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Across 6. a warm blooded egg-laying vertebrate 9. 417-354 million years ago 11. no longer in existence 13. improving the ability to survive 14. a large prehistoric reptile 15. to maintain its original state 16. a living organism typically growing in a permanent site 18. 144-65 million years ago 20. the development of an organism over time 23. 354-290 million years ago 25. based on the methods of science 26. 290-248 million years ago 27. 543 million years ago 28. an invertebrate animal 31. a white colorless mineral consisting of calcium carbonate 33. 248-200 million years ago 34. before the period of written records 35. is measured in hours, minutes, seconds, etc. 37. an animal of a large group distinguished by the possession of a backbone 39. 206-144 million years ago 40. an examination 43. any group of syncytial spore producing organisms 44. an internal framework of bone 45. the existence of a human or animal 48. to rot or decompose 49. a system of ideas to explain something 50. the study of past events

Down 1. a quality or characteristic 2. white tissue making up skeletons 3. to dig up buried remains 4. 490-443 million years ago 5. a scientist who studies fossils 7. types of food eaten 8. containing calcium carbonate 10. belonging to the distant past 12. 543-490 million years ago 17. a group of organisms capable of exchanging genes 19. the surroundings or conditions in which a person, animal, or plant lives 21. a branch of science to do with prehistoric organisms 22. the material structure of an individual life form 24. a natural home or environment of an organism 29. 65-1.8 million years ago 30. facts stating true points 32. 443-417 million years ago 36. a cold blooded vertebrate 38. a super continent 41. science that deals with Earth's physical structure 42. a small arthropod animal 46. remains preserved in rock 47. a group of wild animals