The first thing you notice about a female anglerfish isn’t her fearsome jaws or her midnight-black skin — it’s the rod-like lure jutting from her forehead, a biological fishing pole that has evolved over tens of millions of years to do far more than just snag dinner.
New research tracing the evolution of this iconic adaptation reveals that the anglerfish’s lure began as a simple, motion-based tool around 72 million years ago, during the Late Cretaceous, when a common ancestor first modified a dorsal fin spine into a protruding rod. Over time, as some lineages drifted into the open ocean’s perpetual twilight, the lure transformed: gaining bioluminescence between 34 and 23 million years ago, then growing longer and more elaborate, not only to attract prey but to serve as a beacon for mates in the vast, dark depths.
This dual function — hunting and mating — upends the long-held assumption that the lure exists solely for predation. Scientists from the University of Kansas, working with colleagues at St. Cloud State University, analyzed 118 specimens across 102 species, combining fossil data, museum specimens and computer modeling to map how lure design correlates with habitat and behavior. Their findings, published in *Ichthyology & Herpetology*, show that deep-sea anglerfish with glowing lures leverage them in nuanced ways: some pulse the light like a signal, others waver it to mimic prey, and in at least one case, the lure acts as a shuttered window, modulating glow through muscle contractions.
Only females possess the lure, a trait that shapes the species’ extreme sexual dimorphism. Males, by contrast, are tiny — often less than a tenth the size of females — with enlarged nostrils and eyes adapted to detect faint light or chemical traces. This mismatch suggests the lure evolved not just to catch food, but to bridge the enormous gap between sexes in an environment where encounters are rare. As lead researcher Alex Maile noted, “There have been hypotheses that they’re using the lure to communicate with males. The males have really substantial noses and relatively big eyes.”
The shift to bioluminescent lures coincided with a burst of speciation, particularly in open-ocean species. This pattern mirrors what’s seen in other deep-sea fish like lanternfish and dragonfish, which also use light for intraspecific communication. The ability to flash unique patterns may have helped populations diverge, accelerating evolution in the dark. Meanwhile, chemical lures emerged independently in other lineages — first in batfishes around 49 million years ago, then in a frogfish lineage about five million years ago — showing that evolution repeatedly converged on similar solutions: using light, motion, or chemistry to bridge the gap between predator and prey, or hunter and hunted.
What stands out is not just the lure’s complexity, but its versatility. In shallow waters, some anglerfish rely on simple twitching motions to lure prey. In the abyss, others dangle glowing tips well beyond their bodies, using length to preserve their own dark silhouettes hidden while the light does the work. One lineage even evolved a lure that can slide in and out of the skull, releasing chemicals to ambush buried invertebrates — a tactic suited to worms and clams that follow scent trails rather than movement.
This adaptability helps explain why anglerfish thrive in such disparate habitats: coral reefs, continental shelves, the open ocean, even floating algae mats. Far from being a bizarre anomaly, the lure is a masterwork of evolutionary tinkering — a structure that began as a simple rod and, over millions of years, became a multifunctional tool for survival in one of Earth’s most extreme environments.
How the lure’s dual role changes our understanding of deep-sea evolution
For decades, the anglerfish lure was viewed through a narrow lens: a specialized adaptation for predation in low-light environments. The new research reframes it as a multifunctional trait shaped by both ecological and reproductive pressures. This shift matters as it suggests that traits we assume are purely survival-driven — like bioluminescence — may often serve dual purposes, especially in environments where sensory input is limited and encounters are infrequent. The fact that the lure’s elongation and increased complexity coincided with a surge in species diversity supports the idea that communication, not just hunting, drove evolutionary innovation in these fish.
What the fossil record reveals about the lure’s origins
The lure’s journey began not with light, but with mechanics. Fossil and morphological evidence indicates that the original structure, present in the common ancestor of all modern anglerfish around 72 million years ago, was a simple, non-luminescent rod used to create movement — a visual twitch to attract nearby prey. This ancestral form aligns with what we see in some shallow-water species today, which rely solely on motion. The transition to bioluminescence didn’t occur until lineages invaded the pelagic zone, where sunlight vanishes and visual hunting becomes impossible without self-generated light. That shift, occurring between 34 and 23 million years ago during the Oligocene, marks a pivotal moment when the lure stopped being just a lure and became a signal.
Why male anglerfish evolved to detect, not display
While females carry the elaborate lures, males evolved in the opposite direction: becoming highly specialized detectors. Their disproportionately large nostrils and eyes are not for show — they’re adaptations to detect the faintest traces of light or chemical signals released by females. This extreme sexual dimorphism, where males are often parasitic and fuse to females upon finding them, makes sense only if the lure’s primary role in the deep sea is to act as a beacon. In the vastness of the open ocean, where a female might go years without encountering a male, the ability to broadcast a detectable signal — whether through light, motion, or scent — becomes as critical as the ability to eat.
How old is the anglerfish’s lure?
The lure originated in a common ancestor of all modern anglerfish approximately 72 million years ago, during the Late Cretaceous period.
Do male anglerfish have lures?
No, only female anglerfish possess the distinctive lure; males are significantly smaller and rely on enhanced sensory organs to locate females.
When did anglerfish develop bioluminescent lures?
Bioluminescent lures evolved in deep-sea lineages between 34 and 23 million years ago, after ancestors moved into the open ocean’s dark, pelagic zone.
