April 19, 2011
Randall Munroe, the creator of the webcomic XKCD, isn’t going to like this one bit. Fear of attack by Velociraptor is a running theme in the science-themed series—lazy computer programmers should be especially wary—and two separate discoveries announced last week gave those with a phobia of raptors good reason to barricade the doors and windows. Not only did Velociraptor have an excellent sense of smell, but they also hunted at night.
We don’t know for sure what dinosaur eyes looked like. The soft-tissue structures rotted away between the time of death and preservation. But there was one feature of the skull that allowed paleontologists Ryosuke Motani and Lars Schmitz to approach the question of whether some dinosaurs were active in the dark—a circle of bones called the sclerotic ring.
Though relatively rare in the dinosaur fossil record, sclerotic rings can give paleontologists a general picture of eye size and shape. This is because the bone surrounded the pupil and the iris of the eye. Birds, lizards, and other vertebrates have this feature, too, and the details of the sclerotic ring are closely associated with the light conditions when an animal is active.
Modern-day nocturnal animals tend to have wide sclerotic rings with a very large aperture in the middle relative to eye size. Animals that are more active during the day (diurnal), on the other hand, have smaller apertures relative to their eye size. By tracking this association, Motani and Schmitz were able to detect that dinosaurs were active during all times of the day.
(The study also included analysis of pterosaurs and other archosaurs, but I am going to restrict my comments to the findings about dinosaurs here.)
As a group, the dinosaurs did not all neatly fall into nocturnal and diurnal groups. Herbivorous dinosaurs, in particular, appear to have been cathemeral—they would have been active over short periods of time during the day and night. Rather than foraging continuously from dawn until dusk, herbivorous dinosaurs such as the hadrosaurs Corythosaurus and Saurolophus, the small ceratpsian Protoceratops, the sauropodomorph Plateosaurus and the sauropod Diplodocus were probably most active during the early, cool parts of the day and then again around twilight.
Small, predatory dinosaurs were different. Almost all the carnivorous dinosaurs that were examined had sclerotic rings consistent with a nocturnal lifestyle, including Juravenator, Microraptor and—you guessed it—Velociraptor. Based upon the inferred night-hunting habits of Velociraptor and the cathemeral pattern of Protoceratops, Motani and Scmitz suggest that the deadly encounter between the two species immortalized in the “fighting dinosaurs” specimen probably happened at twilight or in low-light conditions.
Not all theropod dinosaurs stalked prey by night, though. The small predator Sinornithosaurus appears to have had the more varied schedule seen among the herbivores, and this was also found for the omnivorous “ostrich mimic” dinosaurs Garudimimus and Ornithomimus. Early birds—the descendants of small, feathered theropods—were different. Every species in the study—Archaeopteryx, Confuciusornis, Sapeornis and Yixianornis—had eyes specialized for daytime activity. Perhaps, during early bird evolution, there was a transition from nocturnal ancestors to flying descendants active during the day.
These findings change our perspective of what Mesozoic life was like. Dinosaurs were thought to be mostly active during the day, with small mammals—including our ancestors and cousins—coming out at night. Now it seems that the Cretaceous nights were not as safe as had been presumed. With so many agile predatory dinosaurs around, mammals would have much to fear during the nighttime hours.
Then again, the idea that Mesozoic mammals scurried through the night is an assumption based upon the idea that dinosaurs were stomping around during the day. Studies of the mammals themselves will be needed to see how their activity overlapped with that of the dinosaurs. Since mammals lack sclerotic rings, though, some other technique will have to be used. Further studies of dinosaurs will be required, too. Conspicuously missing from the study were large-bodied predators akin to Allosaurus and Albertosaurus. When these giants hunted, and when the mammals under their feet were active, awaits future study.
Motani, R., & Schmitz, L. (2011). PHYLOGENETIC VERSUS FUNCTIONAL SIGNALS IN THE EVOLUTION OF FORM-FUNCTION RELATIONSHIPS IN TERRESTRIAL VISION Evolution DOI: 10.1111/j.1558-5646.2011.01271.x
Schmitz, L., & Motani, R. (2011). Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology Science DOI: 10.1126/science.1200043
March 2, 2011
In 1991, the cable channel A&E ran a four-part prehistoric extravaganza hosted by Walter Cronkite and simply called Dinosaur! I was only eight when it aired, and I remember begging my parents to stay up to watch the episodes. Irrepressible little dinosaur fan that I was, I even convinced my third grade teacher to play a tape of the first episode in class one day.
The shows made quite an impression on me. I didn’t know who they were at the time, but for years afterward I could recall seeing paleontologists like Stephen Jay Gould, James Farlow, Dan Chure, David Weishampel, Bob Bakker, John Ostrom, and others explain the latest fossil discoveries. From time to time, puppet dinosaurs popped up in the show. Until Jurassic Park opened two years later, Dinosaur! seared the mid-1990s image of dinosaurs onto my brain, and I was delighted when I was able to dig up the series on YouTube.
What we have learned about dinosaurs in the 20 years since I last saw the show is astounding. Viewed from our current perspective, the show is something of a cultural fossil—a preserved trace of dinosaur science just as dinomania was sweeping the cultural landscape. There is perhaps no better way to ascertain how far we have come than by watching the final episode of the series, “The Tale of a Feather.”
The final episode focused on two interconnected themes: the dinosaurian origin of birds and the extinction of the non-avian dinosaurs. If only the paleontontologists in the show knew about the discoveries that were just around the corner. Dinosaur! debuted five years before feathered dinosaurs began pouring out of China, and today we know that many traits once thought to be unique to birds—from air sacs to nesting behaviors—were actually widespread among dinosaurs. The difference can most readily be seen in the dinosaur puppets used throughout the show. The puppets were generally drab colored and awkward. They weren’t giant lizards, but they were not especially dynamic or bird-like either, existing in a space between the lumbering hulks of earlier restorations and today’s extremely active dinosaurs. The evidence connecting birds and dinosaurs has far surpassed anything anyone thought possible and forever changed how we reconstruct dinosaur lives.
The show’s treatment of dinosaur extinction is also telling of the time it was made. In 1991, the idea that the end-Cretaceous mass extinction was caused by an asteroid strike was still highly controversial. Scientists could not even agree whether the extinction was sudden or gradual. Today the exact details of dinosaur extinction are still being debated, but the “death from above” hypothesis has become widely supported and defended. In a more subtle shift, two of the paleontologists on the show suggested that the sex of dinosaurs was determined by the temperature of their eggs, and that temperature shifts caused overwhelmingly male populations to be born. This idea—extinction due to a lack of females—has since been tossed out, and a forthcoming paper suggesting this same idea has rightly been panned by paleontologists.
It would be a mistake to deride the A&E program for what we now perceive as mistakes. At the time, it presented some of the latest discoveries about dinosaur lives, and in twenty years I am sure that I am going to look back at some of the things I have written and say, “oh geez, if I had only known then…” Old programs like Dinosaur! allow us to see how far we have come and gauge the evolution of dinosaur restorations over time. Who knows how Walking With Dinosaurs 3D or Reign of the Dinosaurs will look two decades from now?
January 18, 2011
There are many ways to make a dinosaur cake. You could bake one in the shape of a dinosaur, you should create an icing dinosaur on the cake, or otherwise give your delicious creation a prehistoric theme. Unfortunately, this means that there are just as many ways to screw up making a dinosaur cake, and the blog Cake Wrecks has a small gallery of some hilariously bad dinosaur cakes.
Thanks to Sarah Zielinski of our own Surprising Science for pointing me to these catastrophic confections.
November 24, 2010
Tomorrow families all over the United States will be taking part in the ritualized, yearly tradition of dinosaur dissection. Granted, “Thanksgiving” is a much better name than “Annual Dinosaur Dissection Day“, but the fact of the matter is that the turkey on the table has a lot in common with its prehistoric, dinosaurian predecessors.
You don’t have to be a trained anatomist to see the correspondence between a dinosaur skeleton and a turkey skeleton. Take the wishbone, for example. This Y-shaped bone is situated in front of the turkey’s shoulders and was formed by the fusion of two separate bones called the clavicles. The terminology here will become important later. “Clavicle” is the term used when these shoulder bones are separated, whereas the words “wishbone” and “furcula” refer to the fusion of the clavicles into a single Y, V, or U-shaped bone.
For a long time it was thought that dinosaurs lacked clavicles. No one had ever found them, and the apparent absence of these bones caused some naturalists to discount dinosaurs as bird ancestors. Among them was the Danish artist Gerhard Heilmann, and he laid out his reasoning in his 1926 book The Origin of Birds.
In Heilmann’s day it was thought that dinosaurs had evolved from a group of early, crocodile-like creatures called pseudosuchians. These creatures had clavicles, but since no one had ever found a dinosaur with clavicles it was thought that dinosaurs had lost these bones during their evolution. This loss meant that – despite the bird-like anatomy of the coelurosaurs - dinosaurs could not have been ancestral to birds. It would be impossible to lose a trait and then have it spontaneously reappear, and so Heilmann and other paleontologists proposed that birds had a much earlier ancestry among pseudosuchians like Ornithosuchus (the “bird crocodile”).
But dinosaurs really did have clavicles. The trouble was that these bones were either lost during preservation or overlooked. Among the first dinosaurs to be discovered with an intact wishbone was Oviraptor from the Cretaceous rock of Mongolia. When Henry Fairfield Osborn described its skeleton in 1924 he clearly marked a Y-shaped bone as the “interclavicle” – a bone present in some animals between the clavicles – but the bone really represented the entire “missing” wishbone. A wishbone was also found among the bones of the predatory dinosaur Segisaurus in 1936, but the discovery of these bones did not change the consensus that birds had evolved directly from crocodile-like ancestors.
It would not be until the late 20th century that small coelurosaurian dinosaurs would be rightly recognized as being ancestral to the first birds. As scientists discover more about dinosaurs, they continue to find that many “bird” traits – such as feathers and systems of air sacs inside the body – were widespread among dinosaurs, and the wishbone is just one small example of this evolutionary connection. Clavicles, both separate and fused, have been found in all major groups of dinosaurs, but true wishbones were only present among the theropod dinosaurs.
As reviewed in recent studies led by Christine Lipkin and Sterling Nesbitt, respectively, many theropod dinosaurs had wishbones. Even the mighty Tyrannosaurus rex had one, and enough Tyrannosaurus wishbones have been found to even detect variation among their shapes. Indeed, the wishbone was an extremely widespread and ancient trait among theropod dinosaurs, perhaps going back more than 215 million years. The wishbone was not a recent evolutionary innovation of modern birds, but a piece of ancient skeletal architecture which links your Thanksgiving feast with some of the most fantastic creatures to have ever evolved.
From all of us at Dinosaur Tracking, have a warm and happy Thanksgiving!
CARRANO, M., HUTCHINSON, J., & SAMPSON, S. (2005). NEW INFORMATION ON SEGISAURUS HALLI, A SMALL THEROPOD DINOSAUR FROM THE EARLY JURASSIC OF ARIZONA Journal of Vertebrate Paleontology, 25 (4), 835-849 DOI: 10.1671/0272-4634(2005)025[0835:NIOSHA]2.0.CO;2
LIPKIN, C., SERENO, P., & HORNER, J. (2007). THE FURCULA IN SUCHOMIMUS TENERENSIS AND TYRANNOSAURUS REX (DINOSAURIA: THEROPODA: TETANURAE) Journal of Paleontology, 81 (6), 1523-1527 DOI: 10.1666/06-024.1
Nesbitt, S., Turner, A., Spaulding, M., Conrad, J., & Norell, M. (2009). The theropod furcula Journal of Morphology, 270 (7), 856-879 DOI: 10.1002/jmor.10724
H.F. Osborn (1924). THREE NEW THEROPODA, PROTOCERATOPS ZONE,
CENTRAL MONGOLIA American Museum Novitates
October 29, 2010
Halloween is almost here, and soon the streets will be swarming with little ghosts, witches, and—sad as I am to say it—sparklepires. Dinosaurs are classic costume choices, too, and in case you need some last-minute ideas for this year’s spooky holiday, we here at Dinosaur Tracking have you covered.
There are more dinosaur and pterosaur costumes out there than I can count, and many of them are more elaborate than the green jumpsuit with spikes sewn on that I wore as a little tyke. Toddler-sized pterosaur, tyrannosaur, Triceratops, and generic dinosaur costumes are common, but if you want to do things the old fashioned way there are plenty of directions online on how to make a child-size dino costume. eHow has two different sets of instructions for quick-and-easy outfits, and PBS has even put up directions for making a costume of the baby Tyrannosaurus “Buddy” from their Dinosaur Train show.
Dinosaurs aren’t just for kids, though dressing up in a big fuzzy dinosaur suit is more likely to make people think of Barney than a terrifying theropod. (I would also avoid dressing up as a Sleestak, unless you want your friends to question your bad taste in movies.) Granted, this custom pterosaur get-up is pretty cool, as is the self-made dinosaur exoskeleton in the video above, but you’re more like to find dinosaur masks than full costumes. If that’s the way you want to go, have some fun with it. Pair up a Dilophosaurus mask with some camouflage fatigues to be a dinosaur soldier or throw on some scrubs to be a dino doctor (this way you can take the mask off if it gets too hot and still be in costume). If all else fails, just pick up some fake blood, tear up an old t-shirt, and say that you’re a Deinonychus victim.
If you really must have your whole family go as a pack of dinosaurs, there are dinosaur costumes for pets, too. Your dog may tolerate it, but your cat will probably hate you for it and cast up a hairball in your shoes for making it wear such a ridiculous getup.
Other fun stuff:
Maybe dressing up as a dinosaur isn’t for you, but what about carving a dinosaur themed jack-o-lantern? There are a few patterns available on the web, though, with a little imagination, some really awesome designs are possible.
If you end up dressed up as a dinosaur this year or make a dino jack-o-lantern, snap a photo and send it to us at email@example.com. We’ll collect whatever photos we get and put them into the next edition of our Dinosaur Sightings.
Whatever you and your family end up doing, though, we here at Dinosaur Tracking want to wish everyone a safe and happy Halloween!