Paleontoriano

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.

A new species of feathered dinosaur discovered in southern Germany is further changing the perception of how predatory dinosaurs looked. The fossil of Sciurumimus albersdoerferi,which lived about 150 million years ago, provides the first evidence of feathered theropod dinosaurs that are not closely related to birds.


The fossil is described in a paper published in the Proceedings of the National Academy of Sciences on July 2.
"This is a surprising find from the cradle of feathered dinosaur work, the very formation where the first feathered dinosaur Archaeopteryx was collected over 150 years ago," said Mark Norell, chair of the Division of Palaeontology at the American Museum of Natural History and an author on the new paper along with researchers from Bayerische Staatssammlung für Paläontologie und Geologie and the Ludwig Maximilians University.


Theropods are bipedal, mostly carnivorous dinosaurs. In recent years, scientists have discovered that many extinct theropods had feathers. But this feathering has only been found in theropods that are classified as coelurosaurs, a diverse group including animals likeT. rexand birds. Sciurumimus -- identified as a megalosaur, nota coelurosaur -- is the first exception to this rule. The new species also sits deep within the evolutionary tree of theropods, much more so than coelurosaurs, meaning that the species that stem from Sciurumimus are likely to have similar characteristics.
"All of the feathered predatory dinosaurs known so far represent close relatives of birds," said palaeontologist Oliver Rauhut, of the Bayerische Staatssammlung für Paläontologie und Geologie. "Sciurumimus is much more basal within the dinosaur family tree and thus indicates that all predatory dinosaurs had feathers."


The fossil, which is of a baby Sciurumimus, was found in the limestones of northern Bavaria and preserves remains of a filamentous plumage, indicating that the whole body was covered with feathers. The genus name ofSciurumimus albersdoerferirefers to the scientific name of the tree squirrels,Sciurus, and means "squirrel-mimic"-referring to the especially bushy tail of the animal. The species name honours the private collector who made the specimen available for scientific study.
"Under ultraviolet light, remains of the skin and feathers show up as luminous patches around the skeleton," said co-author Helmut Tischlinger, from the Jura Museum Eichstatt.


Sciurumimusis not only remarkable for its feathers. The skeleton, which represents the most complete predatory dinosaur ever found in Europe, allows a rare glimpse at a young dinosaur. Apart from other known juvenile features, such as large eyes, the new find also confirmed other hypotheses.
"It has been suggested for some time that the lifestyle of predatory dinosaurs changed considerably during their growth," Rauhut said. "Sciurumimus shows a remarkable difference to adult megalosaurs in the dentition, which clearly indicates that it had a different diet."


Adult megalosaurs reached about 20 feet in length and often weighed more than a ton. They were active predators, which probably also hunted other large dinosaurs. The juvenile specimen of Sciurumimus, which was only about 28 inches in length, probably hunted insects and other small prey, as evidenced by the slender, pointed teeth in the tip of the jaws.
"Everything we find these days shows just how deep in the family tree many characteristics of modern birds go, and just how bird-like these animals were," Norell said. "At this point it will surprise no one if feather like structures were present in the ancestors of all dinosaurs.
The study was financed by the Volkswagen Foundation and the American Museum of Natural History.

A study with extant mammals refutes the hypothesis on which the assumption that dinosaurs were ectotherms was based.


The work was carried out by researchers from Institut Català de Paleontologia (ICP) and Universitat Autònoma de Barcelona (UAB). It has been published in Nature.
The study analysing the lines of arrested growth (LAG) in the bones of around a hundred ruminants, representative of the specific and ecological diversity of that group of mammals. The results show that the presence of these lines is not an indicator of an ectothermic physiology (does not generate internal heat), as had previously been thought, since all warm-blooded mammals have them. The study therefore dismantles the key argument of the hypothesis that dinosaurs could have been cold-blooded reptiles.
The work was carried out by Meike Köhler, ICREA researcher and ICP palaeontologist; Ronny Aanes, researcher from the Norwegian Polar Institute; Nekane Marín, PhD student at the UAB and Xavier Jordana, lecturer of postgraduate studies at same university.

LAGs are seen in bone sections as dark rings, similar to those seen in tree trunks. The rings are formed, both in the studied mammals and in trees, during the unfavourable seasons (winter or dry season) when the growth of the organism is arrested as a result of a lack of resources. The presence of LAGs in bones was, until now, considered to be the clearest indicator of ectothermy since the seasonal arrest of growth was related to the animal's inability to maintain a more or less constant body temperature (endothermy) during the season of scarce resources.

Meike Köhler explains: "the study we have carried out is very powerful, both in terms of the amount of material and the diversity of species with which we worked, but we did not design it to find a response to the thermophysiology of dinosaurs. We sought to better understand the physiology of extant mammals and how the environment affects them -- how their growth changes as a result of external temperatures, rain and the availability of food and water."

Understanding this was the first step to establishing discussions in paleontological research about the physiology of animals that lived several million years ago.
But the researchers realised that what they observed in the bones of different ruminants refutes the main argument for an ectothermic physiology in dinosaurs. Many hypotheses set out from the premise that large mammals -- endothermic par excellence -- do not have LAGs in their hard tissues since they do not need to arrest their growth responding to external temperature conditions. In fact, since LAGs have been observed in almost all species of dinosaur, many scientists considered that they were cold-blooded reptiles.

The article published in Nature offers the first systematic study, based on an extensive sample of mammals representative of a large variety of ecosystems, which shows that LAGs do not indicate an ectothermic physiology but give us information about how the physiology (metabolism) of an animal changes according to seasonal endocrinal changes, both in cold- and warm-blooded animals. These changes represent a common heritage in all vertebrates and are a kind of internal clock that regulates the animals' needs according to the seasonal availability of resources. Despite the fact that these physiological changes have a strong genetic component, they are also functional and their intensity depends on the ecological conditions in which the animals live. The main ecological factors are more rain and limited supply of food and water, rather than external temperature. This discovery opens up a major line of research into the conservation of biodiversity on our planet today.

"It may seem surprising that until now there has not been a similar systematic study to prove or disprove whether it is only ectotherms that leave these marks in their bones during growth. In fact, there are so many things we do not know that science does not always advance in a linear way. The ideas somehow had long been wandering among the scientific community, but the work we have published organizes them and bases them on data," says researcher Meike Köhler.

In fact, some previous studies had already questioned this hypothesis and among the international scientific community there has been increasing consensus about the idea that LAGs were not necessarily indicators of ectothermy. Similarly, examples of mammals that seemed to have LAGs in their bones had emerged. This study conclusively closes the debate.

The dinosaurs I met as a kid aren’t around anymore. I don’t mean to say that all the classic dinosaurs I saw in the late 1980s were sunk, synonymized or otherwise driven into a second extinction. “Brontosaurus” is the only major example of that (although Torosaurus and Anatotitan may soon follow). No, what I mean is that the tail-dragging, drab, stupid dinosaurs I was first introduced to have all been replaced by agile, brightly-colored, complex animals that were amazingly bird-like.


Our image of what a dinosaur is, and what dinosaur biology was like, has been changing ever since naturalists began scientifically describing creatures such as Megalosaurus and Iguanodon in the early 19th century. Dinosaurs have transformed from 100-foot-long lizards to bizarre creatures with a reptilian gloss, and only by the 1870s, when paleontologists started finding partial skeletons, did we start to get a picture of how unique dinosaurs were. Dinosaurs were re-envisioned as dynamic, bird-like animals by naturalists such as Edward Drinker Cope and Thomas Henry Huxley, only to have their hot-blooded dinosaurs replaced by sluggish swamp-dwellers that fully deserved the extinction that wiped them out. Thankfully, the “Dinosaur Renaissance” of the late 20th century sparked a dinosaur makeover and an interest in dinosaur paleobiology—dinosaurs were transformed into perplexing creatures that lived fast and died young, and the realization that birds are living dinosaurs gave paleontologists a new pool of information to investigate the details of dinosaur lives.


And now we’re in what paleontologist Thomas Holtz has called the “Dinosaur Enlightenment.” While the Dinosaur Renaissance was mostly an image change that raised a slew of questions about dinosaur biology, the Dinosaur Enlightenment is employing new techniques and ideas to approach long-standing questions about dinosaur biology. We’re finally starting to understand how dinosaurs grew up, how they might have mated and even what colors some dinosaurs were. But even the most basic aspects of dinosaur biology are open to revision—for example, paleontologists are trying to find ever-more-accurate and precise ways to estimate how heavy dinosaurs actually were.


Still, a complete and comprehensive perspective of dinosaur natural history remains far beyond our present knowledge. The more we discover, the stranger dinosaurs become. Our general picture of dinosaurs is more accurate than what has come before, but the details will undoubtedly continue to shift, especially as new discoveries are made and speculative ideas are tested. As paleontologist Paul Barrett recently wrote at the Guardian:


We are still in the dark when it comes to some aspects of dinosaur life: how exactly did they die out? Why did some of them prosper while others were short-lived? What were the functions of bizarre features, like Spinosaurus’s “sail”. And which factors led to their runaway evolutionary success? For now, there are still plenty of things we know nothing about – and scientists shouldn’t be afraid to say so.


Dinosaur mysteries will continue to pile up. In another Guardian editorial, paleontologist Dave Hone points out that dinosaurs were far more diverse and disparate than we often appreciate. Everyone knows Tyrannosaurus, Triceratops, Allosaurus, Diplodocus and other classic creatures found during the bone rush of the late 19th and early 20th centuries. These animals are dinosaurian royalty, the most famous of all, but they are only a tiny sampling of the vast array of forms dinosaurs evolved into. In fact, as Hone points out, paleontologists are naming new dinosaurs at an exceedingly rapid pace, and each new discovery adds a little bit more to our understanding of how weird and varied dinosaurs were. Hone writes:


The sheer number of species recovered may itself be notable, but the diversity of forms encompassed in that is probably also under-appreciated. Dinosaurs are famous not just for the huge sizes reached by many, but also their weird and wonderful body types. Animals like Diplodocus, Spinosaurus or Triceratops might seem odd, but there are other dinosaurs out there that stand out just as much compared with their relatives or are simply odd in their own right.


The feathery, ant-eating alvarezsaurs, and the pot-bellied, long-clawed herbivores called therizinosaurs are just two of several dinosaur lineages that paleontologists have only recently recognized, and these puzzling creatures have presented scientists with new, confounding questions about how such creatures lived and what pressures shaped their evolution. The more we learn, the more wonderful and mysterious dinosaurs become.