Yale study debunks theory that asteroid strike triggered tuna evolution

A new study from Yale University challenges a long-standing theory that the asteroid impact which wiped out the dinosaurs 66 million years ago indirectly spurred the evolution of tunas and other large, warm-blooded predatory fish. Published in the journal *Proceedings of the Royal Society B*, the research analyzed genetic data and fossil records to trace the evolutionary timeline of Scombridae, the family that includes tunas, mackerels, and related species. The findings reveal that the K-Pg extinction event did not trigger the development of these fish’s signature traits, such as endothermy and large body sizes, which instead evolved over tens of millions of years independently of the asteroid’s aftermath.

The study, led by graduate student Chase Brownstein and senior author Thomas Near, constructed the most comprehensive time-calibrated evolutionary tree for Scombridae to date. By integrating genetic samples from institutions like the Yale Peabody Museum with fossil evidence, the team found that the origins of the family coincided with the asteroid impact. However, their analysis showed that key adaptations—such as the ability to regulate body temperature and grow to substantial sizes—emerged long after the extinction event. “Our results demonstrate the K-Pg extinction did not trigger the evolution of tunas and related large, endothermic predators,” Brownstein said. “The body plans of these predators evolved over tens of millions of years, with no direct link to the asteroid’s aftermath.”

According to the research, endothermy in Scombridae evolved independently at least three times, with two of these instances occurring 10 to 15 million years after the asteroid strike. The study also found that increases in body size occurred sporadically throughout the lineage’s history, rather than as a rapid response to ecological changes caused by the extinction. The entire evolutionary trajectory of modern tunas and mackerels spanned approximately 50 million years, the researchers noted. This challenges the idea that the K-Pg event created a “niche opportunity” for these fish to dominate marine ecosystems, as seen with mammals following the dinosaurs’ demise.

The implications of the study extend beyond evolutionary biology. Understanding the mechanisms behind endothermy in tunas could provide insights into human metabolic disorders, such as obesity and diabetes, according to Near. “Studying how biodiversity has dealt with similar challenges over time is relevant to better understanding human health,” he said. The research also highlights the importance of conserving tuna populations, which have faced significant declines due to overfishing, particularly the Atlantic bluefin tuna.

While the Yale study refutes the connection between the asteroid impact and tuna evolution, other research has explored the broader consequences of the event. For instance, simulations suggest the asteroid generated a megatsunami with waves up to a mile high, which reshaped global coastlines and left geological evidence of its reach. Additionally, studies of the Chicxulub crater reveal that the impact may have created a hydrothermal system that sustained marine life for millions of years, offering a glimpse into how life rebounded after the extinction. However, these findings focus on the immediate and long-term environmental effects of the asteroid, rather than the evolutionary pathways of specific species.

The Yale team’s work underscores the complexity of interpreting evolutionary relationships from fossil and genetic data. “This paper highlights the need to be cautious when linking species’ traits directly to extinction events,” Brownstein emphasized. The study’s authors, including researchers from Virginia Tech, Purdue University, and the Santa Barbara Museum of Natural History, stress that evolutionary adaptations often unfold over vast timescales, shaped by factors beyond catastrophic events. Their findings contribute to a growing body of evidence that redefines how scientists understand the interplay between mass extinctions and the emergence of new life forms.