An extinct goat species, Myotragus balearicus, that lived on the Spanish island of Majorca for millions of years has been found to have survived by reducing in size and becoming cold-blooded, a characteristic never before seen in mammals. The goat adjusted its growth rate and metabolism to adapt to the scarce resources on the island, similar to reptiles. This unique flexibility allowed the goat to thrive for over five million years. However, they were unable to survive the arrival of humans on the island about 3,000 years ago. The findings were published in the Proceedings of the National Academy of Sciences.
https://phys.org/news/2009-11-extinct-goat-cold-blooded.html