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.

Silesaurus: Beast of the Week

 This week we will be checking out an interesting and a mysterious creature, Silesaurus opolensis!

Silesaurus was a reptile, closely related to dinosaurs, that lived in what is now Poland during the Triassic period, between 237 and 227 million years ago.  Footprints that could have been from Silesaurus, or at the least something very closely related to it, have also been found on the east coast of the United States, including Maryland.  When alive it would have been an omnivore, eating plants and also small animals, like insects.  Adult Silesaurus measured about 7.5 feet (2.3 meters) from beak to tail.  The genus name, translates to "Selesia Reptile" In reference to the region in Poland in which its bones were discovered. 

Life reconstruction of Silesaurus in watercolors by Christopher DiPiazza.

Silesaurus had a narrow snout with a beaklike mouth.  Its teeth were somewhat leaf-shaped and lacked prominent serrations.  Microwear studies on Silesaurus teeth suggest it ate lots of plants but fossilized dung associated with Silesaurus was also found to have beetle shells in it, showing it was more likely an omnivore, eating insects and maybe other small animals on occasion in addition to a mostly plant diet.

Silesaurus skeletal mount on display at Jurapark Science Park, in Poland.

Silesaurus would have walked on all fours most of the time but may have been able to rear up on its hind legs on occasion if it needed.  All four of its limbs were long and slender, making it look like a reptilian greyhound of sorts. (in my opinion at least) It had five very short fingers and claws on each of its hands and its feet each had three toes.  Thanks to tracks we know its thumb and pinky fingers were held off the ground when it walked. The neck was relatively slender and would have been held in a gentle S shape most of the time, a feature similar to dinosaurs. 

Hand (left) and foot (right) tracks from what may have been Silesaurus (or a very close relative) that were found in Maryland, United States, on display at the Natural History Society of Maryland in Baltimore.

Silesaurus is an interesting animal because its exact placement on the tree of life is still highly debated.  That by itself wouldn't be that unusual (loads of fossil animals we don't know the exact natural history of) but what makes Silesaurus' identity especially noteworthy is because the discourse is over whether or not it is a dinosaur. (dinosaurs are popular) The original placement of Silesaurus was that it was an extremely close relative of dinosaurs without quite being a true dinosaur, itself.  It shares a number of dinosaur-like characteristics, like having its limbs positioned directly under it's body, resulting in a fully erect posture while standing and walking.  It also has several diagnostic dinosaur characteristics in its leg and hip bones.  Because of these extreme similarities to dinosaurs, some experts propose that the silesaurid family should be reassigned as true dinosaurs, specifically early ornithiscian dinosaurs, the broad branch of dinosaurs which includes famous taxa like Triceratops, Stegosaurus, and Iguanodon.  This is partially due to the fact that there is very little, if any, ornithiscian dinosaur fossils known from the Triassic period. (unless they're the silesaurids). Other experts, however, are still unconvinced, since Silesaurids still don't possess some other key dinosaur characteristics, like a specialized ridge on the anterior of the humerus for muscle attachments, called the deltopectoral crest, as well hip sockets that form an open window through the pelvis. 

Images of the humerus of Silesaurus (left) from Piechowski's 2020 paper alongside the humerus of early ornithiscian dinosaurs, Heterodontosaurus (middle) and Abrictosaurus (right) from Galton's 2014 paper. Note the Silesaurus bone is lacking the deltopectoral crest at the top of the bone compared to the other two. 

Regardless if Silesaurus was a true dinosaur or not, it very well may have sported feathers of some kind when alive.  This is because both dinosaurs and pterosaurs are believed to have shared a common ancestor with some kind of feathers.  Since silesaurids were at least more closely related to true dinosaurs than to pterosaurs, they likely would have had some kind of feathers as well.  This method of predicting features in fossil groups based on known features in surrounding groups is known as phylogenetic bracketing.  

References

Dzik J (2003). "A beaked herbivorous archosaur with dinosaur affinities from the early Late Triassic of Poland" (PDF). Journal of Vertebrate Paleontology. 23 (3): 556–574.

Galton, P.M. (2014). "Notes on the postcranial anatomy of the heterodontosaurid dinosaur Heterodontosaurus tucki, a basal ornithischian from the Lower Jurassic of South Africa" (PDF). Revue de Paléobiologie, Genève. 1. 33: 97–141.

Nesbitt, Sterling J. (2011). "The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades". Bulletin of the American Museum of Natural History. 352: 1–292.

Piechowski, Rafał; Tałanda, Mateusz (2020). "The locomotor musculature and posture of the early dinosauriform Silesaurus opolensis provides a new look into the evolution of Dinosauromorpha". Journal of Anatomy. 236 (6): 1044–1100. 

Acrocanthosaurus: Beast of the Week

This week we are checking Acrocanthosaurus atokensis!  Acrocanthosaurus was a meat-eating dinosaur that lived in what is now the United States, including Oklahoma, Texas, Wyoming, and even as far east as Maryland, during the Early Cretaceous Period, between 125 and 100 million years ago.  Acrocanthosaurus measured about thirty eight feet (11.5 meters) long from snout to tail, and was likely the top predator in its environment.  The name Acrocanthosaurus, translates to "High Spine Lizard" and is in reference to this dinosaur's particularly tall neural arches, which gave it a distinctive ridge down its back.

Watercolor reconstruction of Acrocanthosaurus by Christopher DiPiazza.

Acrocanthosaurus' spine was interesting in that we haven't found another theropod dinosaur with anything similar.  It is often compared to the unrelated, Spinosaurus' sail-like structure, but Acrocanthosaurus' runs all the way from the back of the skull to about midway down the tail, rather than just the back like in Spinosaurus.  Acrocanthosaurus also has a close relative from Spain, Concavenator, which has a triangular-shaped hump over its hips, but again, this is concentrated to one area of the spine. The purpose of this ridge-like look is a mystery.  Some believe it would have formed a hump rather than a ridge, like what you might see on a modern bison's skeleton.  (Which also have extended neural arches, but mostly over the shoulders.)   As of now the safe answer could always be that Acrocanthosaurus possessed this ridge down its spine for display purposes to other members of its species.  Maybe they were larger in males than in females and played a role in mate selection?  Perhaps it was significantly shorter in juveniles?  There is still a lot we don't know!

Bison skeleton.  Note the tall neural arches above the shoulders.  The living animal has a hump there.

The skull of Acrocanthosaurus is long, low, and narrow in the front, but the back of the lower jaw become increasingly deep, suggesting there was a lot of muscle there in life, allowing this dinosaur to bite down hard.  The teeth of Acrocanthosaurus were slightly curved and serrated on both the front and back edges.  They were also thicker than the very blade-like teeth of its later relatives, like Giganotosaurus and Cacharodontosaurus, suggesting Acrocanthosaurus was more of a generalist hunter.  This is also further supported by the fact that Acrocanthosaurus' range was so widespread across what is now the United States, which would have consisted of multiple different kinds of habitats, and therefore likely different kinds of prey.

Acrocanthosaurus skull from the North Carolina Museum of Natural Sciences.

The front limbs of Acrocanthosaurus were short, but powerful, and had a decent range of motion to them.  Each hand possessed three hooked claws.  It is difficult to say exactly how Acrocanthosaurus would have utilized these arms since they were so short, but they may have played a part when it was going after large prey, like a sauropod, at close quarters.

Acrocanthosaurus skeletal mount on display at the North Carolina Museum of Natural Sciences.

When alive, Acrocanthosaurus, would have coexisted with many other dinosaurs, including the much smaller predator, Deinonychus, the ornithopod, Tenontosaurus, and a few different kinds of large sauropods, like Sauroposeidon and Astrodon on the east coast.  In fact, there is a dinosaur trackway in Texas consisting of large theropod prints that are believed to have been made by Acrocanthosaurus along with those of a large Sauropod.  These tracks show, since at times the theropod prints overlap the sauropod ones, that those of the theropod were made later, and could have possibly been following the larger herbivore.  At one point some scientists believe the theropod even attacked the sauropod, since the meat-eater tracks skip for a while where they finally intersect. (did it latch onto the side of its intended prey?)  This hypothesis can't be fully proven, however.  Even though no bones from either dinosaur were found with this trackway, it is suggested the predator was Acrocanthosaurus because the size, location, and age of the tracks.

Photograph of the tracks believed to have been from Acrocanthosaurus possibly stalking a sauropod in the field in Texas.  You can now see these tracks in person on display at the American Museum of Natural History in New York City.

That is all for this week!  As always please comment below or on our facebook page!

References

Currie, Philip J.; Carpenter, Kenneth. (2000). "A new specimen of Acrocanthosaurus atokensis (Theropoda, Dinosauria) from the Lower Cretaceous Antlers Formation (Lower Cretaceous, Aptian) of Oklahoma, USA". Geodiversitas 22 (2): 207–246.

Lockley, Martin G. (1991). Tracking Dinosaurs: A New Look at an Ancient World. Cambridge: Cambridge University Press. p. 252pp.

Senter, Phil; Robins, James H. (2005). "Range of motion in the forelimb of the theropod dinosaur Acrocanthosaurus atokensis, and implications for predatory behaviour". Journal of Zoology 266 (3): 307–318.

Stovall, J. Willis; Langston, Wann. (1950). "Acrocanthosaurus atokensis, a new genus and species of Lower Cretaceous Theropoda from Oklahoma". American Midland Naturalist (American Midland Naturalist, Vol. 43, No. 3) 43 (3): 696–728.

Thomas, David A.; Farlow, James O. (1997). "Tracking a dinosaur attack". Scientific American 266 (6): 48–53.

Rhamphorhynchus: Beast of the Week

Rhamphorhynchus was a pterosaur that lived in what is now Germany during the late Jurassic period, between 150 and 148 million years ago.  The adults measured about four feet (1.2 meters) long from beak to tail and had wingspans of about six feet (1.8 meters) wide.  When alive Rhamphorhynchus would have eaten meat, mostly in the form of fish and other marine life.  The genus name translates to "Beak Snout" from Greek.  Rhamphorhynchus muensteri is by far the most well known species of Rhamphorhynchus, known from many individual specimens, however, there is also a species known from a single wing fossil found in what is now Dorset, England, called Rhamphorhynchus etchesi.

Rhamphorhynchus muensteri life reconstruction in watercolors by Christopher DiPiazza.

Rhamphorhynchus belonged to the group of pterosaurs that existed from the Triassic to the early Cretaceous periods, characterized by their proportionally smaller heads short legs, and long narrow tails, called rhamphorhynchoids. (named after Rhamphorhynchus, itself.)  In addition to their wings, which form from flexible skin attached from the tip of their fourth finger (which was extremely long and sturdy) to about the ankle, pterosaurs from this group also sported a membrane between their legs, which likely aided in flight.  Pterosaurs from this group also sported teeth, and Rhamphorhynchus was no exception.  The teeth of Rhamphorhynchus, were particularly long, slightly curved, and interlocked when the jaws were closed.  The tip of its jaws also curved into each other and were beaklike.  This seems to be an adaptation for grasping fish, cephalopods, and other slippery marine prey.  

Rhamphorhynchus skeleton on display at the Royal Ontario Museum that showcases preserved soft tissue, like wing membranes and the tail vane.

At the tip of its tail, Rhamphorhynchus sported a fan-like structure, called a tail vane, which may have helped it steer during flight.  Since Rhamphorhynchus is known from many individuals of different stages of maturity when they died with soft tissue preserved, we know that the shape of this structure changed as the animal aged.  The youngest individuals sported narrow, oval-shaped vane, slightly older individuals had vanes that were more pointed and diamond-like, while in the most mature individuals the tip of the vane flared out into an almost sideways triangle shape.  Because of this change it is possible the vane may have had a role in some sort of communication, like sexual display within the species, as well.  Originally, scientists thought Rhamphorynchus consisted of several more species than the two listed at the top of this post, grouping them based on size and tail vane shape.  More recently, however, it was determined they more likely mostly the same species at different developmental stages of life. 

Rhamphorhynchus fossil with imprints of the wing membranes and tail vane cast on display at the American Museum of Natural History in New York.

Since Rhamphorhynchus is known from many specimens of various sizes, paleontologists were able to study and predict how it would have grown as it aged when alive.  Thanks to a study in 2012, examining various specimens of different stages when they died, it was determined that like many modern reptiles, Rhamphorhynchus would have been able to survive on its own soon after hatching, meaning it was likely able to fly right away, and would have grown rapidly early in life.  This growth spurt seemed to slow down at about three years of age, which also seems to be when they were fully mature.  

The environment that Rhamphorynchus lived in would have been a series of islands with lagoons in a relatively shallow sea.  It likely would have hunted over the water, snatching small fish and other marine animals off the surface of the water while flying.  It would have coexisted with fellow pterosaur, Pterodactylus, and the dinosaurs Archaeopteryx and Compsognathus.  

References

Bennett, S. C. (1995). "A statistical study of Rhamphorhynchus from the Solnhofen Limestone of Germany: Year-classes of a single large species". Journal of Paleontology. 69 (3): 569–580.

Prondvai, E.; Stein, K.; Ősi, A.; Sander, M. P. (2012). Soares, Daphne (ed.). "Life history of Rhamphorhynchus inferred from bone histology and the diversity of pterosaurian growth strategies". PLOS ONE. 7 (2): e31392.

O'Sullivan, Michael; Martill, David M. (June 2015). "Evidence for the presence of Rhamphorhynchus (Pterosauria: Rhamphorhynchinae) in the Kimmeridge Clay of the UK" Proceedings of the Geologists' Association. 126 (3): 390–401.

Mei: Beast of the Week

 This week we will look out a dinosaur that helped solidify the connection between extinct dinosaurs and modern birds.  Let's check out Mei long!

Mei was a theropod dinosaur that lived in what is now China, during the Early Cretaceous period, about 125 million years ago.  It only measured about two feet (60cm) long as an adult, about the size of a modern duck, and would have eaten meat and possibly some plant material when alive.  The genus and species name, Mei long, translates from Chinese to "sleeping dragon" in reference to how this amazing fossil was discovered.  

Life reconstruction of Mei in watercolors by Christopher DiPiazza.

Mei's biggest claim to fame is how it was unearthed in a sleeping position, similar to how modern birds sleep with their head curled back and tucked under one wing and legs folded under the rest of the body.  Not only is this interesting purely because we know what kind of posture a dinosaur had millions of years ago, but it also strongly implies this dinosaur had feathers when alive, since the pose of the head tucked under the arm is so often done by modern birds with the use of wing feathers to shield the eyes.  The minerals between and over the bones of Mei imply the dinosaur was buried alive extremely quickly by ash from an erupting volcano, resulting in a beautifully preserved complete dinosaur skeleton for paleontologists to learn from.  

Cast of the juvenile specimen of Mei on display at the American Museum of Natural History in the seasonal "Dinosaurs Among Us" exhibit in 2014.

Mei was a member of the troodontid family of theropods.  Troodontids were birdlike, typically smaller dinosaurs that appear to have specialized in hunting small animals and possibly some plants when alive.  Troodontids typically had proportionally large eyes, narrow snouts, short arms, and long slender legs tipped with sharp claws, including a retractable second toe claw, which could have been an adaptation for pinning prey.  

Mei is known from two specimens, one young juvenile and one adult.  The adult retains what are generally considered juvenile characteristics, like proportionally short snout and large eyes.  Both specimens also exhibit relatively large nares (nostril holes in the skull) which is unusual for troodontids.  

Photograph of the second discovered specimen of Mei from the 2012 paper by Gao et al., which was an adult when it died. 

The environment that Mei lived in during the early Cretaceous appears to have been heavily forested with rivers and lakes throughout with nearby active volcanoes.  Since Mei was so small, it may have relied on hiding in the underbrush, or possibly even climbing trees to avoid predation from larger predators that shared its environment, like the gliding dinosaur, Changyuraptor, or even the large tyrannoysauroid, Yutyrannus.  Mei also would have crossed paths with dinosaurs like Beipiaosaurus and Tianyulong to name a few more.

References

Gao C, Morschhauser EM, Varricchio DJ, Liu J, Zhao B (2012) A Second Soundly Sleeping Dragon: New Anatomical Details of the Chinese Troodontid Mei long with Implications for Phylogeny and Taphonomy. PLoS ONE 7(9): e45203. https://doi.org/10.1371/journal.pone.0045203

Junchang Lü; Li Xu; Yongqing Liu; Xingliao Zhang; Songhai Jia & Qiang Ji (2010). "A new troodontid (Theropoda: Troodontidae) from the Late Cretaceous of central China, and the radiation of Asian troodontids" (PDF). Acta Palaeontologica Polonica. 55 (3): 381–388.

Xing Xu & Mark A. Norell (2004). "A new troodontid dinosaur from China with avian-like sleeping posture" (PDF). Nature. 431 (7010): 838–841.