The other day I mentioned an interesting study on dinosaur embryos, a day or so later a study on incubation strategies in Troodon was published in Paleobiology. I don’t have access to this article so I will have to rely on the the abstract and the press release on Science Daily. Continue reading
I’m currently working my way through the Australopithecus sediba articles mentioned in the previous post. In the meantime, in wandering around the internet there are a number of things make a science story jump out and say “write about me!” First, if it uses a methodology that answers the question “how do we know?” Second, if it is about life history. Third, if it combines the first two with dinosaurs.
Science Daily (World’s Oldest Dinosaur Embryo Bonebed Yields Organic Remains) points us to a research paper that has all three (plus more). The paper, Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains, was published in Nature. I don’t have access to the Nature paper so I will have to rely on the Science Daily press release. Continue reading
I don’t know how I missed this yesterday. National Geographic has an article on an interesting fossil, dating to about 290 MYA (basically, the beginning of the Permian) , that provides some interesting information on food chains.
This is cool! Science Daily is reporting on the discovery of 330 million year old fossil imprints discovered in Pennsylvania. The imprints are not actually fossils in the sense of being mineralized bone, rather they seem to be natural molds of the animals in question.
Since I have an anthropology background I really don’t post that much on plants and insects (What, no bones? Inconceivable!) But I found this really fascinating.
Researchers collected over 3,500 fossils from from 25 quarries in Patagonia. Each fossil was examined for four types of insect damage:
The four feeding groups are those insects that feed on the external leaf, chewing holes, edges and other leaf parts; those insects that mine tissues inside the leaf; those that produce bulbous galls and those that pierce and suck the leaves. Because different insects chew, mine, gall and pierce in different ways, the researchers recognized 52 discrete damage types from the four feeding groups. They applied these categories to both bulk samples from single quarries and to individual leaf species.
Below is an example.
They were then compared to approximately 2700 fossils from three sites in North America. The results:
The researchers found that the number of damage types at each of the four major Patagonian quarries significantly exceeds each of the three North American samples. The number of functional feeding groups is also greater than all North American samples for three of the four major quarries. The diversity of damage types and feeding groups at the Patagonian sites for individual plant species hosts is also highest.
“Insect damage on leaves, the remains of insect meals, is uniquely valuable data,” says Wilf. “While actual insect fossils can give us taxonomic information, leaf damage provides unique ecological data about which and how many kinds of insects were eating and interacting with ancient plant species in the deep past. Also, insect damage on fossil plants, which can be very abundant, can give us a great deal of information about insects at times and places with very few insect fossils.”
The research design was extremely rigorous. The North American fossils were collected by the same team and members of that team helped collect the Patagonian fossils (to insure identical collection methods). Two of the researchers scored all the insect damage (to insure consistency in the scoring). Samples were then adjusted for size. All in all an impressive piece of research. Incidentally, if a creationist ever tells you we can’t learn about the past because humans weren’t around to witness it you can point them to this post – which shows, in a very convincing fashion, that we can.
Also, the same team published an earlier study which gives a few more details. You can find a summary of that earlier work here.
Here is a few paragraphs to tide you over till you get there:
Many Eocene fossil sites in North America have been collected 100 years or more. Laguna del Hunco, though known for 80 years, is now the first of this age from South America to be heavily and quantitatively sampled. Quantitative sampling, where every specimen is tallied and identified, allows sample size to be taken into account when comparing recovered diversity. The age of the deposit was also not well constrained.
The researchers collected more than 1,500 fossils and identified more than 100 different fossil leaf species including dicots, monocots, conifers, ginkgophytes, cycads and ferns. They also identified a variety of seeds, fruit and flowers. In total, they more than tripled the known diversity of the site in two weeks. Using paleomagnetic dating, which uses the Earth’s magnetic pole reversals, and argon argon dating, which compares the amounts of two isotopes of argon one of which is produced by the natural radioactive decay of potassium, the researchers dated the fossils to a half million year interval between 52 and 53 million years ago. These are the first high-precision ages for the deposit, which now can be correlated anywhere in the world.
I will be republishing this, in a slighttly different form, over at Transitions this evening.
The St. Louis Post-Dispatch, on 1/21/05, reported on a recent article in the journal Science. The article, in the Post is Volcanic heat gets blame for extictions.
The extinction event occured approximately 250 million years ago. In the event 90-96% of all species and 50% of all families went extinct. This includes 8 of 17 insect orders, 21 of 27 reptile families, 6 of 9 amphibian families and 70% of all marine invertebrate genra – including all reef building coral.
There is some evidence that indicates that this may have been two separate extiction events separated by about five million years in time. There are several different theories as to the cause of the event(s) divided into three general areas.
1)Changes in oceanic chemistry and sea level.
There is some evidence that indicates a major regression (drop in sea level)event related to the formation of the supercontinent Pangea. Along with this there is some evidence of a short term cooling trend, which may have lead to anoxic conditions in ocean bottoms (due to the shallowing ocean caused by the regression). The cooling temperatures would have lead to overturn (the cooler waters at the ocean top sink forcing anaxic water to the surface) killing most of the shallow water forms such as articulate brachiopods off. In general, the extinction event affected those species with narrow geographic distributions more than those with broad geographic distibutions.
2) Changes in atmospheric chemistry and climate.
There were several different interlinking causes. During the Permian there is evidence of a strong warming trend. There is also evidence of increased volcanic activity (in the siberian flood basalts, for example).This volcanic activity released massive amounts of sulfer dioxide into the atmosphere creating a “volcanic winter” or short term cooling trend which led to the above mentioned overturn in the world’s oceans. One byproduct of the overturn was to release massive amounts of carbon dioxide into the atmosphere which reinforced the warming trend.
A combination of both of the above.
With that in mind, the paper summarized in the Post attributes the extinct event to global warming and oxygen deprivation. The article also finds that there was a gradual extiction for about ten million years followed by a raridly increased extinction rate for another five million years. According to the paper the oceanic regression at the end of the Permian exposed massive amounts of oceanic sediments to the atmosphere, which caused a massive emission of carbon dioxide and methane – two greenhouse gasses. This reduced the diluted the amount of oxygen in the atmosphere from 21% to 16% or less. Since oxygen concentration decreases with increasing altitude this dilution of oxygen would have reduced living space by up to one half. According to the authors only those species living at the oceans surface would have survived. As we saw above, however, most of the species living at the ocean’s surface went extinct. Finally, the authors say that since there was a low oxygen environment, evolution would have favored those organism adapted to it and hypothesize that dinosaurs were adapted to a low oxygen environment. They point out that birds (the decendents of dinosaurs) can live at low concentrations of oxygen. I’m not convinced by this last. Dinosaurs evolved and went extinct over the 190 million years following the Permian. Presumably, the oxygen content would have increased back to 21% and dinosaurs would have adapted to that. Granted, birds can tolerate lower oxygen concentrations but what this means to me is that they evolved to tolerate a wide variety of oxygen concentrations rather than that they adapted to low oxygen concentrations. I should also point out that I have based this on what I read in the newspaper, rather than the paper in Science – which I haven’t had a chance to read yet – so I’m not sure about the accuracy in the Post article.