A study by University of Michigan researchers and their colleagues has revealed that sturgeon have been the fastest evolving fish on the planet in terms of changes to body size.
By many, the fish were thought to be 'living fossils' unchanged for millions of years.
Daniel Rabosky, assistant professor in the U-M Department of Ecology and Evolutionary Biology and a curator of herpetology at the Museum of Zoology, says: "Our study shows that sturgeon are evolving very quickly in some ways.
"They have evolved a huge range of body sizes. There are dwarf sturgeon the size of a bass and several other species that are nearly as big as a Volkswagen."
This finding is only one in a number of studies looking at the rates of species formation and anatomical change in fish.
The main goal of the research project was to test longstanding ideas in evolutionary biology that has not previously been evaluated, says Rabosky.
Charles Darwin coined the term 'living fossil' to describe extant creatures, such as the gar and lungfish, that have survived millions of years yet appear to have remained similar to their origins.
Rabosky and his colleagues' data was so large that new computer programs had to be developed in order to analyse it.
This allowed them to study the correlation between how quickly new species form and how rapid their evolution of body size is.
There was a strong link between rates of species diversification and body size evolution across the more than 30,000 species of ray-finned fish, which is the majority of vertebrate biological diversity.
Rabosky says his team were simply testing ideas that had been around since Darwin but had never been proved, or not, due to lack of data and limited technology.
Most fish groups fall into one of two categories: fish, like gar, form species very slowly and have little range in body size, whilst others, like salmon, do both. They form species quickly and have a wide range of body sizes.
There are 29 species of sturgeon worldwide and the fish has been around for over 100 millions years.
They do not fit the pattern found by Rabosky's team's findings - sturgeon have a great variety in body size but there are few species.