Khaan: Beast of the Week

 This week we will be checking out a dinosaur that gave us insight into its behavior.  Make way for Khaan mckennai!

Khaan was a small birdlike dinosaur that lived in what is now Mongolia during the late Cretaceous period, between 75 and 71 million years ago.  From beak to tail it measured about four feet (1.2 meters) long and its name means "Lord" in Mongolian.  (Doesn't stop dinosaur nerds who are also Star Trek nerds making jokes about it, though.) When alive Khaan was likely an omnivore, eating seeds and plants, but also small animals.  

Watercolor reconstruction of a female and male Khaan mckenai.  There is actual fossil evidence that males of this species may have exhibited courtship dances. (read on)

Khaan was a member of the oviraptorid family, characterized by their overall very birdlike appearance, with long, slender legs and necks, long arms, tipped with hooked claws, and possessing feathers.  They also are known for having unusually blunt skulls with large eye sockets and very short, almost parrot-like beaks.  Many of them also had tall bony crests growing from the front of their faces.  Khaan was a particularly small example of this group, but many, like Citipati were about human-sized, and others, like Gigantoraptor were huge.  

Skull of Khaan on display at the American Museum of Natural History in New York.

Like all oviraptorids, Khaan had a short, tall beak, which many experts think was an adaptation for eating mostly plants when alive.  Others have suggested it was also eating small animals, and even using their seemingly specialized beak for cracking hard-shelled prey like shelled mollusks and crustaceans.  Khaan was actually part of a study that examined the jaws of several kinds of oviraptorids and compared them to those of other kinds of plant-eating theropods, like ornithomimosaurs and therizinosaurs.  This confirmed that for their size, oviraptorids had very powerful bites for their size, and may have been using their jaws for crunching through particularly tough plant material that other, weaker-jawed dinosaurs couldn't access.  

Skeletons of the two Khaan specimens that are thought by experts to represent a male and female.  They may have have even been a pair in life, since they were discovered together. Casts of these skeletons were on display at the American Museum of Natural History in New York for their temporary "Dinosaurs Among Us" exhibit.

Khaan tells us a lot about dinosaur behavior thanks to a few key details about its anatomy.  Two skeletons of Khaan that were adults when they died were discovered right next to each other.  Normally there would be no way to tell if these were the same or different sexes, except for the fact that one of them had slightly longer and differently-shaped tail chevrons (bony extensions on vertebrae) which implies there were more muscles there in life.  This means one of them was using its tail for something the other wasn't.  This had lead to a lot of experts to hypothesize that Khaan may have engaged in courtship dances, like many modern birds do today, like turkeys or grouse, with the males moving their their tails around (probably with feathers on the end) to entice potential partners.  

References

Clark, J. M.; Norell, M. A.; Barsbold, R. (2001). "Two new oviraptorids (Theropoda: Oviraptorosauria), Upper Cretaceous Djadokhta Formation, Ukhaa Tolgod, Mongolia". Journal of Vertebrate Paleontology. 21 (2): 209.

Iv, W. S. P.; Funston, G. F.; Currie, P. J.; Norell, M. A. (2015). "A possible instance of sexual dimorphism in the tails of two oviraptorosaur dinosaurs". Scientific Reports. 5: 9472.

Meade, Luke E.; Ma, Waisum (22 February 2022). "Cranial muscle reconstructions quantify adaptation for high bite forces in Oviraptorosauria". Scientific Reports. 12 (1): 3010.

W. Scott Persons IV; Philip J. Currie; Mark A. Norell (2014). "Oviraptorosaur tail forms and functions". Acta Palaeontologica Polonica. 59 (3).

Glacialisaurus: Beast of the Week

This week we will be looking at a dinosaur that demonstrates how different the world's climate used to be millions of years ago.  Check out Glacialisaurus hammeri!

Glacialisaurus was plant-eating dinosaur that lived in what is now Antarctica during the late Jurassic Period, between 186-182 million years ago.  Although it is only known from a few bones, Glacialisaurus is estimated to have been about 20 feet (6 meters) when from snout to tail.  The genus name translates to "Ice Reptile" in reference to the fact that it was discovered in the now icy Antarctic.  

Watercolor life restoration of Glacialisaurus by Christopher DiPiazza.

Glacialisaurus is considered a basal sauropodomorph, also known as a "prosauropod", which are generally considered the "more primitive" relatives of the long-necked sauropod dinosaurs, like Apatosaurus and Brachiosaurus. Like their more popular relatives, this group of dinosaurs had relatively long necks with small heads.  Unlike them, many of these dinosaurs walked on their hind legs, some being obligate bipeds, and others able to switch between two and four limbs depending on what suited them.  Their robust front limbs ended in five flexible fingers.  The first finger on each hand typically had a particularly long and curved claw, possibly for defense against predators, battling rivals of the same species, grasping branches while feeding, or maybe something completely different nobody's imagined. They had long, somewhat rectangular skulls with slightly downturned jaws, lined with leaf-shaped teeth, ideal for shearing plants.   

All that being said, Glacialisaurus, itself, is only known from a few limb bones, including part of a femur and some of the foot.  Based on these bones, experts can deduct it was a close relative of other basal sauropodomorphs, like Massospondylus.  Its bones were particularly robust compared to many of its relatives, meaning it would have been an overall robust animal for its length.  

Images of Glacialisaurus' foot bones from Smeth Et al. referenced below.

Perhaps the most interesting thing about Glacialisaurus isn't as much about its body but more its habitat, which is now frigid Antarctica.  During the early Jurassic, however, Antarcticta was still attached to South America, Africa, Australia, and India. (India would later separate as an island and eventually crash into southern Asia) It was also closer to the equator at the time, which means it was much warmer than it is today.  This is reflected in the kinds of fossils that have been found, including various plants that are known from warmer climates.  Glacialisaurus also would have coexisted with other animals, including a still unnamed pterosaur related to Dimorphodon, at least one other smaller kind of still unnamed basal sauropodomorph, and the large meat-eating theropod, Cryolophosaurus, which may have hunted it.  

References

Bomfleur, Benjamin; Pott, Christian; Kerp, Hans (2011). "Plant assemblages from the Shafer Peak Formation (Lower Jurassic), north Victoria Land, Transantarctic Mountains". Antarctic Science. 23 (2): 188–208.

Cantrill, David J.; Hunter, Morag A. (2005). "Macrofossil floras of the Latady Basin, Antarctic Peninsula". New Zealand Journal of Geology and Geophysics. 48 (3): 537–553.

Hammer, W. R., & Hickerson, W. J. (1996). Implications of an Early Jurassic vertebrate fauna from Antarctica. The Continental Jurassic, 215–218.

Rauhut, O. W. M.; Holwerda, F. M.; Furrer, H. (2020). "A derived sauropodiform dinosaur and other sauropodomorph material from the Late Triassic of Canton Schaffhausen, Switzerland". Swiss Journal of Geosciences. 113 (1): 8.

Smith, Nathan D.; Pol, Diego (2007). "Anatomy of a basal sauropodomorph dinosaur from the Early Jurassic Hanson Formation of Antarctica". Acta Palaeontologica Polonica. 52 (4): 657–674.

Smith, N.D; Hammer, W.R.; Makovicky, P.J. (2013). "New Dinosaurs from the Early Jurassic Hanson Formation of Antarctica, and Patterns of Diversity and Biogeography in Early Jurassic Sauropodomorphs". Geological Society of America Abstracts with Programs. 45 (7): 405–406.

Unaysaurus: Beast of the Week

 This week we will be checking out an early dinosaur that helps us understand the dinosaur family tree as a whole.  Let's check out Unaysaurus tolentinoi!

Watercolor reconstruction of Unaysaurus by Christopher DiPiazza.

Unaysaurus was a plant-eating, possibly omnivorous, dinosaur that lived in what is now Brazil, during the late Triassic period, about 225.4 million years ago.  From nose to tail it measured about 8 feet (2.5 meters) long.  It's name translates to "black water reptile" from the Tupi language, from near where it was discovered.  This is in reference to the region in which its fossils were found, which is called "Agua Negra" (black water) in Portuguese.  

Unaysaurus is was a member of what is referred to as the prosauropod group of dinosaurs.  Like their generally larger relatives, the sauropods, like Brachiosaurus and Apatosaurus, they possessed long necks and proportionally small heads, but differed in that they often could walk on their hind legs, some of which were actually obligatory bipeds, able to walk on their hind legs only.  It is thought by most experts that the true sauropods evolved from a branch of prosauropods somewhere during the early Jurassic or possibly even the late Triassic period.  Unaysaurus was a particularly small member of the prosauropod group, with other members, like Plateosaurus and Ingentia growing to be quite large in comparison.  What makes Unaysaurus stand out the most, however, is the fact that was especially old for its lineage, predating most other prosauropods by millions of years.  It is considered one of the oldest sauropodomorphs ever discovered alongside its close relative, Macrcocollum.  

Diagram and photograph of Unaysaurus' skull in the paper by Leal et al. referenced below.

Unaysaurus is known from surprisingly a complete skeleton, including an almost complete skull with teeth, arm bones, vertebra, and some leg bones, so we have a decent idea of what it looked like.  Like most prosauropods it had a long, almost rectangular skull, with a slightly downturned lower jaw, which possessed small leaf-shaped teeth.  It likely was primarily a plant-eater but it very well could have eaten smaller animals, as well, like invertebrates or possibly tiny reptiles.  It had proportionally short arms so it was likely an obligatory biped, only able to walk on its hind legs.  Because of its small size and relatively light build, it may have relied on speed or possibly camouflage to avoid predators.  

References

Buffetaut, E.; Suteethorn, V.; Cuny, G.; Tong, H.; Le Loeuff, J.; Khansubha, S.; Jongautchariyakul, S. (2000). "The earliest known sauropod dinosaur". Nature. 407 (6800): 72–74.

Leal, L.A.; Azevodo, S.A.K.; Kellner, A.A.W.; da Rosa, A.A.S. (2004). "A new early dinosaur (Sauropodomorpha) from the Caturrita Formation (Late Triassic), Paraná Basin, Brazil". Zootaxa. 690: 1–24.

Soares, M.B.; Schultz, C.L.; Horn, B.L.D. (2011). "New information on Riograndia guaibensis Bonaparte, Ferigolo & Ribeiro, 2001 (Eucynodontia, Tritheledontidae) from the Late Triassic of southern Brazil: anatomical and biostratigraphic implications". Anais da Academia Brasileira de Ciências. 83 (1): 329–354.

Rauhut, O. W. M.; Holwerda, F. M.; Furrer, H. (2020). "A derived sauropodiform dinosaur and other sauropodomorph material from the Late Triassic of Canton Schaffhausen, Switzerland". Swiss Journal of Geosciences.

Rodrigo Temp Müller; Max Cardoso Langer; Sérgio Dias-da-Silva (2018). "An exceptionally preserved association of complete dinosaur skeletons reveals the oldest long-necked sauropodomorphs". Biology Letters. 14 (11): 20180633.

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.