麻豆淫院

Yale University ecologists reveal a lizard lineage that rode out the dinosaur-killing asteroid event with unexpected evolutionary survival traits. Night lizards (family Xantusiidae) survived the Cretaceous鈥揚aleogene (K-Pg) mass extinction event 66 million years ago (formerly known as the K-T extinction) despite having small broods and occupying limited ranges, a departure from the theory of how other species are thought to have persisted in the aftermath of the event.

Before K-Pg, Earth was a warm, thriving planet with lush forests and diverse ecosystems both on land and in the oceans. Dinosaurs were widespread, diverse, and dominant. Marine reptiles patrolled the seas and pterosaurs soared through the skies. Future humans were still shrew-like, tree-dwelling creatures, part of a small but growing evolutionary experiment into placental mammals.

An asteroid more than six miles across, moving around 43,200 miles per hour, struck the Chicxulub region of Yucat谩n, Mexico, releasing an incomprehensible 10²³ joules of energy. For context, if every explosive that humans have ever made all detonated at once, it still wouldn't come close to the energy released by the Chicxulub asteroid.

A 1,000-mile radius of forest was instantly incinerated by the extreme heat, as the impact gouged a crater more than 100 miles wide and 12 miles deep. Tsunamis, roughly the height of the Eiffel Tower, propagated outward, ravaging shorelines and sea floors across the globe, and rang Earth's mantle like a bell, setting off what today would be city-leveling mega-earthquakes greater than magnitude 10.

And just when the worst seemed to be over, it got even worse. Debris ejected from the impact that had risen above Earth's atmosphere began raining back down. Superheated upon reentry, it pelted the planet with a deadly shower of molten projectiles that started global fires.

Vast amounts of soot, dust, and aerosols were left lingering in the stratosphere, blocking sunlight and plunging the planet into an "impact winter" with plummeting global temperatures. Without photosynthesis, plant life began to die off, and food chains from the smallest ocean plankton to largest dinosaurs were obliterated. Acid rain, produced by vaporized sulfur-rich rocks, induced rapid changes in ocean chemistry, which led to the widespread extinction of plankton, ammonites, and many marine reptiles.

When it was over, 75% of species, the products of billions of years of evolution, were gone. It is a wonder that anything at all survived the event, but life did find a way.

In the study, "Night lizards survived the Cretaceous鈥揚aleogene mass extinction near the asteroid impact," in Biology Letters, researchers combined phylogenetic tip-dating with ancestral-trait reconstruction to determine whether xantusiid lizards originated before the K-Pg boundary and to identify features that may have aided their survival.

Genetic data from 34 living night-lizard species, integrated with fossils ranging from the Early Cretaceous to Miocene strata across North America, Central America, and Cuba, anchored the analyses.

Genetic clocks traced Cricosaura typica, a Cuban species, to the earliest branch in the family tree, splitting off before its North and Central American cousins emerged. Species of Lepidophyma and Xantusia diversified much later, in parallel radiations about 12 million years ago, long after the asteroid had reshaped their ancestral landscape.

On California's Channel Islands, the giant island night lizard evolved from a mainland lineage that dispersed west roughly 10 million years back, crossing temporary land bridges before becoming isolated.

Researchers found the 34 living night-lizard species descended from at least two ancient lineages that began roughly 92 million years ago, and survived the K-Pg boundary. Unlike survivors among birds or mammals, these lizards carried forward a life strategy with comparatively small litters.

Statistical reconstruction estimated that ancestral females produced about two offspring at a time, a figure bounded by the single-egg clutches of Cricosaura and the more prolific broods seen in the larger-bodied island species. Body size and fecundity still move in tandem across the lineage, suggesting that bigger litters evolved later, possibly in response to island habitats.

Authors contend that the persistence of night lizards through the Cretaceous鈥揚aleogene extinction event unsettles assumptions about which traits shield lineages from annihilation. Survival did not depend on broad geographic ranges or large broods, qualities often credited in mammals and birds. Instead, night lizards appear to have crossed the extinction threshold while occupying narrow habitats and producing only one or two offspring per reproductive event.

Because of the intensity of K-Pg, there can be no direct fossil evidence that Cretaceous night lizards (or anything else) occupied the immediate impact region. Instead, the inference of proximity rests on reconstructed ancestral ranges in North and Central America and molecular dating placing their common ancestor in the Late Cretaceous. Together, this offers indirect evidence of a front row seat for the most devastating event in Earth's history.

Insights from these lizards' survival may refine how scientists project which species are likely to weather rapid environmental shifts, especially as the current, human-driven mass extinction accelerates.

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