Biology Now, 2e

The First Bird ■ 253

Mesozoic Cenozoic

Permian Triassic Jurassic Cretaceous Paleogene/Neogene Quaternary

300 250 200 145 65

Age of

reptiles begins

Large plant-eating

dinosaurs thrive

Dinosaurs evolve

and spread

Flowering plants

increase

Humans

evolve

Age of

mammals begins

2.6 0.0

Continents come

together to form

Pangaea; reptiles

dominate life on

land by 265 mya;

mass extinction

at end of period

Early dinosaurs;

first mammals;

mass extinction

at end of period

Continents begin to

separate; diverse

dinosaurs; first birds;

first flowering plants

Flowering plants begin to

dominate life on land; mass

extinction at end of period,

including extinction of the

last non-avian dinosaurs

Continents near

present positions;

increased diversity

of flowering plants,

birds, mammals,

and pollinating

insects

Repeated advance

and retreat of

glaciers; evolution

of humans;

extinction of large

mammals and birds

Q1: During what geologic period did life on Earth begin?

Q2: How long ago did species begin to move from water to land? What period was this?

Q3: In what period would Archaeopteryx have been alive?

other species, was the dinosaurs. Dinosaurs

first appeared about 230 mya, during the Trias-

sic period, and they took over the planet.

Feathered Friends

Xu Xing may not have wanted to be a pale-

ontologist when he went to college, but by the

time he graduated, he was hooked on dino-

saurs. Over the next 20 years, Xu became one

of the most productive researchers in his field.

To d a t e , h e h a s d i s c o v e r e d a n d n a m e d m o r e

than 60 extinct species—mostly dinosaurs,

but also a reptile and a salamander. And the

majority of those dinosaur fossils have feathers

(Figure 14.4).

As scientists traced back the lineage, or line

of descent, from birds to dinosaurs, it became

clear that birds are most closely related to

theropods—fast-moving dinosaurs that ran

Figure 14.4

A feathered dinosaur tail, trapped in

amber

In 2016, scientists discovered a 99-million-year-

old dinosaur tail, complete with its feathers, in a

piece of amber.