Paleontologists have identified an ancestor of modern spiders that lived before the dinosaurs began their long domination of the planet.
The arachnid’s fossil remains were found during the mid-1970s in Europe embedded in an iron-rich mineral, siderite, that is difficult for x-rays to penetrate. Researchers used a synchotron, which emits more powerful x-rays, to identify the organism.
Named Idmonarachne brasieri, the organism was likely a member of a group of arachnids called uraraneids. These animals lacked spinarets, which modern spiders use to spin webs, and instead would have discharged silk in sheets.
“Our new fossil occupies a key position in the evolution of spiders,” Dr. Russell Garwood of the University of Manchester, the lead author of a paper documenting the discovery, said. “It isn’t a true spider, but has given us new information regarding the order in which the bits of the anatomy we associate with spiders appeared as the group evolved.”
Scientists know little of the origin of spiders and the evolutionary path by which such anatomical features as spinarets formed is not well understood.
The paper appears in the March 30 edition of Proceedings of the Royal Society B.
Charles Darwin gained his fame as the man who, along with Alfred Russel Wallace, hypothesized that Earth’s biodiversity is the result of evolution by natural selection. In the century and a half since Darwin’s pioneering publication of “The Origin of Species,” scientists have found that his ideas about how and why species change were essentially correct. Evolution by natural selection is as much a part of the fabric of science and just as important an explanation of how nature works as Copernicus’ contribution that Earth revolves around the sun and Newton’s insights on gravity.
Today is the 183rd anniversary of the date on which Darwin first saw the H.M.S. Beagle, the ship that took him on the journey that changed biology.
You can watch a wonderful short film about Darwin’s life and work here.
This photograph shows the locations of two embryos and one neonate, along with the female ichthyosaur, documented in a new study that indicates marine reptile viviparity may have evolved on land. Image courtesy Ryosuke Motani.
Scientists have discovered a fossil that preserves an infant prehistoric marine reptile in the process of being born, a find that indicates live birth may have first evolved among land-dwelling organisms.
The specimen dates to about 248 million years ago, during the early Triassic period, and is of a female ichthyosaur, along with two embryos and one neonatal individual.
One of the embryos was still inside its mother when death came, another was partially outside the adult individual’s pelvis, and a third was entirely outside its mother.
The position of the embryo that is half-way out of its mother’s body indicates that head-first birth occurred among ichthyosaurs. If so, then the birth may have occurred on land and not in the water, as has generally been presumed by scientists to be likely in the case of early Mesozoic animals.
Viviparity, as live birth of infants is known, has independently evolved across a wide variety of organisms. It is known in fishes, amphibians, reptiles, and mammals and, even among ichthyosaurs, the phenomenon has been observed in fossils dating from the middle Triassic period to the Cretaceous period.
Mosasaurs and plesiosaurs are other Mesozoic era marine organisms that were viviparous. Those reptiles lived during the Cretaceous period.
The fossil preserved individuals of the genus Chaohusaurus would have plied seas near present-day Chaohu and Yuanan, China. The adult specimen was about 100 centimeters long, while the embryos and neonate were about 18 centimeters long.
A paper documenting the fossil discovery appears in the Feb. 14, 2014 edition of PLOS One.
The fossils documented in it are at the Anhui Geological Museum in Hefei City, China.