January 11, 2011
March of the Mammoths: How do you draw a woolly mammoth? Peter Bond walks us through his step-by-step process, and the final version stomped its way over to the ART Evolved elephant gallery. Woolly mammoths dominate the assemblage, but I was glad to see some of my shovel-tusked favorites, like Amebelodon, in there, too.
Everything You Wanted to Know About the Triassic (But Were Afraid to Ask): I have always felt a bit bad for the Triassic. Despite being an important period of change in life’s history, it just doesn’t enjoy the same popularity as the dinosaur-dominated Jurassic and Cretaceous. Nonetheless, our understanding of Triassic life is rapidly increasing, and Chinleana’s Bill Parker has put together an extensive list of academic papers about the Triassic published in 2010. Time to start reading.
A Scrappy Pterosaur: In an Archosaur Musings guest post, paleontologist Victoria Arbour recounts how she discovered and described the first-known pterosaur from British Columbia, Gwawinapterus.
You’ve Got Something in Your Teeth, There: What did ammonites eat for breakfast? Find out at Everything Dinosaur.
One Stegosaur Special, Please: We had a look at the special Swiss Journal of Geoscience stegosaur issue a few months ago (Part I, II, III, IV, V), but Darren Naish of Tetrapod Zoology has offered his own opinions and insights into the new research on the spiky, plated dinosaurs. Check out his take on the Stegosaur Wars, Kentrosaurus posture, and how stegosaurs went about making more stegosaurs (wink, wink, nudge, nudge).
What is it?: Over at Ediacaran, paleontologist Chris Nedin goes on a highly-informative tear about enigmatic animal fossils said to be 770 million years old. Add that to two follow-up posts about other fossil mysteries, and you’ll see why the early history of life is so difficult to study!
That’s a Mating Display if Ever I Saw One: What would the giant Sauroposeidon have looked like in life? SV-POW!’s Matt Wedel uses a restoration by Brian Engh to dive into the soft-tissue anatomy of this dinosaur and explain how to avoid “shrink-wrapped dinosaur syndrome.”
Jurassic Classics: As much time as I spend on this blog nitpicking about dinosaur restorations, I have to admit that I have a soft-spot for drab-colored, anatomically weird, vintage dinosaurs. Those are the dinosaurs I grew up with. If you have an affinity for horribly wrong dinosaurs, too, make sure you check out David Orr’s vintage dinosaur art linkfest at Love in the Time of Chasmosaurs.
Godzilla and Friends: Speaking of disfigured dinosaurs, all this week Monster Brains is featuring posters from all the Godzilla films, as well as those from related man-in-suit monster epics (Rodan, Gappa, Gamera, the Space Amoeba, etc., etc., etc.)
September 15, 2010
The first trace of the plated, spiky stegosaurian dinosaurs was found in Early Cretaceous rock near Grahamstown, South Africa. Uncovered by W. G. Atherstone and A. G. Bain in 1845, the dinosaur was represented by a partial skull and several limb bones. The naturalists felt unqualified to study them and sent the fossils to Richard Owen in England. When Owen eventually got around to describing them, he confused parts of the stegosaur with bones from armored reptiles called pariesaurs which came from South African rock of much older age. Things only got worse from there.
In 1890 the naturalist Richard Lydekker realized that Owen had erred, and he instead attributed all the material to a pariesaur, but Lydekker was wrong, too. When the paleontologist Robert Broom looked at the same material in 1910, he saw that some parts definitely belonged to a dinosaur, which he thought was an ankylosaur. Franz Nopcsa disagreed, casting the fossils as belonging to a stegosaur in his own 1929 study, but it was not until 1981 that paleontologists P.M. Galton and W.P. Coombs straightened things out. The dinosaur was indeed a stegosaur, and is called Paranthodon africanus today.
Paranthodon was not the only cryptic stegosaur with a tortured history. As reviewed by Susannah Maidment in her new paper on the history of stegosaur discoveries, in 1874, just three years prior to the description of the famous Stegosaurus, the scrappy remains of another stegosaur were found in Bedfordshire, England. Described as a partial skull by H.G. Seeley—though actually part of a vertebra—Craterosaurus pottonensis was so incomplete that it was not recognized for what it was until the 1980s.
Another stegosaur, called Omosaurus armatus by Richard Owen (and known as Dacentrurus today), was found the same year in Swindon, England, though its discovery, too, was plagued by confusion over whether its armored plates belonged to the dinosaur or were the head plates of a giant fish. We can look back at them today as the first stegosaurs to be described, although the fossils that initially set the image of what this group was like were the specimens found by O.C. Marsh and E.D. Cope during the “Bone Wars” of the late 19th century.
We have come a long way since Craterosaurus, “Omosaurus,” and Stegosaurus were initially described. Since that time stegosaurs have been found in the Middle Jurassic to Early Cretaceous rock of North America, Europe, Africa and Asia, although the most familiar one is perhaps one of the strangest. Stegosaurus lacked the large shoulder spikes seen among other dinosaurs of its kind, and it had an alternating pattern of plates on its back rather than a combination of back spikes and plates arranged in straight double rows. Even compared to other groups of dinosaurs, though, the stegosaurs were among the most unusual groups of dinosaurs to have ever lived, and new discoveries—such as species with extra-long necks—continue to underscore how bizarre they were.
Maidment, S. (2010). Stegosauria: a historical review of the body fossil record and phylogenetic relationships Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0023-3
February 26, 2009
With small heads, thick limbs, spiked tails, and backs decked with plates, stegosaurs were among the most bizarre creatures ever to have evolved. A new discovery, however, shows that some were even stranger than the weird genera already known. Yesterday a new paper in Proceedings of the Royal Society B by Octavio Mateus, Susannah Maidment, and Nicolai A. Christiansen announced that Miragaia, a long-necked stegosaur, lived about 150 million years ago in what is now Portugal.
Most stegosaurs had relatively short necks for their body size. Miragaia was different. It had 17 neck vertebrae, eight more than earlier ornithischian dinosaurs from which the stegosaurs evolved. This is especially interesting because some of its close relatives, like Stegosaurus, had an increased number of neck vertebrae even though their necks were shorter than that of Miragaia. This suggests that the evolution of the long neck in Miragaia was allowed by evolutionary changes that were already underway among stegosaurs for some time.
To compare Miragaia with the long-necked sauropod dinosaurs like Apatosaurus, you need to go down to the bones. There is not just one way a long neck can evolve. One way, seen in many sauropods, occurred through the lengthening individual vertebrae. The long neck of Miragaia, by contrast, evolved through the addition of vertebrae to the neck.
Some of these were “borrowed” from vertebrae in line behind the neck region, meaning that they once formed part of the upper back but evolved to function like neck vertebrae. This, too, is seen in some sauropod dinosaurs, but how did it happen? The authors propose that a well-known kind of regulatory gene important to organizing the body plan of an animal, called a hox gene, may have triggered the variation that eventually allowed back vertebrae to become neck vertebrae. Unfortunately we cannot test this directly because we do not have preserved Miragaia DNA, but it is an intriguing hypothesis.
Another perplexing question is what selective pressures led long-necked stegosaurs to evolve. The researchers entertained two possibilities: that it was the result of sexual selection or that it allowed stegosaurs with slightly longer necks to browse from a wider array of foliage. Further study will be required to determine whether either of these ideas is correct (or if there is some other cause paleontologists have not thought of yet). Regardless of what the answer turns out to be I am looking forward to the debate and discussion this amazing new fossil stirs up.