Saturday, March 30, 2013

Butch Quetzidy and the Sundance 'Chid

One of my lifelong fantasies is to live in that bygone age of rough-riders, rustlers, rangers, and outlaws in the rootin', tootin' Wild West. I don't know why, I would just love to be part of that era, settling the wild frontier and living the rough-and-tumble life of a cowboy.

So, if I had the opportunity to merge this idea with, say, giant pterosaurs, I would be so much happier. Last year, Mark Witton described what life would be like if we had pterosaurs around, and this particular illustration caught my eye...

YEEEEEEEEEEEEEEEEEEEEEEEE-HAWWWW! Illustration by Mark Witton, from Zazzle (hence the watermark).
Ah, just picture it: swaggering out a dusty saloon, spurs jangling, with a big ol' cowboy hat, boots, and a classy little bolo tie. The Arizona air is hot and dry, the sun beating down as tumbleweeds roll past. And, as the wailing theme to "The Good, The Bad, and The Ugly" starts to play, you hop on your twenty-foot-tall Quetzalcoatlus and, with one swift motion, you're soaring effortlessly above the badlands into the sunset.

Thursday, March 28, 2013

Actual living dinosaurs (for real!)

Nothing grinds my gears more than when people call an animal a living dinosaur when it isn't actually a living dinosaur. Thanks to a little thing called science, we actually do have living dinosaurs today, for real, no jokes. You just have to realize that something doesn't need to be all toothy or scary (or scaly) in order to be a dinosaur.

The foot of a red-legged seriema. Notice the claw on the second toe... Kinda reminds you of something, doesn't it?
If you truly want a glimpse back in time, just check out big birds hunting small animals. It's a rip-roaring good time if you like birds, and if you're a fan of their prey, then it's horribly gruesome and you probably shouldn't watch these videos. These videos do contain some graphic scenes, so if you're not the type who enjoys seeing disemboweled snakes or fish or voles, then you should probably just wait for the next post, which won't be so violent.

First up, we have the southern ground-hornbill, one of my all-time favorite birds. These huge, black birds have bright red wattles on their faced, huge pincer beaks, and, you've got to admit, beautiful eyes. They spend their days stalking the African savannahs in search of small prey, which they make short work of with their powerful bills. They recall an age when dromaeosaurs were doing the exact same thing, without the grass, across the Cretaceous globe.

This next video is really, really, cool, and I say that from a completely biased point of view. I freaking love herons, especially the great blue. They're common around my house, and every summer I make sure to keep my eye out for them on the local lake. While they are perfectly adapted for patient fishing, they are no less proficient on land, as you can see in this video. I love the way it hunts on land, the way it so fluidly goes from walking to crouched into an attack position. It launches its bill forward like a lance; even if it's a slender bird, I would not want to be faced with that weapon. I'm sure such graceful, stealthy hunting styles were common to see in ancient Hell Creek, where Tyrannosaurus and Quetzalcoatlus (okay, not a dinosaur, but still) were apex predators.

How could I close with anything but this guy? That's right... It's everyone's favorite not-pelican, the shoebill! Now, I still have an entire post about these guys that I need to publish still, but I figured I would give you all a nice little tidbit so you can all see how the bird looks in its element. You can really see in this video that, even though it lacks the spearlike build of a heron, it is no less efficient at subduing its prey. Its relatively short, powerful neck makes quick work of a lungfish in this video. The nail-like projection at the end of its bill really comes in handy when grappling with such slimy prey. I'm sure many theropods utilized this full-bodied launch to subdue similar prey on land, throwing themselves are their prey and grappling it with tooth and claw.

We have to realize that dinosaurs were not like Godzilla or anything from Jurassic Park. Just because our favorite dinosaurs are becoming increasingly covered in feathers, or displaying parenting behavior, or not being savage monsters does not mean that they were any less intimidating or powerful.

Sunday, March 24, 2013

Jurassic Park 4: This time, still without feathers

Ever since news came to light that Jurassic Park 4 (IV?) director Colin Treverrow is following the franchise's decision to leave their dromaeosaurs bald, the paleocommunity has been all abuzz with dissatisfaction. It was theorized that dromaeosaurs had feathers even before the release of the first movie, so making three sequels all featuring unfeathered 'raptors' doesn't make the least bit of sense.

For some reason, people just don't like seeing dinosaurs covered in feathers. Look, it's not like the animals were tarred and feathered. It's not an evolutionary punishment. Feathers are the most advanced and complex body covering found in any family, much more diverse and extraordinary than mammalian hair or reptilian scales. Apparently, there are people out there who think that feathered dinosaurs are "lame." If anything, feathers make dinosaurs even more awesome. They do not take away from the fierceness of the species they cover; we don't think that our national symbol, the bald eagle, is any less intimidating because it has feathers. Just because a three-meter-long, sharp-toothed, dangerously-clawed Velociraptor Deinonychus Utahraptor whatever-the-hell-it-is is covered in feathers does not take away from its awesomeness.

The classic Jurassic Park "raptor." Clearly not a Velociraptor. Notice the impossibly-positioned wrists and the complete lack of feathers.
Of course, the JP dinosaurs are genetically modified and cloned and what-have-you, and we're all aware that Jurassic Park is not a documentary. However, it must be made known that dinosaurs had feathers, and there's nothing we can do about it. Even good ol' Tyrannosaurus was probably feathered. I certainly think it was.

Despite its inaccuracies, Jurassic Park was an inspiration to an entire generation of paleo-enthusiasts and paleontologists alike. Ever since dinosaurs made their debut on the silver screen as living, breathing, active animals, a slew of documentaries have been released, exposing the truth about the past maters of the earth. From top-of-the-line graphics to low-budget stop-motion, dinosaur documentaries have picked up the slack that JP left, in terms of accuracy. Documentaries, magazines, and books have set the record straight, and now, more than ever, these resources are available to dino-fans of all ages.

An accurate depiction of Velociraptor. Reconstruction by John Conway.
These resources rid me of any fear for upcoming generations. I do not think that any children who go see JP4 will leave the theaters convinced that dinosaurs stomped around with bunny hands, naked as unfeathered jay birds. They will leave with the image of pop culture's vision of dinosaurs, but they will already know, no matter how young, that real dinosaurs behaved, and looked, much different. Those who wish to believe that dinosaurs are better off bald will continue to do so, though those who know the fossils and the facts will always be around to set them straight.

Thursday, March 21, 2013

Why Dinosaur Planet is my favorite dinosaur documentary thus far

Dinosaur documentaries are the spice of life. I always make sure I'm on top of any scrap of gossip that turns up about new documentaries, what new behavior or species they will show, and who will be the paleontological masterminds behind it. They're just so enjoyable, even the downright horrible ones. If I'm not thoroughly impressed by a documentary, at the very least I need to keep watching to point out inaccuracies. It goes with the paleonerd territory.

Of course, before I delve into my personal favorite dinodoc, I have to pay a little homage to the father of them all, the series that opened an entirely new world of possibilities for recreating the lost worlds of all manner of prehistoric animals. I'm writing, of course, of none other than BBC's Walking With Dinosaurs. This documentary was a total game-changer: not only did it bring accurate dinosaurs to life, but it brought us right into the middle of their world. WWD brought dinosaurs from a legendary, bygone era and portrayed them as they actually were: living animals, surviving as animals do today, playing, hunting, being hunted, courting, mating, calling, laying eggs, urinating and defecating.

Since WWD was released, a number of documentaries have sought to follow in its wake, some with much more success than others. If you asked a pretty standard group of paleo-fans to list their top five dinodocs, I'm pretty sure my favorite would fall in there somewhere. My personal favorite happens to be a four-part series from the Discovery Channel, creatively enough titled Dinosaur Planet*.

*Not to be confused with the equally creatively-titled 2011 BBC documentary, Planet Dinosaur.

Dinosaur Planet was probably the first dinodoc to go beyond just depicting dinosaurs in a natural setting. Each of DP's (if that's an appropriate abbreviation) four episodes stars not just any old dinosaur, but a character. The stars and their representative locations include White Tip, a Velociraptor from Mongolia; Pod, a Pyroraptor from Romania; Little Das, a Daspletosaurus from the United States; and Alpha, a Saltasaurus from Argentina. All of the episodes take place roughly 80Ma, which is another big selling point for me. Perhaps you'll find out in another post why from about 80-70Ma was my favorite time.

Daspletosaurus from "Little Das' Hunt".
Before we get into why I really like it, I can't neglect the visuals of the series. Dinosaur Planet really sticks out in my mind as being the first documentary to give feathers to all species which were proven to have them. All the maniraptors had very realistic plumage, though there weren't enough wing feathers for my taste. However, this was still very early in pop culture's acceptance of fully-feathered dinosaurs, so I can cut some slack. Apart from this major change in dinodoc tradition, DP also succeeded in portraying dinosaurs as living, breathing, active, intelligent, and surprising animals, more than just reptiles. The series features nest-building, parental care, courtship displays, and, surprisingly, a fair share of nonviolent interspecies interaction. Yes, predators do walk past prey without tearing them to shreds.

When watching any good nature documentary, personification is a no-no. But there are documentaries about a number of different extant animals which focus on a specific group, or a well-documented and observed individual. It is in this light that I view DP. Rather than personifying the dinosaurs, this documentary follows the trials and tribulations of each one as they are forced into completely new situations. In each, a life-changing event happens to the main character, making them to do what dinosaurs have proven to do best: adapt!

Einiosaurus form a protective ring around their young in defense against a pack (yesss!!) of Daspletosaurus. The main character, Little Das, can be seen at the far right of the screen.

That's what makes Dinosaur Planet so great. We're not watching a bunch of scattered scenes from one general area, we are focusing intently and following the struggle of a young Daspletosaurus learning how to cooperatively hunt with its sisters and mother; we experience the hardships of a mother Velociraptor searching for food for her chicks in the parched prehistoric Gobi Desert; we follow the entire life of a female Saltasaurus, from her hatching to the first clutch of eggs she lays herself.

White Tip, a female Velociraptor. The landscapes in Dinosaur Planet are beautiful, even if a few of them have grass.
You may be thinking to yourselves, "Wow! This guy sure is a Dinosaur Planet fanatic. Apparently there is nothing wrong whatsoever with this dinodoc!" Oh-ho-ho, not so fast. No dinosaur documentary yet has made me entirely happy. DP has its fair share of things that bug me.

First of all, humans make an appearance in it. Granted, it is paleontologist Dr. Scott Sampson, currently curator of the Utah Museum of Natural History. Sampson makes his appearances describing little snippets of information revealing new theories or fossils which shed a brand new light on dinosaur ecology and behavior. He's a brilliant man, and has done extensive research on the late Cretaceous in general, making him perfect for this series. He's not the narrator, though; that'd be Christian Slater, strangely enough. I dunno, I just never pegged him for the kind of person who would agree to narrate a dinodoc*.

Scientifically, the series has a couple of problems which aren't immediately obvious. Firstly, there is GRASS. See, I bolded and underlined that word to make sure you caught it. One of the most interesting things about the Mesozoic was that so many herbivores evolved in the complete absence of grass, the basic sustenance for most of Earth's herbivores today. Grass makes its appearance in all but one of the episodes of Dinosaur Planet and, of course, the only episode which lacks it is set in a bone-dry desert. The landscapes are still beautiful, there's no doubt about that. They just didn't limit themselves to filming locations which also lacked grass, as WWD did.

A pair of Oviraptor from the episode "White Tip's Journey." Although a bit drab, the DP Oviraptors are my favorite depictions of these animals on the big screen. And look, they don't even have pronated wrists in this scene!
Secondly, a few of the dinosaurs have bunny hands. Bipedal dinosaurs, as well as an increasingly large number of quadrupedal ones, could not pronate their wrists. Their skeletons just did not operate the same way ours do. When we pretend to be dinosaurs (heh... we all do, right?), our hands should be in a clapping position, not a waving one. I'm willing to group this inaccuracy with the lack of arm feathers on maniraptors; it was an air on the side of caution for those who didn't want to see their precious "raptors" turned into what they truly are: flightless birds (in a sense).

So, there you have it. My favorite dinosaur documentary in a nutshell. Notice I didn't go through episode by episode and describe each one to you: yeah, that's right, 'cause I want all of you to go watch it for yourselves. You owe it to this blog! Go do it!

*My favorite dinodoc narrator, by the way, is John Goodman in When Dinosaurs Roamed America.

Monday, March 18, 2013

Birds: putting all their eggs in one "basket" for 120 million years

Boy, was this week good for those interested in bird evolution!

Like placental mammals, non-avian dinosaurs had two ovaries. Well, the females did, at least. Each of these ovaries was capable of producing a single egg independently, meaning mother dinosaurs could lay two eggs at a time. This interesting feature, laying eggs in pairs, is known as monoautochronic ovideposition (Grellet-Tinner et. al, 2006), and, interestingly enough, birds are incapable of this, having only one ovary.

The oviraptorosaur Citipati has provided much information on brooding and nesting behavior. Image D shows two eggs in typical monoautochronic position, as they would have been laid. From Grellet-Tiner et. al, 2006.
The evolution of the single ovary in birds is a very interesting, and oft overlooked, adaptation on the runway to flight. Having two ovaries is fine enough if you're a ground-dweller, but if you're a flying bird, the more weight you can lose, the better. It turns out that this feature has been present in avians long before modern birds made the scene. In a new study by the great Zhonge Zhou, two enantiornithes and a specimen of Jeholornis, one of the largest Mesozoic birds, were all found to have a single ovary (Zhou et. al, 2013).

Fossilized ovaries in a Cretaceous bird. From Zhou et. al, 2013.
Not only was it determined that these specimens had a single ovary, but each ovary contained ovarian follicles - structures within the ovary which hold developing eggs. These females were going to lay their eggs very soon! By counting the follicles, the clutch size of each of the specimens was determined - the largest clutch contained 20 eggs, much more than any modern bird is capable of producing. Another interesting discovery was that these specimens were not skeletally mature yet - their skeletons still contained some unfused bones, indicating they had not stopped growing yet.

This raises a few questions. If these birds already had a single ovary, characteristic of modern birds, why were they producing a greater number of smaller eggs at a younger age, a characeristic of non-avian dinosaurs? Clearly, they were not entirely like modern birds yet, still retaining some features present in non-avian coelurosaurs. The answer lies in the metabolism of these animals. Flight requires a huge amount of energy, and as birds evolved to be the masters of the air, they could expend much more energy on other functions, such as reproduction. As these birds were not expert fliers, and were still very early in their evolution, their metabolism reflected that of other non-avians.

The fossilization of internal organs is a rare and amazing phenomenon. In some cases, oddly-shaped rocks are confused for organs; in other cases, it's definitive that something soft was preserved. Because this is so rare, I was a bit unsure to accept the fact that these fossils truly showed ovaries; I assumed that they were gastroliths, which are known in many avian and non-avian dinosaurs, or possibly seeds, which have been found in the fossilized crop of a Sapeornis. Zhou and his colleagues also considered that the fossils may show stones or seeds, but their placement, size, and shape, convinced them otherwise.

Jeholornis sported teeth, clawed hands, and a long, bony tail, but that doesn't make it a lizard. Reconstruction by Matt Martyniuk.

Considering that enantiornithes had clawed hands and Jeholornis sported a long, bony tail and small teeth, it is amazing that they had a feature which is so commonly associated with modern birds. The days of envisioning Mesozoic birds as half-bird/half-lizard monstrosities are long behind us; we have to accept that birds were well on their way to their modern appearance even 120 million years ago.

Grellet-Tinner, Gerald, Luis Chiappe, Mark Norell, and David Bottjer. 2006. “Dinosaur Eggs and Nesting Behaviors: A Paleobiological Investigation.” Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2–4) (March 22): 294–321. doi:10.1016/j.palaeo.2005.10.029.

Switek, Brian. 2013. “Exquisite Bird Fossils Reveal Egg-producing Ovary.” Nature (March 17). doi:10.1038/nature.2013.12616.

Sunday, March 17, 2013

King Whale-head, Part III

Despite its solitary and quiet lifestyle, the shoebill prefers flat, open areas of wetland, rather than papyrus-choked waterways or covered areas. Any foliage overhead would cause major problems when the shoebill takes off.  Their preferred habitat is wetland with a majority of papyrus, though it avoids all-papyrus wetlands. They are often found perched on floating vegetation near wide waterways. But in stagnant water, there is no current to shape these channels, which criss-cross wetlands of floating plants like city streets.

Typical shoebill turf. Photograph by Jnissa, from Flickr.
These waterways are not formed by currents; rather, they are basically plowed clear by the movement of large wetlands-dwelling mammals. In Africa, this means the elephant and the hippopotamus. The wanderings of these behemoths create the perfect fishing spots for shoebills, and the stirrings of these mammals also causes creatures to rise to the surface.

The shoebill, in turn, doesn’t reciprocate the favor. The hippos and elephants aren’t exactly aware that they’re creating shoebill habitat, and the shoebills don’t have much in their biology to return. It’s a bit of commensalism in action. Though their feeding is greatly benefited by the movement of large mammals, their breeding behavior is very private.

The nest of the shoebill is something I would love to see for myself: a 3m (~10ft) wide mat of floating vegetation amidst isolated tall grasses and sedges. Although the nest is extremely wide, it apparently does not support the weight of a human, which is good, because we don’t need to be living on shoebill nests. The chicks do not hatch with the characteristic bill of their parents; this only begins to grow rapidly after a month. Although up to three eggs are laid, only one chick will survive to leave the nest.
A shoebill feeding its chick. The chick's bill has yet to grow to such ridiculous proportions.
It is the strongest, usually the first-born, is the one who usually lives to maturity: they will bully the other chicks, steal food, and even push them out of the nest. This trend of extreme sibling rivalry can be found in other species of birds as well. While it may seem cruel to us, it ensures that the one chick who survives is the genetically fittest to sire the next generation.
A fledgling shoebill. Judging by that crazed look on its face, I'd say it just committed fratricide. 
We may think that Mommy and Daddy Shoebill are uncaring parents for allowing this to happen. Quite the contrary; they are dedicated parents, and even fill their bills with water to bring to their chicks when the sun is beating down.
A shoebill brings water to its young chick, and apparently misses its target.
The shoebill is a charismatic and incredibly unique bird, and one that should be protected and treasured as much as possible. It is truly an evolutionary oddity, arising mysteriously somewhere in the depths of time, and it has filled such a specific niche that it has, apparently, changed very little in millions of years. They are behaviorally very curious, very caring, and I believe that they will never cease to amaze ornithologists across the globe.

A shoebill towers over all other birds in its habitat. Photograph by Stttijn, from Flickr.

Friday, March 15, 2013

From biplanes to jets: the evolution of bird wings

When the diminuitive gliding microraptorine Microraptor was described, it was an oddity: it sported two winged arms, which was becoming more and more acceptable for non-avian dinosaurs, as well as two winged legs.

The biplane-maniraptor: four-winged Microraptor gui. Photograph courtesy of NOVA.
More recently, several other genera have been found with well-developed leg wings, as well as winged arms. But what use do wings on your legs serve? The nature of these wings, absent in any feathered flyer today, was debated and argued over for many years; it is now accepted that these wings provided their owners with stability and increased maneuverability while gliding from tree to tree.

The discovery of winged legs has fueled the debate as to whether avian flight evolved from the ground up, or from the trees down. The issue is not so cut-and-dry as one might expect, though with more and more fossil evidence, we are discovering more clues as to how flight first evolved among dinosaurs. I support the theory that, while wings evolved from the ground up, the power of flight originated in the trees. Thor Hanson's Feathers provides a great, comprehensive chapter on the entire argument of wings, flight, and this argument.

Wings evolved in many flightless families, and had (and have) many functions besides flight. From Heers & Dial, 2012.
As always, beautifully preserved Chinese fossils reveal that these leg wings were relatively commonplace among gliding maniraptors, though they had never been found in birds. That is, up until now. A review of basal avialian fossils from China reveal that a number of early Cretaceous species sported largely reduced leg feathers, revealing some interesting details about the evolution of flight (Zheng et. al, 2013).

Sapeornis chaoyangensis, an avialian from Yixian and Jiufotang Formations of China. The greatly-reduced leg feathers can been seen around its ankles. Photograph courtesy of Science/AAAS.
Because the leg feathers of these specimens are so reduced, clearly they had to start in a much more developed state. It appears that birds, too, utilized the biplane method of locomotion in their earliest days: as they evolved from gliders to true flyers, these leg wings became more of a hindrance, and slowly they began to evolve smaller and smaller feathers. As the winged arms of these early birds became more and more advanced, slowly losing their claws, becoming more and more aerodynamic, and containing the characteristic powerful muscles needed for flight, the feathers on the legs became smaller and smaller.

Clearly, birds didn't just do away with maneuverability. Birds have mastered the art of flying more than any other animal, and can turn on a dime even in midair. What, then are they utilizing instead of these leg feathers in order to maintain, and improve, their aerial acrobatics?

The remiges (flight feathers on the arm) and rectrices (flight feathers on the tail)
of a Cape May warbler. Photograph by Christopher Hansen.
While we commonly associate flight feathers with wings, these same feathers can be found in the tails of many birds. These feathers, called rectrices (singular: rectrix), allow birds to brake and steer while flying. Perhaps, as the leg feathers of early birds became more and more reduced, their tails became more advanced, providing them with a more aerodynamic, yet still very effective, way to control their flight.

Whether or not the evolution of the modern avialian tail caused, or was caused by, the loss of leg feathers remains to be seen, but I believe this it to be a valid hypothesis. Perhaps a future review of avialian fossils will reveal more crucial clues about the evolution of tails, which, so far as I have seen, have been largely overlooked when discussing the evolution of flight.


Sheridan, Kerry. “Early Birds Had Four Wings, Not Two, Study Reports.” 2013. Accessed March 15.

Zheng, Xiaoting, Zhonghe Zhou, Xiaoli Wang, Fucheng Zhang, Xiaomei Zhang, Yan Wang, Guangjin Wei, Shuo Wang, and Xing Xu. 2013. “Hind Wings in Basal Birds and the Evolution of Leg Feathers.” Science 339 (6125) (March 15): 1309–1312. doi:10.1126/science.1228753.

For more about dinosaurs with leg feathers, see:

Thursday, March 14, 2013

Why... Why couldn't they have chosen somewhere boring?

Those who have met me know that I spent a year between high school and college on foreign exchange in Brazil. I fell in love with the country, the wonderful culture, the always-friendly and helpful people, the tropical weather, the beautiful beaches... Just about everything, really, and more. That's why, from May 23-26, I'm going to be sitting in a corner, crying, wishing I was there again. Why, you ask?

That's because the International Symposium of Pterosaurs is then meeting in Rio de Janiero. It's everything I could ever want: it's pterosaurs. It's Brazil. One of the images on the site is a Tupuxuara sporting a Brazilian-flag-themed crest, for crying out loud. It's just... Too perfect!

Unfortunately, money for me is about as abundant as pterosaurs are. Hopefully, some day I'll be able to attend this pterosaur symposium, when I'm an actual professional. A man can dream of flying reptiles, can't he?

John Conway's Tupuxuara with a crest that is all too familiar to me.

Thursday, March 7, 2013

What’s big, aquatic, warm-blooded, and has rubbery skin? Why, the leatherback sea turtle, of course.

If there was ever a turtle that wanted to be a whale, it would have to be the leatherback turtle. They are gigantic, the largest turtles in the world and the fourth-largest reptile; they are deep-diving and can be found worldwide in virtually every climate; they go on tremendous migrations both to breed and feed; they even have oily, smooth skin in place of a hard shell.

That doesn’t sound like any sea turtles we’re so familiar with, does it? Where did such an offshoot from the “typical” sea turtles come from? It’s not so much that the leatherback is an offshoot from modern turtles; rather, leatherbacks represent a lineage of turtles which were once abundant in prehistoric shallow seas. Close relations to the leatherback include the “ruling turtle” Archelon, which grew to lengths of 4m (13ft) and sported a flipper-span of 5m (16ft). Sadly, the leatherback’s closest relatives are all extinct; other extant sea turtles belong to an entirely different family.

The turtle that wanted to be a whale. Photograph from Projeto TAMAR, IBAMA's sea turtle conservation program.
The family Dermochelyidae, of which the leatherback is the sole living member, has likely been around since the Cretaceous. As such, the family as a whole has had an incredibly long time to adapt to an oceanic lifestyle. The leatherback’s adaptations for living in the open ocean are remarkable, especially for a reptile. Most notably, the leatherback, as its name suggests, completely lacks a shell. Rather, its thick, oily, rubbery skin is embedded with tiny osteoderms. These little bumps in its back form distinct ridges, which give the appearance of a shell; however, skeletally, they appear much like other tetrapods: their ribs and vertebrae are still able to move freely, unlike other turtles in which these bones are fused to the shell.

The leatherback can be found worldwide, from the Arctic Circle to south of New Zealand. They are impressive divers, sometimes submerging over 900m and staying underwater for up to 80 minutes in pursuit of jellyfish, the main staple of their diet. (Sale et. al, 2006) Clearly, they have very different feeding strategies than other sea turtles, which mostly feed on foliage in tropical and subtropical waters. The leatherback’s feeding strategy and range expose it to waters just shy of freezing; one individual was recorded as diving to 61m and experiencing 0.4oC (~33oF) water. (James et. al, 2006) Such temperatures pose a huge threat to the physical health of any normal reptile. But, as we have seen, the leatherback is anything but a normal reptile.

No, the leatherback is something truly special. While most reptiles depend on the temperature of their environment to regulate their body temperature, the leatherback has much more control over its body. They have two distinct layers of fat which insulate its body, a trait found in many cold-dwelling mammals, as well as some open-water fish. (Goff & Stenson, 1988) Under their fat, they have an even more remarkable adaptation for surviving in cold waters. The muscles used in swimming operate completely dependent of temperature. Generally, reptiles require heat in order to keep their metabolism up and, in turn, move around. However, the pectoral muscles of the leatherback were found to operate totally independent of temperatures ranging from 5-38oC (~41-100oF). Interestingly, while the leatherback’s muscles showed higher rates of metabolism at lower temperatures when compared to other sea turtles, they also displayed lower rates of metabolism at higher temperatures. (Penick et. al, 1998) This could mean that they are not only well-adapted to cold water, but in fact, they survive much better in such conditions.

Photograph from Projeto TAMAR.
One surprising part of the leatherback’s body contributes a great deal to thermoregulation: its throat. While leatherback hatchlings have typical reptilian tracheae, composed of rings connected by connective tissue, adults have, in essence, one long, elliptical tube containing plates of cartilage. These plates can close when the turtle dives, eliminating problems faced by all deep-diving animals when venturing far below the surface. When making such dives, the lungs and main airways face the danger of collapsing under the immense water pressure to which the animal is exposed.  The adult leatherback’s trachea is also lined with a network of blood vessels; any air caught in the lungs or trachea is warmed by these vessels, allowing the turtle to breath comfortable, humid air even in frigid environments. (Davenport et. al, 2009)

I hope you can tell why I’m suddenly so fascinated by this turtle. They’re more than just your average sea turtle: their adaptations go above and beyond those of other sea turtles. They aren’t just well-adapted for a life at sea, they’re pretty much perfect for it. Sadly, these giants are critically endangered and face a number of threats, including pollution. We’ll discuss more about the feeding habits and endangerment of the great leatherback in the next post.

Davenport, John, John Fraher, Ed Fitzgerald, Patrick McLaughlin, Tom Doyle, Luke Harman, Tracy Cuffe, and Peter Dockery. 2009. “Ontogenetic Changes in Tracheal Structure Facilitate Deep Dives and Cold Water Foraging in Adult Leatherback Sea Turtles.” Journal of Experimental Biology 212 (21) (November 1): 3440–3447. doi:10.1242/jeb.034991.

Goff, Gregory P., and Garry B. Stenson. 1988. “Brown Adipose Tissue in Leatherback Sea Turtles: A Thermogenic Organ in an Endothermic Reptile?” Copeia 1988 (4) (December 28): 1071–1075. doi:10.2307/1445737.

James, Michael C., John Davenport, and Graeme C. Hays. 2006. “Expanded Thermal Niche for a Diving Vertebrate: A Leatherback Turtle Diving into Near-freezing Water.” Journal of Experimental Marine Biology and Ecology 335 (2) (August 8): 221–226. doi:10.1016/j.jembe.2006.03.013.

Penick, David N., James R. Spotila, Michael P. O’Connor, Anthony C. Steyermark, Robert H. George, Christopher J. Salice, and Frank V. Paladino. 1998. “Thermal Independence of Muscle Tissue Metabolism in the Leatherback Turtle, Dermochelys coriacea.” Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 120 (3) (July 1): 399–403. doi:10.1016/S1095-6433(98)00024-5.

Sale, Alessandro, Paolo Luschi, Resi Mencacci, Paolo Lambardi, George R. Hughes, Graeme C. Hays, Silvano Benvenuti, and Floriano Papi. 2006. “Long-term Monitoring of Leatherback Turtle Diving Behaviour During Oceanic Movements.” Journal of Experimental Marine Biology and Ecology 328 (2) (January 24): 197–210. doi:10.1016/j.jembe.2005.07.006.

Saturday, March 2, 2013

We Are the Whorled

Helicoprion was one of a myriad of bizarre cartilaginous fish which swam the earth’s oceans from the late Carboniferous to the early Triassic. This fish is known from puzzling, yet beautifully preserved, teeth, as many cartilaginous fish are. That’s the problem with fossilized sharks and rays: while bones are easily fossilized under proper conditions, cartilage is very rarely preserved. Unlike most sharks and rays, Helicoprion is not merely known from isolated teeth or even jaws. All we know about this animal comes from curiously coiled whorls of teeth.
A Helicoprion whorl. The teeth line the outer edge of the spiral. Photograph by Chip Clark.
Ever since its discovery, the animal has been shrouded in mystery. Being known only by these whorls, no one had the slightest idea of how the rest of Helicoprion looked. Some even proposed that the coiled teeth may in fact be the shells of ammonites.  However, when Alexander Petrovich Karpinsky coined the name in 1899, he demonstrated that Helicoprion was a sharklike fish rather than a mollusk. His idea about the function and placement of the whorl on this animal, however, was completely off.

Former depictions of Helicoprion range from the reasonable to just plain goofy. Artwork by the brilliant artist, a personal favorite of mine, Ray Troll.
Karpinsky proposed that the whorl was actually located on Helicoprion’s nose. While this idea is ridiculous compared to what we now know about this animal, it was nowhere near the most outlandish, or creative, idea. The whorl has been speculatively placed everywhere from within the fish’s throat to the tips of its fins and tail. More recent reconstructions place the whorl in a sort of buzzsaw-like placement at the end of the lower jaw, which is usually depicted as being elongate. A new study by Lief Tanapila and Jesse Pruitt agrees with the buzzsaw placement of the whorl, but it reveals much more about the evolution and overall appearance of Helicoprion.
Most modern reconstructions display Helicoprion with a buzzsaw-like, elongated jaw. Reconstruction by Dmitri Bogdanov.
Using CT scans, Tanapila and Pruitt discovered a number of intriguing features of this fish. While comparing the lower jaw of Helicoprion to a buzzsaw may seem like a stretch, both the shape and the function of this dentition was very similar to such a tool. As the jaw closed, the whorl slightly rotated. Another puzzling discovery was that Helicoprion lacked teeth on its upper jaw altogether; the whorl was the fish’s only set of teeth. Such adaptations are ideal for a very specialized niche, which we will examine in a couple of paragraphs.
The spotted ratfish, rather than true sharks, is the closest living relative of Helicoprion. Photograph by Dan Hershman.
Perhaps even more surprising than Helicoprion’s physical features is its newfound phylogenetic placement. While commonly referred to as a shark (you don’t know how hard it was not to refer to it as such in this post; I’ve always known it to be a shark), Helicoprion is actually more closely related to ratfish than it is to true sharks. Ratfish are part of the class Chondrichthyes (cartilaginous fish), but they are not sharks; they are part of a different subclass. Helicoprion was found to be part of this separate subclass, very close to the point at which sharks and ratfish diverged. (Tanapila et al., 2013)

A brand-new look for Helicoprion, and it only took over 114 years to discover it. Reconstructions by Ray Troll.
The fact that such a large fish, sometimes reaching 8m (~25ft) long, was so common and yet only distantly related to true sharks reveals a lot about the environment in which it lived. With no large marine reptiles yet ruling the seas, and certainly no whales, all of the major niches were filled by fish. Helicoprion was able to grow to great sizes as it filled a niche which, it seems, no other animals were exploiting: hunting cephalopods and other soft-bodied creatures. (Lebedev, 2009) Helicoprion was unlikely to be the only specialized holocephalan at this time; the diversity of such fish was far greater back then. Eventually, such strange fish did go extinct, and in their wake, sharks and rays evolved to fill their niches.

It is a wonder that over 100 years after its discovery, we are only now discovering new information about Helicoprion. It has had a confusing, misfortunate, and pretty hilarious history, but it seems that all the speculations and hypotheses of the function and position of its characteristic whorl can be put to rest. While not as outlandish as some depictions, the real Helicoprion was no less unusual or unique.

Lebedev, O. A. (2009). A new specimen of Helicoprion Karpinsky, 1899 from Kazakhstanian Cisurals and a new reconstruction of its tooth whorl position and function. Acta Zoologica, 90, 171–182. doi:10.1111/j.1463-6395.2008.00353.x

Tapanila, L., Pruitt, J., Pradel, A., Wilga, C. D., Ramsay, J. B., Schlader, R., & Didier, D. A. (2013). Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion. Biology Letters, 9(2). doi:10.1098/rsbl.2013.0057