An investigation reveals the true diversity of a group of ferns present in Cretaceous sites on the Iberian Peninsula, specifically Las Hoyas (in Cuenca) and El Montsec (in Lleida), whose paleontological content dates from between 125 and 130 million years ago.
The study was carried out by Candela Blanco Moreno and Ángela Delgado Buscalioni, both from the Paleontology Unit in the Department of Biology of the Autonomous University of Madrid (UAM) in Spain.
The findings in this research show an unexpected similarity between the species and reveal details about the evolution of these ferns in relation to the first flowering plants in Cretaceous ecosystems.
The researchers studied fossils previously identified as belonging to the genera Coniopteris and Sphenopteris at both sites. And they came to the conclusion that most of the specimens belong to the same species, Coniopteris laciniata, described for the first time at the Las Hoyas site in the year 2000 by researchers from the Natural Sciences Museum of Madrid and the Complutense University, both institutions in Spain.
The specimens from the El Montsec site, which present a morphology similar to that of Coniopteris laciniata, had previously been described as the species Sphenopteris wonnacottii in 2003. However, the new study shows that these two species are actually one, due to their morphological similarity and the equivalence in the construction of their leaves. The name remains as Coniopteris laciniata following the law of taxonomic priority.
Reconstruction of a complete Cretaceous plant and its typical relationship with the environment. (Illustration: Candela Blanco Moreno)
The study describes the complete morphology of this small fern, which has an elongated rhizome from which grouped leaves emerge, up to 9 centimeters long. Its main characteristic is that it presents compound leaves with two different types of segments: some are lobed, similar to a clover leaf, and others are elongated and ribbon-shaped.
In both sites, leaves with only one type of segment had been identified, as well as leaves that present both types at the same time, with intermediate shapes. These last specimens were identified as Coniopteris laciniata in Las Hoyas and Sphenopteris wonnacottii in El Montsec.
However, multiple specimens identified as other Coniopteris or Sphenopteris species at both sites are actually Coniopteris laciniata leaves with unique leaf segment morphology.
The cause of the variation in the morphology of the segments was attributed to different reasons in previous investigations. In the case of the specimens from the Las Hoyas site, it was proposed that the ribboned segments corresponded to the fertile part of the leaf, which would have suffered a reduction in the width of its blade, as occurs in many ferns.
On the other hand, in the case of the specimens from the El Montsec site, it was suggested that the ribboned morphology could be due to the fact that these segments developed underwater, while the lobed segments would have developed under aerial conditions. The new study, using morphometric analysis, shows that the second hypothesis is more likely, since the architecture of the two types of segments is very different.
The reconstruction of this plant allows a better understanding of the plant communities that lived in the vicinity of the aquatic systems of Las Hoyas and El Montsec. In addition, it points to a greater similarity between these two localities, which already share many groups, both plant and animal. One of these species is Montsechia vidalii, one of the first confirmed records of flowering plants globally.
The presence of this small fern, probably from the Polypodiales group of modern ferns, in the same ecosystem in which the first flowering plants inhabited, could confirm that the diversification of these two groups occurred at the same time. Thus, this discovery provides valuable data to understand the evolution of ferns and their relationship with the first flowering plants in Cretaceous ecosystems.
The study is titled “Revision of the Barremian fern Coniopteris laciniata from Las Hoyas and El Montsec (Spain): Highlighting its importance in the evolution of vegetation during the Early Cretaceous”. And it has been published in the academic journal Taxon. (Source: UAM)
