A review of 100 years of fossil evidence reveals that 100 million years ago part of the Sahara Desert was arguably the riskiest place on our planet,wih a concentration of large predatory(食肉的）dinosaurs unmatched in any comparable modern ecosystem on land. The analysis of fossils from theso-called Kem Kem beds shows the presence in the area of large-scale predatory dinosaurs,reptiles and other hunters, all living together in what was at the time a river system full of very large fish, rather than a desert.

Paleontologist Nizar Ibrahim, lead author of the study, said that the Kem Kem ecosystem was a highly enigmatic place,ecologically speaking, since typically ecosystems present a larger number of plant-eating animals than predators, and predators themselves will come in a variety of sizes,with one larger predator being dominant. In the Kem Kem beds,fossils of predators outnumber those of plant-eating dinosaurs, and several of the predators living together in the area, such as the Carcharodontosaurus, the Spinosaurus,the Abelisaur and the Deltadromeus, were as big as a Tyrannosaurus rex (T.rex) - one of the largest dinosaurs that ever lived. This is strange “even by dinosaur standards,” according to Ibrahim, since the T. rex, which was present in North America tens of millions of years later, was “the unarguable ruler of its ancient ecosystem.”

It is unlikely that the large predators in the Kem Kem ecosystem ate one another. What's more realistic, according to Ibrahim, is that they ate the abundant and supersized fish present in the area - fish like coelacanths"the size of a car” and sawfish that could reach 25 feet in length.

The study of the Kem Kem beds carried out by Ibrahim and a group of international researchers across the U.S., Europe and Africa draws attention to the importance of learning more about Africa,which remains paleontology's forgotten continent.It shows that African ecosystems"do not simply copy the ones we know from North America,Europe or other better-known places,"and it also reveals clues about what happens to life when dramatic changes in climate come into play.

Earthworms don’t move fast. But humans can accelerate the worms’ spread. Fishermen often use invasive(蔓延性的) earthworms to catch fish. Many have introduced invasive earthworms to rivers, streams and lakes previously unexposed to these animals. Gardeners who use earthworms to make their soil rich may unknowingly introduce invasive ones. The worms even give rides in the mud on wheels, potted plants and road materials shipped around the nation.

But they’re not everywhere yet. In the Great Lakes region, “20 percent of the land is earthworm-free,” says Cindy Hale, a research biologist. Of the remaining 80 percent of land, half of the land has fewer than two earthworm species-meaning there isn’t yet too much impact on the ecosystem, she explains. For these regions, she says, now is the time to take action. According to Hale, educating the public, especially fishermen, is one approach to stopping the spread of invasive earthworms. Identifying which lands are currently earthworm-free is another.

Ryan Hueffmeier, a program coordinator for Great Lakes Worm Watch, has been working on a model that will help create large maps of areas with minimal(最小的) or no damage from earthworms. Ultimately, landowners can use it to identify earthworm activity on their property. once identified, lands with minimal or no earthworm damage should be protected.

But scientists suspect that once invasive earthworms arrive they can’t be removed. And even if all could be, affected forests might never return to the way they were. “It’s very much a story of learning to live with them,” concludes Lee Frelich of the University of Minnesota’s Center for Forest Ecology.

Forest ecologists have called earthworms “ecosystem engineers” because they can change or create habitats that otherwise would not be present. Whether this is a good thing depends on the situation.

“What the earthworms do and how we value it is what really matters.” said Hale. “In one place-farm fields or gardens-we really like European earthworms and what they do, so we consider them good. In native hardwood forests, we really don’t like what they do-so we consider them bad. You really have to understand how an organism(微生物) affects an ecosystem. Things aren’t black and white.”