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Home » Why are there so few crocodiles? Climate and competition tell the tale

Why are there so few crocodiles? Climate and competition tell the tale

Under the guidance of scientists at the University of York, a research team meticulously charted the ancestral lineage of the formidable ambush-predators and their extinct kin, collectively known as Pseudosuchia. Delving into the fossil record, the researchers sought to unravel the intriguing question of why crocodiles exhibit a scarcity of extant species, particularly when compared to their close living relatives—the birds, which boast an impressive count of 11,000 species.

In their investigation, the researchers uncovered that the diversity of modern-day crocodiles and their extinct counterparts has been significantly influenced by climate change and competition with other species. However, the study also brought to light an unexpected revelation: the , whether species inhabit the sea, freshwater, or land, played a pivotal role in their survival.

Analysis of the data revealed a correlation between rising global temperatures and an increase in the number of species among sea-dwelling and land-based relatives of crocodiles. Conversely, heightened competition for resources, potentially with predators like sharks, marine reptiles, or dinosaurs, emerged as a probable driver for the extinction of these species. Intriguingly, freshwater-dwelling relatives of crocodiles remained unaffected by temperature changes but faced the greatest risk of extinction due to rising sea levels.

Published in Nature and under the title “Decoupling speciation and extinction reveals both abiotic and biotic drivers shaped 250 million years of diversity in crocodile-line archosaurs,” the study not only contributes to our understanding of the intricate evolutionary history but also holds implications for efforts.

With seven crocodile species classified as Critically Endangered and an additional four labeled as vulnerable, the study's findings offer valuable insights for conservation strategies, especially in the context of the ongoing climate changes. Dr. Katie Davis, the senior author of the study from the Department of Biology at the University of York, emphasized the significance of considering ecology in predicting species responses to contemporary climate shifts, highlighting the richness of the fossil record as a key resource for understanding the past and guiding .

Poposaurus, from a group of extinct relatives of the crocodile known as Poposauroidea. This crocodilian was around four meters long and lived alongside dinosaurs from 237 to 201.3 million years ago. Credit: Jagged Fang Designs

In the face of the imminent peril threatening a million plant and animal species with extinction, unraveling the crucial factors driving species disappearance has assumed unprecedented significance. The vulnerability of crocodile species adds a poignant dimension, as many inhabit low-lying areas susceptible to the irreversible transformations brought about by rising sea levels linked to global warming.

Crocodiles, sharing a lineage with birds and dinosaurs, collectively form the archosaurs, or “ruling reptiles,” a group extending back to the Early Triassic, inclusive of pterosaurs. Pseudosuchia, within this framework, represents a subset of archosaurian reptiles more closely related to crocodiles than birds.

In this comprehensive study, researchers constructed an extensive phylogeny—a familial tree—for all crocodiles and their extinct relatives. This intricate map allowed them to discern patterns of species emergence and extinction. Integrating this information with historical climate data, specifically temperature and sea level variations, enabled the assessment of the interplay between species dynamics and climate change.

The investigation also delved into the potential influence of species interactions, such as competition, employing Information Theory—a mathematical approach. By estimating species numbers over time and comparing them against instances of new species emergence and extinctions, the researchers gained insights into the direct impacts of climate change and species interactions on the evolutionary trajectories.

Dr. Davis emphasized the unique perspective that crocodiles and their extinct relatives provide in understanding the intricate interplay between climate change and . The findings, extending insights into the past, present, and future, contribute significantly to our comprehension of the factors shaping life on Earth.

Source: University of York

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