Key fossil discovered to understand the evolution of an aquatic plant

Echinochara pontis is the name of a species of aquatic plant from brackish waters of the Lower Cretaceous reconstructed by Jordi Pérez Cano and Carles Martín Closas, paleobotanists from the Faculty of Earth Sciences, the Biodiversity Research Institute (IRBio) of the University of Barcelona and the Catalan Institute of Paleontology. The reconstruction of the plant has been made from its organs found in a stratum of rocks within the municipality of La Pobla de Benifassà (Castellón). 

This plant from 145-140 million years ago allows us to better understand the evolution of aquatic plants. Echinochara pontis belongs to the group of charophytes, multicellular algae considered to be the ancestors of vascular plants that were found in freshwater and brackish water lakes. During the Early Cretaceous, a now extinct family called Clavatoraceae was dominant in that environment. Echinochara is the oldest genus of this family, which appeared during the Middle Jurassic. However, it is the least known genus, due to its complex structure, which often makes its identification difficult. Until now, there was a 23-million-year gap in the fossil record of this genus, between Echinochara peckii from the Kimmeridgian (ca. 155–149 million years ago) and Echinochara lazarii from the Barremian (126–121 million years ago). This lack of descriptions of Echinochara populations did not allow us to understand the evolution of the genus. 

The new species, Echinochara pontis, described in this interval, presents a unique combination of morphological characters that place it between the two species. For example, it shares the bilateral symmetry of fruiting with Echinochara lazarii and the twisting of the thallus with Echinochara peckii, as well as presenting its own features such as the unique structure of the cells that covered the oospore. 

The paleoecological study indicates that Echinochara pontis inhabited brackish water areas, forming monospecific turfs in a similar way to the other species of the genus. This information is very important since it allows us to know the type of rock in which to look for remains of Echinochara in the fossil record to deepen our knowledge of the genus and its evolution, as well as to better understand the characteristics of brackish water lakes from the geological past. 

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Figure 1: Remains of Echinochara pontis and their interpretation. A) internal series; B) external series; C) thallus. 

Figure 2. Evolution of the genus Echinochara.