Sturgeons are an ancient group of fish, recognizable by their elongated bodies covered with rows of bony plates, known as scutes. They also possess four sensitive barbels near their mouths, which they use to navigate and find food on river and lake bottoms. Their millions of years in aquatic ecosystems make them a subject of scientific study.
Their Ancient Lineage
The lineage of sturgeons (Acipenseriforms) first appeared in the fossil record during the Early Jurassic period, 174 to 201 million years ago. This places their origins well before the peak of dinosaur diversity. True sturgeons, belonging to the family Acipenseridae, emerged later in the Upper Cretaceous, around 100 to 94 million years ago. They have successfully navigated multiple global extinction events, including the one that ended the age of dinosaurs.
A Living Fossil Story
Sturgeons are often called “living fossils” because their body plan has remained remarkably consistent over vast stretches of geological time. Their morphology includes a heterocercal tail, resembling that of a shark, and a mouth positioned on the underside of their snout, suitable for bottom feeding. They also have a largely cartilaginous skeleton, which, while appearing primitive, is a derived characteristic from ancestors with bony skeletons.
Several biological traits contribute to their long-term survival and evolutionary stability. Sturgeons exhibit slow growth rates and can live for many decades, with some individuals reaching over 100 years. They also reach sexual maturity quite late, often between 8 to 15 years for males and 14 to 33 years for females, and do not spawn every year. Their generalist feeding habits, large size, and protective bony scutes have allowed them to adapt to changing environments without major evolutionary shifts.
Unearthing Their History
Our understanding of sturgeon history comes primarily from paleontological evidence. Early true sturgeon fossils, such as a partial skull from the Cenomanian age (100-94 million years ago), have been found in places like Alberta, Canada. More recent discoveries have helped fill gaps in their distribution during the late Cretaceous period. A Maastrichtian-age fossil in Morocco indicates their past presence in northern Africa.
Scientists determine the age of these ancient remains using dating techniques. Relative dating places fossils in chronological order based on their position within rock layers, with deeper layers generally being older. More precise ages are obtained through absolute dating methods, such as radiometric dating, which measures the decay of radioactive isotopes in the surrounding rocks or sediments. Fossils are rarely dated directly due to their fragility.
Sturgeons in the Modern World
Modern sturgeons, about 27 species worldwide, inhabit subtropical, temperate, and sub-Arctic rivers, lakes, and coastlines across Eurasia and North America. Many species can grow quite large, typically ranging from 2 to 3.5 meters in length. Despite their long evolutionary success, sturgeons face challenges today.
Human activities have led to a decline in their populations. Overfishing for their valuable roe used to produce caviar, combined with habitat destruction from dams, pollution, and river fragmentation, has impacted many species. The International Union for Conservation of Nature (IUCN) reports that over 85% of sturgeon species are at risk of extinction, making them the most threatened group of animals globally.