August 30, 2012
How big was Spinosaurus? The croc-snouted, sail-backed theropod was heralded as being even bigger and more menacing than Tyrannosaurus rex thanks to Jurassic Park III, placing Spinosaurus among the ranks of Giganotosaurus and Carcharodontosaurus as challengers to the vaunted title of the biggest flesh-eater to ever walk the earth. Depending on who you ask, Spinosaurus was about 41 to 59 feet long, making it as large as–if not larger than–old T. rex.
Asking “Which dinosaur was the biggest?” isn’t very helpful, though. “Bigness” isn’t something scientists actually measure. Consider the contemporaneous sauropods Apatosaurus louisae and Diplodocus carnegii. So far as we know, both grew to about 80 feet long, but Apatosaurus was a much bulkier dinosaur. Which is the more important feature for deciding which dinosaur was bigger–mass, length or a combination of the two? In this case, Apatosaurus would seem to win out through its combination of bulk and length, but what if you have two dinosaurs that are about the same size, but the shorter one seems to be stouter than the longer one? What then?
Dinosaur comparisons are especially fraught when dealing with partial skeletons and scientific estimates. How hefty we think a dinosaur was depends on the techniques we use to reconstruct mass. Paleontologists can come up with a probable range that encompassed the variation of a dinosaur species, but, sadly, we can’t weigh an Apatosaurus or Carcharodontosaurus to find out if we’re on the mark.
Length would seem to be a better option for comparing dinosaur size. With a little mathematical work to fill in the extent of cartilage and soft tissues between dinosaur bones, paleontologists can turn to the fossils themselves to gauge dinosaur size. Only, many of the largest dinosaurs are only known from scrappy skeletons.
Very few dinosaurs are known from complete skeletons. This is especially true of the largest dinosaurs. With the exception of specimens like the T. rex “Sue“, one of the most complete large dinosaurs ever discovered, many giants are only known from bits of skull, spine and limbs. Despite being touted as an absolute giant, for example, very little of Spinosaurus has been described. We don’t know how long this theropod truly was–paleontologists can only estimate using more complete dinosaurs as guides for what to expect. And even in relatively compete dinosaur skeletons, few specimens are found with complete tails. The delicate bones near the tip of the tail, especially, are rarely found.
Paleontologist Dave Hone examines how tails–or lack thereof–contributed to dinosaur size in the latest issue of Journal of Vertebrate Paleontology. In his survey of museum collections and the literature, Hone only identified a few dinosaur specimens with tails complete enough to fully comprehend how the organ contributed to the dinosaur’s size. Specimens of the ankylosaur Dyoplosaurus, ceratopsian Centrosaurus and tyrannosaur Gorgosaurus, among others, have complete tails, while individuals of dinosaurs such as the sauropodomorph Lufengosaurus and the oviraptorosaur Caudipteryx have tails missing five vertebrae or less.
When Hone examined these informative fossils, he found that dinosaur tails complicated the question of how long certain varieties of dinosaur were. Tails varied in their proportions among members of the same evolutionary lineage–one species of dinosaur may have a very short tail while its closest known relative may have an exceptionally long tail. And, not surprisingly, individuals of the same species varied in their tail lengths. In essence, statements such as “Spinosaurus was 45 feet long” are rough estimates that are significantly complicated by both variation and a lack of complete tail specimens. On his blog, Hone explained that these estimates affect how we envision dinosaurs and study their biology:
This is not a facile question, aside from the obvious public interest (when was the last time you saw a report on a new dinosaur that didn’t suggest how long it was, if only in terms of double decker buses?). Total length is a measure that’s been used by various researchers (myself included) over the years as a proxy for the mass of dinosaurs. If we’ve been over- or underestimating these values it could potentially affect our results quite a bit, so knowing whether or not these measures are right is worth checking.
This problem isn’t unique to dinosaurs. Natural variation even complicates length estimates of extant species. Take crocodiles, for example. For a long time, herpetologists thought that you could multiply a crocodile’s skull length by seven to get a fairly accurate estimate of the animal’s full stretch. Simple enough. But this rule appears to break down among the biggest individuals, particularly thanks to variations in their tail length. Researchers face the same problem with other reptiles. In estimating the size of extinct, giant monitor lizards, for example, paleontologists consider the length of the snout to the lizard’s “vent” at the base of the tail. This is because tails are variable, and may make an individual animal longer or shorter based on how it is reconstructed. Considering size from the tip of the nose to the base of the tail is a less unwieldy way of measuring size and comparing individuals.
What’s a paleontologist to do? Hone suggests cutting the tail out of dinosaur length estimates. While total length figures will never go out of fashion in popular articles and books, researchers may be better served by estimating the snout-vent length, or similar measurement, that allows for more accurate estimates of dinosaur size. As Hone states, dinosaur bodies from the snout to the back of the hip seems to vary less than tails, so this measurement may present more reliable estimates for dinosaur size. Hone is not saying that paleontologists should totally abandon measurements of total length for dinosaurs, but instead suggests that “snout-sacrum length” would be a better measurement that would coincidentally bring examinations of dinosaurs into line with studies of other tetrapods. The “My dinosaur is bigger than yours” contests will never end, but Hone’s paper suggests a new way of measuring the size of the contestants.
David W. E. Hone (2012): Variation in the tail length of non-avian dinosaurs, Journal of Vertebrate Paleontology, 32:5, 1082-1089 DOI: 10.1080/02724634.2012.680998
August 2, 2012
There’s no shortage of dinosaur myths. Paleontologist Dave Hone recently compiled a list of eight persistent falsehoods over at the Guardian–from the misapprehension that all dinosaurs were huge to the untenable idea that Tyrannosaurus could only scavenge its meals–but there was one particular misunderstanding that caught my attention. For decades, popular articles and books claimed that the armor-plated Stegosaurus and the biggest of the sauropod dinosaurs had second brains in their rumps. These dinosaurs, it was said, could reason “a posteriori” thanks to the extra mass of tissue. It was a cute idea, but a totally wrong hypothesis that actually underscores a different dinosaur mystery.
Dinosaur brain expert Emily Buchholtz outlined the double brain issue in the newly-published second edition of The Complete Dinosaur. The idea stems from the work of 19th-century Yale paleontologist Othniel Charles Marsh. In an assessment of the sauropod Camarasaurus, Marsh noticed that the canal in the vertebrae over the dinosaur’s hips enlarged into an expanded canal that was larger than the cavity for the dinosaur’s brain. “This is a most suggestive fact,” he wrote, and, according to Buchholtz, in 1881 Marsh described a similar expansion in the neural canal of Stegosaurus as “a posterior braincase.”
Sauropods and stegosaurs seemed like the perfect candidates for butt brains. These huge dinosaurs seemed to have pitiful brain sizes compared to the rest of their body, and a second brain–or similar organ–could have helped coordinate their back legs and tails. Alternatively, the second brain was sometimes cast as a kind of junction box, speeding up signals from the back half of the body up to the primary brain. That is, if such an organ actually existed. As paleontologists now know, no dinosaur had a second brain.
There are two intertwined issues here. The first is that many dinosaurs had noticeable expansions of their spinal cords around their limbs–a feature that left its mark in the size of the neural canal in the vertebrae. This isn’t unusual. As biologists have discovered by studying living species, the enlargement of the spinal cord in the area around the limbs means that there was a greater amount of nervous system tissue in this area, and dinosaurs with larger expansions around the forelimb, for example, probably used their arms more often than dinosaurs without the same kind of enlargement. The expansion of the neural canal can give us some indication about dinosaur movement and behavior.
But the so-called “sacral brain” is something different. So far, this distinct kind of cavity is only seen in stegosaurs and sauropods and is different than the typical expansion of the neural canal. There was something else, other than nerves, filling that space. Frustratingly, though, we don’t really know what that something is.
At the moment, the most promising idea is that the space was similar to a feature in the hips of birds called the glycogen body. As sauropod expert Matt Wedel has pointed out, this space stores energy-rich glycogen in the hips. Perhaps this was true for the sauropods and stegosaurs, too. Again, though, we hit a snag. We don’t really know what the glycogen body does in birds–whether it helps with balance, is a storehouse for nutritious compounds that are drawn upon at specific times or something else. Even if we assume that the expansion in dinosaurs was a glycogen body, we don’t yet know what biological role the feature played. Dinosaurs didn’t have hindbrains, but the significant spaces in the hips of stegosaurs and sauropods still puzzle paleontologists.
April 4, 2012
Earlier this week, the rotting corpse of a discarded dinosaur idea rose from the depths. Brian J. Ford, a television personality and self-styled independent researcher, decided that Apatosaurus, Allosaurus and kin just looked wrong ambling about on land. Unfettered by the accumulation of scientific evidence about how dinosaurs moved and the environments they lived in, Ford decided to set scientists straight by floating an idea that had been sunk decades ago—that all large dinosaurs spent their lives in water. And, like the bad science it is, the idea strained to explain everything about dinosaur biology. Not only did the idea supposedly explain why non-avian dinosaurs went extinct—their watery homes dried up, of course—but the aquatic setting also explained the small arms of the tyrannosaurs. The great tyrants, Ford said, would catch fish and hold them close for visual inspection before downing the sashimi. Ford’s speculation is a buffet of nonsense. There is so much wrong with it, it’s hard to know where to start.
Ford certainly has a right to his opinion. The weight of the evidence absolutely crushes his ill-formed idea, but there’s no rule against making poorly substantiated claims on the internet. Heck, much of the web is sadly founded on such sludge. But I was taken aback by how many news sources not only took Ford seriously, but cast him as a kind of scientific underdog. In a BBC4 Today interview—which helped spread this swamp of insufficient evidence and poor reasoning—host Tom Feilden cast Ford as a Galileo-type hero, boldly defending his revolutionary idea while the stodgy paleontological community refused to budge from its orthodoxy. Despite Natural History Museum paleontologist Paul Barrett’s admirable attempt to set Feilden straight, the radio host concluded that Ford’s idea was a new and exciting notion, even though the image of wallowing sauropods was part of the old image of dinosaurs that had been cast out in the 1960s. As artist Matt van Rooijen highlighted in his latest Prehistoric Reconstruction Kitteh cartoon, it would seem that the old is new again.
Other news sources followed Feilden’s lead. At the Daily Mail, a source not exactly known for reliable science coverage, reporter Tamara Cohen recapitulated Ford’s argument. Paul Barrett again offered a dissenting view at the bottom of the article, but the article promotes Ford’s idea anyway. “Dinosaurs DIDN’T rule the earth: The huge creatures ‘actually lived in water’ – and their tails were swimming aids,” the headline gasped. Hannah Furness did much the same in the Telegraph, summarizing Ford’s statements at length before, in the last line, plunking down a quote from Barrett saying that Ford’s idea is nonsense. Elsewhere, FOX News and Australia’s Sky News ran a syndicated version of the story that followed the same form, and the Cambridge News didn’t even bother to get a second opinion on Ford’s work. But my favorite howler came from the internet-based TopNews, which concluded that “it had [sic] become all the more imperative that further research is done on [Ford's] theory so that some sort of conclusive findings can be presented.” No, it isn’t imperative at all. Ford’s idea is not even close to a theory, or even science. Ford’s evidence-free approach doesn’t make any testable predictions, and there is no actual scientific debate to be had here. Repeating “Dinosaurs look better in water” ad infinitum isn’t science, no matter how many journalists are enamored with the idea.
Paleontologists quickly jumped on the idea. Dave Hone and Mike Taylor called out Ford’s idea as old-school nonsense. Scott Hartman dug in at length in his post “When journalists attack!” and Michael Habib wrote a takedown of the bog-dwelling sauropod idea from a biomechanical perspective. And, earlier today, Don Prothero rightly cast the controversy as yet another media failure in reporting science. Prothero writes:
Once again, we have a glorified amateur playing with his toy dinosaurs who manages to get a gullible “journalist” to print his story with a straight face and almost no criticism. Feilden didn’t bother to check this guy’s credentials, consulted with only one qualified expert and then only used one sentence of rebuttal, and gave the story the full promotion because it was a glamorous topic (dinosaurs) and challenged conventional wisdom.
Poor reporting is entirely to blame here. “Amateur, armed with dinosaur models, says all of dinosaur paleontology is wrong” would be a more accurate way to cast the story, and seen that way, it isn’t really worth talking about. But it seems that merely having a controversial, unfounded opinion can be the price of admission for wide media attention.
This is hardly the first time poorly supported paleontology claims have received more attention than they deserve. While it was a minor event, in February io9 ran a story highlighting the unsubstantiated notion that the little pterosaur Jeholopterus was a vampiric little biter that supped on dinosaur blood. The author, Keith Veronese, was clear that the idea was not accepted by paleontologists, but he still romanticized the idea of an outsider rattling the academic cage. The paleontologists behind the Pterosaur.net blog refuted the vampire pterosaur idea and questioned the usefulness of promoting ideas that lack any solid evidence, though I have to wonder how many people found the specialist rebuttal.
And then there was the legendary hyper-intelligent, artistic squid. Last October, a number of journalists fell for the spectacularly nonsensical idea of a Triassic “Kraken” which supposedly created self-portraits from ichthyosaur skeletons. While veteran science reporters wisely avoided the hyped story, enough journalists paid attention that the hype spread far and wide through syndication. I tore into the nonsense, calling out what I believed to be terrible reporting, and I heard a lot of tut-tutting from my writer colleagues that I was unfairly bashing all of science journalism.
To which I wanted to ask “Well, where were you in all this?” I’m thrilled that the New York Times and Wall Street Journal didn’t parrot the fantastic claims, but the story was still copied and pasted to places like Yahoo!, FOX News, MSNBC, and elsewhere. The story was put in front of a lot of eyeballs, even if cherished journalistic institutions didn’t take part. While nonsense is proliferating, should we really feel smug and self-assured that we didn’t fall into the same trap? Don’t we, as people who care about accurately communicating the details of science to the public, have a responsibility to be whistleblowers when spurious findings are being repeated without criticism? I believe so. We all snicker and sigh as the usual suspects promote sensational claims, but I think it’s important to take that frustration and call out credulous, gullible, over-hyped reporting whenever it might bob to the surface.
March 5, 2012
Though only about the size of a turkey, Velociraptor still looked like a formidable predator. With snatching hands, a jaw set with recurved teeth and, of course, a retractable claw on each foot, almost every end of this dinosaur was sharp. But what did this well-equipped Cretaceous killer actually eat?
One of the prime candidates for a Velociraptor entree has been the small horned dinosaur Protoceratops. A truly spectacular fossil cemented the connection between these dinosaurs. In 1971, a Polish-Mongolian expedition to the Gobi Desert found “fighting dinosaurs“—a Velociraptor and Protoceratops preserved in the throes of fatal combat. While the Velociraptor had kicked its deadly foot claw into the neck of the Protoceratops, the little ceratopsian had crushed the right arm of the predator, and the two remained locked together in death. The trouble is that we can’t know why these two dinosaurs were fighting. Was the Velociraptor trying to hunt the Protoceratops? Or was the little predator itself attacked by a territorial Protoceratops? That the dinosaurs battled each other is obvious, but the reason for their combat remains a mystery.
But a recently described fossil confirmed that Velociraptor or a very similar dinosaur ate Protoceratops flesh. In 2010, paleontologist Dave Hone and co-authors reported a set of Protoceratops bones that had been scratched and scored by the teeth of a small predatory dinosaur. How the horned dinosaur died was unclear, but the toothmarks indicated that the carcass had almost been entirely stripped by the time the carnivorous dinosaur came along to pick off the remaining scraps. Since Velociraptor shared the same habitat and was of the right size to leave the bite marks, the dinosaur is a good candidate for being the scavenger.
Another fossil provides an even closer connection between Velociraptor and its prey. In a paper to be published in Palaeogeography, Palaeoclimatology, Palaeoecology, Hone and co-authors Takanobu Tsuihiji, MahitoWatabe and Khishigjaw Tsogtbaatr describe part of a Velociraptor meal preserved inside the dinosaur’s body cavity. Represented by a single bone, the gut contents show the dinosaur had fed upon a pterosaur.
The broken pterosaur bone was probably inside the dinosaur’s stomach when it died. How that bone found its way into the Velociraptor digestive system is another matter. Based on the anatomy of the bone and the pterosaurs that were around at the time, Hone and colleagues hypothesize that the ingested pterosaur was an azhdarchid, one of the long-legged, long-necked pterosaurs that included the largest flying animals of all time.
This particular pterosaur was not a giant by pterosaur standards—Hone and colleagues estimate that the animal probably had a wingspan over six feet across and weighed more than 19 pounds. But it would have been large compared to the relatively small Velociraptor that consumed it. This would have made the sharp-beaked pterosaur “a difficult, and probably even dangerous, target [for] a young dromaeosaur,” Hone and co-authors suggest, and therefore “unless the pterosaur was already ill, infirm or injured, it seems unlikely that this would be a case of predation.” And the fact that the dinosaur consumed a large bone further suggests this might have been another instance of Velociraptor scavenging. If the pterosaur carcass was fresh, the Velociraptor probably would have consumed the available soft tissues first. The fact that the dinosaur ate bone may be an indication that the pterosaur had been picked over and there was only a little meat left clinging to the carcass.
This isn’t the first time evidence of small dromaeosaurs scavenging on pterosaurs has been found. In 1995, paleontologists Philip Currie and Aase Roland Jacobsen reported a partial skeleton of an azhdarchid pterosaur that had been bitten by a small predatory dinosaur. A tooth embedded in the skeleton identified the scavenger as Saurornitholestes, a dromaeosaurid cousin of Velociraptor from Cretaceous North America.
Although Velociraptor is often celebrated as a vicious and cunning predator, the accumulating evidence shows that the dinosaur wasn’t above scavenging. This isn’t surprising. Even highly active predators will regularly scavenge if the opportunity arises. And while I consider the ballyhooed argument over whether Tyrannosaurus rex was primarily a hunter or scavenger to be dead and buried—the tyrant dinosaur was certainly both hunter and scavenger—it is worth noting that even small, apparently highly predaceous dinosaurs at least occasionally scavenged. In outlining his case for “Tyrannosaurus the scavenger,” paleontologist Jack Horner pointed to Velociraptor as the epitome of what a predatory dinosaur should look like. Yet this new paper, as well as other recently reported indications of dinosaur hunting and scavenging, underscores the fact that the hunting-scavenging dichotomy is too narrow a view on nature. As Hone and colleagues wrote near the beginning of their paper, many carnivores hunt and scavenge. The trick is figuring out which type of flesh-acquisition behavior was more important to a particular species.
Frustratingly, though, we’re more likely to find evidence of dinosaur scavenging than active predation. Relatively small predators like Velociraptor, which may have specialized on even smaller prey, are especially troublesome in this regard. Unless someone is lucky enough to find a small mammal, dinosaur, or other creature in the gut contents of Velociraptor, we may never know what this dinosaur primarily hunted. When predatory dinosaurs wrenched tattered bits of flesh from denuded carcasses, though, they often left tell-tale signs of damage behind, and these traces are more likely to be preserved than are gut contents. Despite its celebrity, we are still just beginning to put together a picture of how Velociraptor hunted and fed.
Currie, P., & Jacobsen, A. (1995). An azhdarchid pterosaur eaten by a velociraptorine theropod Canadian Journal of Earth Sciences, 32 (7), 922-925 DOI: 10.1139/e95-077
Fowler, D., Freedman, E., Scannella, J., & Kambic, R. (2011). The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028964
Hone, D., Choiniere, J., Sullivan, C., Xu, X., Pittman, M., & Tan, Q. (2010). New evidence for a trophic relationship between the dinosaurs Velociraptor and Protoceratops Palaeogeography, Palaeoclimatology, Palaeoecology, 291 (3-4), 488-492 DOI: 10.1016/j.palaeo.2010.03.028
Hone, D., Tsuihiji, T., Watabe, M., Tsogtbaatr, K. (2012). Pterosaurs as a food source for small dromaeosaurs Palaeogeography, Palaeoclimatology, Palaeoecology : 10.1016/j.palaeo.2012.02.021