Tag: 江苏夜网娱乐地图

first_imgScientists may be close to unraveling one of the longest-standing questions in evolutionary biology — whether limbs, particularly hind limbs, evolved before or after early vertebrates left the oceans for life on land.Following an examination of pelves and a partial pelvic fin of Tiktaalik roseae, a 375-million-year-old transitional species between fish and the first legged vertebrates, a team of researchers found evidence that early hind legs began as enhanced hind fins, suggesting that their evolution began in the oceans, earlier than scientists initially believed. The late Farish Jenkins, who was the Alexander Agassiz Professor of Zoology and longtime curator of vertebrate paleontology at Harvard’s Museum of Comparative Zoology, was part of the team. The study is described in a Jan. 13 paper in the Proceedings of the National Academy of Sciences.Discovered in 2004 by Jenkins, Professor Neil Shubin of the University of Chicago, and Edward Daeschler, associate curator of vertebrate zoology at the Academy of Natural Sciences of Drexel University, Tiktaalik roseae represents the best-known transitional species between fish and land-dwelling tetrapods.A lobe-finned fish with a broad flat head and sharp teeth, Tiktaalik looked like a cross between a fish and a crocodile, growing to a length of 9 feet as it hunted in shallow freshwater environments. File photo by Stephanie Mitchell/Harvard Staff Photographer“There has been a great deal written about how limbs evolved, and in what sequence — did forelimbs evolve first, and then hind limbs, or vice versa — and the findings of this paper help resolve some of those competing hypotheses,” said James Hanken, the Alexander Agassiz Professor of Zoology and director of the Museum of Comparative Zoology. “It appears that hind-limb dominance had begun to evolve in these aquatic creatures, so Tiktaalik was poised to give rise to tetrapods, because it had already started to evolve some of the features that facilitate life on land.”“Previous theories, based on the best available data, propose that a shift occurred from ‘front-wheel drive’ locomotion in fish to more of a ‘four-wheel drive’ in tetrapods,” said Shubin. “But it looks like this shift actually began to happen in fish, not in limbed animals.”A lobe-finned fish with a broad flat head and sharp teeth, Tiktaalik looked like a cross between a fish and a crocodile, growing to a length of 9 feet as it hunted in shallow freshwater environments. It had gills, scales, and fins, but also tetrapodlike features such as a mobile neck, robust ribcage, and primitive lungs. In particular, its large forefins had shoulders, elbows, and partial wrists, which allowed it to support itself on land.Until recently the only Tiktaalik specimens that had been described included just the front portion of the animal.As researchers investigated additional blocks recovered from their original and subsequent expeditions to the dig site in northern Canada, they discovered the rear portion of Tiktaalik, which contained the pelves as well as partial pelvic fin material. The fossils included the complete pelvis of the original ‘type’ specimen, making possible a direct comparison of the front and rear appendages of a single animal.Almost immediately, scientists were struck by the pelvis, which was comparable to those of some early tetrapods. The Tiktaalik pelvic girdle was nearly identical in size to the shoulder girdle, a tetrapodlike characteristic. It possessed a prominent ball-and-socket hip joint, which connected to a highly mobile femur that could extend beneath the body. Crests on the hip for muscle attachment indicated strength and advanced fin function. Although no femur bone was found, pelvic fin material, including long fin rays, indicated the hind fin was at least as long and as complex as its forefin.“This is an amazing pelvis, particularly the hip socket, which is very different from anything that we knew of in the lineage leading up to limbed vertebrates,” Daeschler said. “Tiktaalik was a combination of primitive and advanced features. Here, not only were the features distinct, but they suggest an advanced function. They appear to have used the fin in a way that’s more suggestive of the way a limb is used.”Tiktaalik pelves were still clearly fishlike, with primitive features such as an undivided skeletal configuration, as opposed to the three-part pelvic girdle of early tetrapods. However, the expanded size, mobility, and robustness of the pelvic girdle, hip joint, and fin of Tiktaalik made a wide range of motor behaviors possible.“It’s reasonable to suppose with those big fin rays that Tiktaalik used its hind fins to swim like a paddle,” Shubin said. “But it’s possible it could walk with them as well. African lungfish living today have similarly large pelves, and we showed in 2011 that they walk underwater on the bottom. Regardless of the gait Tiktaalik used, it’s clear that the emphasis on hind appendages and pelvic-propelled locomotion is a trend that began in fish, and was later exaggerated during the origin of tetrapods.”In addition to shedding new light on the development of tetrapods, the paper is noteworthy as one of Jenkins’ final academic works, Hanken said.“This may not be the last paper that will ever be published with his name, but it certainly is one of them,” he said of the scholar, who died in 2012. “Farish made a number of very important discoveries in the course of his career, and Tiktaalik was one of them. This is a very important paper, and it’s wonderful to see his work being completed.”Visitors to the Harvard Museum of Natural History can see a model of Tiktaalik roseae as part of its Evolution gallery, and learn more about ongoing evolution research at Harvard, from exciting new discoveries about human origins to surprising insights from new genetic and developmental studies on Darwin’s finches.last_img read more

Read more

first_imgThe U.S. Army Corps of Engineers, Portland District, is conducting an industry day to discuss potential upcoming pipeline dredging contracts within the District.According to the Corps, the purpose of this meeting is to discuss future projects in an attempt to partner and communicate openly with the dredging industry early with the intent to have a better contract.The projects being discussed are Chinook Channel, Garibaldi Boat Basin Entrance, Depoe Bay, South Beach Marina at Yaquina Bay, Bandon Boat Basin, and Rogue River Turning Basin and Entrance to Boat Basin.The above mentioned project include:The dredging at Chinook Channel, approx 150,000 cubic yards, will include beach nourishment on East Sand Island. The purpose of this project is erosion control and payment will be based on placement;The dredging at Garibaldi, approx 45,000 cubic yards, will be in-water placement with tidal restrictions;The dredging at Depoe Bay, approx 25,000 cubic yards, will include dredging with surf zone placement, and excavating and trucking material from the check dam;The dredging at South Beach Marina, approx 25,000 cubic yards, will be upland placement;The dredging at Bandon Boat Basin, approx 9,000 cubic yards, will be in-water placement with tidal restrictions;The dredging at Rogue River, approx 80,000 cubic yards, includes both upland placement at a rehandle location, and surfzone placement.The industry day meeting will be held on May 23, 2017 from 10:30 AM until 11:30 AM at the Block 300 Building in Portland, Oregon.[mappress mapid=”24041″]last_img read more

Read more

first_imgOsewa is fast becoming a slow starter as he had to come from a set down to win four of his five matches at the last AJC in Pretoria in South Africa where he lost to Damien Laporte of the Seychelles in the final.“It was a very difficult and tough match. The Ivorian opponent was playing with so much powerin the first set and Osewa kust don’t know how to contain him. However, he (Osewa) took control of the game in the second match which he won convincingly; the same thing happened in the final set,” Nigeria’s coach, Mohammed Ubale said after the match.In the girls’ 16 and under, Omolade Aderemi also triumphed over Dami Kouche of Togo 6-1, 6-0 while Michael Ayoola defeated Umar Fouma of Mali 6-3, 6-2 in the boys’ category. Nigeria’s fine run was somehow dented as Toyin Asogba fell 6-0, 6-3 to Kpadonu of Togo in the girls’ 16 and under.Nigeria’s Oyinlomo Quadri will be in action on Thursday as she bid to defend the girls’ 14 and under title she won in Abuja last year.The tournament which is open to 15 countries serves as qualifiers for the AJC billed for March in Pretoria.Share this:FacebookRedditTwitterPrintPinterestEmailWhatsAppSkypeLinkedInTumblrPocketTelegram Nigeria began her defence of the 2017 ITF/CAT African Junior Championship West and Central Africa qualifiers yesterday in an impressive note with most of her players securing victories in their opening matches at the tournament holding in Lome, Togo.Wilson Igbinovia was the first among the Nigerians in action to bag a victory by beating Maiga Quattara of Burkina Baso 6-1, 6-2 in the boy’s 16 and under category. It was a dream AJC debut for the 13-year-old, who was the surprise element in the Nigerian team after playing his way to the team during the camping in Ekiti.But while Igbinova had it easy, Michael Osewa was made to work off his socks before beating Haya Koune of Cote d’Ivoire 4-6, 6-2, 6-3.last_img read more

Read more