and soon went extinct. 很快灭绝

135. it would soon cover one-fifth of the land.
     不久将覆盖五分之一的陆地
136. But the endless plains were no paradise for the mammals.
     但无尽的平原并不是哺乳动物的天堂
137. Many couldn't digest grass
     许多无法消化草的动物
138. and soon went extinct.
     很快灭绝
139. Twenty million years later,
     2000万年之后
140. and today's grazing mammals
     今天的食草哺乳动物
141. remain locked in an arms race with this green invader.
     仍在与这绿色入侵者 继续展开军备竞赛

来自《我们星球上的生命 第一季 第七集 Life on Our Planet S01E07 地球继承者》第 138 行