17．When very small dinosaur bones were found in a Germany mine people thought they were from baby dinosaurs．（48）Hower，scientist Martin Sander's work shows that they were probably fully grown and belong to the smallest giant dinosaur species ever found．
Growth marks on dinosaur bones are similar（49）to growth rings on trees．The rings are far apart while the animal is young and growing quickly．（50）They get closer as growth slows．"It is exactly these tight ring marks that we found in the fossil （化石） bones，"says Sander．So the fossils must have been from adult animals．
（51）why was this German dinosaur so much smaller than other giant dinosaurs，which grew up to 45metres long and weighed as much as a thousand humans？
150million years ago，most of Germany was underwater．Scientists think that （52）as water levels rose，there was less and less land and food available．The dinosaur was forced to adapt and evolved into（53）a smaller animal needing （54）lessspace and food．
Since 1998，scientists have dug up more than 1，000dinosaur fossils in the mine．It is one of the few places in the world （55）wherethe bones and footprints of dinosaurs have been found together．
