compulsory (adj)
immediately (adv)
extinct (adj)
palaeontology (n)
professor (n)
ancestor (n)
ecology (n)
a university teacher of the highest rank
the study of the relation of plants and living creatures to each other and to their environment
the study of fossils as a way of getting information about the history of life on Earth
a person in your family who lived a long time ago
no longer in existence
that must be done because of a law or a rule
without delay