Constructing life

Any recipe for life on Earth requires a source of essential elements, a source of energy to stimulate chemical reactions between these elements, and time for these reactions to take place.

In 1952 researchers at the University of Chicago took a mixture of ammonia, methane, and hydrogen to simulate the early Earth atmosphere and applied a spark to simulate a natural source of energy-lightning-and after 8 days found that amino acids—the building blocks of DNA-- had formed in this oxygen-free atmosphere.

In the half-century since this experiment scientists have modified their ideas about the composition of the early earth atmosphere, but the Miller-Urey experiment still stands as the first example of synthesizing organic compounds from inorganic precursors—a process that occurred in the Early Earth in some form, as our own existence is evidence that it happened.

For more on the Miller/Urey experiment, see this site.

What is life?

The oldest fossil record of life on earth is photosynthesizing cyanobacteria found in stromatolites. However, photosynthesis is a complex process, and these cyanobacteria probably had precursors that are yet unknown. What were these first hypothetical life forms like?

To answer that question we must first decide on a definition of what constitutes a living thing. This definition is not as clear-cut as it might appear.

Living things grow and reproduce, but inorganic crystals do this, too. Viruses are not regarded as living, as they require a host in order to survive and reproduce, but the existence of viruses highlights the fuzzy line between life and non-life, and reflects the fact that life must have originated from a non-living, “prebiotic” stage.

The British biologist J.B.S. Haldane concluded that “The line between living and dead matter is …somewhere between a cell and an atom.”

Photo and information on research on artificial life here.

Big numbers. Really. Big.

This week GeoLog will begin a trip through time, exploring the physical and biological changes on Earth through the more than four-and-a-half billion years of its history, as told through the rocks and fossils that are the physical evidence of these changes. But first, a few words about our frame of reference:

Geologists tend to use numbers like 4.6 billion without a second thought. In fact, the scope of what we call geologic time is ENORMOUS and extremely hard to comprehend, especially for those of us who spend our days counting seconds, minutes and hours.

After all, our own life spans are on the order of 10s to one hundred years; known civilization goes back only thousands of years, and there were no modern humans around millions of years ago.

Our ability to comprehend the vast eras of geologic time is severely challenged by the remoteness and scope of these events.

Links for some help in visualizing these large numbers:

This site measures millions and billions in pennies, and the image of one billion pennies (above) is from here.

Teachers can find an exercise for class use on big numbers here, and the geologic time scale here and here.

T. rex: Top predator for Road Kill King?

Despite its fearsome, pointed, serrated teeth and portrayal in the movies, some scientists suspect that T. rex scavenged carcasses instead of hunted down prey.

This conclusion comes from studies of modern predator/prey ecosystems, estimating the number of prey needed to support an animal of T. rex size. One group of researchers estimate that in Africa’s Serengeti grasslands, enough herbivores die daily to feed a 6,000 kg T. rex, if the dinosaur was cold-blooded, spent half a day foraging and had senses to detect carrion up to 80 meters away.

But what if T. rex were warm-blooded and had to maintain a higher metabolism? It would need more food, but it would also be able to more faster and cover more ground.

Original work: Graeme D. Ruxton and David C. Houston, 2003. could Tyrannosaurus rex have been a scavenger rather than a predator? An energetics approach. Proceedings of the Royal Society of London. B. Download their article here.

Was Sue sick?

Sue, the largest, most complete Tyrannosaurus rex found to date may have been laid low by microscopic parasites.

Paleontologists have puzzled over smooth, round holes in Sue’s jaws. Originally thought to be bite marks from another T. rex, a new analysis concludes that the holes were the result of a parasitic infection that is known to affect modern avian raptors like hawks and eagles.

The infection probably caused lesions and swelling in Sue’s mouth and throat, prompting one researcher to speculate that the infection may have killed Sue as she found it increasingly hard to swallow as the infection spread, and she may have starved to death.

It is difficult to determine the cause of death for an animal that died millions of years ago, but this finding suggests that modern birds may owe their susceptibility to this parasite to their therapod ancestors.

Research from Ewan D.S. Wolff, et al., Common avian infection plagued the tyrant dinosaurs. PLoS One

Veggie rex

Tyrannosaurus rex belongs to a group of dinosaurs called theropods. These dinosaurs generally have serrated, knife-like teeth that are typical of meat-eating carnivores.

The discovery of a small theropod dinosaur in China, however, shows that this group had more diversified dietary habits. This new dinosaur, named Incisivosaurus, for its large front teeth, shows wear marks on its teeth that are typical of tooth wear seen in plant-eaters.

Incisivosaurus teeth also lack the serrations typical of carnivore teeth. The discovery of a plant-eating theropod indicates that these dinosaurs were more diverse that previously thought, and occupied a variety of ecological roles in ecosystems 60 million years ago.

Source: Xu, X., Cheng, Y.-N. Wang, X.-L., and Chang, C.-H. (2002). "An unusual oviraptorosaurian dinosaur from China." Nature, 419: 291-293. For more information, click on the title of today's post.

Dino Dads

Analysis of adult dinosaur bones found near nests of dinosaur eggs suggests that the male dinosaur parent was caring for the eggs.

Paleontologists from Montana State University examined the adult dinosaur bones found by these nests and discovered that they lacked a distinctive layer called medullar bone, a bone type that characterizes many species of female birds and that has been found in other dinosaurs, including Tyrannosaurus and Allosaurus.

If dino dads were in fact caring for their young, this could explain the origin of male parental care that we see in the descendents of these dinosaurs—birds. The large number of eggs found in these dinosaur nests--up to 30—also compares with the clutch size of modern birds in which the dads care for the young.

A reminder that Father's Day is coming up soon!

Summary in sciencenews.org Jan. 17, 2005 (Laura Sanders). Illustration of dino dad from here. Original research article: David J. Varricchio, et al., 2008. Avian paternal care had dinosaur origin. Science 322:1826-1828.

Birds of a feather

The discovery of feathered dinosaurs led to our understanding that birds are the descendents of dinosaurs, specifically the group of dinosaurs that includes the sauropods, like Apatosaurus and the theropods like Tyrannosaurus.

However, the discovery of feather-like structures in a small dinosaur from the other major dinosaur lineage—the group that includes Triceratops and Steogsaurus—complicates things.

Tianyulong is a small herbivorous dinosaur from China with feather-like structures along its spine and tail. Paleontologists are not yet sure whether these are feathers as seen in other feathered dinosaurs, or some other sort of body covering evolutionarily unrelated to true feathers.

Scientists refer to the structures on Tianyulong as “dinofuzz”, a fitting term because this new fossil fuzzes up our picture of dinosaur-bird relationships, at least for now.

Source: Xio-ting Zheng, et al., 2009, An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458:333-336.

Modeling dinosaur "flight"

An unusual feathered dinosaur discovered in China raises questions about the origin of flight.

Other small dinosaurs have been found with traces of feathers on the front two legs but Microraptor had feathers on the back legs, as well. Its asymmetrical feathers indicate that the animal was capable of gliding or flying, so it assumed that Microraptor made its home in trees and glided, or flew from tree to tree like modern flying squirrels.

To test these ideas, researchers at the University of Kansas constructed a model of Microraptor, using pheasant feather for its wings, and designed a slingshot to launch it. The Microraptor model glided 24 meters, or 26 yards.

Of course, a plastic model with pheasant feathers may not be an accurate model of an extinct feathered dinosaur, but it is a first step in attempting to understand how this unique animal lived.

Summarized in Earth, May, 2009, p. 13 (Emily Lant); research by David Alexander & David Burnham, University of Kansas. Click here for a video of the model's flight!

Original report on Microraptor: Xu, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F. and Du, X. (2003). "Four-winged dinosaurs from China." Nature, 421(6921): 335-340, 23 Jan 2003. http://www.nature.com/nature/journal/v421/n6921/full/nature01342.html

Bulking up on veggies

Sauropod dinosaurs, like Diplodocus and Brachiosaurus, hold the record for the largest land animals, weighing up to 80 tons, and stretching more than 60 meters from head to tail.

To support their size, these herbivorous dinosaurs must have spent most of their time eating and searching for food.

They had a mouthful of incisors, good for clipping off plants, but not designed for chewing. They had no molars for pulverizing their food, so they must have swallowed their food whole.

The giant bulk of these dinosaurs is more puzzling when considering their relatively tiny heads, but their small heads were supported by long necks, which may have been critical to the sauropod’s success.

Their long necks allowed these dinosaurs to stand in one place and browse vegetation from a large radius, allowing them to collect a lot of food without expending much energy.

Based on research by P. Martin Sander and Marcus Clauss, 2008. Sauropod Gigantism. Science 322: 20-201

Illustration from http://www.scorcher.ru/journal/art/art_pic/diplodocus_2.jpg

Thwarting T. rex

How can an herbivore protect itself from carnivorous predators?

Strategies seen today among predators and prey of the African Serengeti apparently existed among dinosaurs in ancient ecosystems.

Paleontologists from Ohio University counted growth lines in the legbones of hadrosaurs, a group of herbivivorous duck-billed dinosaurs. By counting the number and spacing of growth rings, paleontologists can determing the animals’ age and its relative growth rate—the fast growth seen in juveniles is characterized by widely-spaced growth rings; growth slows or stops at adulthood, shown by close spacing of the growth rings.

The scientists found that hadrosaurs reached their adult size by age 13. In contrast, the carnivorous Albertosaurus reached full size at 20-30 years. Maturing quickly gave hadrosaurs an advantage over their predators, as they could produce offspring at an earlier age, and their offspring grew quickly to maturity.

Source: Drew Lee, Royal Society London B, Aug 5, 2008

A new spin on an ancient predator

More than 100 years after its discovery the Middle Cambrian Burgess Shale of British Columbia Canada, continues to offer up new insight into the history of life.

One of the many enigmatic soft-bodied animals of the 500 million year old Burgess Shale of British Columbia is Nectocaris (fossil shown above) long thought to be a shrimp-like arthropod (reconstruction, above, left), but a recent study shows that the animal is most likely a cephalopod, ancestral to the group includes modern squid, octopus, and the pearly Nautilus (reconstruction above, right).

This re-classification of Nectocaris extends the geologic range of the cephalopods back 30 million years and dramatically changes hypotheses of cephalopod evolutionary history.

Nectocaris does not have an external shell, as did other ancient fossil cephalopods, and this discovery scuttles previous hypotheses that cephalopods evolved the ability to float and then swim after the evolution of their chambered shell. Nectocaris shows that cephalopods shells evolved later in cephalopod evolution, possibly in response to increased predation during the Late Cambrian.

Martin Smith and Jean-Bernard Caron, Nature 2010. Photos by the authors. Reconstructions from Discover Magazine blog

The pitter-patter of thunder lizard feet

A dozen tiny, three-toed footprints were discovered in rocks about 120 million years old in coastal South Korea.

The tracks, no bigger than one and a half centimeters long, were originally made in mud, now hardened to shale, along a Jurassic riverbank. The tracks resemble those of therapod dinosaurs, the bipedal carnivores.

These tracks are not necessarily evidence of a new species of diminuative dinosaur; paleontologists previously found larger fossil footprints in the area and so these miniature tracks were probably made by a hatchling.

The size of the tracks can be used to estimate the size of the hatchling, which was probably no more than 4 centimeters at the hip. For now, these are the smallest dinosaur tracks known.

Photo credit: Kyung Soo Kim of Chinju National University of Education in Jinju, South Korea

The first beetle

The oldest known fossil beetle has been discovered not in an outcrop, but in a museum drawer. A 296 million year old insect has been reclassified as a beetle, pushing back the origin of beetles by millions of years.

The evolutionary success of beetles is traditionally explained by their two-stage life style—they pass through ecologically distinct larval and adult stages that allow them to exploit different niches.

However, the new find creates a large gap between the first appearance of beetles and the diversification of beetles that occurred 65 million years later, and suggests that the innovation of the two-stage lifestyle was not the initial cause of beetle diversity.

This opens the door to other explanations for beetle success, such as the proliferation of the plant species that was favored by the beetle larvae.

Reference: Journal of Paleontology November, 2009, The Earliest Beetle identified (Olivier Bethoux)

Photo credit: This is a much younger fossil beetle from the Eocene (15 million-year-old) Florissant Fossil Beds of Colorado, which preserves a wide variety plant and animal life. Click on today's title for more information.

A New Last Occurrence

Headlines in paleontology usually center on the oldest or first find of a fossil species. However, determining the youngest or last occurrence of a now-extinct species is just as important.

A youngest occurrence was recently confirmed for an extinct group of echinoderms, the phylum that includes starfish, sand dollars, and brittle stars.

Edrioasteroids are one of a number of bizarre echinoderms that went extinct by the end of the Paleozoic Era for reasons not yet understood. These silver-dollar sized, disc-shaped animals lived attached to shells or other hard surfaces on the sea floor.

This discovery comes as paleontologists focus their energy on looking for these fossils in younger rocks to answer questions about the reason for their demise.

Photo credit: drydredgers.org

For more pictures of edrioasteroids click on today's title.

Reference: Journal of Paleontology November, 2009, First definite record of Permian Edrioasteroids: Neoisorophusella from Russia

Great Fossil Faunas, V: The La Brea Tarpits

All the previously described lagerstatte are deposits of organisms from a marine environment. The fifth and final pick for "greatest fauna" is something completely different: The fossils encased in the La Brea tarpits were land-dwellers who became entrapped in a natural asphalt spring, and if for no other reason, the unique environment and fossilizing agent earn the La Brea tarpits a place on our list of top 5 fossil faunas.

How can an animal be so stupid as to fall into an asphalt pool? These were probably not steaming or bubbling pits like the mudpots and geysers of Yellowstone, but still pools of dense oil muck camoflaged by plant debris and perhaps even holding a pool of water.

Animals that came to take a drink got stuck, their distress cries were heard by predators who themselves became ensnared, and finally scavengers that came along for the easy pickings became mired in the muck—leaving a record of the whole food chain, from plants to insects to mammoths to saber tooth tigers and vultures—650 species of plants and animals so far identified, on the basis of 3.5 million fossils recovered, an astonishing diversity of animals that gives us an unprecedented window into an ice-age ecosystem.

Photo from www.papermag.com/blogs/2008/11/mr_mickeys_mustsee_guide_to_la_1.php

Great Fossil Faunas, IV: Solnhofen Limestone

This famous lagerstatte from southern Germany is an obvious choice for a “greatest fossil fauna” list because it is in these fine-grained limestones representing the deposits of an ancient lagoon that the fossils of Archaeopteryx were found.

Archaeopteryx was the first evidence for a link between birds and reptiles, and the discovery of the first specimen came only a few months after Charles Darwin published Origin of Species, in which he made the case for a common ancestry for all organisms.

One of Darwin’s most vexing problems was the apparent lack of the transitional forms between major groups that his theory predicted, and the discovery of Archaeopteryx was an answer to this dilemma.

The lagoon that preserved Archaeopteryx down to its feathers also preserved insects, crustaceans, and echinoderms in exquisite detail, and give us a glimpse into a 150-million-year-old nearshore ecosystem.

For more info on Archaeopteryx click on the title of today's blog.

Great Fossil Faunas, II: The Ediacara Fauna

The oldest known fossils of multicellular organisms are known from rocks of what was formerly called the Precambrian Eon.

The Precambrian was long regarded as a time before life appeared, as there were no known fossils from the ancient rocks. The appearance of abundant shelly fossils was taken to mark the end of the Precambrian and the beginning of the subsequent Cambrian Period.

Because of the presumption that Precambrian rocks contained no fossils, the first discovered Ediacarian organisms were not recognized as being organic remains. It was only after multiple similar faunas from Newfoundland, Africa, Australia, and England were discovered that the true significance of these strange creatures was appreciated.

For smashing one of the earliest paradigms of fossil distribution, the Ediacara biota earns a spot on our list of 5 great fossil faunas.

For more information on the Ediacaran organisms click on the title, above.

Great Fossil Fauna, I: Gunflint Chert Flora

The Gunflint chert is part of a sequence of 1.8 billion-year-old rocks exposed in the Gunflint Range of northern Minnesota and western Ontario along the north shore of Lake Superior.

These rocks contain stromatolites, organo-sedimentary structures formed by cyanobacteria trapping and binding sediment, and when examined under the microscope, small spheres, rods and filaments less than 10 micrometers in size are visible in the chert layers--microfossils preserved in near-pristine 3-D.

The discovery of the Gunflint chert caused a paradigm shift in paleontology, as it proved that under exceptional conditions, even very ancient lifeforms could be preserved.

For its role in opening our eyes to the presence of life in very ancient rocks, the Gunflint chert earns a place on our list of “top 5 fossil lagerstatte”

Photo credit: http://www.fas.org/irp/imint/docs/rst/Sect20/A12.html

Fossil "Mother Lodes"

The history of life on Earth is a story told in photographs made of stone--the rocks and fossils preserved when and where conditions were favorable. Some of these photos are time exposures in which events blur together, others, much rarer, are snapshots of an instant in time. These snapshots commonly are the result of the sudden, rapid burial of the organisms living in the environment, as through an ocean storm surge or river flood or avalanche or entrapment in a mucky bog or sticky pit of natural asphalt. These snapshots are characterized by exquisite preservation of anatomical details not usually fossilized, and fossil deposits of this sort are referred to by a German word, lagerstatte, which is a mining term that refers to a "mother lode" or abundance of ore. Fossil lagerstatte are "mother lodes" of exceptionally preserved fossils. The Pennsylvanian (320-286 million year old) Mazon Creek fauna, from which the bizarre Tullymonstrum (the state fossil of Illinois, seen here from the side of a U-Haul truck) is known is one example.

This week's GeoLog challenge is to describe the 5 most significant fossil faunas or lagerstaette, fossil "mother lodes." Despite the relative rarity of exceptional preservation, the list of lagerstaette, for example the list posted on the Wikipedia website, takes up a whole page, so some selection criteria need to be imposed. My "top 5" lagerstaette were chosen to include different geological periods, different depositional or geological environments, and a variety of organisms, from microfossils to dinosaurs, and for their historical significance.

Paleontologically, all lagerstaette are important, because we've learned things from each of them about the variety and diversity of life that we would not have known otherwise.