End-Cretaceous extinction

Definition

The End-Cretaceous extinction, also known as the Cretaceous-Paleogene (K-Pg) extinction event, refers to the mass extinction that occurred around 66 million years ago, leading to the disappearance of approximately 75% of Earth's species, including the non-avian dinosaurs. This event marks a significant turning point in the evolutionary history of the animal kingdom, paving the way for the rise of mammals and eventually humans.

5 Must Know Facts For Your Next Test

1. The End-Cretaceous extinction event was marked by rapid environmental changes caused by an asteroid impact and volcanic activity.
2. It resulted in the extinction of non-avian dinosaurs, marine reptiles, and many other species, dramatically reshaping ecosystems worldwide.
3. The fossil record shows that certain groups of organisms, like mammals and birds, flourished in the aftermath of the extinction event.
4. Evidence for this extinction includes a global layer of sediment containing high levels of iridium and shocked quartz.
5. The End-Cretaceous extinction had long-term effects on evolutionary pathways, allowing mammals to diversify and become the dominant terrestrial vertebrates.

Review Questions

• Discuss the causes and effects of the End-Cretaceous extinction on biodiversity and evolutionary history.
  • The End-Cretaceous extinction was primarily caused by an asteroid impact and extensive volcanic activity, leading to drastic climate changes. The immediate effect was a significant loss of biodiversity, with about 75% of Earth's species vanishing, including all non-avian dinosaurs. This mass extinction opened ecological niches that allowed surviving groups like mammals to thrive and diversify, setting the stage for future evolutionary developments in the animal kingdom.
• Evaluate the evidence supporting the asteroid impact hypothesis for the End-Cretaceous extinction.
  • The asteroid impact hypothesis is supported by several lines of evidence, including the presence of the Chicxulub Crater, which dates to around the same time as the extinction event. Additionally, a global layer of sediment rich in iridium has been found in various locations, indicating a sudden influx of extraterrestrial material. The discovery of shocked quartz and other markers consistent with high-energy impacts further strengthens this hypothesis and explains many immediate environmental changes observed in fossil records.
• Analyze how the End-Cretaceous extinction influenced mammalian evolution and their subsequent dominance in ecosystems.
  • The End-Cretaceous extinction drastically altered ecological dynamics, eliminating many competing species and allowing mammals to emerge as dominant terrestrial vertebrates. With vast ecosystems available for colonization and fewer large predators, mammals diversified into numerous forms and sizes. This adaptive radiation led to significant evolutionary innovations among mammals, including changes in size, reproductive strategies, and feeding behaviors, ultimately shaping modern mammalian diversity and their ecological roles.

Related terms

Chicxulub Crater: A large crater located on the Yucatán Peninsula in Mexico, believed to be the impact site of the asteroid that contributed to the End-Cretaceous extinction.

Mammals: Warm-blooded vertebrates that possess hair or fur and typically give live birth; they became dominant after the End-Cretaceous extinction.

Iridium Layer: A distinct layer of sediment found in the geological record, rich in iridium, which supports the asteroid impact hypothesis for the End-Cretaceous extinction.