f
JANUARY 2002
K/T Fern Spike found in Australia
The K/T boundary extinction event is thought by many to have been caused by the bolide collision in the Yucatan. In North America there is evidence of deforestation after the event 65 MYA which was followed by an environment dominated by a few species of fern (the fern spike). A Science report by Vivi Vajda et al finds sites in New Zealand with glassy material that usually indicates an extraterrestrial impact. Here there is a coal seam with unusually high levels of iridium (71 ppb), chromium, cobalt and arsenic. There are Late Cretaceous pollen species below the boundary with dominant gymnosperms, abundant ferns and many angiosperms. At the boundary 90% ferns are found with a few gymnosperms and no angiosperms. The lower lever tolerant ground ferns are replaced over time by tree ferns that need warm humid conditions. There is then a decline in ferns and in increase in gymnosperms as it cooled and later the angiosperms reappear. These same levels were found at two locations in New Zealand and compare favorably with a Japanese site. They are also similar to the fern spike found in North America. The authors interpret this to indicate that the K/T boundary devastation was a global one. It is thought that the huge dust cloud generated cooled the earth, destroying most of the vegetation and slowing the seeds and recovery of the warm climate vegetation. The discovery of fullerenes in New Zealand in the K/T boundary clays supports the worldwide wildfire hypothesis also. The plant record supports the theory that the carbon cycle was disrupted for over a million years with mass injection of CO2 into the atmosphere and the extinction of plankton in the seas. It will be interesting to see what others think of this data as this argument is an active one.
Obituary – Ned Colbert
Famed Paleontologist Ned Colbert died last week in Flagstaff Arizona at the age of 96. He spent 40 years as curator of fossil reptiles and amphibians at New York’s American Museum of Natural History and was a leading authority on dinosaurs. For the 30 years since his retirement he has been honorary curator of vertebrate paleontology at the Museum of Northern Arizona. He published more than 425 scientific publications from 1931 until his death, including 17 books. I have three of his books myself, including "The Little Dinosaurs of Ghost Ranch".
Woolly Mammoth Story
The fossil record of mammoths has provided a very complete and interesting story of the history of these animals as reported in Science of November 2 in an article by Adrain Lister et al. European species have been historically divided into three groups: Early Pleistocene M. meridionalis dated from 2.6 to 0.7 MYA; the early Middle Pleistocene M. trogontherii dated from ).7 to 0.5 MYA; and the Middle and Late Pleistocene woolly mammoth, M. primigenius, dated from 0.35 to 0.01 MYA. There were steady changes over this range with shortening and heightening of the cranium, increase in the molar crown, increase in the number of enamel bands in the molars and enamel thinning. These are thought to be related to an increased resistance to abrasion that is correlated to a shift from woodland browsing to grassland grazing. Over time they have seen that the lamellar frequency or the number of enamel plates per 10 cm length of crown has increased (although this could partly be due to overall change in size of animals). The earliest mammoth dating from about 4 MYA is from South Africa (M. subplanifrons) and had a plate count (P) of 7-9 and a HI (hypsodonty index for crown height) of 0.6 to 0.9 indicating a shallow crown. The earliest European mammoths are dated at about 2.6 MYA and have an intermediate plate count of 9-11, but the HI is already about 1.2. M. meridionalis has a plate count of 12-14 and an HI of about 1.2 by about 2.3 MYA. About 190kya there is a bimodal distribution of P values (from 18 to 24). Samples from Siberia show similar changes but seem to be ahead (with higher plate numbers) of those in Europe. They were also more consistent in higher HI figures. So, in Europe they find long periods of stasis in these two teeth elements, but in the 2 periods of transition, there is a wider range of values (sometimes bimodal). The fact that the more advanced forms were earliest in Siberia suggests that they were the origin points (although they probably developed from the Early European animals) and that they then moved to Europe where they displaced the earlier forms. This may be the result of the earlier change to grassland in Siberia causing the teeth adaptations that later moved to Europe as the grassland extended there also.
Origin of Placental Mammals
The origin on placentals is unknown. Some think they began in the Cretaceous some 80 MYA (based on molecular data), but others believe they arrived after the K/T. A new fossil, Kulbeckia kulbecke, from the Late Cretaceous of Uzbekistan is dated about 85 to 90 MYA. It was named for teeth found in 1993 and subsequent trips have revealed dentaries, a partial skull and postcrania material. This animal is an early member of zalamdalestids, an extinct relative of rabbits and rodents. I am always amazed at the difficulty in telling the early mammal story with only very few teeth and some skull material to go by. I guess I am spoiled by all our big dino bones.
After the Sixth Extinction
From what we have learned about the past five major extinctions, some are projecting what to expect if we are indeed heading in that direction now. Many say we are heading for a biodiversity crisis, losing three species a day. It is felt that people hasten the process by destroying habitat, destabilizing ecosystems, and making way for invasive species. After each of the last extinctions the Earth was dormant for as long as 9 million years (after the Permian; the post Cretaceous one is estimated as 200,000 years). They think the future will be quite bleak with few large mammals but with grasses, insects and rodents enduring. They feel that if people survive then it is possible that recovery will never occur. We do not know now how many species we have; about 1.75 million species are now recorded, but total estimates range from 5 to 100 million. Today’s tropical forests are the home for an estimated 70% of the world’s species and they are disappearing at a rate of 0.5 to 2.0 % a year. Some feel that today’s extinction rate is somewhere between 100 to 1,000 times the background extinction rate (although David Raup at the University of Chicago believes these values are too high). Because of the strong interactions between species the loss of one species causes a chain reaction that can cause the loss of many more dependent species. It them takes a very long time to rebuild those interactions. For a species to survive they must have a wide geographical range and be able to adapt to environmental changes (generalists). After the Permian extinction a single species of synapsid (a mammal-like reptile) populated much of the world for about 5 million years. The pests including the cockroaches will be among the survivors. 80% of the largest mammals (over 200 kg) are now on the endangered list. Will man survive? Some say that because we are so adaptable that we should be able to live for another 5 to 10 million years (the average for animal species). But we will probably be living with the rats if there is a major extinction event. This is from an article in Science News magazine by Charlotte Schubert called "Life on the Edge".
Karen Nordquist, ESCONI Paleontology Study Group
Featured Web Sites
Field Museum of Natural History
SVP Society for Vertebrate Paleontology
Return To Home Page | Return To Karens Komments | Return to December
Last Updated 4/7/2002
Number Of Visitors Since 3/23/2005