.
Mass Extinctions and Survival
Crocodiles miraculously escaped two major mass extinctions in the past: the Permian-Triassic extinction and the Cretaceous-Paleogene extinction. The former led to the dominance of crocs over dinosaurs in the Triassic period, but crocs faced a decline when dinosaurs diversified in the Jurassic and Cretaceous. The latter extinction wiped out the dinosaurs but spared many crocodile species that were semi-aquatic or lived in buffered ecosystems. Crocs survived and re-diversified, competing with mammals and adapting to changing climates.
Current State and Challenges
Today, there are approximately 25 recognized species of crocodiles, which is a relatively small number compared to their historical diversity. Their current diversity is mostly concentrated around the tropics and subtropics, with some species facing the risk of extinction. Climate change, habitat loss, and human activities pose significant threats to crocodile populations. Nevertheless, crocs still display evolutionary potential, with ongoing research aiming to understand their past, present, and future diversification, as well as their relationship with climate change and other factors.
Unanswered Questions and Future Research
Several unanswered questions remain in crocodile evolution. Researchers are intrigued by the reasons behind the survival of crocs during mass extinctions and their subsequent diversifications. They seek to understand why crocs never regained the same level of diversity as in the past, why some crocs ventured into marine environments while others remained on land, and what drove their adaptations and ecological specializations. Advances in technology like CT scanning and ancient DNA analysis offer promising avenues for investigating these questions and shedding more light on the evolutionary history of crocodiles.
Melvyn Bragg and guests discuss the remarkable diversity of the animals that dominated life on land in the Triassic, before the rise of the dinosaurs in the Jurassic, and whose descendants are often described wrongly as 'living fossils'. For tens of millions of years, the ancestors of alligators and Nile crocodiles included some as large as a bus, some running on two legs like a T Rex and some that lived like whales. They survived and rebounded from a series of extinction events but, while the range of habitats of the dinosaur descendants such as birds covers much of the globe, those of the crocodiles have contracted, even if the animals themselves continue to evolve today as quickly as they ever have.
With
Anjali Goswami
Research Leader in Life Sciences and Dean of Postgraduate Education at the Natural History Museum
Philip Mannion
Lecturer in the Department of Earth Sciences at University College London
And
Steve Brusatte
Professor of Palaeontology and Evolution at the University of Edinburgh
Producer Simon Tillotson
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