Early Mammals and Plants

Objectives

• Outline the evolution of birds
• Outline the evolution of early mammals
• Summarize the evolution of modern mammals
• Outline plant evolution

Birds are thought to have evolved from a groups of bipedal dinosaurs called theropods.

Ancestor of birds was probably similar to the theropod Deinonychus.

Deinonychus

• Lived about 110 million years ago in North America
• Predatory carnivore
• Had feathers and wings
• Strong legs with clawed feet
• Jaws with teeth; claws at the tips of wings

Evolution of Flight

• Ancestor leapt to avoid predators or catch prey
• Ancestor lived in trees

Early Mammals

The earliest mammals evolved from cynodonts.

Types of Mammals

• Monotremes
• Marsupials
• Placental

Monotremes

• Probably split off first
• Steropodon may have been ancestor of the platypus
• Lay eggs and have cloaca

Marsupials

• Evolved about 130 million years ago
• One of the earliest was genus Sinodelphys
• Remained most common and diverse in Australia

Placental Mammals

• Evolved about 110 million years ago
• Ancestor may be genus Eomaia
• Eomaia fossils found in China
• Eomaia about 10 cm long
• Placental mammals became dominant mammals

In 2007 scientists compared the DNA of all known species of living animals to create a supertree of mammalian evolution.

The supertree indicates that mammals started to evolve 95 million years ago.

At that time, Earth's temperature was dropping, and flowering plants were spreading.

The supertree shows that another diversification occurred 50 million years ago. At that time temperature rose.

Plants

Plants are thought to have evolved from an aquatic green algae protist.

Plants later evolved adaptations for land, including vascular tissues, seeds, and flowers.

The earliest plants probably were simliar to stonewart, and aquatic algae. Stonewart has rhizoids instead of roots.

Land could not be colonized by other organisms until land plants became established.

This happened as early as 700 million years ago. The first land plants probably resembled liverworts.

Absorbing enough water was a challenge, so early land plants were small.

The evolution of vascular tissue allowed plants to grow larger and endure drought.

Other Plant Adaptations

• Lignin - tough hydrophobic material
• Leaves
• Roots for absorption and anchoring