Hold your arms out with your palm oriented vertically, as if you were trying to shake someone’s hand. Now without moving your forearm, bend your hand downwards towards the floor. Unless you are freakishly flexible, you will only have managed to a measly acute angle. But if you were a bird, you could bend your wrist so that your hand pointed back towards your body. These incredibly flexible wrists allow birds to fold their wings and they help with flying. And many dinosaurs could do something similar.
Many older depictions of small raptors, including the Jurassic Park films, have them holding their arms in a zombie-like stance – arms out at the front and hands palms-down. More recently, artists have portrayed them with more bird-like postures, with their hands bent back towards the forearm. How far the hand could actually bend has been an open question, so Corwin Sullivan from the Chinese Academy of Sciences decided to answer it by piecing together the evolution of the raptor wrist together with Dave Hone (who blogs at Archosaur Musings), Xing Xu and Fucheng Zhang,
Sullivan examined the hands of several dinosaurs, from large hunters like Allosaurus, to smaller, more bird-like species like Caudipteryx and Deinonychus, to living examples like the turkey. He showed that the asymmetric wrists first appeared in this dynasty of predators. They gradually became increasingly asymmetric and backward-bending, culminating in the flexible versions of early birds. This is particularly a tale of two wrist bones – the radiale, which became increasingly wedge-like, and the semilunate carpal, which developed a rounded, convex dip.
These changes to the raptor wrist were already well underway before the group developed powered flight and possibly even before the evolution of long feathers on the arms. For the moment, it’s not clear what advantage the dinosaurs would have gained from their slightly more flexible wrists.
Snakes have been around for nearly 100 million years and scientists have found many fossils of extinct species. But this astonishing specimen is different. This serpent is Sanajeh indicus. It is sitting in a dinosaur nest and its coils surround three eggs and the body of a hatchling.
There are many reasons to think that this prehistoric tableau represented a predator caught in the act of hunting, rather than a mash-up of unconnected players thrown together by chance. The snake is perfectly posed, with its head resting atop a coil and its body encircling a crushed egg. All the pieces are very well preserved and very little of the snake, the dinosaur or the crushed egg have been deformed. All of this suggests that the animals were caught unawares and quickly buried in sediment.
The hatchling in question is a baby sauropod part of the dinosaur lineage that included the largest land animals of all time. It was probably a titanosaur, and being in India, that narrows things down to two known species – Isisaurus and Jainosaurus. The adults were formidable animals, 20-25 metres in length and protected by bony armour running down their backs. But even the largest dinosaurs must have hatched out of a small egg, and at that point, they were vulnerable. The hatchling that Sanajeh was about to dispatch was just 50 centimetres long, while the snake itself was measured 3.5 metres.
Despite this size discrepancy, the hatchling would still have been a substantial mouthful. Most modern snakes wouldn’t have any problem with that. Their lower jaws can unhinge to give them a massive gape and their flexible skulls are made of bones that can move against each other.
Sanajeh was halfway towards developing these specialisations. It didn’t have the fixed skulls and narrow gapes of the most primitive of modern snakes, nor could its maw open quite as wide as today’s record-breakers. Nonetheless, it could certainly swallow a sauropod infant and that ability earned Sanajeh inidcus its name. The words are Sanskrit for “ancient gape from the Indus”.
Dinosaur books have become more colourful affairs of late, with the dull greens, browns and greys of yesteryear replaced by vivid hues, stripes and patterns. This has largely been a question of artistic licence. While fossils may constrain an artist’s hand in terms of size and shape, they haven’t provided any information about colour. But that is starting to change.
The fossils of some small meat-eating dinosaurs were covered in filaments that are widely thought to be the precursors of feathers. And among these filaments, a team of Chinese and British scientists have found the distinctive signs of melanosomes, small structures that are partly responsible for the colours of modern bird feathers.
Melanosomes are packed with melanins, pigments that range from drab blacks and greys to reddish-brown and yellow hues. Their presence in dinosaur filaments has allowed Fucheng Zhang to start piecing together the colours of these animals, millions of years after their extinction. For example, Zhang thinks that the small predator Sinosauropteryx had “chestnut to reddish-brown” stripes running down its tail and probably a similarly coloured crest down its back. Meanwhile, the early bird Confuciusornis had a variety of black, grey, red and brown hues, even within a single feather.
Zhang’s discovery also launches another salvo into a debate over the very nature of “feathered” dinosaurs. Beautiful fossils, mainly from China, show that several species of dinosaur had feathers akin to the flight-capable plumes of modern birds. Species like Caudipteryx and the four-winged Microraptor had true feathers with asymmetric vanes arranged around a central shaft.
It’s a dinosaur tooth, and clearly one that belonged to a predator – sharp and backwards-pointing. But this particularly tooth, belonging to a small raptor called Sinornithosaurus, has a special feature that’s courting a lot controversy. It has a thin groove running down its length, from the root to the very tip. According to a new paper from Enpu Gong of the Chinese Academy of Sciences, it was a channel for venom.
Thanks to a certain film that shall remain nameless, a lot of people probably think that we already know that some dinosaurs are venomous. But the idea that Dilophosaurus was armed with poison, much less spat its toxins at its prey, is non-existent. Some scientists had speculated that they were venomous based on their bizarrely notched and allegedly weak jaws. But these notches have since been found in many other species and no one has ever actually measured the strength of Dilophosaurus‘s jaws.
The best sign that a dinosaur was venomous would be the presence of grooved or hollow teeth. With some notable exceptions, most animals with poison bites use grooves like these to channel their toxins from glands in their mouth to whatever they bite. And grooves are exactly what Gong and his colleagues found in Sinornithosaurus‘s well-preserved skull. Bryan Fry, who discovered venom glands in Komodo dragons earlier this year, says, “It is an absolutely fantastic piece of work. I actually got goose-bumps reading it! Other studies have suggested dinosaurs may be venomous but this is the most solid piece of evidence.”
Sinornithosaurus (meaning “Chinese bird-lizard”) is a small feathered dromaeosaurid (or, more commonly, ‘raptor’) and an early distant cousin of the birds. Its teeth are unusually large and Gong says that those in the upper jaw are “so long and fang-like that the animal appears to be saber-toothed”. They’re very similar to the fangs of back-fanged snakes like boomslangs and vine snakes.
Gong says that other aspects of the skull in support of his venom hypothesis. His team noticed that Sinornithosaurus has a small hollow on the side of its jawbone that could have housed a venom gland. They also found a thin groove running along the animal’s jaw, with small pits at the top of each tooth. They interpret this canal as a “collecting duct” that channelled venom from the gland to the teeth, and each pit could have acted as small, local venom reservoirs. David Burnham, a co-author on the paper, says, “Other fossil animals (dinosaurs, lizards, mammals) have been suggested to be venomous simply on the presence grooved teeth but out work found multiple lines of evidence.”
Meet Raptorex, the “king of thieves”. It’s a new species of dinosaur that looks, for all intents and purposes¸ like the mighty Tyrannosaurus rex, complete with large, powerful skull and tiny, comical forearms. But there’s one very important difference – it’s 100 times smaller. Unlike the ever-shrinking world of music players and phones, it seems that evolution crafted tyrannosaur technology with much smaller specifications before enlarging the design into the giant predators of the late Cretaceous.
Raptorex is a new species of meat-eating dinosaur, discovered in northwest China by Paul Sereno from the University of Chicago. The specimen is a young adult, but it wouldn’t have grown to more than 3 metres in length. It stood about as tall as a human, and wouldn’t have weighed much more. And yet Raptorex looked very much like a scaled-down version of its giant future relatives. All the features that made tyrannosaurs so recognisable and such efficient killers (except their enormous size) were present in this animal.
It really is a beautiful transitional fossil. As Sereno says, “Raptorex really is a pivotal moment in the history of the group where most of the biologically meaningful features of tyrannosaurs came into being, and the surprising thing is that they came into being in such a small animal.” Raptorex clearly shows that natural selection initially honed the distinct body shape of these giant predators at a 1/100th scale. This design was then scaled up with remarkably few modifications.
It had a skull that had clearly been developed into the animal’s primary weapon. It was unusually big for its body size (40% of its torso length), it was structurally reinforced against the stresses of heavy bites, it had large places where powerful jaw-closing muscles attached and it was armed with sharp teeth.
Its limbs also had classic T.rex proportions – strong hind legs that that were fit for running, but miniscule forearms. In contrast, other early tyrannosaurids, such as Guanlong, Dilong, Eotyrannus and Stokesosaurus, looked very different with arms that were long and useful, and proportionally smaller heads (just 30% of its torso length). Only a few distinctive parts of their skeleton mark them out as early tyrannosaurids.
Raptorex brain was also large for its size. For comparison, the Jurassic predator Allosaurus had a brain that was just 60% bigger, despite having a body that was 10 times heavier! Raptorex‘s sense of smell was particularly well-developed, just as Tyrannosaurus‘s was. A scan of its skull showed a large area for its olfactory bulbs – the parts of its brain devoted to smell. These bulbs take up a full 20% of the brain’s total volume, a proportion that exceeds that of all meat-eating dinosaurs except the giant tyrannosaurs.
Despite what many newspapers will assuredly tell you, Raptorex isn’t the ancestor of Tyrannosaurus although it probably looked very much like what this hypothetical animal would have done. It’s more like an early cousin, but one that’s clearly more closely related to T.rex and its giant kin than any of the other smaller species so far discovered.
Based on his new fossil, Sereno tells a three-act story of tyrannosaur evolution. Act One was set in the Jurassic and early Cretaceous periods, with a cast that included Eotyrannus and Dilong. Their snouts had become stronger and their jaws more powerful, but they were typical of other predators of the time. It was only during Act Two, around 125 million years ago, that this dynasty of predators started to become truly specialised, enhancing the skull, lengthening the legs, and shrinking the forearms.
All of these features were present in Raptorex, setting the stage of the final act in tyrannosaur evolution – getting really big. The lineage grew in bulk by around 100 times. By the end of the Cretaceous, the meat-eating scene in the northern continents was dominated by tyrannosaurids – predators such as Albertasaurus, Gorgosaurus, Daspletosaurus and Tarvosaurus, each weighing in at 2.5 tons or more.
It would be fascinating to see if the same story could be told for other lineages of predators, if the abelisaurids, carcharodontosaurids and spinosaurids all had their own mini-prototypes.
Reference: Science 10.1126/science.1177428
Images: Reconstruction by Todd Marshall; other images from Science/AAAS
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There is a reason why there are no dinosaur geneticists – their careers would quickly become as extinct as the ‘terrible lizards’ themselves. Bones may fossilise, but soft tissues and molecules like DNA do not. Outside of the fictional world of Jurassic Park, dinosaurs have left no genetic traces for eager scientists to study.
Nonetheless, that is exactly what Chris Organ and Scott Edwards from Harvard University have managed to do. And it all started with a simple riddle: which came first, the chicken or the genome?
Like almost all birds, a chicken’s genome – its full complement of DNA – is remarkably small. DNA is made up of millions of units called ‘base pairs’, just like a book contains millions of letters. A typical bird genome is made up of about 1.5 billion of these base pairs, just half the number of the comparatively flabby human genome. Like their bodies, bird genomes are feather-weight and streamlined.
Some scientists have suggested that, over the course of evolution, birds shrunk their genetic packages to help them fly. Smaller genomes involve less DNA, which in turn can be housed in smaller cells. And smaller cells are more energy-efficient than larger ones, in the same way that a Mini is more efficient than a gas-guzzling SUV.
These cells look like fairly typical bone cells. They appear to be connected to each other by thin branch-like projections and are embedded in a white matrix of fibres. At their centres are dark red spots that are probably their nuclei. But it’s not their appearance that singles out these extraordinary cells – it’s their source. You’re looking at the bone cells of a dinosaur.
They come from an animal called Brachylophosaurus, a duck-billed dinosaur that lived over 80 million years ago. By looking at one of its thigh bones, Mary Schweitzer from North Carolina State University has managed to recover not just bone cells, but possible blood vessels and collagen protein too. Their presence in the modern day is incredible. Time usually isn’t kind to such tissues, which decay and degrade long before harder structures like bones, teeth and armour are fossilised.
This is the second time that Schweitzer’s team have recovered ancient protein from dinosaur bones. Two years ago, they pulled off a similar trick with collagen protein from the bones of Tyrannosaurus rex. That discovery was a controversial one, and many scientists were justly sceptical. Last year, one group reinterpreted the so-called soft tissues as nothing more than bacterial biofilms, “cities” of bacteria not unlike the plaque on your teeth or slime on moist rocks.
Now, Schweitzer has returned with another volley in the debate, and one which considerably strengthens the case for preserved Cretaceous proteins. From the bone of Brachylophosaurus, she has uncovered tissues that bind to antibodies designed to target collagen and other proteins not found in bacteria, including haemoglobin and elastin. And her experiments were duplicated by independent researchers from five different laboratories. It seems that her Tyrannnosaurus discovery was far from a one-hit wonder.
What happens when you find a feathered dinosaur that really isn’t meant to have feathers? That’s the question set by a spectacular new fossil that adds a confusing dimension to the origin of feathers.
The concept of dinosaurs with feathers is no longer surprising. Birds certainly have them and they are now considered to be living dinosaurs. The infamous Velociraptor and its relatives were covered in plumes, which ranged from the simple quills of Sinosauropteryx to the flight-capable plumes on Microraptor‘s four wings. We know about these prehistoric feathers through the beautiful fossil impressions they have left behind, but a new set of impressions may be the most impressive yet.
They were discovered by Chinese scientists led by Xiao-Ting Zheng, who named their new discovery Tianyulong confuciusi, after the museum that Zheng works in and the famous Chinese philosopher. Its small, agile body, about the size of a cat, was covered in long, hollow filaments that closely resemble the primitive “proto-feathers” (or colloquially, “dinofuzz”) of other dinosaurs. What makes Tianyulong unique is that it is a very distant relative of all these other feathered species.
So far, all feathered dinosaurs are theropods, a group of two-legged and (mostly) carnivorous animals that included Tyrannosaurus and Velociraptor, and indeed, modern birds. The theropods belong one of the two major groups of dinosaurs, the Saurischia. Tianyulong, however, is a clear member of the other dinosaur lineage, the Ornithischia, which include the various armoured, horned, spiked and duck-billed species. This is the first time that anyone has discovered an ornithischian with feather-like structures all over its body.
More specifically, Tianyulong is a heterodontosaur, a group of small plant-eaters that are the most primitive of the ornithischians. Its position in the dinosaur family tree raises big questions about the origins of feathers. If its filaments are related to the proto-feathers of the theropods (which is possible but not certain), they either evolved independently or were derived from filaments that covered the very earliest of dinosaurs.