Cretaceous-Paleogene

Definition

The Cretaceous-Paleogene (K-Pg) boundary marks a significant transition in Earth's history, approximately 66 million years ago, characterized by a mass extinction event that led to the demise of about 75% of all species, including the non-avian dinosaurs. This boundary is crucial for understanding the evolution and composition of reef ecosystems, as it signifies the transition from diverse Mesozoic reef systems dominated by rudist bivalves to modern coral-dominated reefs in the Cenozoic era.

5 Must Know Facts For Your Next Test

1. The Cretaceous-Paleogene boundary is known for one of the most dramatic mass extinctions in Earth's history, which drastically altered terrestrial and marine ecosystems.
2. This event is believed to have been triggered by a combination of volcanic activity, climate change, and a massive asteroid impact near present-day Chicxulub, Mexico.
3. Before the K-Pg boundary, reef ecosystems were largely dominated by rudist bivalves, which were wiped out during the mass extinction.
4. Following the extinction event, coral reefs began to flourish and diversified rapidly, leading to the establishment of modern reef systems that we recognize today.
5. The changes in reef ecosystems at this time laid the foundation for modern marine biodiversity and altered ocean chemistry, influencing the evolution of many species.

Review Questions

• How did the Cretaceous-Paleogene boundary influence the evolution of marine ecosystems?
  • The Cretaceous-Paleogene boundary caused a mass extinction that eliminated many marine species, particularly rudist bivalves that dominated reefs at that time. This significant loss allowed for ecological niches to open up, leading to new evolutionary pathways. In particular, coral reefs began to thrive post-extinction, marking a major shift in marine ecosystems from Mesozoic to modern structures.
• Discuss the role of environmental changes associated with the Cretaceous-Paleogene boundary in shaping reef ecosystems.
  • Environmental changes at the Cretaceous-Paleogene boundary, including climate shifts and the aftermath of an asteroid impact, drastically altered ocean conditions. These changes resulted in increased nutrient levels and shifts in ocean chemistry that favored coral growth over rudist bivalves. Consequently, this transition marked the rise of modern coral reefs as dominant marine habitats, facilitating a diversification of marine life that persists today.
• Evaluate how the transition from rudist-dominated reefs to coral-dominated reefs post-Cretaceous-Paleogene impacts our understanding of modern biodiversity.
  • The transition from rudist-dominated reefs to coral-dominated ecosystems after the Cretaceous-Paleogene boundary is critical for understanding modern biodiversity. This shift illustrates how catastrophic events can reshape ecological communities and drive evolutionary processes. By studying these changes, we can appreciate how resilience and adaptability in marine environments contribute to current biodiversity patterns and highlight potential future responses to ongoing environmental challenges.

Related terms

Mass Extinction: A rapid decrease in the biodiversity on Earth, typically defined by the extinction of a large number of species within a relatively short geological timeframe.

Rudist Reefs: Reef systems primarily built by rudist bivalves during the Late Cretaceous, which were significant contributors to marine ecosystems before the K-Pg extinction event.

Coral Reefs: Complex marine ecosystems formed by coral polyps that provide habitat for numerous marine species and have developed significantly after the K-Pg boundary.