Cretaceous Life: Dinosaurs, Marine Reptiles, Mammals, Plants, Invertebrates, & Microbes | GEO GIRL

The Cretaceous was the last period of the Mesozoic Era from ~145 to 66 million years ago. Life in te Cretaceous was drastically different than today. Dinosaurs dominated the terrestrial realm and huge marine reptiles dominated the oceans. Marine reptiles were later replaced by marine mammals in the Cenozoic. Smaller ocean dwellers, like ammonites were also abundant in Cretaceous oceans. Still smaller micro phytoplankton, coccolithophores, became so dominant in the Cretaceous they invented a new rock type! Coccolithophores made such thick chalk deposites during this period that the Cretaceous got its name from chalk (creta means chalk). Siliceous sponges (glass sponges), on the other hand, became less abundant because radiolarians and diatoms took so much silica from the oeans that hardly any was left over for the sponges. Reefs in cretaceous oceans were made of mollusks instead of corals or sponges. Rudists were the dominant reef builders in the Cretaceous because the ocean chemistry favored aragonite precipitation which rudists and coccolithophores secrete. Corals secrete calcite rather than aragonite, so they were not dominant reef builders until the Cenozoic when ocean conditions favored calcite again. Moving back to land, plants also underwent a major event during the Cretaceous, angiosperms, flowering plants, evolved! Angiosperms diversified along with insects in the Cretaceous and throughout the Cenozoic. Laslty, mammals remained small in the Cretaceous, but after the KPg extinction were able to come back and diversify greatly in the Cenozoic, or Age of Mammals.

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0:00 When was the Cretaceous?
0:28 Chalk forming organisms!
1:46 Glass reefs came to an end
2:28 Cretaceous plants
3:22 Reason for Angiosperm success
5:09 Cretaceous invertebrates
6:40 Rudist reefs vs coral reefs
8:00 Marine predators in the Cretaceous
9:20 Marine reptiles dominated Cretaceous oceans
11:35 Cretaceous dinosaurs
13:28 Cretaceous mammals
15:01 Related videos & references

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