Rethink of fossils hints dinosaurs still thrived before asteroid hit

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Study: Dinosaur Extinction Debate Reignited by Fossil Availability

A recent study suggests that dinosaurs were likely not in decline before a massive asteroid impact eradicated them, but rather, the scarcity of fossils from that critical period may be skewing the narrative. This research re-examines the long-standing debate surrounding dinosaur populations in the lead-up to their extinction approximately 66 million years ago during the late Cretaceous period.

Fossil Record Bias Challenges Dinosaur Decline Theory

The question of whether dinosaur populations were flourishing or diminishing when a colossal asteroid collided with Earth has been a subject of intense discussion. Notably, a perceived decrease in discovered dinosaur fossils dating from the era immediately preceding the asteroid event has prompted some scientists to posit that these colossal creatures were already headed toward extinction irrespective of the cataclysmic impact.

However, new research challenges this viewpoint by focusing on the limitations of the fossil record itself.

Analyzing Fossil Data from North America

Christopher Dean and his team at University College London conducted an analysis of a comprehensive dataset encompassing over 8,000 fossils. These fossils represented four distinct dinosaur groups inhabiting North America between 84 million and 66 million years ago. The study included well-known species such as the formidable Tyrannosaurus rex and the horned Triceratops.

Their findings revealed a significant number of dinosaur fossils from the period spanning 84 million to 75 million years ago. Subsequently, the fossil count decreased in the ensuing 9 million years leading up to the Chicxulub impact event. Despite this drop, the team investigated potential reasons for this apparent decline.

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Accessibility of Fossil-Bearing Rocks

Dean’s team considered the crucial factor of land accessibility for paleontological research. They assessed the amount of land surface currently available to paleontologists that originates from the period preceding the asteroid impact. Additionally, they factored in the number of excavation expeditions conducted in these regions.

Their analysis indicated a notable limitation: there simply aren’t abundant quantities of the appropriate rock formations accessible for contemporary scientists to investigate.

Dean explains that paleontologists search for fossils within ancient layers of the Earth’s crust that have become exposed at the surface. This process is akin to working on “a puzzle where half the pieces are missing,” due to the incomplete nature of the exposed rock record.

Ecological Models Suggest Stable Dinosaur Populations

To gain further insights, the research team employed ecological models to estimate the likely dinosaur population sizes in these regions. These models incorporated geological and geographical data relevant to that era.

The calculations suggested that, contrary to the decline theory, overall dinosaur populations remained stable leading up to the asteroid impact. Dean asserts, “It looks like our ability to detect dinosaurs is influencing the patterns that we see in the fossil records more than anything else,” implying that the apparent drop in fossils might not reflect a real decline in dinosaur numbers.

Broader Research Context and Dinosaur Diversity

Manabu Sakamoto from Reading University, UK, who was not involved in this particular study, acknowledges that this research strengthens the growing body of evidence pointing to a potential bias in fossil accessibility from North America in those crucial 9 million years. However, Sakamoto contends that this finding does not fundamentally alter the larger perspective of a long-term decline in dinosaur diversity.

Sakamoto’s research indicates that even if dinosaur populations were substantial and dominant towards the close of the Cretaceous period, their species diversity appeared to be diminishing. Over the vast 175 million years of dinosaur existence, the rate of new dinosaur species emerging was generally slowing down. This trend resulted in a higher rate of dinosaur species extinction compared to the emergence of new species.

Long-Term Diversity Decline Persists

Sakamoto maintains that this broader trend of diminishing dinosaur diversity over extended periods remains valid, even considering the new study’s findings about potential biases in fossil availability. He concludes, “Those two things are not mutually exclusive of each other,” suggesting that both fossil record limitations and a genuine long-term decline in dinosaur diversification might be at play.

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