With over 26,000 species, teleosts represent 96% of all fish living today.
In short: From the tiny, six-millimeter anglerfish to the massive, two-ton ocean sunfish, teleosts have conquered almost every aquatic environment on Earth. Their secret weapon? A highly specialized, protruding jaw mechanism that revolutionized how fish capture prey, allowing them to dominate the world's oceans, rivers, and even extreme mountain lakes.
The term teleost, derived from the Greek words for 'complete' and 'bone,' describes a group defined by a unique skeletal architecture. Unlike other bony fish, teleosts possess a movable premaxilla—a bone in the upper jaw that is unattached to the braincase. This allows them to protrude their mouths forward, creating a circular opening that lowers internal pressure and sucks prey inside. This mechanical advantage, paired with a homocercal tail where the upper and lower lobes are equal in size, has enabled them to evolve into a staggering variety of forms.
Their evolutionary success is marked by significant skeletal refinements. Teleosts have reduced their lower jaw to just three bones and evolved a lighter, strut-based bone structure rather than the dense, cancellous bone found in more basal fish. Many also possess a second set of jaws in their throats, known as pharyngeal jaws. In derived species, these have fused and gained specialized muscles, allowing them to grind food rather than simply transporting it. This versatility has allowed them to occupy diverse niches, from filter feeders and parasites to high-speed predators.
While most teleosts are cold-blooded, some have developed remarkable physiological workarounds. Tuna, for instance, use a counterflow heat exchange system to keep their muscles warmer than the surrounding water, boosting their swimming efficiency. Others, like the desert pupfish or the amphibious mudskipper, have adapted to extreme conditions, including high salinity, low oxygen, or even temporary life on land. This adaptability, combined with a history of diversification that accelerated after the mass extinction event 66 million years ago, ensures their continued dominance in the modern aquatic world.
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Sources
- Summary by Intellect · source: Teleost
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