The Order Ricinulei holds a famous place in paleontology because they are one of the very few organisms discovered as fossils before they were ever found alive. While today's surviving species are highly light-avoiding and secretive, their ancestors were once thriving and diverse during the Paleozoic Era. Roughly three-quarters of all known Ricinulei fossil species come from the Late Carboniferous coal measures, primarily found in Europe and North America. Paleontologists group these ancient members into the extinct suborder Palaeoricinulei. A Shift to the Trees: Extinct members preserved in amber (such as Hirsutisoma grimaldii under the suborder Primoricinulei) show a different ecological niche. Based on their hairy body structures and leg adaptations, scientists believe that during the Cretaceous, they lived on tree bark as arboreal predators, rather than staying buried in the soil. Ricinulei is a very small, mysterious order of arachnids. They are commonly known as "hooded tickspiders," although they are neither true spiders nor ticks. They are predatory arthropods that live in leaf litter or caves, usually measuring less than 1 centimeter in length. Period: Cretaceous (100 million years old) Location: Hukawng Valley, Myanmar Size: Amber 22*14.5*5 mm