Evolution Of Wounders

This is the story of the evolution of a group of non-avian dinosaurs, including troodons, that survived the extinction of most other non-avian dinosaurs.

Evolution
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time approximately 66 million years ago. With the exception of some ectothermic species like the turtles (especially leatherback sea turtles) and crocodilians, almost no tetrapods weighing more than 100 pounds (25 kilos) survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.

In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth's crust but abundant in asteroids.

As originally proposed in 1980 by a team of scientists led by Luis Alvarez, it is now generally thought that the K–Pg extinction was triggered by a massive comet or asteroid impact 66 million years ago and its catastrophic effects on the global environment, including a lingering impact winter that made it impossible for plants and plankton to carry out photosynthesis. The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180-kilometre-wide (112 mi) Chicxulub crater in the Gulf of Mexico in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred at the same time as the impact provides strong situational evidence that the K–Pg extinction was caused by the asteroid. It was possibly accelerated by the creation of the Deccan Traps. However, some scientists maintain the extinction was caused or exacerbated by other factors, such as volcanic eruptions, climate change, or sea level change, separately or together.

A wide range of species perished in the K–Pg extinction. The most well-known victims are most of the non-avian dinosaurs. However, the extinction also destroyed a plethora of other terrestrial organisms, including certain mammals, pterosaurs, few kinds of birds, some kinds of lizards, insects, and plants. In the oceans, the K–Pg extinction killed off most plesiosaurs (except Elasmosaurus, which survived to modern times) and the giant marine lizards (Mosasauridae) and devastated some groups of fish, most sharks, mollusks (especially ammonites, which became extinct) and many species of plankton. It is estimated that 60% or more of all species on Earth vanished. Yet the devastation caused by the extinction also provided evolutionary opportunities. In the wake of the extinction, many groups underwent remarkable adaptive radiations—a sudden and prolific divergence into new forms and species within the mostly disrupted and emptied ecological niches resulting from the event. Mammals in particular diversified in the Paleogene, producing new forms such as horses, whales, bats, primates, carnivorans, and many others. Birds, fish, lizards, and perhaps frogs also radiated.

However, scientists discovered fossils of some species of dinosaurs, such as troodons, that were above that layer, confirming that not all non-avian dinosaurs perished, so some dinosaurs like troodons had survived extinction, making them among the last non-avian dinosaurs remaining. Their descendants are still alive today, including Eastern wounders (the most primitive troodon species alive today, which resembles their ancestors that survived the K-T extinction, and like their ancestors, can survive and adapt really well even in harsh conditions), Western wounders, dwarf wounders, and others, which most are native to modern North America (which is one of the last place where native non-avian dinosaurs live in, along with Asia). Despite competition from mammal predators and bird predators that came and vanish over millions of years, troodons and some other non-avian dinosaurs have thrived over millions of years to modern times, with some species remaining mostly unchanged from their Cretaceous ancestors.