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Tiny flora from the past

Fruits and seeds from the Cretaceous seen with X-ray tomographic microscopy

Else Marie Friis Fruits and seeds from the Cretaceous seen with X-ray tomographic microscopyElse Marie Friis

The earliest flowering plants, called angiosperms, appeared on the planet between 130 and 100 million years ago and must have been very small indeed. Fossils discovered in recent decades have indicated that the flowering plants that began blooming on the Earth around that time – the Early Cretaceous – were the size of herbaceous plants or, at most, bushes, did not live long, and were among the first species to colonize disturbed habitats. Scientists from Sweden, Switzerland, Denmark, and the United States have obtained evidence that confirms the idea that the first angiosperms displayed these characteristics. Using X-ray tomographic microscopy, the paleobotanist Else Marie Friis and collaborators analyzed the internal structures of fossil seeds from 75 groups of angiosperms belonging to 11 flora that existed between 125 and 110 million years ago in what is now Portugal and North America. Among the nearly 250 imaged seeds, all were less than 2.5 millimeters long; about 50 included a tiny embryo that was partially or wholly preserved and associated with nutrient storage tissues (Nature, December 24, 2015). In these cases, the seeds were dormant and had not germinated. According to the scientists, the size of the seeds analyzed in this and other studies is consistent with what is to be expected based on fossil records and on the ratio observed between the size of small plants and their seeds today. The tiny size of the embryos and the fact that they were dormant would have ensured that the seeds of those ancestral angiosperms could survive until conditions were favorable for germination.