Monday, December 31, 2012

Dino (and Mammal)-Eating Crocs Part 3: The First Neosuchians

*Before I start, I must apologize for misusing the term Crocodilian in my last post concerning these animals. Crocodilian is used to define all the members of the Crocodilia, which include living crocodiles and all their closest extinc relatives, and not the Notosuchian + Neosuchian branch Metasuchia. Instead, the more broad term in considered to be Crocodylomorph, which is what I will use in this post.
 
Image of Stomatosuchus inermis, a large Crocodylomorph from mid Cretaceous Africa.
Its toothless lower jaw and possibly pelican-like throat pouch are just one example of diversity in the Neosuchia.
As I had shown in the previous post concerning Notosuchians, during the Mesozoic all kinds of these reptiles were running around under the feet of dinosaurs, and in some cases, directly competed with them for resources, territory, and living space. However, the other group of Crocodilimorphs, known as the Neosuchia, were just as, if not more diverse as their Neosuchid brethren, and exploited another type of environment; the water. Such a high level of diversity should really be expanded longer than a single blog post, but in an effort to save time, I'll be just quickly scanning though a few of the various groups and families.

The earliest known Neosuchian, called Calsoyasuchus valliceps, dates back to the early Jurassic, and predates the Neosuchia by almost 90 million years. However, despite being so old, Calsoyasuchus is a fairly derived form of Crocodilimorph, being a member of the Goniopholididae family, and suggests the Neosuchia originated even earlier. Goniopholididae were the first group of semi-aquatic Neosuchians, and would've resembled modern crocodilians in many ways. However, they lacked many defining characteristics, such as a well-developed secondary palate which allows them to breath while their body is submerged, and would've probably needed to lift most of their head out of the water to get a gulp of air.

More primitive Neosuchians only occur later in the fossil record. The Atoposauridae are often thought to be the most primitive family within the Neosuchia, but they don't appear until the late Jurassic, leaving another 30 million year gap between them and Calsoyasuchus. They seem to have been primarily land-living animals that resembled armored monitor lizards, and were probably filling a similar niche to them in the shadows of dinosaurs. As time went on, however, this certainly did change. While both the Goniopholididae and the Atoposauridae represent the earliest offshoots to the group, the second offshoot, however, has been getting more press with the discovery of Dakosaurus; the Thalattosuchia, or sea-crocodiles.


Image showing just a few species of Metriorhynchids with a diver for scale.
Despite the image portraying a 4.5m Dakotosaurus, some species may have rivaled
Plesiosuchus in size.
The Thalattosuchia are as far as we know the only crocodilians adapted towards a fully pelagic existence. They evolved during the mid Jurassic and persisted into early Cretaceous times, and are separated into two families; the very crocodilian-like Teleosauridae and the very fish and whale-like Metriorhynchidae. The Teleosauridae  have elongated jaws, and are thought to have been primarily shallow water piscivores, although some members like Machimosaurus have their teeth regularly found embedded within turtle shells. They show numerous adaptations for diving, however, such as big neck muscles and short, compact bodies, but still hold onto the elongated crocodile-like tail of their ancestors. The Metriorhynchidae were much more whale-like in appearance as well as feeding methods, sporting killer whale-like teeth, and many having shorter porpoise-like snouts. These were presumably the toothed whales of the age, and being equipped with well-developed salt glands, fish-like tails, and flippers, they lived a fully aquatic existence. They are also currently believed to be the only members of the Archosauria to be ovoviviparous, in that they likely held onto the young in the body and gave live birth to them.

However, despite often being considered members of the Neosuchia, some recent cladistic analysis of these animals have suggested that they may be more primitive, perhaps even outside of the Metasuchian branch altogether, and thus I shouldn't be including them in this post. For a more in-depth review of this as well as any information you may want to know about these creatures, see Darren Naish's recent article concerning these animals.

Next are possibly one of my favorite families among the primitive members of the Neosuchian branch, the Mahajangasuchidae. So far the family has only been identified by two species, both from Africa, Mahajangasuchus insignis from Madagascar and Kaprosuchus saharicus from the Sahara. They are characterized by their short and deep jaws, horn-like projections over the eyes, and fused nasal bones, the latter trait they share with the tyrannosauridae. They also both show adaptations in their skulls that suggest a largely if not fully terrestrial existence, such as more laterally positioned forward-facing eyes. In the case of Kaprosuchus, it had six pairs of elongated teeth and an armored nose, which may have allowed the animal to kill large, land-based prey.

Kaprosuchus has been getting some attention ever since its discovery, and has been portrayed on National Geographic's special When Crocs Ate Dinosaurs, as well as the British television series Primeval. Despite not really realizing it, Mahajangasuchus has gotten some screen time as well. In the 2005 remake of King Kong by Peter Jackson, they portrayed in a short scene a crocodile-like creature chasing after the lead heroine Ann Darrow before getting eaten by a T-rex-like animal. The creature was later confirmed in a "Natural History Book" about Skull Island to be known as Foetodon ferrus, but looking over its anatomy, its overall build and size shows an uncanny resemblance to Mahajangasuchus, and I wouldn't be surprised if it was based on the latter.


Image comparing the giant extinct Pholidosaurid Sarcosuchus to a living crocodile.
Their has been a debate as to what Sarcosuchus was eating; mostly land-based dinosaurs,
 or mostly fish. I personally find the later more likely. Sorry Sarco fans...
The Tethysuchia are a group of crocodilians which evolved near the end of the Jurassic, and survived into the Paleogene epoch. Within this group their are two families, the Pholidosauridae and Dyrosauridae. The Pholidosauridae, which includes Pholidosaurus, Meridiosaurus, and the infamous "Super Croc" Sarcosuchus, which was one of the largest Crocodylomorph to have ever existed. They were primarily long-jawed predators of fish with widened, bulbous noses, but some species of bucked this long-jaw trend entirely; Oceanosuchus had jaws similar to a modern day Alligator. The Philosauridae went extinct about 90 million years ago, likely after suffering heavy losses after the Cretaceous Thermal Maximum (CTM).

The Dyrosauridae were similar to the Pholidosauridae in many aspects, and are their sister group, but came about 20 million years later in geological time. They appeared about 70 million years ago and survived the K/T event that wiped out the dinosaurs. Most had, like the  Pholidosauridae, elongated jaws with numerous teeth, suggesting again, a mainly piscivorous lifestyle, though some species, such as Phosphatosaurus, had more traditional crocodilian-like teeth and jaws. This group survived up until their extinction in the Eocene, likely being victims of another small extinction event hat occurred at this time, although their disappearance could also be explained by competition withthe more advanced crocodilians.

Next come quite possibly, in my opinion, the most extreme members of any Crocodylomorph lineage. The Stomatosuchidae were a small family, like the Mahajangasuchidae, and have only two currently accepted genera. The first discovered was Stomatosuchus, which was unearthed by Ernst Stromer during one of his expeditions to Egypt, but was sadly lost along with the original Spinosaurus and Carcharodontosaurus remains during WW2. The second was Laganosuchus, which was described and discovered by Paul Sereno in 2009.

The original remains of Stomatosuchus were not very complete, but it suggested that the animal was over 30ft in length. Laganosuchus was probably smaller, reaching a little over 20ft. The upper jaw had tiny teeth, but the lower jaw may have been toothless (although Laganosuchus has small teeth in it's lower jaw). While Sereno has suggested that these animals may have been ambush predators, waiting jaws open for something to swim into them, I'm sceptical of this. The wideness of the jaws would produce a lot of drag in water, preventing them from being closed effectively at high speeds. Any rapid movement of such wide jaws would've also produced currents that would alert the fish of the danger through it's lateral lines, if not carry the fish out of their jaws entirely.

I instead believe that, since their jaws show similarities to living whales, these animals may have been hunting fish through filter-feeding. Perhaps they actively followed after schools of fish, swallowing them in gigantic mouth fulls. It would've certainly been a niche that they could fit into nicely, seeing as the only other creatures hunting like this at the time were gigantic fish in the family pachycormidae, and even these huge fish were likely feeding on tiny plankton rather than other fish species. So it seems the stomatosuchidae had this unique lifestyle and feeding habits to keep all to themselves. (although another  Crocodylomorph family, the aegyptosuchidae, may have been doing similar things)
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So their we go. I know it is a bit short, but I told everyone I'd try to get this done before the end of the month, and I was running out of time.

Still, I'm not done yet, and I'd really like to get into some more crocodilians next time, including more modern crocodilians that are all scattered across the past. I've also been facinated by a species of land-living (if not arboreal) crocodilan that may have crossed paths with early Homo sapiens, and you can be sure it will be talked about sooner or later. ;)

Monday, December 24, 2012

Happy Holidays!

Hey everyone! Just making this quick little post to wish you all a Happy Holidays and great New Year. The next crocodilymorph post is almost done, although I may have to separate it into two parts since the Neosuchia is such a vast family to cover. Other than that, I'm hoping I'll be able to post some more things on here for the next few weeks before school starts again. I'm also working on some other post (if you haven't realized it yet, I just right about whatever I'm looking into at the present time) and hope they'll be done before school starts next year.

Anyways, as I said before, I wish you all a very Happy Holidays and hope to see you all soon....

Saturday, December 22, 2012

Anatomy and Paleobiology of Spinosaurid Dinosaurs

Illustration by Brian Engh depicting two Spinosaurus aegyptiacus doing what their family does best:
fishing, and swimming.
Recently, I have been speaking with a number of people online concerning the life habitats and paleobiology of the spinosaurid dinosaurs, which is a family of highly specialized theropods that had evolved aquatic habits and are known to eat fish. The information we've been discussing has certainly inspired me to do a post on these animals, and they're one of my personal favorites among theropods due to their bizarre appearance and specialized behaviors.
 
Spinosaurids were a family of dinosaurs within the megalosauroid radiation of tetanuran theropods which seem to have evolved during the late Jurassic. While original spinosaurids remain limited their range to North Africa, South America, and Europe in predominantly swampy and tropical paleoenvironments, the last five years has revealed remains from every continent (excluding Antarctica, although I bet we'll eventually find them there). An ungual phalanx from the famed Morrison formation is also thought to be from one of these animals, and a neck vertebrae from Australia has been found to come from a juvenile spinosaurid. The latter is from the same locality that we're currently finding a number of polar dinosaur species, proving that these animals weren't limited to swampy environments.
 
Combinations of stomach contents, shed teeth, and even embedded bones from prey within the jaws of these animals prove that they were piscivores, and fed on a diet of fish. A study of oxygen isotope levels in spinosaurid teeth have also shown that they were indeed spending the majority of their time submerged within water, and perhaps actively swimming after fish in their underwater world. However, the discovery of bones from a sub-adult Iguanodon within the European Baryonyx specimen, along with a pterosaur vertebrae with part of a spinosaur tooth embedded within it prove that despite their fishy diets, they were still capable of feeding on land-based prey. The fact they were aquatic may also suggest that some of these theropods were feeding on marine reptiles like plesiosaurs and icthyosaurs. We have found marine reptile bones and teeth in some of the same deposits, but this is all speculative until any evidence is found that they preyed upon these animals.
 
Body Builders of the Mesozoic?


Image of armature paleontologist William Walker with the thumb claw of Baryonyx walkeri in his hand.
The individual Baryonyx who left this claw was about 9 meters long, and it was not even fully grown!
 
A common trait seen in many, if not all members of the spinosauridae is their well-developed arms. Despite many people claiming that these animals had long arms, they aren't particularly long compared to other theropods, the obvious exceptions being tyrannosaurs and alvaresaurids among others. Instead they are well-muscled and very robustly built. The lower arm bones are relatively short, but the humerus length makes up for it. The fingers show a high degree of flexibility like many big theropods, and the thumb was tipped with an extremely large thumb claw.
 
Many have suggested that these arms were used for fishing, rather like how a bear will use its forelimbs to catch salmon. However, similar robust arms are also seen in earlier Megalosauroids, so perhaps their use was the same throughout the group. Megalosaurs are thought to have used their robust arms to help with dispatching large land-based prey animals, and we know currently that Spinosaurids at least occasionally fed on dinosaurs, so perhaps their arms were used to kill them as well. Still, they would have also served very effective for fishing when the time came.
 
Billboards, Fish Traps, or Giant Humps?

Skeletal reconstruction by Scott Hartman showing the full extent of some Spinosaurus vertebral spines
Wonder if I could advertise my blog on one of those things....
 
The most noticeable part of any spinosaur must be the elongated dorsal neural spine along their backs, producing a "sail" or ridge along the backbone. In some species these became very elaborate: Spinosaurus itself has neural spines which were over five feet tall, and Ichthyovenator had not one, but two sails along its back.
 
The evolution and purpose of these sails has been at the center of a hot debate. Some scientists think that they may have served a thermoregulatory function. Many of these creatures were living in some of the hottest environments the Mesozoic had to offer, and these vertebrae could serve as extra surface areas to cool down the animal during the hottest parts of the day. However, if the animals were really spending a lot of time submerged in water, this may not have been a problem for them, as the water would keep them cool. The sails may also have served as visual display organs. Similar structures are found in other dinosaurs and living animals, and may have served as billboards to advertise to other animals their age, size, gender, species, and overall health. The sheer number of sail shapes and forms found within the group supports the idea they were for some form of visual communication, and I agree that that is likely one of their functions.
 
Another theory I have heard be suggested is the fishing lure idea. Some living birds like herons use their wings to shade the water around them, which attracts fish to the animals where they can then be easily snatched up in their bill. Some have suggested the same thing was happening with spinosaurids, using their sails to shade the water and attract fish, but I personally find myself disagreeing. Many species have low ridges that could not serve such a function, and the sails are thought to appear as an offset to sexual maturity, further suggesting the visual idea.
 
Stromer had his own idea for the sail, however. He suggested that the sail may have supported a hump-like structure filled with muscles. While originally dismissed for the sail-backed animal, Jack Bailey resurrected the hypothesis in 1997, and reconstructed what looked like a giant terrestrial crocodile with a bison-like hump on its back (similar to the extinct archosaur Arizonasaurus). However, this posture and reconstruction now seems, at best, unlikely, but the hump theory still isn't out of the question. As both he and Stromer noted, the sail is made up of thick and strong vertebral extensions, a far cry from the thin extensions in some sail-backed animals, like Dimetrodon, but very similar to the thicker extensions in living hump-backed animals, like bison and camels.
 
Living bison use these muscular humps on their backs to power huge neck muscles for both plowing through snow and head-butting mates during the breeding season. Camels use their humps to store fat (NOT water) while traveling over large desert landscapes. Bears also have muscular humps over their shoulders to power huge arm muscles while hunting, digging, and moving large objects (in some cases even boulders weighing over a ton), but how would the spinosauridae possibly use such a structure?
 
Investigation into the neck vertebrae in spinosaurids suggests that, while they had rather weak side-to-side motion in the neck, they had well-developed muscles responsible for the up-down motions. Such a fast up-down motion might be good when catching fish and raising them out of the water while swimming, and any muscles in this sail may have assisted them while hunting. The well-developed arms of spinosaurs may also have been powered by muscles that extend into these structures, although as I mentioned about megalosaurs, they would have still been powerful without them.

 
One of the best and most used skull reconstructions of Spinosaurus I've seen on the net, with the rear proportions based off its relative Irratator.
The image is from Andrea Cau's Theropoda blog, although I don't know the exact origins of it (except it's modified by S. Maganuco).
 
Leaving their vertebrae, we of course come to their next most defining feature in spinosaurids: their heads. The skulls of spinosaurs were all low and elongated, similar to a crocodile, and due to their fishy diets it's no wonder why. However, despite this general shape, the skulls between different species can differ dramatically between the two subfamilies; the Baryonychinae and the Spinosaurinae.
 
The skulls of members of the baryonychinae are known for their moderately raised nostrils, rounded eye socket, numerous closely-spaced teeth, shallow lower jaw, and extremely small, but numerous serrations on the teeth. These animals include Baryonyx walkeri and Suchosaurus cultridens from Europe (although the latter may be dubious), the African Suchomimus tenerensis, possibly Ostafrikasaurus crassiserratus (if it's not more primitive), and Cristatusaurus lapparenti (again, the latter may be dubious), the Asian Ichthyovenator laosensis, and presumably the newly discovered Australian specimen, Morrison specimen, and a Campanian tooth from China all belong to members of the the baryonychinae.
 
The defining skull features members of the spinosaurinae share is their extremely high nostrils (half way up the skull), raised teardrop-shaped eye sockets, widely-spaced and relatively longer teeth, deeper lower jaw, and lack of serrations. These members so far include the African Spinosaurus aegyptiacus, the South American Irritator challengeri, the extremely fragmentary Oxalaia quilombensis, and possibly Siamosaurus suteethorni (since its teeth closely resemble those of Spinosaurus).
 
Both groups have raised nostrils, which helps them to breathe while submerged. In the spinosaurinae they are especially high up, which allows them to still breathe in deeper water, and the eyes are also partially raised, allowing them to also see while submerged. This could possibly indicate that the spinosaurinae were more aquatic than the baryonychinae, and the large sizes of some members of the spinosaurinae (both Spinosaurus and Oxalaia could get larger than Tyrannosaurus) may have been supported by the weightlessness of this lifestyle.
 
The differences in jaw morphology may also reflect different lifestyles among the two groups, most notably spaces between their teeth. The teeth of the baryonychinae were uniformly-spaced, while the teeth of the spinosaurinae had spaces which varied. The former arrangement is more similar to living fish-eating gharials, which have interlocking teeth to allow them to more successfully catch small slippery fish. However, the latter spinosaurinae have an arrangement that is more similar to other types of crocodilians, and might suggest that like them, their diet was more varied. Alternatively, varied spaces between teeth are also seen in crocodilians which feed on larger prey, so it is also possible that the spinosaurinae were feeding on larger prey items than the baryonychinae.
 
Comparisons between the skulls of different types of spinosaurids have been going on for a while now. Donald M. Henderson started it off in 2002 when he examined Suchomimus's skull and found that it was weaker in comparison to the skulls of the much smaller dinosaurs like Dromeosaurus. This was due to the skull's weaker build compared to other theropods, which have taller skulls in order to counter-act stresses while biting. In 2007 Emily Rayfield made similar findings in the closely related Baryonyx walkeri. However, paleontologist Andrea Cau posted on his blog Theropoda about the skull of Spinosaurus as well as members of the spinosaurinae, and suggested that unlike the baryonychinae, it may have had a much stronger bite.
 
He noted numerous adaptations in the skull which could be responsible for a more powerful bite force, and I quote:
 
"How powerful was that bite? A precise quantification is not possible, however, it should be noted that increasing the length of the rostrum, increases the moment of the force exerted by the muscles mandibular end of the rostrum. The long skull of a Spinosaurus was adapted to withstand the forces exerted by its own bite? The cross section of the rostrum, triangular, the presence of the long nasal dorsal ridge which served as a point of discharge of the forces and the presence of the long secondary palate (a mechanical expedient to resist torsion), all adaptations are intended to support the intense stresses caused bites very powerful. A further indication of this capability is given, at least in Spinosaurus, from the retracted position of the nostrils: this odd fact that the entire region was placed in front of the nostrils consists of only compact bone, with no cavities or soft part, and then allowed to exercise precisely at the level of the rostrum of the considerable pressures without the risk of damaging vital parts such as the nostril."
 
This suggested to me that unlike members of the baryonychinae, the spinosaurinae were better adapted to feeding on a range of animals from fish, to pterosaurs, to dinosaurs with their more powerful bites. However, while writing this article I came across yet another paper concerning the strengths in spinosaur skulls published in 2011 (again by Emily Rayfield). This study was similar to the Baryonyx one in that she digitalized the skulls of 7 different theropod species, including Suchomimus and Spinosaurus, and put them under stress in a 3D computer program to see which ones were most effective at distributing it. The results were surprising.
 
Out of all the dinosaurs in the study, the three largest theropods, Acrocanthosaurus, Carcharodontosaurus, and Spinosaurus had the highest levels of stress in the skull. Spinosaurus especially showed levels off the main curve, and was likely unable to feed on larger dinosaurs, being restricted to smaller prey. Ironically, this study found that despite Henderson's stating that the skull of Suchomimus was incredibly weak, this study found that it was in fact just as good at distributing stresses as the other theropods graphed, and the skull was overall much stronger than Henderson thought.
 
I am, however, reluctant to make these seem like conclusions since Emily herself stated that they could not be 100% sure that the results were accurate based on the resources she had. She instead suggested that the study should be considered more of an educated prediction, and should be tested with the offset of better 3D models in the future. I personally can't wait until such advances are made and we can more accurately find out how these skulls worked, and thus learn how these creatures behaved.
 
Why, what big teeth you have!


Image of the jaw of Baryonyx from Emily J. Rayfield's paper reguarding its skull
As you can clearly see from image B, spinosaurid teeth were extremely long.
 
But of course, one of the most interesting things I'd like to get into is these animal's teeth. The teeth of all spinosaurs show some of the greatest examples of convergence within the theropods, greatly resembling crocodilian teeth to the point that we have trouble telling isolated examples of the two apart. Both croc and spinosaurid teeth are nearly conical in shape and appearance, but in the baryonychinae, these teeth still held onto serrations along the front and back like other theropods, but are so small that they can only be seen with a microscope. The spinosaurinae teeth have become truly conical and have no serrations present, but also tend to be thicker as well as larger than baryonychinae teeth. Both groups also show large amounts of wear on their teeth. Similar wear is seen in crocodilians, marine reptiles, as well as some toothed whales, further evidence that these were aquatic animals.
 
Oxalaia is also unique from all other theropods in one regard. The tooth in the third row has shown not one replacement tooth behind the functioning one, but two. This is unusual as replacement teeth tend to grow one at a time in most theropods. For those that don't know, both dinosaurs and crocodiles replace their teeth by resorbing the existing tooth at its base to make room for the replacement. The replacement eventually moves to a position within the functional tooth, and when resorption is largely complete, the existing tooth falls away, allowing the new tooth to take its place.
 
The fact that Oxalaia has two replacement teeth within one socket means that it would've been resorbing and producing two teeth at the same time within one another, almost like Russian nesting dolls. Due to the fact we only have one extremely fragmentary Oxalaia specimen, we can't tell if this was a "freak" individual or a trait the species had as a whole, but it certainly shows these animals were weird in their own ways. However, I haven't even gotten to one of the most significant things about these teeth in my opinion: their sheer size.
 
Many people just don't realize that how big spinosaurid teeth were. At first glance the teeth of spinosaurids may seem about the same size as those of other theropods, despite their odd shape. But CAT scans of the skull have shown that their roots were extremely deep, sometimes embedded half-way within the socket. Similarly deep roots are also seen in, again, crocodilains, but in Spinosaurus itself these teeth may have been over 10 inches long, rivaling T-rex's banana-sized 12 inch teeth for the longest theropod tooth! It has surprised me just how little documentation exists about the size of spinosaurid teeth, and very few people I've talked to know how long they actually are. Many scientists have referenced the length of these teeth in the past, such as Thomas Holtz, who has talked about their length in the documentary Monsters Resurrected  as well as while answering questions online.
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So that's it. Thanks to everyone who I've been talking to about these fascinating creatures, and hopefully talking about these crocodile mimics will get me back in the mood to write about actual crocs....
 
Eh-hem....
 
As always, feel free to ask any questions you may have. But to make it seem a bit more exciting around here, you get extra points if you understand the Holtz reference. Until next time, stay sharp and see ya around the net. ;)

Tuesday, December 4, 2012

Digging on the Net: Birds of Paradise

A few weeks ago, I found myself walking down my driveway after a long day of school. I turned to my left and saw the mail had come in, so I decided to grab it and save my parents some trouble. However, I noticed I got a new edition of National Geographic magazine in the mail, and one of the sections listed on the cover said something about the Birds of Paradise, scientifically known as the Paradisaeidae, and are best known for their spectacular and diverse plumage in males. I entered my house, dropped all my things on the way up to my room, and quickly indulged into the world of these spectacular and diverse birds.

It turned out that after 8 years of looking and studying Birds of Paradise, photographer Tim Laman and Cornell University ornithologist Ed Scholes were able to be able to document and photograph every living member of the family, including the never-before photographed and rarely ever witnessed Buff-Tailed Sicklebill. Their discoveries and footage include never-before seen views of these animals, and completely unexpected realizations about their mating behaviors. I wasn't going to make a post about this, but a recent National Geographic Live! interview has given me a good chance to show you all just how spectacular these creatures are:


I know there's been a lot of bird-related things on this blog recently, but expect it, since birds are the living representatives of Dinosaurs, and in my opinion, we should be basing Dinosaur behavior off them. In my opinion, if a bird practices some type of behavior, then Dinosaurs probably would've done similar, of not the same behavior. And yes, that includes the possibility that male T-rex were dancing around, clearing areas on forest floors in order to make them seem sexier to females of their species.

Yes, I know, I'm working on the Neosuchian post. I'm just stuck on this one part and currently looking for the information to refresh my memory on it. It'll be within the month, but expect some shorter posts in the meantime.

Thursday, November 22, 2012

Happy Thanksgiving

Two male Wild Turkeys performing their characteristic "strutting" behavior.

For this quick post, I'd like to say Happy Thanksgiving to all my American followers here, and talk briefly about one of America's National emblems, the Wild Turkey (Meleagris gallopavo). Often taken for granted by us humans, and often described as very dumb birds, Wild Turkeys are greatly misunderstood animals, which encourages me to devote a few paragraphs here to discussing them on what should be considered their own national holiday.

The Turkey is the largest living member of the Galliformes, or gamebirds, a group of about 290 species of mostly terrestrial birds that have compact bodies, small heads, short beaks, and high-wing loadings. Galliforme young are precocial, which means that they are able to walk within hours of birth, and in the case of Megapodes (large gamebirds from Australia and surrounding areas of land) their young are superprecocial, and are able to fly within their first day out of the egg.

Gamebirds as a whole are a very successful group; they've colonized every continent except Antarctica, and are found everywhere from tropical rain forests to frozen tundra. They are well known for often showing extreme forms of sexual dimorphism, and males are often larger than females and have almost excessive amounts of display plumage, which reaches its most extreme in peacocks and some pheasants. In some species of gamebird, males have an enlarged spur on their hind feet that can be used in both territorial battles, and as a defense against predators. (I think that a similar function might have encouraged the evolution of enlarged claws in dromeosaurids, iguanodontians, and prosauropods, although I doubt sauropods used their thumb claws in this way, since they seem more likely to have been used in foraging, according to recent studies.)

Male Turkey displaying coloration of 
his head and waddles
Turkeys in particular are very interesting gamebirds if you've seen them before. I've seen them myself on a few occasions, and they look and act like very proud animals. The males even have a behavior called "strutting" where they walk around displaying to both females and other males while dragging their wings, puffing up their tail and chest feathers, and pulling in their head. During this behavior, males have been known to change the color of their head based on how they're feeling, similar to what cassowaries and chameleons do, with blue heads signaling excitement, and red heads signaling aggression. They can also engorge the skin and waddles around their head with blood, causing them to swell up almost to the point where the eyes and beak are concealed.

The bare, blood-filled skin and thick body feathers in males doesn't come without consequences. Some studies has shown that overheating is a problem at times, and males will often rest in the shade for hours at a time, and have been known to pant on hot days like dogs and crocodiles do. Females, with less body plumage and more plumage on the head when compared to males, don't have as much of a problem, and are free to forage for food most of the day without resting. The diet of a Turkey includes grain, leaves (including conifer needles), nuts, seeds, berries, roots and insects. They have also been observed eating small vertebrates, including frogs, lizards, and even snakes.

Female Turkey with Chicks

As with almost all gamebirds, males play no role in parental care, and are polygamous, mating with multiple females in a season. The female is thus left entirely responsible for taking care of the offspring, which can sometimes be up to 14 juveniles. The eggs are layed about one day apart in a shallow dirt impression, and they all hatch after about 28 days and leave the nest within their first 24 hours. The female will then watch over the young for the next 8-10 months until they are large enough to take care of themselves. If confronted by a predator, turkeys prefer to run rather than fly, using their long, athletic legs to escape danger, although if forced to they have been known to be quite agile fliers, and will sometimes roost in trees to sleep in relative safety.

Native Americans have long relied on turkeys, and they were considered a vital food source for many eastern tribes. During the first Thanksgiving, the governor of Plymouth sent out four men to catch turkeys for the big feast, and came back with enough turkeys to last them a week. However, turkeys weren't the only animals being served. Deer, geese, ducks, swans, passenger pigeon, fish, eels, shellfish, mussels, clams, and lobster were also on the menu. After the first Thanksgiving, British trading ships brought the animals back to Europe as food. They were forced to travel through Constantinople in Turkey before reaching other countries. People then associated the birds with that nation, which is where their name comes from.

Sadly, it seems that food is one of the only things Turkeys are remembered for in history, but one famous historical figure thought highly of Turkeys. Benjamin Franklin wanted the Turkey to be the national bird of the United States rather than the Bald Eagle. He believed the Turkey to be a more noble and proud bird than the Bald Eagle, as he had witnessed Bald Eagles stealing food from other smaller birds, and basically bullying them into submission (many Raptors are known do this). Many disagreed with him, however, preferring the stronger and more powerful Bald Eagle over what they viewed as the comical turkey. I'm happy with the Bald Eagle as America's national bird, but I'm also glad that Franklin looked past the non-traditional beauty of the Turkey and saw an attractive and proud creature behind that plump body.

I wish you all a Happy Thanksgiving, and hope you will respect the animal who gave their life for your meal today. As for me, I'm a vegetarian, so I'll be staying away from these birds today and hope those that did not end up on your plates will get fed just as well as I will today. What will I eat if not Turkey, you ask? Cauliflower bisque, herb-crusted tofu with mushroom gravy, chestnut sage stuffing, cranberry sauce, green bean casserole, candied yams, and delicious pumpkin pie are all on the menu tonight. Whatever is on your menu tonight, enjoy the holiday with your family and friends! And expect a lot of posts next month, since I'm going to be off for the Holidays.

Friday, November 16, 2012

OH MY GERSH! Where's RaptorX?

 

A Common Potoo having a panic attack.


Hey everyone, bet you were all expecting a Croc post last week. Sadly I haven't been able to get on it yet, I've been busy working on some other things, some of which I'd like to tell you all about.
The first news is that I'm writing an article for a new online magazine, called AncientPlanet Online Journal. The magazine looks nice and I''m excited that some of my articles will be appearing in it. It's every two months though and I'm trying to balance out getting info for the articles, and getting my school work done. I also have a YouTube account now if anyone is interested in talking to me on there. I might also start making videos, but I'm not sure yet, as it'll make me even more busy than I am now.

As for Crocs, it might be a while before I get to writing that post. In the meantime you might want to go over to Darren Naish's blog Tetrapod Zoology. He recently wrote a few articles on Neosuchid crocodiles, and even though I know a lot about these things, I still probably can't explain them the same way an actual scientist can.

As for the meme, it's made by yours truly. The image is of a Common Potoo, which is a type of nocturnal bird from South America related to nightjars, swifts, and hummingbirds. It's an insect eater and uses its enormous mouth to gulp down moths and other insects in flight, and is famous for its amazing camouflage capabilities, being able to mimic a broken tree stump almost perfectly. It also is known for the strange call it emits, which sounds almost like a human saying "poor me, all alone." Here's some less comical images of Potoos:

Head profile of a Common Potoo. The huge mouth has tiny bristles inside which help trap any insects that get caught.
This Common Potoo was curious of the camera when this photo was taken. A Potoo's large yellow eyes are used to help them see in the dark, but give them somewhat of a bug-eyed look.
Common Potoo hiding in plain site. It might not seem wise to close its eyes when hiding from predators, but Potoos have small notches in their eyelid which allow them to see even when their eyes are closed.

Common Potoo showing its young the art of hiding. Potoos and their relatives have such good camouflage that they can fledge chicks directly on a bear tree branch, and sometimes even open ground without ever being spotted by a predator.



Sunday, October 28, 2012

Dino-Eating Crocs Part 2: Success of the Notosuchia

A depiction of Baurusuchus eating a turtle. These crocodilians were taking up the roles of Dinosaurs near the end of the Cretaceous, and were proving to be deadly adversaries.
When you think of the paleoecology of the Cretaceous period, normally you think of dinosaurs filling up all the niches available, as this period was the height of their success. But this couldn't be further from the truth. During the Cretaceous, many forms of animals took up the intermediate roles between the folds of nature, and while some think these areas were ruled by mammals, that's actually not the case either. It seems that these niches were mostly filled by a group of crocodiles, known as the Notosuchia.

The Notosuchia are a well known group to scientists. We first found their bones more than a hundred years ago, but they remain mysterious and unknown to the public. Their fossils have been unearthed in South America, Africa, Europe, and even as far as East Asia. They were fully terrestrial, as shown by their un-flattened tails, level nostrils and eyes, and long legs, and ranged in size and shape from small little animals no larger than a housecat, to fairly large animals that could've given theropods a run for their livelihood. Their strange teeth and dietary preferences have made them famous in the paleontological world.

The best description of their teeth is that they're mammal-like, although they really have no close resemblance to any animal living or extinct, and were probably more competitive with mammals than dinosaurs ever were, as they occupied the same niches. Some even seem to have given up a diet of meat and evolved towards herbivory, such as Chimaerasuchus from China and Malawisuchus from Malawi. Others were opportunistic omnivores, such as Notosuchus from Brazil and Araripesuchus from all over the Southern Hemisphere. The latter's genus also lasted from 125 - 65 mya, meaning it survived for more than 60 million years, longer than most other land vertebrates from the Mesozoic and certainly longer than any dinosaur genus I know of.


Chimaerasuchus, a 6ft herbivorous croc from Early Cretaceous China.
The location where this fossil was found is the farthest
the group ever got from the Equator.
There were many bizarre members of the Notosuchia, but it's interesting to note that many resemble living mammals. Armadillosuchus has probably the most prominent name of the group, resembling a living Armadillo, and having armor carapaces along its back for defense. Mariliasuchus looked profoundly like a gopher or other burrowing mammal, and has actually been found lying within possible burrows along with associated eggs. Notosuchus had fleshy lips, and might have had either a hog-like snout, or possibly even a trunk like a tapir. Some looked like cats, such as Pakasuchus, which has large eyes and a similar body form to modern felines.Their were even alien-looking animals like Yacarerani, which had a bizarre dentition that looked a lot like a rat or other rodent. All these similarities with mammals, along with the fact that they had upright legs and likely exhibited active lifestyles, has suggested to some researchers that these crocodilians were endothermic, but an examination of this idea has yet to be performed.

These animals were definitely filling up mammal niches, and it's probably due to this group, not the dinosaurs, that most mammals in the Southern Hemisphere stayed small. However, in many places that these small crocs roamed, we're now finding that herbivorous dinosaurs were absent, suggesting that they were also taking up dinosaur roles in the environment. Take South America for example, almost all kinds of hypsolophodont from the northern side of the continent were gone by the Late Cretaceous, but in their place we found these little animals scurrying around. The same is also true of Late Cretaceous Madagascar, we've yet to find one Ornithopod or Ceratopsian in the environment, their niches completely filled with crocs instead. The occurrence of Chimaerasuchus in China also roughly coincides with the disappearance of many small ornithopods in that region. However, the disappearance of Chimaerasuchus also roughly coincides with the diversification of many plant-eating theropods, possibly meaning that once these crocs left the region, theropods filled the niches that both groups had held previously.

The most competitive, and probably my favorite members of the group were the sebecosuchia, which occupied not the niches of small ornithopods and mammals, but were predators taking up the roles that small- to mid-sized theropods had. Along with the mammal-like teeth of other members of the Notosuchia, members of the sebecosuchia also evolved theropod-like teeth, and in some members like Stratiotosuchus, canine-like teeth evolved. They evolved stiff backbones and longer legs, better for actively running after prey, and resembled giant reptilian dogs. These were also the largest members of the Notosuchia, with some species reaching about 15-20ft.

I imagine these animals to be ambush predators, lying in wait along game trails, waiting for an unsuspecting dinosaur to wander by, and possibly even pursuing the animal for a short distance at high speeds until they tired. This behavior, along with their ecological niche, would've put them right at the same level as large theropods, and would've been just as dangerous to the local herbivore populations. In many fossil sites around the world, these animals seem to have even replaced theropods as the top predators as time went on.

A Stratiosuchus preying on some kind of Titanosaur.
Image by MaurĂ­lio Oliveira.
This is most strikingly the case in a formation called the Adamantina Formation, which is a layer of rock in Brazil that dates back from 90-83mya. This could be called the Lost Land of the Crocodiles, and the entire fauna is dominated by these animals, with more than 15 species present and virtually no dinosaurs or mammals represented. Instead of mid-sized theropods we see Baurusuchus, Campinasuchus, and Stratiotosuchus filling these roles; in place of ornithomimids and oviraptors, we instead have pig-like animals like Armadillosuchus and Mariliasuchus; and in place of ornithopods and mammals, we have a whole dynasty of herbivorous species present in the fossil layers. The only dinosaurs present are Sauropods, which seem to have been the only dinosaur group these animals couldn't match in ecological role. However, I've recently heard of some unidentified theropod material that's come from the formation, and a fossil Barusuchid apparently has some theropod bite marks preserved on its bones, which might indicate that these dinosaurs were present. But still, the majority of animals in the formation were Notosuchids, and it seems that they took control of this specific region. Why exactly? We may never know.

At the end of the Cretaceous, after all the major dinosaur faunas went extinct, leaving only birds and mammals to take their roles, these crocs didn't go back into the water to join their Neosuchid kin. In fact, the discovery of numerous members of the sebecidae found in Cenozoic rocks proves that these animals survived the disaster at the end of the Cretaceous, and were still as big, powerful, and competitive as ever, and ready to try and take up the roles as predators of mammals. In South America scientists have found the sebecids Sebecus, Bretesuchus, Langstonia, and Lorosuchus in the same fossil rocks as members of the Phorusrhacidae and Sparassodonta, which we believed for a long time were the only large predators on the continent. Not just that, but Bergisuchus from Germany and Eremosuchus from Algeria also shows that they survived in places outside of South America.

Seeing how the group was comprised of large, active, possibly even warm-blooded predators, how did they survive the K-T extinction event? Well, apparently one articulated Baurusuchus specimen suggests the possibility that even these large animals dug burrows, possibly in order to hibernate during tough times as seen in modern day Nile Crocodiles. This behavior could have helped them survive the extinction 65mya that wiped out the dinosaurs, and allowed them to live on through the Cenozoic. But then, why aren't they around nowadays?

There are many mysteries surrounding the extinction of the Notosuchids, however the extinction does coincide with a sharp decrease in global temperatures, known as the mid-Miocene disruption, which might have spelled doom for a group of crocs without any form of insulation to keep them warm. Still, these animals must have been magnificent to see in their glory, and it certainly proves that crocs were definitely not lying down on their lazy bellies by the water's edge during much of their evolution. They were active, powerful, and quite capable of giving even the "Terrible Lizards" a good run when they were alive.
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There we go, part one of the Crocs done, and I'll be posting part two within a few weeks, so I'll see you all then!

Sunday, October 14, 2012

Dino-Eating Crocs Part 1: Introduction to a Croc-Filled World

The notosuchid Baurusuchus, a ten-foot crocodilian which evolved a canine-like body, mammal-like teeth, and was completely terrestrial. Oh, and it was out-competing theropods in their ecological role of top predator in Cretaceous ecosystems.
 No big deal, right?
A few months ago, I was lucky enough to purchase myself the new paleontological book The Complete Dinosaur Second Edition, which I must say, has to be one of the best books about dinosaurs I've read in a long time, and I recommend it to any dinosaur enthusiast like myself. The book is made up of numerous sections and chapters on different dinosaur topics and debates, and leading experts from around the world have sent their research and findings to be presented in the book. Thomas Holtz, one of the world's leading experts on theropods, writes the entire theropod section of the book. Jack Horner, who was the first person to find dinosaur eggs in the Western Hemisphere, helps to write the section on dinosaur eggs and nests. And Darren Naish, who is an expert on fossil vertebrates (specifically birds), writes the section on both living and extinct groups of birds. I was actually very pleased with the bird section, since it's about time we got some living dinosaurs in a dinosaur book.

Ann Darrow and the fictional crocodile Foetodon from Peter Jackson's King Kong
Amazingly, there was a fossil crocodilian that resembles the latter in size and form.
Anyway, I've been spending the last few months reading this very in-depth book, reading through sections by Kristina Curry Rogers, Peter Makovicy, and Gregory S. Paul just to name a few. Finally I came across a section titled Non-Dinosaurian Vertebrates written by Nicholas C. Fraser, whom you might know from his recent book In the Shadow of the Dinosaurs (which I have yet to read). The section reviewed the many fossil vertebrates that lived alongside the dinosaurs, such as plesiosaurs, pterosaurs, mammals, and numerous other fossil groups from the Mesozoic. The section was strangely short, only about 26 pages long compared to the 40 pages some of the other paleontologists wrote (not including references). Still, I was pleased with the chapter, and it taught me many things that I didn't know about non-archosaurian reptiles from the age. So why am I bringing this up exactly? Simple, I was extremely disappointed at the crocodile section of the chapter.

The recently described Kaprosuchus (or Boar Croc) from North Africa, one of
Paul Sereno's newly discovered fossil crocs from the region. 
The section had very little content on the fossil crocodilians during the Mesozoic; less than three paragraphs are dedicated to the entire evolution of the group. And what is covered in the section is largely already known by most dino-nerds like myself, such as the already well-known super crocs of the age and the sea-going metriorhynchids. It's somewhat ironic because Fraser even states at the beginning that crocodiles were as diverse as dinosaurs and pterosaurs, yet he devotes three whole pages on the evolution and diversification of the pterosauria.

This is not meant by any means to be an attack on Fraser, as I said I absolutely loved the section. I'm just disappointed that he devoted such little space to the crocodilians when there is so much to cover, especially since fossil crocs are finally getting some much-deserved media attention for their quirkiness.

Notosuchus was a terrestrial crocodile that lived in South America during the Late Cretaceous.
You might call it the Mesozoic equivalent of a pig, with its hog-like snout and fleshy lips.
The crocodilian group as a whole, by which I mean the Metasuchia, was actually so diverse that I can't do the group justice in a single post, so this will be played out in two separate posts I'm working on. The first will be on the now-extinct, but extremely diverse group called the Notosuchids, which includes many mammal-like members that resemble everything from armadillos to house cats. In fact, they were so successful that they took over all kinds of dinosaur habitat and ruled whole regions where theropods and ornithopods once roamed. The second will be on the still living Neosuchia, which includes living crocodilians, the super-crocs of the Mesozoic, and some rather bizarre members, including some that seem almost Cetacean-like in anatomy and ecological role. They primarily avoided competition with dinosaurs and land animals, preferring an aquatic existence. However, there were certainly many exceptions to this rule.
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So the next few topics will likely be on these crocodilians. In fact, I've basically got the next few months of blogs planned out unless I get more requests. Along with crocodiles, I'm hoping to write about spinosaurid skulls, extinct giant birds, dinosaur footprints, and hopefully raptors. Also, since I happened to bring up The Complete Dinosaur Second Edition, I may do a review of it in the future. If a review would be of interest, let me know in the comments.  Until next time, stay sharp!

Sunday, September 30, 2012

Ornithopod Biodiversity and Evolution

Requested by MrGorsh
Diversity of the Ornithopods

Ornithopods were a hugely successful group of herbivorous dinosaurs, ranging from a little larger than a house cat, to 50-foot giants like Shantungosaurus that rivaled sauropods in size. The key to their success was the ability to process plant matter more efficiently than other dinosaurs. While ankylosaurs and ceratopsians also possessed the ability to chew, it was only in ornithopods that advanced dental batteries and unique jaw joints evolved. This allowed them to dominate an environment filled with tough plants species that were evolving. Many people overlook ornithopods because they tend to seem less interesting than other "sexier" dinosaurs like T-rex and Triceratops, but their lifestyles, evolution, and anatomy are just as interesting as those of any other animal group. However, before I start, I will note that ornithopod evolution and classification is an extremely debatable subject, especially  since the group was historically a taxonomic wastebasket of bipedal herbivorous dinosaurs. So I'll try my best to explain the many theories surrounding their origins and evolution based on my own sources.

The most primitive ornithopods we know of are commonly called the "hypsilophodontids." Although considered a natural group in the past, many now consider the "hypsolophodontids" an unnatural group, and some genera are actually closer relatives of iguanodonts than other "hypsolophodonts" (this is why I'm putting quotations around their name). The earliest known "hypsolophodontids" appear in the fossil record during the Late Jurassic, like Othnielosaurus and Agilisaurus, and survived all the way up till the extinction event 65 million years ago, with species like Thescelosaurus and Orodromeus present. They lived on every continent and tended to all have a similar body plan; the majority were small, with short skulls, large eyes, short beaks, long stiff tails, and long legs with proportions evolved for running at high speeds. They likely used this speed  to escape from predators, since they were without any other noticeable defense. This makes me think of them as being very skittish animals, ready to use their high speed to run at any sign of danger, like rabbits or deer today.

Some odd members of this group include the Australian polar Leaellynasaura, which had a tail close to three times it's own body length, and owner of the most vertebrae of any ornithopod outside of hadrosaurs. It's also famous for its apparently large eyes, however, this was based on the discovery of a juvenile skull; adults actually have the same sized eyes as other "hypsolophodontids." Another member I personally find very interesting is the long-snouted Thescelosaurus, made famous by Willo, a dinosaur that was first thought to have its heart preserved. While this has now been shown to instead be a sand clump, it still has a very strange skeletal anatomy. Thescelosaurus has a very long, thin snout, very unlike the short snout of other "hypsolophodonts," and leg proportions that would've hindered running speed (a long femur, a short tibia, and a short metatarsus). Nobody quite knows how Theselosaurus lived, but one theory that I've found interesting in recent months is the idea that it might have lived like modern capybara, spending time in the water for protection (as suggested by its short legs and long skull, both adaptations for aquatic life) and coming out on land at night to feed. This theory hasn't been popularized yet, and many people haven't even heard of it, but I'm open-minded and certainly find it possible after looking through its anatomy.

Numerous discoveries from North America and Australia also suggest that these animals, like rabbits and some species of kangaroos, might have been burrowers, their large, robust shoulders and hands being used to excavate tunnels, and their self-sharpening beaks being used to help carve openings in the dirt. These animals also have a small bone, called the palpebral, over the eyes that would've supported skin that could shade the eyes. A similar bone has been found in modern day birds of prey, who use the bones to help prevent glare when spotting prey. But "hypsolophodontids" were predominantly herbivorous, at most the animals might eat some insects from time to time, but certainly not in need of any predatory "sunglasses." Instead, scientists have suggested that they were used to protect the eyes while digging, by keeping rocks and dirt from damaging the delicate structures. Some hypsolophodonts also have been found with large, bony plates on the ribs. These don't seem to be very good for protection, as they were extremely thin and fragile, not suited for predatory attacks. So far nobody can agree on the function of the plates, but some have suggested that they have something to do with the respiratory system.

Despite these animal's success, they still hadn't evolved the advanced ways of processing food found in later ornithopods, and while their chewing was still better than many ornithischians, it was primitive and needed work. Ornithopod feeding got more advanced with the evolution of iguanodonts, who took the already present chewing of "hypsolophodonts" and added to it. They developed a enlarged premaxila that lacks any teeth and a deep dentary with parallel dorsal and ventral margins. These simple modifications helped with food processing so well, that they quickly started to dominate the local fauna, and evolved into much larger sizes. They seemed to have evolved during the middle of the Jurassic, as suggested by a single femur known by the name Callovosaurus (this also suggests "hypsolophodonts might have appeared earlier in the fossil record).

Callovosaurus is thought to be a dryosaurid, the most primitive type of iguanodont and looked very similar to "hypsolophodonts" in appearance, with long legs, small heads, and big eyes; in fact, they probably lived very similar to them as well. After them quickly evolved the camptosaurids, which were larger, had more elongated skulls, and were more heavily built than dryosaurids. They were also the first group where a thumb claw is seen present, which in later iguanodonts became enormous (I'll discuss this more further down). From them quickly evolved more advanced members, like Iguanodon and Dollodon, which were the most successful animals of their day. Their decendants included advanced members of the hadrosauroids, but we'll get to them later.

Some species of iguandontians, however, seem to be a bit difficult to find a good place to fit onto this tree, most notable is the famous American genus Tenontosaurus. What used to be thought of as a hypsolophodont, is now thought to be a type of basal iguanodontian in its own group, but where it fits exactly on the tree is still a matter of research. Tenontosaurus' most noticeable feature is its extremely long, deep tail, which took up 2/3 of its total body length, and a short nasal ridge that could have been used for display. It's also famous for supposedly being attacked by a pack of Deinonychus, but some recent evidence suggests otherwise. Another very primitive group of iguanodonts are the rhabdodontidae, which were a group of late-surviving iguanodonts that lived in Europe during the late Cretaceous. Scientists always had a hard time trying to pin down the rhabodonts' evolutionary relationships, as they were originally considered ceratopsians, but we seem to have a much better idea about them now. They were also, notably, some of the weirdest of ornithopods, having enormous skulls and teeth compared to their body size, and to this day we still don't know what they used them for.

During the iguanodont's evolution, many groups evolved different ways of living, but what was most noticeable was that many iguanodonts seem to have evolved in similar ways to tyrannosaurs, with some species being extremely robust and others being very gracile in anatomy. These gracile and robust morphs, seemed to have evolved to avoid competition with each other. This is reflected in fossil finds — you will often see robust and gracile iguanodonts living side by side at the same fossil site, but it's rare to see two of the same type. One of the most gracile forms of an iguanodont yet found is the African Ouranosaurus, which is well known for its elongated vertebrae, and was likely able to run away from potential predators at very high speeds. On the opposite side of the spectrum, one of the most robust of all iguanodonts lived alongside Ouranosaurus in Africa, known as Lurdusaurus. Lurdusaurus was immensely stocky and robust, with an extremely wide hip and stomach, short arms and legs with wide toes, a short, thick tail, and powerful arms; it was the sumo-wrestler of ornithopods. Many scientists have compared it to ankylosaurs in terms of its massively wide hips and robust build, but why get this robust in the first place? Well, many scientists looking over Lurdusaurus' anatomy have suggested that it was the dinosaur equivalent of a hippo, using its huge girth to keep afloat in water.

Along with being quite possibly the most aquatic herbivorous dinosaur ever found, Lurdusaurus also has one of the largest hands of any ornithopod, equipped with one of the largest thumb spikes. The thumb spike of iguanodonts has always been thought of as a defensive weapon, and certainly they would use it if their life was at stake. However, gracile morph iguanodonts have tiny thumb spikes, not suited for protection against large predators, and wouldn't their speed be enough anyway? Not just that, but later hadrosaurs completely lost their thumb spikes, and Lurdusaurus still has one present despite the fact it would've caused stress on its bones if it reared up to use it on land. This has led many scientists to think that the thumb claw instead was used like the spurs on roosters, in territorial battles, and the enormous size of the claw and arm on Lurdusaurus suggests that these animals dealt serious damage to each other when fighting, bringing to mind, again, the modern hippo. Alternatively, some think it could have been used to break open large seeds, but then again, would you really need a thumb spike a foot long to break open a little seed?

Of course, when you think about ornithopods nowadays, you don't think of lumbering aquatic animals anymore; that's the old view. Many people instead think of the hadrosauroids, the last group of ornithopods to evolve. Hadrosauroids, during their reign, were the largest, most numerous, and most biologically successful group of ornithopods to evolve. In North America alone we have close to 60 species of hadrosauroids present in the fossil record, each with its own characteristic body shape and build. Along with that, they also just happened to have evolved the most successful way of processing food of any dinosaur. They were surely the pinnacle of the ornithichian's success.

The hadrosauroids were able to tweak the iguanodonts' feeding apparatus and make it even more efficent than it was, adding to it an elongated snout to allow a larger number of teeth in the jaws. The snout broadened at the tip, producing the characteristic duck-like shape, and allowing for a larger amount of food to be taken in. The jaw also started forming complex dental batteries so that when one tooth fell out, another immediately took its place. These newly evolved jaws were what made the hadrosaurs able to out-compete their more primitive iguanodontian ancestors, thus the majority of iguanodonts went extinct.

Hadrosauroids are separated into two groups, the hadrosaurinae (also known as saurolophinae) and the lambeosaurinae (however, there are members that seem more primitive than either group). The hadrosaurinae are characterized by their low, elongated skulls with large nasal openings and wide beaks for taking in large quantities of vegetation. Some of these dinosaurs include Edmontosaurus, who at the moment is one of the best known fossil hadrosaurs and lived alongside T-rex, Maiasaura, who is the first dinosaur in the western hemisphere for which we found eggs and could attribute a nest, Tethyshadros, a island-living hadrosaur that has some of the strangest anatomy I've seen on a dinosaur (I get headaches just thinking about this guy), and Shantungosaurus, the largest hadrosaur, largest ornithischian, and largest dinosaur outside of the sauropods. The other group, the lambeosaurinae, are characterized by shorter, taller skulls, with small nasal openings and less wide beaks for more selective feeding. They are also well known for their large nasal crests that extend high above the top of the head. Some of these species include Parasaurolophus, a rare dinosaur that lived throughout a number of localities in North America, Corythosaurus, which is one of the best known lambeosaurs, Tsintaosaurus, which is also known as the "Unicorn" dinosaur for its straight tubular crest, and finally, the recently discovered giant known as Magnapaulia, quite possibly the largest lambeosaur ever.

These animals make up the majority of the dinosaur fauna during the late Cretaceous, and have been found on every continent with the exception of Africa and Australia (although the former is probably due to lack of good sampling sites), but they were at their most diverse in North America, and for quite a while we didn't really know why. However, a study that came out a few months ago put forth a possible explanation. At the same time that we are seeing this boom in hadrosaur diversity, the Rocky Mountains were rising, and the giant inland sea that was present at the time cut the continent in half. This caused many hadrosaurs, ceratopsians, and tyrannosaurs to be isolated within valleys between mountain chains and the ocean, and would cause isolation within a population and accelerate the process of evolution, causing many different animal forms to appear, but would likely have low populations. We've connected the dots even more and found that, when the inland sea started to recede, and the Rockies started to decrease in size with more erosion, dinosaurs weren't isolated anymore. This caused the diversity of ornithopods to decrease, and instead you would have large populations of a few dinosaur types. Who knew hadrosaurs could tell us so much?

Based on the evidence of bone beds, trackways, and communal nesting sites we've uncovered, it has been interpreted that Hadrosaurs were very social animals. While some species, like Parasaurolophus, were very rare among their local fauna and probably lived in very small herds, some bone beds have been found to contain thousands of individuals, likely representing herds moving across the landscape. This means that these dinosaurs likely needed ways to communicate, and they evolved the ability to communicate advanced messages throughout their nasal cavities. Lambeosaurs evolved a series of long, looping canals throughout the crests on their head, which produced a loud, trumpet-like sound when air was forced through it. Not just that, but since not just every species, but every individual has a slightly different shape to their crest, individuals could recognize each other through their calls. Hadrosaurs, however, didn't have large cranial crest to help communicate, yet we know they lived in herds. So what some scientists think they did was use their large nasal openings to communicate by inflating and deflating skin around them, causing a honking noise similar to geese.

Hadrosaurs also are notable for being very good parents, as shown by their complex social lives, and the discovery of fossil nests that were organized in a similar way to birds. The nests themselves are actually very similar to modern day megapode birds, which are a type of bird from southeast Asia and Australia, and evidence suggests that the nests were used year after year. The nests are also perfectly spaced, exactly one hadrosaur body-length apart. The nests themselves were bowl-shaped and filled with vegetation to help incubate the eggs. Baby hadrosaurs and fossil embryos have been discovered and show that the limb bones were poorly developed, suggesting the young were nest-bound and that parents probably brought food back to the nest to feed them. Growth rates from hadrosaurs show that they reached close to 3 meters in just a year or two of growth, one of the fastest levels of growth seen in the animal kingdom.

While many of these discoveries have been made in North America, as I stated above, they were not limited to that area. Both the largest and most primitive members are actually from Asia, and it is likely that that is where they originated. Dwarf hadrosaurs are also known to be found in Europe, which was once a scattering of small islands at the time. Other fossil hadrosaurs and complete nests have been found in South America, and we've even found them as far south as Antarctica. All these fossil finds clearly show that these animals weren't just tyrannosaur chow, but they were brilliantly evolved creatures ready to do what they needed to do to survive. Too bad their reign was cut short by extinction, I would've loved to have seen them in their glory.
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So there you have it. I hope that I answered your questions, MrGorsh. If there is still anything you might be wondering please feel free to leave a comment below, and for everyone else I hope you find this topic as interesting as I do.

For my next post I really don't know what I want to write about since I have so many ideas. Maybe something either about other Mesozoic animals, or perhaps something from more recent times? If you give me some feedback, I'll make sure to address topics you want to know more about. Until then, stay sharp!