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/