Out of all the dinosaurs, the most famous must be Tyrannosaurus rex. This famous dinosaur belonged in the group of theropods known as tyrannosaurs. This group of theropod dinosaurs first evolved in the Middle Jurassic from much smaller theropods such as the weird-looking Guanlong. However, from the Middle Jurassic-mid Cretaceous, almost all tyrannosaurs were small and weren't much bigger than a Velociraptor. It wasn't until the Late Cretaceous when the giant tyrannosaurs such as T. rex and Tarbosaurus evolved.
However, the split in this alternate timeline happened in the Early Cretaceous, before the tyrannosaurs became large. As a result, the tyrannosaurs stayed small during the Late Cretaceous in this alternate timeline. The glaciation gave the tyrannosaurs time to adapt to the colder climates and allowed them to survive the K-Pg mass extinction. Despite this, the tyrannosaurs continued to stay small during the Paleocene and Eocene since the carnosaurs mostly held the niche for large apex predator. However, during the Oligocene, the carnosaurs started to decline due to the sauropod prey also declining. Because of this, at the end of the Oligocene, the tyrannosaurs started to grow in size.
By the end of the Miocene, the tyrannosaurs had finally grown to the same sizes as T. rex and Tarbosaurus. They also spread to South America during the Pliocene and drove the South American abelisaurs to extinction. There's even fossil evidence of African tyrannosaurs in Early Miocene deposits of this alternate timeline. However, the African tyrannosaurs probably went extinct during the Pliocene when the gigaraptors evolved. The tyrannosaurs reached their peak in the Pleistocene when giants such as the now extinct Gigasaurus evolved. Today, the tyrannosaurs are successful apex predators that live in the Americas and Eurasia.
Crowned Tyrants (Family: Stemidae)Edit
These small tyrannosaurs got their name because the male of each species has a unique crest designed to attract mates. They are small scavengers that are very diverse in Eurasia, ranging from Europe to India. These small theropods are also a source of prey for larger predators when food is scarce. Since they are such small dinosaurs, there fossil record is poor. However, their fossil record dates back to the Mid Oligocene. There are also dozens of species of crowned tyrants, from the Indian False Guanlong (Neoguanlong indus) to the Desert Dweller (Incola deserto).
Cruncher Beasts (Family: Ursisauridae)Edit
While some of the tyrannosaurs in this alternate timeline are small or carnosaur-like, this group is very different. The crusher beasts are the only group to have a similar design to that of T. rex and Tarbosaurus. The cruncher beasts get their name because they are powerful predators similar to bears in our timeline. Despite being fierce predators, they are covered in a coat of feathers for warmth in their cold environment. They first evolved in the Miocene when the carnosaurs died out in Asia. They also crossed the Bering land bridge during the Pliocene. Today there are four species of cruncher beasts living in Eurasia and North America. They are also restricted to a single genus, Ursisaurus.
- Siberian Cruncher Beast (Ursisaurus siberianus)
- Canadian Cruncher Beast (Ursisaurus canadiensis)
- Mongolian Cruncher Beast (Ursisaurus mongoliensis)
- Alaskan Cruncher Beast (Ursisaurus alaskanus)
False Carnosaurs (Family: Carnosauridae)Edit
While these tyrannosaurs have an insulating coat of feathers, they have three-fingered hands and carnosaur-like skulls and teeth. They are also a very ancient group, they first evolved in the Mid Paleocene as small dromeasaur-sized predators. However, they didn't become larger until the Late Oligocene, when the true carnosaurs started to decline. They reached their peak during the Pliocene when the true carnosaurs went extinct. However, they went extinct in Africa during the Pliocene due to competition from gigaraptors, and went extinct in Northern Asia and North American due to competition from the cruncher beasts. Today, the false carnosaurs are restricted to Southern Asia and South America.
- Indian Mega Tyrant (Ingentisaurus indicus)
- Indonesian Dwarf Tyrant (Ingentisaurus pygmaeo)
- Chinese Mega Tyrant (Ingentisaurus sinensis)
- Amazon Mega Tyrant (Magnasaurus amazona)
- Patagonian Mega Tyrant (Magnasaurus patagonia)
- Mexican Mega Tyrant (Magnasaurus mexicanus)
|Sauropsida||Archosauria||Theropoda||Abelisauroidea • Aves • Dromaeosauridae • Gigaraptornae (Dinosaurs of the Ice Age) • Ornithomimosauria • Therizinosauria • Tyrannosauroidea|
|Ornithischia||Ankylosauria • Ceratopsia • Ornithopoda|
|Lepidosauromorpha||Plesiosauria • Squamata|
|Mammalia||Eutheria • Metatheria • Monotremata|