33940
Herbivorous animals , which depended on plants and plankton as their food , died out as their food sources became scarce ; consequently , the top predators , such as " Tyrannosaurus rex " , also perished .
 Tyrannosaurus rex
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Tyrannosaurus rex