Priconodon: Beast of the Week

 This week we will be checking out the coolest armored dinosaur most people never heard of.  Make way for Priconodon crassus!

Priconodon was an armored dinosaur that lived in what is now Maryland, United States, during the early Cretaceous period, about 115 million years ago.  It's name translates to "Pine Saw Tooth" in reference to its distinctive teeth, which it used to eat plants when alive.  Priconodon shows evidence of being the largest armored dinosaur ever discovered, possibly growing to 45 feet (13.7 meters) long from beak to tail.  

Watercolor of an adult Priconodon with two roughly human-sized Deinonychus in the foreground.  Fossil evidence suggests Priconodon may have been a behemoth of an armored dinosaur.

Despite being barely known even among dinosaur fans, Priconodon has been known on the fossil record for a very long time, being one of the first dinosaurs ever to be formally described from North America back in the late 1800s.  The first fossils from this dinosaur were in the form of teeth, which experts at the time were able to deduct were from some sort of armored dinosaur, and as time went on and more dinosaur bones were discovered elsewhere, more specifically a nodosaur.  Nodosaurs were armored dinosaurs in the ankylosaur group that were often adorned with large spikes but lacked tail clubs. (Europelta and Gargoyleosaurus are two examples of other nodosaurs that have been covered here)  Some of the Priconodon teeth unearthed were incredibly large, dwarfing the teeth of any other armored dinosaur.  Based on the size of the teeth compared to other more completely-known nodosaurs, it was known even back then that Priconodon was huge, likely the largest armored dinosaur known, but it was difficult to envision to what extent based on only teeth.  Another interesting trait of the teeth is that most of them show evidence of being water-worn, implying Priconodon may have preferred to feed on plants in or near the water.  This makes sense considering all of Priconodon's fossils have been found in what would have been a slow-moving riverbed or swamp during the early Cretaceous.

Priconodon tooth.  Image from the Smithsonian Museum of Natural History.

Priconodon tooth compared to the teeth of related nodosaur, Peloroplides.  Peloroplides measured about 20 feet from beak to tail.  Based on the difference in tooth size, Priconodon could likely have grown to be much larger.

Finally in 2023, over a century later, several fossils other than teeth from Priconodon were discovered from the same fossil site as its teeth in what is considered the first true dinosaur bone bed on the eastern part of the United States.  Several limb bones and osteoderms (armor pieces), including a large curved spike were uncovered.  Most impressive, however, was a GIGANTIC tail vertebra.  Combined with the largest teeth, when compared to the same parts of more completely known ankylosaurs, this vertebra implies that Priconodon may have grown to 45 feet long from beak to tail, making it the largest armored dinosaur ever discovered by a huge margin. (At the time of me writing this paper there is no formal paper describing any material from Priconodon other than teeth.  Bones from this dinosaur are still being found and prepped from the site in Maryland where it was found and a formal paper is still at least a few years away.  This is why there are no sources for the 45 foot estimate nor the bones below.  Please understand that estimate is a rough number and is of course subject to change.)

Priconodon tail vertebra (with one of the side processes missing) next to my hand, discovered in 2023.  Stay tuned for a formal paper on this and possibly more bones from this amazing armored giant in the future.

Priconodon would have shared its environment with a number of other dinosaurs known from the same fossil bed in Maryland where it was discovered, like Astrodon, Aquilops, Deinonychus, and Acrocanthosaurus, to name a few.  

References

Carpenter, K., and Kirkland, J.I. (1998). Review of Lower and middle Cretaceous ankylosaurs from North America. In: Lucas, S.G., Kirkland, J.I., and Estep, J.W. (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14:249-270.

Coombs, Jr., W.P. (1978). The families of the ornithischian dinosaur order Ankylosauria. Palaeontology 21(1):143-170.

Marsh, O.C. (1888). Notice of a new genus of Sauropoda and other new dinosaurs from the Potomac Formation. American Journal of Science 135:89-94.

Megaloceros: Beast of the Week

Today we shall be getting familiar with a prehistoric mammal that once called the plains of Ice Age Eurasia home.  Megaloceros giganteus, or as it's commonly referred to, the "Irish Elk", was the largest tallest deer to ever walk the earth, measuring almost seven feet tall at the shoulder.  It's antlers were by far the largest of any animal's, measuring twelve feet wide.  They lived not only in Ireland but across most of Europe and Asia during the Pleistocene alongside mammoths and early humans.  The oldest known Megaloceros specimen is 1.2 million years old, while the youngest is from 7,700 years ago.  The genus name translates to "Great Horn".  Despite its common name, Megaloceros' closest living relative is the Fallow Deer, and not elk.

Life reconstruction in watercolors of Megaloceros, by Christopher DiPiazza.  During the late fall, like all deer, Megaloceros would have shed a velvety layer off its antlers, revealing the horn-like antlers underneath.

There is much debate surrounding why the Irish Elk's antlers were so large.  The most likely answer is probably sex.  Like most species of animals with antlers, it is likely that only male Megaloceros had them. (Few exceptions exist, like Reindeer, where females also have antlers.)  Sexual selection probably pressured the males to evolve more impressive antlers over time to attract the females and to combat rival males.  Despite how antlers this large seem like they would have been more of a burden than an advantage in life, as long as they increased a male's chances of mating before he dies, they would continue to be passed on.  This is actually the case with most animal courtship displays.  They communicate that the individual sporting them is healthy enough to thrive despite the burden, and therefore is worthy of being chosen for mating by potential partners.

Megaloceros skeleton at the Natural History Museum in Dublin, Ireland.

Some scientists proposed that the huge antlers may have been the Megaloceros' ultimate demise, regardless of how sexy females found it.  This was proposed for a few reasons.  The first is that the antlers were believed to be so wide that towards the end of the ice age, when there were more trees and foliage growing, made it difficult for male Megaloceros to maneuver in their environments, who were more adapted to open tundra landscapes.  Another hypothesis is the antlers became too expensive to maintain.  Antlers, unlike horns which are part of an animal's skull, fall off and regrown every year.  In order to grow such large structures within a period of just a few months, the animal must consume more nutrient-rich food.  Modern deer have even been observed and documented killing and eating other animals (yup, predatory deer) to supplement their diets during this rapid growth stage.  Don't believe me?  Check out this video.  Also notice that the deer is in the process of growing a new set of antlers.  So imagine how much nutrient rich food, plant or animal, Megaloceros must have needed to get in order to maintain itself during this time.  Now imagine the dilemma it must have faced when its environment, including its food sources, suddenly changed at the end of the ice age.  

The last hypothesis about their extinction is common for most large animals that lived during the end of the Pleistocene; over hunting by humans.  We know that our ancestors probably hunted them sometimes thanks to Megaloceros appearing in cave paintings, but there is really no solid evidence that humans were the exact cause of their extinction.  

Painting of Megaloceros done by prehistoric humans found at the Cougnac Caves in France.  Note how there are individuals with and without antlers shown.  Also note the hump over the shoulders and the dark pattern at the top of the neck and on the body.  Photo found at Don's Maps.

Perhaps one the coolest things about Megaloceros, is since it lived alongside humans, we have hints of what it looked like when it was alive from those humans in the form of cave paintings! On a cave wall in France that could be as old as 22,000 years, what are almost certainly Megaloceros are heavily featured.  They were painted with and without antlers, supporting the idea that females did not have them, unlike reindeer.  Those people also depicted them with a prominent hump over the shoulders, which must have been full of fat, since the actual skeletons of these deer do not suggest such a feature.  Lastly, the paintings also include dark markings under the chin and also across the body in two stripes originating from the hump.  Some argue these are meant to represent the animal's actual coat pattern.  

References

Gould, Stephen J. (1974): Origin and Function of 'Bizarre' Structures - Antler Size and Skull Size in 'Irish Elk', Megaloceros giganteus. Evolution 28(2): 191-220. 

Lister, A. M. 1994. The evolution of the giant deer, Megaloceros giganteus (Blumenbach). Zoological Journal of the Linnean Society 112, 65-100.

Lister, A. M., Edwards, C. J., Nock, D. A. W., Bunce, M., van Pijlen, I. A., Bradley, D. G., Thomas, M. G. & Barnes, I. 2005. The phylogenetic position of the ‘giant deer’ Megaloceros giganteus. Nature 438, 850-853.

 Moen, R.A.; Pastor, J. & Cohen, Y. (1999): Antler growth and extinction of Irish Elk. Evolutionary Ecology Research 1: 235–249. 

Stuart, A.J.; Kosintsev, P.A.; Higham, T.F.G. & Lister, A.M. (2004): Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth. Nature 431(7009): 684-689.

Avisaurus: Beast of the Week

 This week we will be looking at a true bird that lived alongside some of the most famous dinosaurs.  Check out Avisaurus darwini!

Avisaurus was a bird (theropod dinosaur) that lived in what is now Montana, United States, during the latest Cretaceous period, about 66 million years ago.  Based on the bones that are known it would have been roughly the same size as a modern hawk. Possibly weighing about 2lbs (.9kg) and having a wingspan of about 4 feet (1.2 meters).  (Again these numbers are very rough estimates based on literally some foot bones and are therefore subject to change/variation.). The genus name translates to "Bird-Lizard" because it was initially thought to be a different kind of theropod, and not a bird.  The species name is in honor of the famous scientist, Charles Darwin.  When alive, Avisaurus, was likely a meat-eater, which we will discuss more below. 

Avisaurus darwini life reconstruction in watercolors by Christopher DiPiazza.  Parallels between Avisaurus' foot bones and the same bones of modern birds imply it may have been a hunter of larger prey, including smaller dinosaurs. In this case it is shown with a captured baby Acheroraptor.

Unfortunately fossil birds are usually only known from very fragmentary remains because they tend to have hollow bones, which often decompose before they fossilize. Avisaurus, which is only known from some foot bones, is no exception. That being said, scientists were still able to learn a lot of interesting information about this prehistoric bird based on the little material they did find.  The parts where the foot bones would have met the toe bones are similar to the foot bones of certain modern birds, like hawks, eagles, owls, and falcons.  All these birds have extremely flexible and powerful toes, tipped with hook-like talons for capturing prey.  Here it is important to note that Avisaurus was not directly related to modern birds, but evolving this trait common to modern birds of prey isn't outlandish.  This is due to the fact that most modern birds of prey aren't related to one another and evolved these predatory feet independently of one another.  That's right, owls, falcons, and hawks/eagles are all from completely separate families of birds and do not share a common ancestor with grasping talons. (falcons in particular are much closer to parrots than they are to other birds of prey.) So it isn't outlandish for an extinct lineage of bird from the Cretaceous to have independently evolved this trait as well.

Foot bones from Avisaurus darwini. Photo from paper by Clark et. al., referenced below. 

We know nothing else about what Avisaurus looked like other than its feet, but based on more completely-known fossil birds that were related to it we can make a few educated guesses.  It likely had clawed fingers under its wings.  (A trait still present in certain modern birds, like ostriches and chickens, but was more widespread in more ancient birds) It also may have had some teeth in its mouth, unlike the toothless beaks of all living birds.  

When alive, Avisaurus would have lived in a seasonally wet, almost swampy environment.  It almost certainly could fly, and based on its feet, was likely hunting smaller animals, like insects, reptiles, small mammals, other birds, and likely even small/baby dinosaurs and pterosaurs.  It would have shared its world with some of the most famous dinosaurs, like Tyrannosaurus, Triceratops, Edmontosaurus, Ankylosaurus, Pachycephalosaurus, to name just a few.  

References

Chiappe, Luis M. (1992) "Enantiornithine (Aves) Tarsometatarsi and the Avian Affinities of the Late Cretaceous Avisauridae" "Journal of Vertebrate Paleontology" September 3, 1992, Volume 12 no. 3 pp. 344-350

Clark, Alexander D.; Atterholt, Jessie; Scannella, John B.; Carroll, Nathan; O’Connor, Jingmai K. (2024-10-09). "New enantiornithine diversity in the Hell Creek Formation and the functional morphology of the avisaurid tarsometatarsus". PLOS ONE. 19 (10): e0310686.

Mononykus: Beast of the Week

 This week we'll be going over an interesting little dinosaur with unique arms.  Check out Mononykus olecranus! 

Mononykus was a small, bird-like, likely feathered dinosaur that lived in what is now Mongolia, during the late Cretaceous period, about 70 million years ago.  It only measured a little over 1 meter (between 3 and 4 feet) long from nose to tail and was likely a meat-eater, specializing in insects, when alive. The name, Mononykus, translates to "one claw" because it only had one large functional claw on each hand.  

Life reconstruction of Monoykus in watercolor by Christopher DiPiazza.

As the name implies, Mononykus possessed only one claw on each hand, which is perhaps its most distinctive trait.  The claws are proportionally large and curved, and are backed up by extremely stubby but powerful arms.  In fact, despite their length, Mononykus' ulnas (outer forearm bone) extend out past the upper arm bones, implying they had large muscle attachments there in life.  We see similar features in living animals like aardvarks, which use those kinds of muscles and large claws to dig into termite mounds.  Even though aardvarks and dinosaurs are not closely related at all, this may provide insight as to how Mononykus was using its unusual anatomy.  

Arm bones of a modern Aardvark(top) and Mononykus (bottom).  Note the extended ulna.

Other parts of Mononykus' anatomy imply it may have been digging for insects other than the arms and hand claws.  Its vertebra would have been interlocked in a way that stiffened the spine in life, making it more sturdy, another trait that would benefit digging.  The inside of the skull suggests Mononykus had superb hearing, comparable to that of modern owls, who are specially adapted for hunting prey they cannot see.  Again, this is a useful trait to have for an animal that is hunting for insects underground or inside of dead logs.  Other, more completely known, relatives of Mononykus, imply it likely had a narrow, toothless, beaklike mouth, and large, forward-facing eyes.  

Mononykus may have used its superb hearing to detect insects underground or inside logs, then would have needed to press its body against that surface in order to dig them out with its short arms.

As stated before, Mononykus had extremely short arms, which seems to be the only trait inconsistent with animals that dig for their food.  The arms are so short, in fact, that the only way for Mononykus to have even reached a surface to dig is if it's torso was pressed up against it.  I can imagine Mononykus listening to the outside of a dead log, and then rapidly positioning itself to a diffing position with its body pressed against the log, vigorously tearing at the bark with its claws, and then hopping back up to a standing position to listen again or root out the now exposed insects with its beak-like snout.  

Mononykus skeletal mount on display at the American Museum of Natural History in New York.

Mononykus also had extremely long and slender legs.  This implies it was a fast runner when alive, which would have been a useful trait for avoiding predators, but it also has another function that may also be related to finding food.  Long legs means Mononykus could have more easily walked long distances without getting tired.  Since we know Mononykus lived in a desert, it would have needed to regularly travel across large expanses of land in order to find areas where insects actually were, like oasises, or sparsely occurring logs in an otherwise barren environment.  

When alive, Mononykus would have shared its environment with other dinosaurs, like Prenocephale, Gallimimus, Deinocheirus, Therizinosaurus, and the large tyrannosaur, Tarbosaurus, to name a few.  It likely avoided confrontation with the vast majority of these other animals by possibly being nocturnal.  

References

Choiniere, Jonah N.; Neenan, James M.; Schmitz, Lars; Ford, David P.; Chapelle, Kimberley E. J.; Balanoff, Amy M.; Sipla, Justin S.; Georgi, Justin A.; Walsh, Stig A.; Norell, Mark A.; Xu, Xing; Clark, James M.; Benson, Roger B. J. (2021-05-07). "Evolution of vision and hearing modalities in theropod dinosaurs". Science. 372 (6542): 610–613.

Perle, A.; Norell, M. A.; Chiappe, L. M.; Clark, J. M. (1993). "Flightless bird from the Cretaceous of Mongolia". Nature. 362: 623−626.

Perle, A.; Chiappe, L. M.; Rinchen, B.; Clark, J. M.; Norell, M. A. (1994). "Skeletal morphology of Mononykus olecranus (Theropoda, Avialae) from the late Cretaceous of Mongolia". American Museum Novitates (3105): 1−29.

Spectrovenator: Beast of the Week

 This week we will be showcasing a dinosaur with a particularly spooky name.  Check out Spectrovenator ragei!

Spectrovenator was a meat-eating dinosaur that lived in what is now Brazil during the early Cretaceous period, about 125 million years ago.  From snout to tail it only measured about 2.5 meters (8 feet) long.  It's genus name translates to "Ghost hunter" in reference to how it was found during the month of October (Halloween!) plus the fact that it was found serendipitously while paleontologists were excavating the bones of a larger dinosaur, called Tapuisaurus. Almost as if the Spectrovenator's bones were hiding...like a ghost.

Life reconstruction of Spectrovenator in watercolors by Christopher DiPiazza

Spectrovenator belonged to a group of theropod dinosaurs called ceratosaurs, known first appearing on the fossil record during the early Jurassic period, almost 200 million years ago, and persisted all the way to the end of the Cretaceous period, 66 million years ago.  Ceratosaurs were particularly diverse group of theropods, evolving a wide variety of shapes and sizes during the long time they existed on earth.  Spectrovenator was specifically part of the abelisaurid family of ceratosaurs, known for having extremely short snouts and tiny arms.  Their arms were so small, in fact, that they lacked the ability to use their fingers, which were reduced to mere stubs in most cases.  Later abelisaurids, like Carnotaurus, would lose the ability to bend their elbows, having small stumps for arms that could only swivel on one joint at the torso.  Spectrovenator was an earlier form of the abelisaurid group, appearing to be a somewhat transitional form between earlier Jurassic forms and later Late Cretaceous forms.  For instance, its snout was relatively short compared to most theropods, but not as short as the almost bulldog-like face of its later relatives, like Carnotaurus.

Spectrovenator had long, curved teeth that were serrated, like steak-knives on the anterior edge, ideal for slicing through meat.  Its lower jaw was relatively slender, implying it had a weaker bite force than its later relatives, possibly specializing in snatching smaller prey or slashing, rather than crushing or overpowering its prey.  The top of its skull, over the snout and eye sockets, possessed a rough texture, implying there could have been bony keratin there in life, possibly some sort of ornamentation for display.  

Skull of Spectrovenator from the paper by Zaher et. al. referenced below.

Spectrovenator also had relatively long and slender legs, implying it would have been a fast runner when alive.  This would have been helpful for a small predator for running down prey, and possibly escaping even larger meat-eaters it shared its environment with.  

References

Hendrickx, Christophe; Mateus, Octávio (2014). "Abelisauridae (Dinosauria: Theropoda) from the Late Jurassic of Portugal and dentition-based phylogeny as a contribution for the identification of isolated theropod teeth". Zootaxa. 3759: 1–74.

Senter, P. (2010). "Vestigial skeletal structures in dinosaurs". Journal of Zoology. 280 (1): 60–71.

Zaher, H.; Pol, D.; Navarro, B.A.; Delcourt, R.; Carvalho, A.B. (October 2020). "An Early Cretaceous theropod dinosaur from Brazil sheds light on the cranial evolution of the Abelisauridae" (PDF). Comptes Rendus Palevol. 19 (6): 101–115.

Meniscoessus: Beast of the Week

 This week we'll be checking out a beast that shows us that mammals were actually thriving, not merely surviving, during the Mesozoic.  Enter Meniscoessus robustus! 

Meniscoessus was a roughly house cat-sized mammal that lived during the late Cretaceous Period, between 70 and 66 million years ago, in what is now North America, specifically Alberta in Canada, and Wyoming, Montana, and South Dakota in the United States.  From nose to rump it measured about two feet (60 cm) and was likely an omnivore when alive.  The genus name translates to "Small Crescent Tooth" in reference to its rodent-like front teeth.  There are actually several species of Meniscoessus that lived during the later Cretaceous period, but today I'll be focusing on Meniscoessus robustus, which is known from many fossil specimens.

Meniscoessus life reconstruction in watercolors by Christopher DiPiazza.

Meniscoessus was a mammal that belonged to a broader group of mammals called the multituberculates.  Multituberculates are a completely extinct group of mammals, despite superficially resembling rodents in many ways.  In fact, this group of mammals was separate from the three major groups of mammals alive today, the monotremes (egg-laying mammals), the monotremes (give birth to tiny underdeveloped young that finish growing in the mother's pouch), and placentals (young develops for a relatively longer period of time inside the uterus, and lack bones in the pelvis allowing for birth of larger babies).  Scientists have speculated that multituberculates likely did not lay eggs, and were more likely similar to placentals and monotremes in how they gave birth, although some research suggests they evolved this trait independently, instead of sharing a common ancestor that gave live birth.  Multituberculates actually survived past the extinction caused by the meteorite that wiped out most of the dinosaurs, not going extinct until the late Eocene, about 35 million years ago.  

Meniscuessus robustus skull on display at the Smithsonian National Museum of Natural History's temporary "Last American Dinosaurs" exhibit.  Photo credit: Eden, Janine and Jim

Meniscoessus had teeth in the front of its mouth that resemble the incisors (front teeth) of modern rodents.  Unlike rodents, who's front teeth are continuously growing, the front teeth of Meniscuessus, however, underwent the same replacement process as most mammal teeth.  They likely used these teeth like rodents do today, to chew through tough plant material, possibly even gnawing the bones of dead animals to access calcium as well.  The back teeth had multiple cusps and the fourth back tooth on the lower jaw was notably larger than the others, a trait common to the multituberculate group.  Yet another unique trait of this kind of mammal is how their jaws would have moved front to back, rather than side to side, as they chewed.  It is possible Meniscuessus was an opportunistic omnivore, not hesitating to eat insects, eggs, and possibly smaller vertebrates.  

When alive, Meniscoessus robustus would have shared its habitat with Tyrannosaurus, Acheroraptor, Pectinodon, Anzu, Triceratops, and Edmontosaurus, to name a few.  It likely would have been preyed upon by the carnivorous dinosaurs, and may have been nocturnal or crepuscular (most active during dawn and dusk) to best avoid crossing paths as many dinosaurs as possible, sleeping and hiding either underground or trees during the day.  In turn, however, Meniscoessus may have eaten dinosaur eggs as a source of protein when it could.  

Meniscuessus, and its family in general, are important in reminding us that although mammals were generally much smaller during the Mesozoic, they were by no means struggling in an evolutionary sense, but rather diversifying and thriving in their own ways.

References

Cifelli, Richard; Eberle, Jaelyn; Lofgren, Donald; Lillegraven, J.; Clemens, William (2004). "Mammalian Biochronology of the Latest Cretaceous in North America"

Cope, E.D. (1882). "Mammalia in the Laramie Formation". American Naturalist. 16 (10): 830–831.

Mao, Fangyuan; Li, Zhiyu; Wang, Zhili; Zhang, Chi; Rich, Thomas; Vickers-Rich, Patricia; Meng, Jin (2024-04-03). "Jurassic shuotheriids show earliest dental diversification of mammaliaforms". Nature. 

Osborn, Henry Fairfield (1891). "A Review of the "Discovery of Cretaceous Mammalia"". The American Naturalist. 25 (295): 595–611.

Weil, Anne (June 1997). "Introduction to Multituberculates: The 'Lost Tribe' of Mammals"

Ouranosaurus: Beast of the Week

 This week we will be checking out a beautiful and unique plant-eating dinosaur.  Get ready for Ouranosaurus nigeriensis!

Ouranosaurus was an ornithopod dinosaur that lived in what is now central Africa, specifically Niger and Camaroon, during the early Cretaceous period, between 121 and 113 million years ago.  It was a plant-eater when alive and adults would have measured about 25 feet (7.6 meters) long from beak to tail.  The genus name, Ouranosaurus, translates to "Courageous Lizard" from a combination of Arabic and Greek languages.  The species name, nigerensis, is in reference to the country, Niger, where its bones were first discovered. 

Ouranosaurus life reconstruction in watercolor by Christopher DiPiazza

Ouranosaurus was an ornithopod dinosaur closely related to Iguanodon and Mantellisaurus.  Like them, it would have been able to walk on all fours or its hind legs.  Its arms were proportionally long and ended with five digits on each hand.  The first digit, like those of Iguanodon, consisted of a thumb-spike, but it was proportionally smaller.  Its second, third, and fourth fingers were likely fused in life and would have supported its weight as it walked on all fours.  Its fifth finger was relatively long, but not flexible.  

Mounted skeleton of Ouranosaurus on display at the Natural History Museum of Venice in Italy. Photo from Felippo Bertozzo's 2017 paper (referenced below).

Ouranosaurus had a long and laterally flattened snout, with its nostril holes facing upwards, a trait similar to some more distantly related hadrosaurs ("duck-billed" dinosaurs).  Ouranosaurus had a broad beak at the front of its mouth, and small closely-spaced teeth, forming what is referred to as a dental battery, in the back of its jaws, for processing plants.  The bones that make up the top of Ouranosaurus' snout were actually unfused to the rest of the skull, suggesting flexibility in life, possibly an adaptation for feeding a certain way.  

Image of Ouranosaurus' skull from Taquet's 1976 paper (listed below) Red arrows pointing to two rounded knobs on the top of its head where the nasal bones begin.  Some think there were small horns or crests there in life while others point out the surface texture does not suggest any such characteristic.

The most notable feature of Ouranosaurus is definitely its extremely tall neural arches, the sections of its vertebra that extend upwards from its back.  This is a feature that has independently evolved in several kinds of dinosaurs and other animals across history.  The most famous example of this feature is probably the theropod dinosaur, Spinosaurus, but many other prehistoric animals as well as many modern reptiles have evolved this trait in varying degrees.  In life, this structure would have formed a meaty sail-like structure on Ouranosaurus', back, drastically expanding the dinosaur's profile.  Experts have suggested such a bold adaptation could have been for display within the species or possibly to help control the Ouranosaurus' body temperature by expanding its surface area to either absorb warmth from the sun or expel excess heat if it became too hot.  

Clockwise from tom left, Sailfin Chameleon (Trioceros montium), Green Basilisk (Basilicus plumifrons), and Sailfin water dragon (Hydrosaurus pustulatus), are all modern lizards that independently of one another evolved tall spines on their vertebra, forming fleshy sails on their backs.

The environment Ouranosaurus lived in would have been a seasonally wet floodplain and it would have coexisted with a number of other dinosaurs, including fellow herbivores, Lurdusaurus and Nigersaurus, as well as the large spinosaur, Suchomimus.  

References

Bertozzo, F.; Dalla Vechia, F.M.; Fabbri, M. (2017). "The Venice specimen of Ouranosaurus nigeriensis (Dinosauria, Ornithopoda)". PeerJ. 5: e3403.

McDonald, A.T.; Kirkland, J.I.; DeBlieux, D.D.; Madsen, S.K.; Cavin, J.; Milner, A.R.C.; Panzarin, L. (2010). Farke, Andrew Allen (ed.). "New Basal Iguanodontians from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs". PLOS ONE. 5 (11): e14075.

Taquet, P. (1976). "Géologie et Paléontologie du Gisement de Gadoufaoua (Aptien du Niger)" (PDF). Cahiers de Paléontologie. Éditions du Centre National de la Recherche Scientifique, Paris: 1–191.