They found that the fossil embryos appeared to bear the features of those of bilaterians, which are complex animals with mirror symmetry and digestive tracts, such as the spider, butterfly, dinosaur and human being. The embryos were discovered having polar lobes, fingerlike appendages that ensured a crucial strategy for introducing asymmetry into the embryos and allowing them to form different tissues in adults. As an essential feature to complex organisms, many mollusks and some worms on Earth today use polar lobes in their embryonic development.
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