February : Killer instinct drove evolution of mammals’ predatory ancestors | News and features | University of Bristol
The ancestors of all modern mammals, the synapsids, first appeared in the fossil record long before the dinosaurs. Some were vegetarian while others were the top land predators for 60 million years before being replaced by the dinosaurs. Their evolution followed the same pattern of an arms race with their prey species in which the carnivores had to get better at killing to survive.
This gives the lie to the claim of any involvement of a single intelligent designer in their evolution since no intelligent designer worthy of the name would compete with itself in an arms race in which there are no winners or losers while all the time additional complexity is needed to keep up.
Tell me all about the synapsids, please. Synapsids are a group of vertebrates that includes mammals and their extinct relatives. They are characterized by several key features, including a single temporal opening behind the eye socket, teeth set in sockets, and a more erect posture compared to earlier reptiles. Synapsids first appeared during the late Carboniferous period, about 315 million years ago, and they were a dominant group throughout much of the Permian and Triassic periods. Here are some key points about synapsids:Now a team of researchers from Bristol University, together with a colleague from the Open University, Milton Keynes, have traced the evolution of the carnivorous synapsid jaw and body size and discovered a major change in the jaw about 270 million years ago which would have been associated with a shift in the behaviour of these carnivores as they became better at killing their prey more quickly, so reducing the risk of injury.Overall, synapsids are a fascinating group of vertebrates that played a significant role in the evolutionary history of life on Earth, ultimately giving rise to the diverse and successful lineage of mammals that we see today.
- Evolutionary History: Synapsids evolved from reptilian ancestors, specifically from a group called the pelycosaurs. One of the most famous pelycosaurs is Dimetrodon, which lived during the early Permian period and is often mistakenly identified as a dinosaur. Synapsids evolved further into two main groups: the therapsids and the cynodonts.
- Therapsids: This group includes the most mammal-like synapsids. They had more advanced jaw structures, with larger temporal fenestrae (openings behind the eye socket) and specialized teeth. Therapsids diversified during the Permian period, with some species evolving into large herbivores like the iconic sail-backed Dimetrodon, while others were carnivorous predators. Towards the end of the Permian, some therapsids gave rise to the first true mammals.
- Cynodonts: Cynodonts were a subgroup of therapsids that emerged during the late Permian and diversified extensively during the Triassic period. They exhibited several mammalian characteristics, including a more upright posture, specialized teeth, and possibly hair-like structures. Some cynodonts were quite small and likely had a lifestyle similar to modern mammals, while others were larger predators.
- Mammalian Evolution: The transition from cynodonts to true mammals occurred during the Triassic period. Early mammals retained many reptilian features but also displayed characteristics that are distinctly mammalian, such as lactation and specialized jaw joints. By the end of the Triassic period, mammals had become more diverse and widespread.
- Impact on Evolutionary History: Synapsids, particularly therapsids and cynodonts, played a crucial role in evolutionary history. They were among the dominant land vertebrates during the Permian and Triassic periods, occupying various ecological niches as herbivores, carnivores, and omnivores. The extinction of many synapsid groups at the end of the Permian, possibly due to environmental changes and the effects of the Permian-Triassic mass extinction event, paved the way for the rise of dinosaurs as the dominant land vertebrates during the Mesozoic Era.
- Modern Descendants: The only surviving descendants of synapsids are mammals, which have diversified into a vast array of species occupying nearly every terrestrial and aquatic habitat on Earth. From tiny shrews to massive whales, modern mammals exhibit remarkable diversity in terms of size, shape, behavior, and ecological adaptations.
Their findings are the subject of an open access paper in Communications Biology and is the subject of a Bristol University news release: