Were there any mice during the Jurassic period?
Short answer – no. The Jurassic was the heyday of the big reptiles and while there were mammals about they were small “proto-” mammals similar to modern-day opossums. The mammals of that era had yet to specialize into the diverse groups we have today and occupied very narrow ecological niches. Undoubtedly there were mammals then that were a lot like mice but with the big reptiles dominating things there was no opportunity to evolve and take advantage of the available food supplies. When the big meteor impact of 65 million years ago ended the reign of the reptiles mammals then became the dominant life forms.
