Scientists Know That Birds Began to Evolve Prior to the Cretaceous

question 10

Short Answer

Scientists know that birds began to evolve prior to the Cretaceous due to the fossil ____________________.

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Definitions:

Embryonic Stage

The stage of prenatal development that lasts from implantation through the eighth week of pregnancy. It is characterized by the development of the major organ systems.

Teratogens

Agents or factors that cause malformation of an embryo or fetus, such as certain drugs, chemicals, or infections.

Vulnerable Period

A timeframe during which an individual or system is more susceptible to damage or harm due to exposure to stresses or adverse conditions.

Congenital

Present at birth; resulting from the prenatal environment.