The discovery of around 250 exquisitely preserved seeds from the early Cretaceous period has enabled researchers to build a more complete picture of the landscape the dinosaurs inhabited, while at the same time improving our understanding of the evolutionary roots of modern plant life.
The seeds which are aged between 110 and 125 million years were found in soft sediments in 11 locations across Portugal and North America. Using a technique called synchrotron radiation X-ray tomographic microscopy (SRXTM), scientists were able to analyze the internal features of these specimens, which belonged to about 75 different groups of angiosperm, or flowering plants.
In doing so, they found that around 50 of the seeds contained partially or completely preserved embryos, all of which were extremely small in relation to seed size, ranging from 1.5 percent to 3.4 percent. The remaining space within the seeds was filled with nutrient storage tissue, indicating that the embryos had not shrunk over the years, but were indeed this small at the time of the seeds distribution.
SRXTM reconstructions of embryos embedded in seeds. Else Marie Friis et al.
Since the embryos were all too small to be able to germinate, the researchers conclude that they were most likely in a state of dormancy when the seeds were spread. During dormancy, seeds are prevented from germinating amid periods of unfavorable climatic conditions for plants to flourish. As such, it allows the seeds of early angiosperms to survive until optimal conditions for germination arise.
Publishing their findings in the journal Nature, the study authors use this information to support current theories about the nature of early angiosperms. According to these hypotheses, ancient flowering plants were opportunistic, early successional colonizers of disturbance-prone habitats.In other words, they existed in ecosystems that tended to experience regular drastic environmental changes, which may have been caused by extreme weather events or other natural phenomena such as volcanic eruptions.
Within such volatile environments, dormancy provided a key mechanism by which these seeds could wait out periods of unfavorable conditions, germinating only during times when circumstances were optimal.
Close-up imagery and a SRXTM reconstruction of a seed of the Sarcandra genus. Else Marie Friis et al.
However, the researchers note that, in comparison to modern-day angiosperms, the relatively tiny size of the dormant embryos and paucity of nutrient reserves would have restricted the speed atwhich germination could occur when the setting was right. The authors therefore conclude that early angiosperms would have been unable to match the very rapid germination of many angiosperms that evolved later.
Thus, the research provides a fascinating comparison of the adaptability of angiosperms that existed during the age of dinosaurs with those of today. For instance, among the modern flowering plants that exhibit seed dormancy are the likes of tobacco plants and petunias, both of which are considerably more efficient in this regard than their Cretaceous predecessors.