These daily podcasts build upon previous episodes, so the best way to work through them is by starting with the oldest, January 1. But you don't have to do that.
Most episodes are two to 10 minutes long. It's October, so we're moving through the Jurassic Period.

Saturday, October 25, 2014

October 25. Sauropods





Diplodocus painting by C.R. Knight (1911)
Sauropods are another well-known group of dinosaurs that became gigantic during the Jurassic. Sauropods include such famous dinosaurs as diplodocus, brachiosaurus, and Apatosaurus. For many years, one of the most popular Sauropods was the brontosaurus, but that name was a result of the “bone wars” between paleontologists Marsh and Cope, in the 1870s. It turns out the bones used to define brontosaurus were from a juvenile variety of Apatosaurus, and the Apatosaurus name had seniority. Marsh’s huge reconstruction of a brontosaurus at the Yale Peabody Museum popularized the animal in the public consciousness, but that reconstruction used a Camarasaurus head. So today, there’s no such thing as a brontosaurus.

But the real Sauropods were huge, with long necks and long tails balancing a big, oval body. They are almost certainly the largest animals ever to live on land, and their only competition in terms of size are aquatic mammals like the blue whale. Diplodocus, a common Jurassic sauropod, was up to 170 feet long, and some brachiosaurs were as much as 60 feet tall, four times the height of a modern giraffe. The smallest Sauropods were around 20 feet long.  Many of the most famous specimens of Sauropods came from the Jurassic Morrison Formation of western United States, especially in Colorado, Wyoming, and Utah, where Marsh and Cope worked in the 1870s and 1880s. 

In contrast to early depictions that indicated these animals were so big they had to live in water to be supported, the modern interpretation is that Sauropods certainly walked on dry land. Or not-so-dry land: the environment of the Morrison Formation was wet mud flats and river flood plains, and sauropod footprints show that they lived in such areas as well as wet, coastal environments.

Although Sauropods appeared in the late Triassic, they diversified and grew to gigantic sizes throughout the Jurassic and into the Cretaceous. By Jurassic time they were widespread. Even though few complete, or even reasonably complete fossils are known, their bones are common enough that we know Sauropods were present on every continent, including Antarctica.

Sauropods appear to have been herd animals that traveled in groups segregated according to age. That fact can be interpreted to suggest that they did not exhibit much parental behavior, and that juveniles quickly began to flock together, but some fossil assemblages include mixtures of individuals of different ages, which could mean there was some parental care for the young. Some of the oldest fossil eggs with well preserved embryos, from the early Jurassic of South Africa, are from prosauropods that are probably an ancestral or sister group to the Sauropods. They’ve been interpreted to suggest that the animals crawled on four feet before learning to walk and rear up on two legs. Sauropods were not bipedal, but they probably could lift themselves on their hind legs to reach high into trees to get at leafy vegetation there.

You might expect sauropods’ feet to be something like those of modern elephants, but that’s not correct. Their front feet did not splay, like elephants’, but in many species were almost a stiff bony column with the digits reduced to near-invisibility. Big stumps, more or less. The hind feed did have claws, and I think that’s the basis for the name, which means “lizard-foot.”

As you can imagine, there’s a vast literature on sauropod dinosaurs and a lot of it is readily available online. What I’ve given here is just a basic outline.
—Richard I. Gibson

Brontosaurus story
Prosauropod eggs and embryos 
Painting of diplodocus rearing, by Charles R. Knight, 1911 (public domain via Wikipedia)

Friday, October 24, 2014

October 24. Jurassic life of China




Today, let’s talk about another lagerst├Ątte – not as well known as the Solnhofen Limestone, but pretty cool nonetheless. It’s called the Daohugou Bed or Daohuguo biota, and it’s found in northeastern China. That part of the world was warm and wet in late Jurassic time, about 160 million years ago or a bit older – but there is some controversy as to the age. Rocks deposited in this setting actually extend from the Jurassic up into the Cretaceous, where the fossils are called the Jehol biota. Whatever the age, and I think most researchers accept a late Jurassic age, a lush forest ecology developed. 

Preservation is outstanding because the area was occasionally covered by thick, fine ash falls that likely killed the animals and preserved them intact, including exceptional detail of soft parts. For example, there’s a bee whose proboscis is preserved. 

Pencil drawing of gliding mammal Volaticotherium
by ArthurWeasley; head based on skull image published by
Meng in Nature, Dec 2006. Used under Creative Commons license 
The Jurassic rocks contains the fossil of Juramaia – not the bullfrog, but the early mammal we talked about October 13.  Other life in that forest included undisputed feathered dinosaurs – the first one was found there in 1996. The first gliding mammal, which looked an awful lot like a modern flying squirrel, was described from these beds in 2006. Like Juramaia, it was an insectivore. 

Castorocauda was an aquatic mammal that lived in the lakes of the region. At 2 pounds and 17 inches, it was probably the largest Jurassic mammal, and shows that mammals were adapting to various niches including the water world early in their evolution. Castorocauda probably occupied ecological niches similar to those occupied by beavers and platypuses today. Its scientific name actually means “beaver tail,” and it did have a wide tail similar to those of modern beavers. It also had webbed feet. Castorocauda is another of those critters that may or may not have quite been true mammals. It depends on your definition and on the interpretation of fine details in the fossils.

Along with the small feathered dinosaurs, some of which appear to have been adapted to climbing trees, the fossils include several different types of pterosaur, the flying reptiles that were not closely related to the dinosaurs or their descendents, birds. Some of the pterosaurs had wingspans close to three feet, making them some of the largest animals in the Daohugou beds. The feathered dinosaurs, including Eosinopteryx, were generally small, perhaps a foot in length – but reconstructions of some of them look an awful lot like birds. No actual birds have been found in the rocks, but they’re still looking.

The forest where these animals lived was dominated by conifers, horsetail rushes, cycads and ferns, and gingko-like trees. No flowering plants of the modern sort. The insect life included lots of flies, various spiders including an orb-weaver, mayflies, and water beetles. Plenty of prey for the insectivorous mammals, salamanders, and small dinosaurs that lived there.

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J. Tuzo Wilson was born October 24, 1908, in Ottawa, Canada. In many ways, he was the architect of the concept of plate tectonics, which grew out of the idea of continental drift and sea-floor spreading. He synthesized many of the disparate ideas into an overarching theory. He also recognized the nature of transform faults, like the San Andreas, and their role in plate interactions.

Tuzo Wilson explaining transform faults (video)
—Richard I. Gibson

Chinese lagerstatte

Pencil drawing of gliding mammal Volaticotherium by ArthurWeasley; head based on skull image published by Meng in Nature, Dec 2006. Used under Creative Commons license 

Thursday, October 23, 2014

October 23. Morrison Formation



The Morrison Formation, named for Morrison, Colorado, west of Denver, has been the most prolific source of Jurassic dinosaur fossils in North America. The original stegosaurus and many others came from the Morrison. 

Camarasaurus skull in wall of Dinosaur Quarry,
Dinosaur National Monument, Utah. USGS photo.
The Morrison is mostly reddish and greenish mudstones and shales reflecting different oxidation states of iron, together with some channel sandstones, thin lake beds that include limestones, and swamps in some places. Taken together, the rocks portray a vast, relatively flat flood plain of a complex river system. The Morrison strata contain the sediments that were being eroded from the uplifts in the west – the mountains resulting from the Nevadan Orogeny in eastern California, where subduction was creating a magmatic arc. We talked about it October 10 – the Sierra Nevada Batholith today is essentially the roots of the volcanoes that developed above that subduction zone. 

Rivers flowing to the east from the mountains spread sediments across a zone from Alberta to New Mexico. Deposition spanned about 9 million years, from 156 to 147 million years ago, in the late Jurassic. The rocks include volcanic ash – no surprise, since the mountains providing the sediment were volcanoes. The situation must have been somewhat like Patagonia today, a wide sloping plain east of a high volcanic mountain chain. But unlike the Andes and Patagonia today, the Morrison was laid down in a warm, wet setting. North America in late Jurassic time was subtropical, or at least in the warmer parts of the wide temperate zone.

The remnants of the Sundance Sea were still around too, so parts of the Morrison include possible marine sediments, but for the most part it was a low-relief terrestrial flood plain. Dinosaurs apparently loved it. 

One of the best places to see Jurassic dinosaurs in their original position is the Dinosaur Quarry at Dinosaur National Monument, Utah. A steeply tilted rock face exposes hundreds of fossils within a coarse sandstone bed of the Morrison Formation. The interpretation is that the bodies of many dinosaurs were washed onto a sandbank in a large river, perhaps during a flood. They collected there and were entombed by later deposits. The titling that helped expose the layer took place about 80 million years later, during the Laramide Orogeny, which we’ll get to late next month.

In addition to its famous dinosaur fossils, the Morrison Formation has been one of the primary sources of uranium in the United States. The uranium minerals occur in lenses and layers a few feet thick, concentrated in the sandstones of the Morrison. Their shape in cross-section gives these ore bodies the name C-roll deposits, which probably form when mineral-bearing waters flowed through the porous rock. The Uravan area – for uranium and vanadium – lies in western Colorado and eastern Utah. This mineral belt supplied half the world’s supply of radium in the 1910s, and uranium mining continued at Uravan, Colorado, until 2009 when low prices closed the last operating mine. In 2008, the United States imported 85% of the uranium it consumed for nuclear power, mostly from Canada, Australia, Russia, Kazakhstan, Namibia, Uzbekistan, and South Africa.

The geologic map symbol for the Morrison is Jm – capital J for Jurassic, little m for Morrison. Legions of geology students learning about the stratigraphic section in the Rockies have referred to it as the Jim Morrison formation.

* * *

Today is the day the earth was created, according to Bishop James Ussher of Dublin, Ireland. His analysis of the Old Testament was published in 1654. In that work, he determined that creation took place on October 23, 4004 B.C. The exact time of day is somewhat debated.
—Richard I. Gibson