Valuable lessons from gore-kings and thieves

Oh, yes. This pic again. Lythronax by Andrey Atuchin.

The Cretaceous was undoubtedly one of the most tumultuous times in earth’s history. Life was rapidly changing: over the course of eighty million years, the world saw a wave of never-before-seen groups of life, including flowering plants (and their accompanying pollinators), snakes, and “modern” birds. By the late Cretaceous, the world would have been alien to any animal living in the Jurassic. This was a world of giants, oddballs, tyrants, and tanks. The Cretaceous, despite being the last period of the Mesozoic, was the golden era for dinosaurs worldwide.

As the Cretaceous progressed from its vaguely Jurassic beginnings to its cataclysmic end, faunal groups the world over were surprisingly homogeneous. In North America and Asia, there was a relatively consistent fauna. Generally, the families that were present in such faunal group can be linked to Asian origins. It would make sense, then, that such species, over the course of tens of millions of years, migrated from their Asian motherlands to the brave new world of western North America. With each successive generations moving farther and farther across the land bridge connecting the two continents. However, two newly-described species contest this unidirectional migration. They seem to show that our understanding of late Cretaceous faunal shifts and the evolution of the families composing these faunal groups did not take straightforward paths to reach their eventual burial sites; rather, the migration between the two continents was much more complex.

A "tyrant map" from Wiki. Click to embiggen. The abundance of
tyrannosaurids in North America, and their lack in Asia, were thought
to represent the Asian origin of Tyrannosauridae.

The first recently-described species to raise intriguing questions about dinosaur biogeography and evolution is one that has been making the media rounds lately: Lythronax agrestes, the nowfamous “goreking of the southwest.” Apart from winning Most Badass Scientific Name of the Year, Lythronax reveals interesting aspects of tyrannosaurid evolution. It is the earliest known tyrannosaurid, dating back to about 80 million years, to a time when the North American dinosaur fauna was starting to take the form it would keep until the last day of the Mesozoic. Alongside Lythronax lived some of the first centrosaurine ceratopsians, which themselves would become major ecological players in a few more million years (more on that in an upcoming post), as well as hadrosaurine hadrosaurs. What makes Lythronax special is that it dispels the idea that tyrannosaurids first evolved in Asia. The earliest tyrannosauroids, as well as several species of advanced tyrannosaurids, have been found in China and Mongolia, leading to this logical conclusion. However, it appears that tyrannosaurids may have emerged in North America, evolving their characteristic juggernaut build and binocular vision there before migrating back to Asia. And, although only one Asian ceratopsid has been described thus far, it is likely that the centrosaurines with which Lythronax shared its environment travelled the same way, migrating north in giant herds to the floodplains of Canada and Alaska before returning to Asia.

Acheroraptor by Emily Willoughby. 

Another recently-described species has actually been known for quite a while, but has only recently been given a name. Acheroraptor temertyorum is a dromaeosaurid from Hell Creek, a formation bearing rocks from the end of the Cretaceous. The fauna of this formation is unmistakable, consisting of some of the most wellknown dinosaurs of all time. Tyrannosaurus was the apex predator, stalking lowland plains and forests populated with Triceratops, Ankylosaurus, and Edmontosaurus. For many years, it was labelled as a close relative of the Canadian Dromaeosaurus, a dromaeosaurine dromaeosaurid. Dromaeosaurines were North Americanan through and through, with no other species thus far discovered outside of the continent. It would make sense to assume that Acheroraptor shares a similar story, evolving from endemic early Cretaceous dromaeosaurines. However, Acheroraptor appears to have its roots not in North America, but yet another continent: it was not a dromaeosaurine, but a velociraptorine, an almost entirely Asian group. Even at the very end of the Cretaceous, species were still migrating between the continents of the northern hemisphere.

The relationship between where a species is found and where it comes from are not as straightforward as they may seem. Evolution is an enormous tale of unexpected outcomes and unlikely beginnings, as well as the forces which dictate such results. The wealth of fossil information we have found on ancient biogeography reveals a great deal of surprising new insight into the outward reasons for their long, successful time on this earth. 

Inside the mind of the hadrosaur

Hadrosaurids have been making headlines more often than usual in the past few weeks. Starting with the discovery of hadrosaur tails in both Alberta, Canada and Coahuila, Mexico, new discoveries of the dominant herbivores of the Cretaceous are popping up quite regularly. Since the two tails were uncovered, the youngest-known specimen of Parasaurolophus sp. was discovered and affectionately nicknamed “Joe.” Joe reveals much about lambeosaurine ontogeny in a tribe of lambeosaurines which are pretty poorly understood in terms of how ontogeny and gender affect the development of their signature tube-like crests (Farke et. al, 2013).

Amurosaurus riabinini. Reconstruction by Sergey Krasovskiy. 

Perhaps the most important news relating to hadrosaurs is the recent publication of cranial endocasts of the lambeosaurine Amurosaurus riabinini of Russia. These endocasts allow paleontologists to examine the structure of the brain’s outermost regions, allowing conclusions to be drawn my correlating the size of a given region to its importance to the animal. This, subsequently, allows us to speculate further on the behavior of these animals.

It has been theorized that the volume of the dinosaurian brain took up about half of the available space within the braincase. The recovered Amurosaurus, however, reveals that its brain took up around 60% of the braincase. Being an herbivorous reptile, this does not indicate a significantly higher level of intelligence than any standard reptile; however, this larger brain does indicate that, despite being huge, stolid animals, hadrosaurs were not dull.

Not only were they not dull, but compared to other herbivorous dinosaurs, hadrosaurids had among the highest brain-to-body ratios! The Amurosaurus brain reveals that its Reptilian Encephalization Quotient (REQ), or the ratio of a reptile’s actual brain-to-body mass to its expected mass, was higher than those of ceratopsians and sauropods, but lower than those of even some of the earliest theropods. This latter discovery is not surprising, as the instincts and brainpower needed to hunt are far greater than those needed to graze or browse.

The cranial endocast of A. riabinini. Scale bar represents 2cm for A, B,
and C, and 10cm for D. From Lauters et. al, 2013.

What makes the brain of Amurosaurus particularly important, and what does this show us about hadrosaurs? The detail of the endocast reveals an interesting aspect  of hadrosaur brain physiology: the pituitary gland is enlarged, possibly explaining one part of just how hadrosaurs attained such massive sizes in a relatively short period of time. A hadrosaur could grow from a five-foot-long hatchling to a thirty-foot-long adult in just 12 years, reaching their maximum size in just half the time it took contemporary predators to reach adulthood. The astonishing growth rate of hadrosaurs is part of the reason they prevailed in the late Cretaceous; reaching sexual maturity at just three years old, hadrosaurs could produce many offspring while being too large for most predators to tackle. The larger-than-expected size of the lambeosaurine brain is consistent with the notion that hadrosaurs, in general, were animals with relatively complex social interactions (Lauters et. al, 2013). The need for intraspecies communication between herd members is essential for maintaining herd structure. An enlarged brain processes more auditory and visual signals around it, giving credence to the theory that the large and elaborate crests in lambeosaurines were used for communication as well as courtship displays.

It is a common misconception that dinosaurs were truly dumb animals. Compared to their body size, it is true, their brains are much smaller than a mammal of the same dimensions. However, this does not exclude them from having engaged in complex behaviors which are comparable to those of modern animals. We now know from cranial endocasts of serveral taxa spanning various families that dinosaurs, in general, were much more complex, active, and interesting than previously thought.

References

Cranial Endocast of the Lambeosaurine Hadrosaurid Amurosaurus riabinini from the Amur Region, Russia

Ontogeny in the tube-crested dinosaur Parasaurolophus (Hadrosauridae) andheterochrony in hadrosaurids

What the extinction of the western black rhino should mean to you

Despite the recent increase in social media concerning the extinction of the western black rhinoceros Diceros bicornis longipes, the subspecies was actually declared extinct in 2011, and the last sighting of wild individuals all the way back in 2001. However, the lesson we can learn from the plight of the western black rhino, as well as all other subspecies and species of rhino, is an extremely important one.

The demise of the worldwide rhino population, regardless of range or species, is intrinsically tied to the use of the animal’s horns in traditional Chinese medicine (TCM). Although the TCM trade has largely diminished, with several bans restricting the import of rhinoceros products into Middle Eastern and Eastern Asian countries, poachers still manage toslaughter wild rhinos at an astonishing, not to mention growing, rate.

The situation of the rhino is the same the world over – although some species are more abundant than others, no species is truly common, and two of the six* living species are critically endangered: the Indonesian Javan rhinoceros Rhinoceros sondaicus sondaicus is limited to the last 50 or so members of its subspecies, and the Vietnamese Javan rhino R. s. annamiticus was declared extinct in 2011 as well. The next most common rhino species, the Sumatran Dicerorhinus sumatrensis, has a wild population of about 200 individuals.

*Although most resources cite five rhinoceros species (black, white, Sumatran, Javan, and Indian), the northern and southern subspecies of white rhinoceros Ceratotherium simum have been found to be two distinct species.

The sadness associated with the extinction of a species, especially ones which have such an important ecological role, as well as worldwide recognition and popular appeal, is a sadness largely associated with the regret of not saving a species which the opportunity is present. We, as a species, as doing a fair amount to save the world’s remaining rhinoceros populations, but we truly need to do more if we wish to truly save these animals. Of course, as any biologist will tell you,  there are a myriad of species out there which are much smaller or lesser known than any rhinoceros species and which require much more of our attention. But no species deserves to be loosed to the whims of extinction in a rapidly changing world.

The fate of rhinoceros populations worldwide lies in our hands.

When the first historical anthropogenic extinctions occurred, the very notion of extinction was an alien thought. The fact that an entire species could be wiped out was beyond comprehension in a world in which an almighty power had personally created each and every species. By the time scientific minds had pieced together why, for example, no one had seen a dodo in years, it was far too late to do anything about it. When concern began over the fate of the western black rhinoceros, it was likewise already too late. An aerial survey tallied just 10 remaining individuals in northern Cameroon, and the odds of those individuals finding one another and breeding the population back into health were infinitesimally small. It is frustrating to admit when something natural is beyond any help, but, with our potential and the resources available to us, this does not have to be the only option. We can still work to save the world’s rhino species, and if we are truly concerned for their well-being, there is nothing to stop us from protecting them.

The earth is a cruel place, and all species eventually go extinct. What separates us, now in the 21^st century, from those Portuguese and Dutch explorers who killed and ate all that they discovered, is that we have the awareness and the power to change the destiny of another species. Now, more than ever, we need to realize this potential and be responsible for the planet we are dismantling. What happened to the western black rhino is a reason to pity, but more than anything it is a reason to take action.

To find out more about rhinoceros conservation and how we can all help, visit these pages:

https://www.rhinos.org/

http://www.savetherhino.org/

John R. Platt wrote a very detailed synopsis of the history of the western black rhinoceros, including its extinction. Check it out here:

http://blogs.scientificamerican.com/extinction-countdown/2013/11/13/western-black-rhino-extinct/

Game of Bones: Erratum

Upon sharing yesterday's post to Facebook, Dr. Thomas Holtz mentioned something important which I completely didn't realize. Triceratops and Torosaurus were not just "floating heads." This is, of course, obviously true, but represents a side of the debate unexamined in Longrich & Field (2013). In order to truly determine whether the two warrant their own respective genera can only be determined once the postcranial elements of both are examined.

Tyrannosaurus asks Torosaurus if he is, after all, a valid genus. By the great Luis V. Rey.

This is tricky because, well, we don't really have too many postcranial Torosaurus fossils. That's why the study focused entirely on the skull. If more Torosaurus bodies were known, the debate would probably never have arisen; indeed, the fact that such few bodies are recovered is part of the mystery of the animal in the first place. But, as any paleontologist can tell you, fossilization relies on very precise conditions, and even though we know a huge amount about the world of the past, there is much that we will never know.

Let's hope one that one day the debate can really come to an end. As of right now, although it seems likely that Torosaurus is not Triceratops, and while the evidence is present, the case is not closed just yet.

In Montana, it rains sheep and cougars

Scenes of intense predatory action are commonplace in nature documentaries. The poise, grace, and stealth of apex predators is unparalleled, and we are all captivated by such incredible feats of athleticism in the natural world.

Well, even top predators manage to botch things once in a while.

In Glacier National Park, a photographer (anyone know who?) spotted two bodies lying on a closed road. Not human bodies, thankfully, but the bodies of a predator and its prey that both met their demise in the heat of pursuit. The bodies were of a Dall sheep Ovis dalli and a cougar (mountain lion, puma, panther, what-have-you) Puma concolor. 

Lying at the bottom of a sheer cliff, the bodies not only tell of an incredible and clearly lethal fall, but of just how hard the two animals fell. The sheath of the sheep's horn came clean off upon impact (seen above, left), and its hind right leg had a severe compound fracture.

Interestingly enough, it doesn't seem like the cat was too far off from getting a nice mutton meal before the two met their untimely departure: the cougar died with a tuft of the sheep's fur in its mouth!

In the wild, slight miscalculations of distance or steepness, bad weather, and plain old bad timing can lead to terrible consequences. No animal is perfect at what it does. There is no species which kills 100% of the prey it intends to, and many risk death in the pursuit of one meal. And this doesn't just apply to today's animals; we have many instances of accidental death in the fossil record as well. Perhaps, if the conditions were right, the sheep and the cougar would form a fossil just like this...

For more photos of this scene, click here. Some of the photos are pretty gruesome, so proceed at your own discretion.

Game of Bones: The true identities of America's last ceratopsians

While we can learn a lot from fossils, there is still much we cannot determine just by examining petrified bones, feathers, and other structures. For one, it is difficult to determine whether or not a specimen represents an already-known species or is an entirely new one. This phenomenon occurs more often than one would think, and many extinct genera have a score of junior synonyms which were once considered to be different species. These often turn out just to be juveniles of already-known species, or display some pathology which had rendered them to appear different from the rest of their kind.

Of course, all adult animals known from fossils had to start somewhere – obviously, we have fossils of various dinosaurs ranging in age from embryonic to adult-most forms. Our knowledge of the ontogeny of dinosaurs ranges from species to species – in the case of some, such as Allosaurus and Maiasaura, we have records of complete life histories. In other species, juveniles can often be reassigned as other species or genera simply due to a lack of information on the species as a whole.

The two three-horned titans in question: Triceratops (left) and Torosaurus (right). Illustration by Nicholas Longrich.

One such ontogenetic debate originated last year concerning one of America’s fossilized sweethearts – none other than the three-horned darling that is Triceratops. Fossilized remains of Triceratops are abundant in the American west and are known from young individuals to adults. However, Triceratops wasn’t the only three-horned beast roaming North America at the end of the Cretaceous. Torosaurus,  a closely-related chasmosaurine, has been found alongside Triceratops from Colorado to Montana. However, unlike the remarkably complete life history we have of Triceratops, Torosaurusfossils are largely adult specimens.

Triceratops growth series by Gregory S. Paul. The bottom-most skull, and those
at right, represent Torosaurus. This series represents the logic of Horner et. al (2010).

The absence of young Torosaurus in the fossil record led Jack Horner et. al (2010) to believe that Torosaurus is not its own species, rather it represents the most mature specimens of Triceratops. It makes sense at first: we know animals get larger and, in some cases, more impressive as they age, and Torosaurus’ massive head and elongated frill are much more spectacular than the shorter, square frill of Triceratops. However, size and exaggeration of features do not necessarily contribute to the maturity of any given specimen, and this determination is even harder to make when all we have to work with are fossils.

When news broke that the world may lose Triceratops to cladistic lumping, a panic spread: what would we do without everyone’s favorite three-horn? How would museums cope with the innumerable info-graphics which would need to be reprinted? And the children… How would our children grow up in a world in which Triceratops was no longer a valid genus?

Thankfully, there is no need to worry. First of all, Triceratops was named in 1889, whereas Torosaurus was named in 1891, giving our herbivorous hero precedent over the long-frilled foe. Second of all, a paper has finally been published which puts this whole debate to rest. Well-known specimens of both genera were compared and analyzed, put through a gauntlet of 24 visibly-testable features which diagnose the chasmosaurines as juveniles or more mature specimens.

Testing such features as the curvature of the postorbital horns, the degree of scalloping of the parietals (bumps around the edge of the frill) and squamosals (pointed cheek bones), and the fusion of major bones of the skull allowed Nicholas Longrich and Daniel Field (2013) to put an end to this long-winded argument.  A total of 36 specimens from both genera were analyzed for the test.

Comparative ages and diagnostic features of the ontogenetic stages of Triceratops and Torosaurus. From
Longrich & Field, 2013.

When Horner cited Torosaurus as being just a mature Triceratops, he cited the fact that no juvenile specimens of the former have been discovered, whereas many young Triceratops have been discovered. Longrich and Field discovered that, while the overwhelming majority of Torosaurus specimens are, in fact, adults, at least one specimen represents a slightly younger animal, which instantly puts a hole in Horner’s logic. If young Torosaurus did exist, displaying ontogenetic characteristics diagnostic of a young animal far different from adult Triceratops, then it is impossible for the latter to be a “stepping stone” to the former. So, in your FACE, Horner! Torosaurus juveniles DO exist! Which means…

"And you read this in my voice!"

But, in all seriousness, both genera are valid. While they are both extremely similar in body-shape and lifestyle, they represent two different animals. And I’m sure Tyrannosaurus thought they tasted the same anyway.

A similar story of mistaken identity occurred between these three sympatric pachycephalosaurs. From left
to right, the specimens range from young to old.

Horner has proposed this lumping before with other species; coincidentally (or not), they all hail from about the same time and place. Besides Triceratops/Torosaurus, he is a strong proponent of Nanotyrannus representing a juvenile Tyrannosaurus, which has also recently been tested and supported. More closely related to the horned creatures in question, he has also suggested that the pachycephalosaurids Dracorex, Stygimoloch, and Pachycephalosaurus also represent three ontogenetic stages in the life of the lattermost species. I’m a bit hesitant to accept that Stygimoloch represents an intermediate between the other two, partially because I grew up with ol’ Styg as one of my favorite dinosaurs. Plus, the name is just awesome: Stygimoloch translates to “devil of the River Styx.”

I think we can all rest a bit easier tonight knowing that Longrich and Field have put an end to the attempted assassination of Triceratops as a genus. I know I can, anyway. 

Turn To Stone (on Lake Natron)

Lake Natron, in northern Tanzania, is an alkaline lake whose water has the pH of household ammonia. The water temperature can reach well above 100 degrees Fahrenheit, and supports only those species which are evolved enough to handle such a deadly environment. If there was ever a little slice of Hell on Earth, Lake Natron would be a contender.

A calcified African fish eagle Haliaeetus vocifer perches
above deadly Lake Natron. Photograph by Nick Brandt.

The water is so deadly to those not used to it that anything that merely touches it is calcified. Photographer Nick Brandt captured several spectacular shots of several calcified creatures who fell victim to the illusion of a crystalline, placid lake, only to emerge from the water and become preserved in stone.

A whydah Vidula sp.

When islands form on the caustic lake, they attract scores of both lesser and greater flamingos. The flamingos take advantage of the disappearing islands, constructing their mud-tower nests and breeding, all the while feeding on invertebrates in the more saline areas of the lake. However, like bathers on a shark-infested beach, even these seasonal visitors sometimes fall victim to the deadly water.

Even seasonal visitors, such as this lesser flamingo Phoenicopterus minor, still fall victim to the caustic water. Photograph by Nick Brandt.