Researchers from the University of Bristol, the Open University and China University of Geosciences found that although brachiopods are evolving in new directions, this is not leading to an increase in the number of species. The findings, published in the journal Nature Ecology & Evolution, reveal some of the core principles of modern biodiversity evolution.
In the current ocean, there are many kinds of molluscs such as clams, oysters and snails, with more than 50,000 species, while brachiopods are relatively rare, with only 394 species currently known. But this is not always the case. The team found that brachiopods were evolving new shell shapes and ecological behaviors after experiencing the end-Permian mass extinction, which impacted their populations.
Dr. Guo Zhen of China University of Geosciences, who led the research, said: "During the Paleozoic era from 540 million to 250 million years ago, brachiopods dominated the seafloor. Sometimes called lampshells, brachiopods were usually located on the seafloor, filtering tiny food particles in the seawater. Most of them are small - you can hold twenty in your hand; but some have large, thick shells and live for a long time. Their shells vary from round to widely spread, and some have smooth shells, while others have deep ridges and grooves."
"Brachiopods were devastated by the end-Permian mass extinction 252 million years ago," said co-author Professor Michael Benton, from the University of Bristol's School of Earth Sciences. "Molluscs may have disappeared completely, and in fact, molluscs have become increasingly successful since then. For a long time, it was thought that the reason brachiopods remained rare was because the survivors stuck to just a few life modes."
Dr Tom Stubbs from the Open University added: "In fact, post-extinction brachiopods have been innovating and trying new life patterns. From the end of the Permian to the present, one group of brachiopods - the terebratulids - have continued to diversify in body shape and ecological function, but their diversity has not increased."
Professor Chen Zhongqiang of China University of Geosciences said: "This is quite unexpected. Brachiopods were far from losers after their extinction at the end of the Permian. They were evolving in new directions and exploring new life patterns, just like their contemporaneous molluscs. But this did not translate into evolutionary success in terms of species numbers. Although they evolved by leaps and bounds in form and function, they were unable to spread widely, and the exact reasons for this are still unclear."
The new study is based on an analysis of a database of more than 1,000 brachiopod genera spanning the past 250 million years. For each genus, analysts recorded dozens of measurements of the shell's overall shape, external carving, and internal anatomy. By combining these features, the overall shape diversity of each major brachiopod group at each time point can be measured. This measure of "shape diversity", often called "disparity," can be compared between different points in time to show the extent of shape innovation.
Guo Zhen concluded: "Our research has consumed a lot of energy." But it is important to understand modern biodiversity from the processes behind it. If we only look at modern brachiopods, we fail to understand their rich past and how innovative they have been in evolution. But our discovery that difference and diversity are decoupled in brachiopod history is both novel and unexpected. Brachiopods have been very creative in evolving new shell forms, but this has not translated into many new species."
Compiled from /ScitechDaily