Mesozoic and Cenozoic Eras: Evolution, Climate, and Fossils

Mesozoic Era (250-65 Ma)

No geological evolution. Towards the end of the Paleozoic and Mesozoic, all continents of the Earth united to form Pangea. The distribution of land and sea undergoes major changes during this era, during which continents separate.

Life in the Mesozoic

In the Mesozoic, a major diversification of marine fauna, especially molluscs and echinoderms, occurred due to the fracturing of Pangea. Reptiles experienced significant diversification, colonizing air, aquatic, and terrestrial environments (dinosaurs).

Types of Dinosaurs:

• Teropods: Carnivorous with short front legs equipped with strong claws and enormous teeth.
• Sauropods: Large quadrupedal herbivores with very long necks and tails, and columnar legs.
• Ornithopods: Bipedal herbivores.

During the Jurassic, reptiles evolved into birds, and mammals first appeared in the Triassic. Regarding flora, conifers dominated during the Triassic and Jurassic, and the expansion of angiosperms began in the Cretaceous.

The Cretaceous period ended with a major extinction of species, likely due to the impact of an asteroid on the Yucatan Peninsula. The dust, ash, and smoke blurred the atmosphere, preventing entry of solar radiation, leading to intense cold and lack of light.

Climate

The climate was generally warm but more arid in the Triassic and Jurassic, and wetter in the Cretaceous. The seas and land were temperate or warm, and glaciers did not exist at the poles.

Fossils

Ammonites: Molluscs with shells. Belemnites: Squid and cuttlefish with bullet-shaped shells. Reptiles: Flying reptiles (pterosaurs) and marine reptiles (ichthyosaurs) lived in the Mesozoic seas off the coast.

Mesozoic: Triassic (placental mammals), Jurassic (large reptiles), Cretaceous (angiosperms).

Cenozoic Era (65-0 Ma)

Tertiary Period (65-1.5 Ma)

Geological Evolution

Continents continued their separation, and the opening of the Atlantic Ocean occurred. Subduction and continental collisions resulted in the Alpine orogeny. During this time, orogenic pulses originated the formation of mountain chains like the Himalayas. This mountain formation continues today.

Life

Mammals multiplied rapidly. Marine environments also underwent major renovation after the extinction event. Flora was dominated by angiosperms, and the wide dispersal of herbaceous plants formed the basis for feeding mammals.

Climate

At the beginning of the era, warm weather persisted. However, the climate changed due to shifting ocean currents. The large increase in plankton organisms caused a decrease of CO2 in the atmosphere, leading to a cooling culminating in the development of ice at the poles.

Fossils

Foraminifera: Marine protozoa with shells. Gastropods: Molluscs that inhabited both marine and freshwater environments. Mammals. Angiosperms: Fossils from the leaves of a walnut.

Quaternary Period

Geological Evolution

Continents acquired their current positions.

Life

Mammals developed significantly, both in number and size. The most significant species is the presence of hominids and the appearance of Homo sapiens. The flora is similar to the Tertiary period.

Climate

During the Quaternary period, four glacial periods occurred, taking their name from the rivers of the Danube tributaries.