Going back in time

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Across
  1. 3. fin on the back
  2. 7. scramble vote louin to move forward
  3. 9. shape that helps fast movement ahead
  4. 10. place in Dorset famous for full fish-lizard fossils
  5. 11. I leave my tracks behind as clues
  6. 15. literally your backbone
  7. 17. in Germany where blackish shale contained bones
Down
  1. 1. fleshing out from these remains
  2. 2. extinct arthropods with different lifestyles in the seas
  3. 4. large marine reptiles from the past
  4. 5. living on land
  5. 6. country in Europe where whole fossils were found
  6. 8. the worm of a thousand feet
  7. 12. bones on the outside
  8. 13. rocks from the sea bed in layers
  9. 14. animals that suckle their young
  10. 16. living in the ocean