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.

Friday, October 31, 2014

October 31. India takes off

The end of the Jurassic is marked by a relatively minor extinction, perhaps only regional in extent rather than global. I talked a little about it a few days ago. It did significantly impact the distribution and numbers of Sauropods and stegosaurids as well as ammonites and other marine animals, but no major groups were wiped out completely as far as I can tell.

Tectonically, Pangaea’s break-up was increasing. By the end of the Jurassic, East Gondwana, one of the two big pieces of Gondwana that had stayed pretty much intact for hundreds of millions of years, was beginning to fragment. We talked earlier this month, on October 5, about the Karoo Volcanics that resulted from the initial rifting though parts of East Gondwana. The rifts, cracks, that allowed the volcanics to erupt were followed by a period of crustal stretching throughout much of the Jurassic period. By about 150 to 155 million years ago, within 10 million years of the end of the Jurassic, East and West Gondwana were probably fully separated from each other, albeit by a narrow, strait-like ocean. And at the same time, India plus Madagascar, which was part of East Gondwana rather than West Gondwana and Africa, began to separate from Australia.

Gondwana when it was intact
Also in the late Jurassic, the eastern side of what is now Australia was also fragmenting, with continental blocks now known as the Lord Howe Rise and New Caledonia pulling apart from the Australia portion of Gondwana.

Pretty close to the end of the Jurassic – it might have been a bit into the Cretaceous, but this whole process is millions of years, so it’s a little silly to point to an instant of geologic time as the time when continents separated – so close enough, at the end of the Jurassic, rifting between India and Antarctica and Australia and Antarctica were also well underway. Those separations continue into the Cretaceous (and in fact to the present day) so we may discuss them again, but they got started about the end of the Jurassic.

The maps of the world at the start and end of the Jurassic Period were remarkably different from each other. From Pangaea – admittedly with some cracks, but still pretty much one supercontinent – to a global distribution of continents that was becoming almost recognizable as the continents of today.

Tomorrow, the Cretaceous begins.
—Richard I. Gibson

Australia separates from Antarctica

Gondwana map based on original by Petter Bockman, public domain, via Wikipedia. 

Thursday, October 30, 2014

October 30. A big predator

Where there are herbivores, there are carnivores. The gigantic Sauropods of the Jurassic must have been a feast for the gigantic carnivorous dinosaurs – whether they killed them or scavenged on dead bodies. Just this year, 2014, a new species of predatory dinosaur was described from Europe, and it may be the largest Jurassic predator known.  

Torvosaurus in Museum of Ancient Life in Lehi, Utah, U.S.A.
Photo by leon7 used under Creative Commons license 
Portugal has late Jurassic rocks containing many of the same dinosaur species found in the Morrison Formation of the western United States. The Jurassic Lourinhã Formation was laid down in a flat coastal plain along the shore of the newly formed Atlantic Ocean. Rifting here began in the Triassic, as Iberia began to pull away from Newfoundland. The rift that ultimately became the Atlantic Ocean was established a bit to the west, so this area remained a low-lying zone near the margin of the ocean. The setting was much like that of the Morrison Formation, although the Morrison was along the shores of an inland sea, while the Portuguese rocks formed along a real ocean coastline. 

In both the Morrison and in Portugal, the top predator was a dinosaur of the genus Torvosaurus – a carnivore that at a glance looks a lot like Tyrannosaurus, which is a Cretaceous dinosaur. Torvosaurus was about 10 meters, 33 feet, long, and bipedal. Despite all the exploration in the Morrison formation, it wasn’t until 1971 that the first Torvosaurus specimens were found in Colorado. The Portuguese specimens, discovered in 2000, have just this year been described as the second species within the genus Torvosaurus. The differences with the Morrison species are not huge, and the species are differentiated on the basis of the number of teeth and the shape of the mouth.

The Portuguese rocks have also yielded eggs and embryos that are ascribed to Torvosaurus. The specimens are the oldest theropod dinosaur eggs with a single layer to the shell.

The Portuguese specimen is the largest land carnivore known in Europe, and among the largest Jurassic carnivores anywhere. Other carnivores shared its ecosystem, including Allosaurus and Ceratosaurus.
—Richard I. Gibson
Largest predator in Europe 

Lourinhã Formation 

Torvosaurus in Museum of Ancient Life at Thanksgiving Point in Lehi, Utah, U.S.A. Photo by leon7 used under Creative Commons license 

Wednesday, October 29, 2014

October 29. Cycads and Gingkoes

We’ve touched on the prolific plant life of the Jurassic several times. It resulted at least to some extent from the greenhouse conditions that prevailed over much of the globe for much of the period. And I mentioned yesterday that there were pretty much no flowering plants. The Jurassic forests were still dominated by conifers, ferns, rushes, and cycads. Not too different from the Carboniferous.

Cycads have cones with exposed seeds, and they first appear in the fossil record during the Permian, with some possible Carboniferous examples. They flourished during the Jurassic, so that they were characteristic of many Jurassic forests, to the point that the Jurassic is sometimes called the Age of Cycads. They are the primary constituents of many Jurassic coal beds. 

Jurassic gingkoes from Oregon.
USGS Monograph XLVIII, by Lester Ward, 1905.
Cycads are gymnosperms, with cones containing exposed seeds. They range from tiny plants only a few centimeters tall to large trees, and while many of them looked like palms, they are not closely related. Cycads today live mostly in tropical environments, but some varieties are found in desert conditions. Modern cycads have been called “living fossils” because they seem to be pretty much unchanged from their Jurassic ancestors, but a recent study has suggested that modern cycads only date to the past 10 million years or so – a second wave of cycads that evolved independently, and not the survivors of the Mesozoic varieties. According to that research based on DNA analysis, cycads probably went extinct at the end of the Cretaceous. I’d say the jury is still out on this idea. There may be cycads in the 65 million to 10 million years ago time frame, which would be evidence for cycads continuing in diminished ways after the end Cretaceous extinction.

The giant herbivorous dinosaurs, Sauropods and others, undoubtedly munched on cycads as part of their diet. 

Gingkoes were also common in Jurassic forests. They are fairly closely related to cycads and conifers, although their precise relationship is not certain. The earliest fossils of the Gingko genus come from the early Jurassic, and while their abundance and diversity peaked during the Jurassic, gingkoes declined during the Cretaceous and later, so that today, there is only one living species, Gingko biloba, native to China.

Jurassic gingkoes lived across the northern continents, what are now North America, Europe, Siberia, and China. Today’s gingko trees can be well over 100 feet tall, and Jurassic varieties were probably of similar size. Gingko leaves dominate some fossil assemblages.

* * *

It’s appropriate that today’s birthday is Othniel Charles Marsh, one of the most prominent students of Jurassic vertebrate fossils in the United States. He was born October 29, 1831, near Lockport, New York, and he spent most of his career with Yale University and the U.S. Geological Survey. O.C. Marsh’s competition with Edward Cope in the rush to find and identify dinosaur fossils is known as the “bone wars,” but we’d probably say Marsh won the wars – he named at least 43 orders, families, and genera of dinosaur, and described 80 new species to Cope’s 56. The legacy of both Marsh and Cope is dinosaur fossils in museums around the United States.
—Richard I. Gibson

Modern cycads not so old?