Mammals in the shadow of dinosaurs.Dinosaurs spent 170 million years on Earth before they suddenly died out about 65 million years ago. After dinosaurs disappeared, mammals took over.
It turns out that small mammals lived during the reign of dinosaurs, too. And over the last few years, a flurry of new discoveries has revealed what these creatures were like.
They were not the pathetic, little creatures that scientists had previously imagined. In fact, these mammals were well-adapted to their habitats, and they survived alongside dinosaurs quite well.
Last year, for example, researchers looked at the remains of a chipmunk-like creature that lived 150 million years ago. Fossils included a lower jaw, skull fragments, and 40 percent of a skeleton.
Based on their size, shape, and arrangement, the animal's foot and limb bones indicate that it did a lot of digging. It's the first animal of that era shown to have this type of behavior.
Also last year, paleontologists analyzed two skeletons of a type of predator that belonged to the genus Repenomamus. These mammals lived in China about 130 million years ago.
One species of Repenomamus is the largest mammal mammal, an animal of the highest class of vertebrates, the Mammalia. The female has mammary glands, which secrete milk for the nourishment of the young after birth. yet discovered from the dinosaur age. It measured 1 meter (3.3 feet long) and weighed up to 14 kilograms (31 pounds). It looked like a badger.
Another species of Repenomamus was about the size of an opossum opossum (əpŏs`əm, pŏs`–), name for several marsupials, or pouched mammals, of the family Didelphidae, native to Central and South America, with one species extending N to the United States. . One specimen was found with the remains of a baby dinosaur in its stomach (see "Dino Takeout Takeout
A financing to refinance or take out another loan. for Mammals").
"These are spectacular discoveries," says Jason A. Lillegraven, a paleontologist at the University of Wyoming UW is a national research university prominent in the fields of environment and natural resource research, specializing in agriculture, energy, geology, and water resource related fields. in Laramie. "They show a degree of diversification [of early mammals] that we hadn't recognized before."
The most recent addition to the growing list of ancient mammals is called Castorocauda lutrasimilis Castorocauda lutrasimilis is the name given to a small, semi-aquatic relative of mammals living in the middle Jurassic period, 164 million years ago, in lakebed sediments of the Daohugou Beds (possibly a member of the Jiulongshan formation) of Inner Mongolia. , which means "beaver-tailed creature that looks like an otter otter, name for a number of aquatic, carnivorous mammals of the weasel family, found on all continents except Australia. The common river otters of Eurasia and the Americas are species of the genus Lutra. The North American river otter, L. ." It lived about 164 million years ago in northeastern China.
At 50 centimeters (19.7 inches) long, Castorocauda was about the size of a platypus platypus (plăt`əpəs), semiaquatic egg-laying mammal, Ornithorhynchus anatinus, of Tasmania and E Australia. Also called duckbill, or duckbilled platypus, it belongs to the order Monotremata (see monotreme), the most primitive group . It probably weighed some 800 grams (1.8 pounds). That's more than 10 times heavier than other mammals living at that time.
The animal's back teeth were shaped like the teeth of modern seals and were useful for both biting and grinding food. Like seals, it probably ate fish and invertebrates that lived in the water.
Until recently, most evidence that scientists had of these unique mammals came from fossilized fos·sil·ize
v. fos·sil·ized, fos·sil·iz·ing, fos·sil·iz·es
1. To convert into a fossil.
2. To make outmoded or inflexible with time; antiquate.
v.intr. teeth. While plentiful and well-preserved, teeth can reveal only so much. Future finds should help scientists piece together the history of mammalian evolution, both during the time of dinosaurs and beyond.
http://www.sciencenewsforkids.org/articles/20060322/Note3.asp From Science News for Kids March 22, 2006. Copyright [C] 2006 Science Service. All rights reserved.