An impressive trove of fossil-filled amber has come to light at a 110-million-year-old site that has already yielded聽dinosaur bones in Ari帽o, north-eastern Spain. The amber contains an unusually diverse range of insect, plant and vertebrate fossils and provides a rare insight into the life that inhabited what would have been a coastal freshwater swamp during the Cretaceous period.
鈥淗aving two different yet complementary windows of preservation from a given fossil [site] 鈥� the bonebed and the amber at Ari帽o 鈥� is exceptional,鈥� says at the University of Barcelona.
脕lvarez-Parra and his colleagues spent a week excavating at an outcrop within the Santa Maria coal mine, in a sloped geological layer called AR-1, which is a few metres wide. The team uncovered a remarkable variety of fossils within pieces of so-called aerial amber, which forms when resin drops from tree branches or trunks onto the forest floor below.
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Finds included mites, crickets, flying insects, a caterpillar, three types of wasp, a feather fragment, spiderwebs and preserved faeces. Earlier excavations at the AR-1 site had uncovered more than 10,000 dinosaur and vertebrate fossils, but only one amber-preserved fossil containing three mammalian hairs had been identified.
The team found the aerial amber in two locations, each around a few metres wide, which lay roughly 15 metres away from piles of dinosaur and vertebrate bones.
鈥淲hen unearthed, amber is covered by an opaque crust, so the interior is not visible until the surfaces are polished,鈥� says 脕lvarez-Parra. 鈥淎fter months [searching for the fossils] in the laboratory, the results were astonishing. The Ari帽o amber contained an unusually high abundance of [organisms], some of them outstandingly well-preserved.鈥�
Together with previously documented fossils, the findings allowed the team to paint a rich picture of the ecosystem at this site. Small mammals, turtles, crocodiles and fern-eating dinosaurs would have walked the swampy forest floor, while blood-feeding flying insects, parasites and mites would have fed on and recycled organic matter. Meanwhile, spiders would have spun webs to trap flying insects and molluscs would have filtered tiny aquatic organisms from the freshwater.
鈥淎mber is a very powerful tool and contains a wealth of information. The use of amber in the present study provides a rich dimension鈥� that is not available in nearly enough sites,鈥� says at The Palm Beach Museum of Natural History, Florida.
Nevertheless, not all living things in a given ecosystem fossilise, and only a minuscule portion of these will ever be discovered, says 脕lvarez-Parra.
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