Tyrannosaurus Rex: Butcher of the Cretaceous

Tyrannosaurus Rex: National Museum of Natural History. Washington, D.C

Since its discovery in the summer of 1902 by Barnum Brown, no other dinosaur has captured the human imagination quite like the Tyrannosaurus Rex. Upon its discovery, Barnum Brown wrote this to Henry Fairfield Osborn, friend, and curator of the American Museum of Natural History in New York. “It is as if a child’s conception of a monster had become real and was laid down in stone” (Kindall,2022). Though most of the skull and tail were missing, everything about this monster would overwhelm the human imagination. The specimen that Brown found stood 13 feet tall at the hips, its jaws measured over 4 ft in length, and would have weighed 6-8 tons. This was the only known specimen to science as was given the appropriate name Tyrannosaurus Rex by Henry Osborne in the fall of 1902. Tyrannosaurus which means “tyrant lizard” in Greek and “rex” which means “king” in Latin; Tyrannosaurus Rex, the king of the lizards, no other name would capture in two words the sheer power contained within this beast.

Who was this creature? What was the nature of this tyrant lizard? Without the restless adventuring spirit of Barnum Brown who unearthed the first T-Rex and captivated the imagination of people everywhere, dinosaurs would have remained nothing more than a novelty never inspiring people to devote the necessary resources and energy to understand this creature and the world in which it lived. Without Tyrannosaurus Rex to grace museum halls, only herbivores would represent the giants of the Mesozoic. Without Tyrannosaurus Rex there would be no Jurassic Park, no dinosaurs toys, no children in dinosaur pajamas, and no creature to stand at the intersections of popular culture and modern science. Without T-Rex, our world would look very different and our understanding of the past would be incomplete. The discovery of Tyrannosaurus Rex did more than draw the public to Natural History Museums, Tyrannosaurus Rex started a revolution in understanding our world. In this post, we will reach out with our imagination and touch the bones of this incredible creature from another time and place.

Tyrannosaurus Rex “Walter” biting down on a Triceratops. National Museum of Natural Hisotry, Washingron, D.C.

Tyrannosaurus Rex was the ultimate predator, the largest and deadliest animal to walk the earth. Ruling the American Midwest for millions of years, Tyrannosaurus Rex brought down massive armored prey Triceratops and Inkeylosaurs tanks of the Cretaceous. At an average of 40 feet long, 18 feet tall, and weighing 6-8 tons, Tyrannosaurus rex was a mouth on legs, the butcher of the Cretaceous. The skull of T-rex is the most impressive anti-tank weapon evolution ever produced. The jaws of this theropod are infamous, 5 feet long, and filled with 60 piercing and bone-crushing teeth with a bite force 16 times stronger than an alligator. Constructed of 64 bones, the skull, and attached 2 ft thick neck muscles could lift a hippo. Counterbalancing the massive skull is a tail weighing a ton combined with a pelvis and legs that anchor and account for half of the T-rex’s weight.

Ironically, the teeth of Tyrannosaurus Rex are the bluntest of all the Tyrannosauroid family, meaning that the oral weaponry of this colossal theropod was for bone crushing which brings into question adaptions for scavenging. It is clear from the braincase of Tyrannosaurus skulls that the olfactory region is prominent, indicating that the T-Rex had superb smelling capabilities that aided in sniffing out carcasses or kills from other carnivores. Contrary to Jurassic Park, Tyrannosaurus Rex could detect even the slightest movement. At 16 inches apart and 18 feet high, the eyes of T-Rex possessed stereoscopic binocular vision and could discern fine detail at a distance of 4 miles, six times further than a human with 20/20 vision. The human eye requires the aid of binoculars to see details at this distance.

If impeccable vision and olfactory senses were not enough, brain case studies of Tyrannosaurus show that this apex predator could hear sounds below 40 Hz at great distances. While unable to discern the chirps of birds or the buzz of insects, T-Rex could perceive the low grunt of a distant meal or the low-frequency call of a potential mate. If T-Rex could hear low-register sounds, it stands to reason that it could produce low-register sounds. Contrary to Cinema, Tyrannosaurus could not roar as often depicted in dinosaur thrillers. However, in the absence of a roar, Tyrannosaurus vocalizations would be felt as vibrations. The human ear is unable to discern sounds below 20 Hz, but we can perceive vibrations produced by sounds below this audible register. While unable to hear the vocalizations of the approaching T-Rex, we could sense the vibrations produced like rolls of distant thunder. While not as dramatic as cinema depictions of encounters, the experience of an ever-increasing vibration as the Tyrannosaurus Rex approached in the dark of night in a wooded environment would be terrifying. Millions upon millions of years in the making, Tyrannosaurus Rex is the ultimate apex creature of evolution.

Tyrannosaurus Rex “Walter” tail. The tail of T-rex weighed a ton to counterbalance the large 5 foot skull. National Museum of Naturl History. Washington, D.C.

To fully understand Tyrannosaurus Rex, we need to understand its origins. The apex predator of the late Cretaceous, Tyrannosaurus Rex was the final and one of the largest carnivores that evolution ever produced. What adaptions took place along T-rex’s lineage to create such an amazing creature? Why did Tyrannosaurus have tiny arms and why was the skull so massive? All the answers to these questions lie in T-rex’s evolutionary history starting with the Permian Extinction, which ushered in the first dinosaur.

Tyrannosaurs began 100 million years ago and like all dinosaurs, they started as small, underdogs living in the shadows of the other apex predators at the beginning of the Triassic, behemoths such as postosuchus apex archosaur, and other carnivores of the Triassic. 240-230 million years ago, dinosaurs like Herrerasaurus and Eoraptor evolved from their cat-size dinosaurmoprhs ancestors when the earth hosted the once giant supercontinent Pangea. Although one united land mass, Pangea was a challenging environment for primitive dinosaurs to both live and evolve. Dryland extended from pole to pole, but on the other side was an open ocean-Panthalassa. Because currents could travel from the equator to the poles without interference, low latitudes were warm preventing ice caps from forming. The Arctic and Antarctic were tropical with summer temperatures a temperate 70 to 80 degrees year-round and winter temperatures barely below freezing. Because Pangea was centered on the equator, and the other half was cooling down in the winter, this land orientation caused violent air currents to traverse the supercontinent. These air masses triggered megamonsoons, bringing torrential downpours to the land mass, and causing flooding and deadly storms. (Brusatte, 2018)

The global megamonsoons divided Pangea into regions based on varying amounts of precipitation, winds, and temperatures. Within this landmass were the mid-latitudes. These regions were cooler with a moist and wet climate that was hospitable to life. Here Herrerasaurus, Eroraptor, and other dinosaurs lived and thrived. Pangea with its extreme weather and dangerous unpredictability was the evolutionary stage set out for the dinosaurs. From the ashes left by the Permian Extinction, dinosaurs evolved in this harsh world with many challenges but they weren’t alone.

Herrerasaurus: Image Credit

Evolving alongside the dinosaurs were other creatures that were larger and stronger. One of these adversaries was the metopsoaurus a giant amphibian. Metoposaurus was a monster with a head the size of a coffee table and jaws with hundreds of piercing teeth. Metospsoaurus was the ancestor of today’s frogs, toads, newts, and salamanders and it dominated the shore regions of many of Pangea’s lakes and rivers, particularly in the midlatitude humid belts. Small primitive dinosaurs such as Eoraptor were on the menu and had to approach the shore regions with great caution. Dicynodont, a therapsid, pig-like mammal that ate roots, leaves, and insects completed with the primitive dinosaurs for food and habitat. Saurosuchus a crocodile cousin and mightly apex predator and one of the largest Rauisuchians was a tyrant forcing the dinosaurs into their role as underdogs in the ecosystem.

When life in Triassic Pangea seemed bleak and antagonistic towards the primitive dinosaurs, two important things happened that gave them an edge. First, the humid belt region that was dominated by the rhynchosaurus and dicynodonts began to see their numbers decrease and finally disappear. (Brusatte, 2018). It’s not understood why these creatures faced extinction but the effect was in the dinosaur’s favor. The niches vacated by these large herbivores gave the primitive sauropod dinosaurs such as Panphagia and Saturnalia a new and abundant food source. Plateosaurus, a well-documented primitive sauropod thrived 225-215 million years ago during this time. Second, around 215 million years ago, the first dinosaurs began inhabiting the subtropical arid regions of the Northern Hemisphere, now the American South West (Brusatte, 2018). It is thought that climate change and monsoon patterns made these regions more tolerable, allowing the dinosaurs access to these once-arid regions.

Plateosaurus: Image Credit

Among these primitive dinosaurs that exploited the newly unoccupied and available food sources and once arid regions of Pangea was Coelophysis. A dog-size, lightweight, fast-running, sharp-toothed Triassic dinosaur who was the earliest member of a theropod dynasty that would one day produce Velociraptors, Birds, and Tyrannosaurus Rex-the largest carnivore to ever walk the Earth (Brusatte, 2018). This is where the story of T-rex began, the humblest of beginnings in the Triassic arid regions of Pangea.

Coelophysis: Image Credit

Coelophysis was first discovered in 1889 from a massive bone bed found on Ghost Ranch in New Mexico. During the bone wars (a fierce rivalry between Edward Drinker Cope and Othniel Charles March) these men discovered a vast number of dinosaur specimens naming many of the most well-loved dinosaurs throughout their rivalry. It was Cope who later named Coelophysis in 1889. The Ghost Ranch bone bed dates back to 220 million years ago when a Triasic megamoonson flood overtook a herd of Coelophysis and buried them so rapidly that their bodies were protected and fossilized in the sediment.

As the Triassic continued, the primitive dinosaurs along with the dominant archosaurs evolved, multiplied, and occupied more regions of the Pangea supercontinent. The dinosaurs continued to diversify and thrive as they occupied vacant niches left by the waning populations of dicynodonts and some Rauisuchian species. Then about 201 million years ago, the earth began to rumble. Miles below the surface, plate tectonics, the engine that drives the continents came to life.

The supercontinent Pangea began to split, and North America separated from Europe and Africa. The Atlantic Ocean occupies the region that these continents once claimed. But before the continental divorce was finalized, the Earth hemorrhaged lava unlike anything today. Massive volcanic eruptions raged for 600,000 years, and megavolcanoes erupted along what is the Atlantic Seaboard today. Unlike vulcanism today, these mega volcanoes erupted in four violent pulses siring the edges of the continents, followed by the flood basalts of the Central Atlantic Magmatic Providence (CAMP). CAMP is a milestone in Earth’s history, a gravestone, and the cause of the Triassic Extinction. CAMP is the largest igneous province in the solar system, an estimated 11 million kilometers, and the eruptions belched tidal waves of lava and flames similar to the Siberian Traps. Waves of lava flowed across the land, incinerating everything in the path. Like the Permian Extinction, massive amounts of carbon dioxide and sulfur dioxide were released into the atmosphere causing intense global warming followed by cooling. The oceans are acidified due to the temperature fluxations, starving the waters of oxygen and triggering an ecosystem collapse on land and in the water. An estimated 30 percent of species died, including all archosauromorphs, crocodylomorphs, pterosaurs, and some dinosaurs. Other groups that died out were aetosaurs, phytosaurs, and rauiuschids. After the dust settled and the volcanoes subsided, the dinosaurs became great survivors of the global meltdown.

As Pangea unzipped, the earth hemorrhaged lava: Image Credit

Underdogs and forced to remain small in the shadow of the much larger and dominant archosauromorphs, crocodylomorphs, and pterosaurs, the dinosaurs were better able to scratch out a living in the aftermath of the Pangea supercontinent breakup. Inheriters of the Earth and now a dominant force, the dinosaurs responded by getting bigger, much, bigger, ushering in the time of the Age of the Dinosaurs and the Jurassic Giants.

In dinosaur evolution, there are two major clades of Dinosauria categorized by a forward or backward-facing pubis bone. Saurichians (“lizard-hipped”) dinosaurs have a forward-pointing pubis and (Ornithischians (“bird-hipped”) dinosaurs have a backward-facing pubis bone. Saurischia contains all theropod and sauropod dinosaurs. Ornithiscia contains armored and horned dinosaurs such as Triceratops, Ankylosaurus, and all Hadrosaurs such as Edmontosaurus. Another distinguishing feature is that Saurinchia possesses air sacs, spaces within the bones that make the skeletons lighter. It is, for this reason, that titanosaurs could raise their long necks and birds can achieve flight by efficiently utilizing oxygen in their bodies.

Forward Facing Pubis of Tyrannosaurus Rex: Image Credit
Backward-facing Pubis Bone of Edmontosaurus (Hadrosaur): Image Credit

Tyrannosaurus Rex, is a tyrannosaur, a clade of theropod tyrant dinosaurs. Once thought that Tyrannosaurs were descendants of Allosaurus, a member of a Carcharodontosauroid clade that produced the largest theropod to ever walk the earth, Giganotosaurus. However, physical characteristics in the skulls, hips, forelimbs, and hindlimbs separated the tyrant dinosaurs from this carnosaur group. Tyrannosaurs have large skulls relative to body size, solid roofs in their mouth which increased their lethal bite, blunt snouts, eyes aimed forward producing stereoscopic vision, and scraper teeth in the front of their upper jaws, a trait unique to tyrannosaurs. Then in 2004, a little dinosaur from the Early Cretaceous was found in Chona’s Yixian Formation.

Dilong, early Tyrannosauroid directly related to Coelurosaurs. Image Credit

Dilong, a little theropod no more than 5 feet long looked like a much earlier Coelurosaur with a few traits that are only found in Tyrannosaurs – a large skull for body size, a blunt snout, and little scraper teeth in the front of its jaws useful for nipping and scraping meat from bones. The discovery of this little dinosaur removed Tyrannosaurus as a distant relative of Allosaurus and placed T-Rex in Coelurosauria, a clade of theropod dinosaurs directly related to birds. T-Rex is no longer considered a Carcharodontosauroid but rather an overgrown Coelurosaur or giant chicken.

Then in 2010, a smaller dinosaur was discovered in Siberia. Kileskus is the oldest tyrannosaur found in rocks dating back to about 170 million years ago, firmly in the middle part of the Jurassic. This new tyrannosaur was small, 7 feet long, a few feet tall, and weighed less than 100 pounds with large nostrils and sinuses and a solid roof, many of the characteristics seen in Tyrannosaurus Rex. 

Kileskus: Image Credit

Kileskus and Guanlong (another tyrannosaur) were about the same size and had similar tyrannosaur characteristics, three-fingered hands, and head crests utilized for show. These primitive tyrannosaurs are a good picture of how the early tyrannosaur clade looked and behaved. While nowhere near the likeness of T-Rex, these small tyrannosaurs thrived in their ecosystem hunting bugs, small mammals, and other small things they could catch. They were fast, had sharp teeth, and feared Sinraptor and Monolophosaurus, cousins of Allosaurus, the large apex carcharodontosaur carnivores of the time.

Kileskus linked to an earlier discovery in 2009 that firmly locked another tyrannosaur puzzle piece into place. Sinotyrannus, a large tyrannosaur measuring 30–33 ft and weighing 2.5 metric tons was the oldest large basal tyrannosaur known. This discovery proved that tyrannosaurs gradually increased in size throughout the Jurassic and Early Cretaceous.

In 2012 the most remarkable tyrannosaur discovery was announced. A nearly complete skeleton of a new dinosaur found in China dating to 125 million years ago with protofeathers, Yutyrannus. Yuthrannus (YOO-tie-RAN-us), a coelurosaur- the theropod clade that contains T-Rex and birds-raised the prospect that coelurosaurs had feathered including the most famous tyrannosaur, Tyrannosaurus Rex.

Yutyrannus: Image Credit

Knowing T-Rex’s origin is only part of the question, the other question to answer is how did Tyrannosaurus Rex become so big. Not a lot is known about this period, the fossil record has yet to yield those secrets. What we do know is that about 94 million years ago the climate began to change. Temperatures spiked and sea levels oscillated and acidification starved the oceans of oxygen. Similar to the Permian Extinction but not as severe. During this time the large theropods of the time the carcharodontosaurs and spinosaurs died off leaving a niche that the tyrannosaurs filled. Tyrannosaurus Rex the remaining tyrannosaur responded by growing larger and starting the reign as the Tyrant King.

T-Rex’s small arms are a defining trait of this famous theropod, where did they come from? T-Rex is not the only dinosaur to have small arms, many theropods have small arms compared to the size of their bodies. There have been many theories presented to explain the evolutionary adaption of small arms, from protection during group feeding to the reduction of harm when fighting over mates or territory. The most likely scenario comes from a paper published in Acta Palaeontologica Polonica, suggesting that instead of the arms shrinking, theropods simply outgrew their arms making them appear smaller compared to body size.

Argentinaosaurus (Titanosaur) and Giganatosaurus (Thereopod); Image Credit

During the Jurassic, an arms race took place between herbivores and carnivores. As the herbivores increased in size, so did the carnivores. The giants of the Jurassic were the Titanosaurs, the largest land animals ever recorded in Earth’s history roamed from place to place in search of food. The large carnivores of that time, Allosaurus and Giganotosaurus stalked the herds of Titanosaurus as they marched across the land in yearly migrations. To take on one of these giants, theropods had to be large. Becoming large is calorically expensive and traits not necessary for survival are not selected. In the case of theropods, as their bodies and skulls became larger, arms did not follow suit. Evolution selected large jaws with powerful muscles yielding a lethal bite over arms in the arms race between herbivores and carnivores. By the time T-Rex arrived on the scene in the Cretaceous, arms were all but useless with evolution favoring the large boxy skulls with jaws full of 6-inch serrated steak knife teeth as the preferred mode of survival.

As the Jurassic yielded to the Cretaceous period, the large theropods that competed with the Tyrannosaurs died out. Ceratosaurus, Allosaurus, and Torvosaurus were gone by the beginning of the Cretaceous. Moving into the Cretaceous were two main theropod clades, Carcharodontosauria represented by Giganotosaurus (Southern Hemisphere), Tyrannosaurs represented by Abelisaurus (Southern Hemisphere), and Tyrannosaurus Rex (North Hemisphere). Together these clades of theropods stalked herds of herbivores and hadrosaurs in their respective regions. Then 90 million years ago, Giganotosaurus representing Carcharodontosaurs was out-competed by the tyrannosaurs and became extinct, leaving the rule world to the tyrannosaurs. For the remaining millions of years spanning the Late Cretaceous, Tyrannosaurus Rex reigned as King of the Lizards till one day 66 million years ago when the Age of the Dinosaurs came to an end.

Tyrannosaurus Rex was the apex predator of all time, the pillar of evolution. From the humblest of beginnings in the once arid regions of Pangea embodied in Coelophysis to the King of the Lizards, T-rex was a feat of evolution produced by millions upon millions of years of adaptions that created the most iconic creature of the Mesozoic. It seems as if Tyrannosaurus Rex was unstoppable, with nothing to fear or almost nothing. 66 million years ago T-Rex witnessed one of the worst days the world has ever seen. A rock 6 miles wide fell out of the sky smashing into the earth with unimaginable force bringing the reign of T-Rex and the Age of the Dinosaurs to a close. For 66 million years Tyrannosaurus Rex lay entombed in the sedimentary rock of the Hell Creek Formation in the American Midwest, exposed for the first time in 1902 by Barnum Brown, and changed our world forever.

No other creature has inspired the human imagination quite like Tyrannosaurus Rex. Since its discovery, T-Rex stands at the intersection between popular culture and modern science inspiring countless people, paleontologists, and dinosaur enthusiasts like myself to understand the world from which it lived. Tyrannosaurus changed our world in ways we may not realize. Without T-Rex, there would be no Godzilla, no dinosaur toys, no children in dinosaur pajamas, no Jurassic Park or Jurassic World, no inflatable dinosaur costumes, no creature to grace museum halls, and no counterpart to the countless herbivores from the Mesozoic. Without T-Rex our understanding of the Mesozoic would be incomplete, our heritage starting from cynodonts to primates would look very different, and we would look very different. T-Rex forced our rat-like ancestors to remain small, living under the feet of the dinosaurs in burrows or above their heads in the canopy. Without T-Rex, our evolutionary line would be forever changed. It is clear. I and my fellow man owe our existence to that chance rock that fell out of the sky 66 million years ago causing the great extinction event that brought the age of the dinosaur to a close. But life is resilient, our mammal ancestors rose out of the ashes left by T-Rex just like Coelophysis rose out of the ashes of the Permian. T-Rex’s story is our story, and our story can only begin when their story ends.

Our story begins because their story ends. ~ Noelle K. Moser ~ Sketched by me.

Barnum Brown’s T-Rex still stands on the fourth floor in Manhattan, New York surrounded by the sounds of one of North America’s largest cities. Visitors look up and gaze at the largest carnivore to ever walk the earth 66 million years ago. Frozen in time, Tyrannosaurus Rex is the witness of a world that we will never see but can only experience through bone.

Tyrannosaurus Rex found by Barnum Brown. American Museum of National History. New York, New York. Image Credit

I regret that I will never see a living Tyrannosaurus Rex, my closest encounters will be standing at the feet of these amazing creatures, looking up, reaching out, and touching bone. The only link I have to their world is through my backyard chickens, in their veins pump the blood of dinosaurs as they are coelurosaurs and directly related to the mighty T-Rex. I observe in their behavior the majesty that T-Rex possessed and can imagine how he walked and sounded. The crow of my roosters is a sound from another world, an ancient world that I will never see. But it is clear, that if Tyrannosaurus Rex had not perished in that chance asteroid impact, I would not be here. He stands as a testament and witness to that earth-shattering day. I am here because my small rat-like ancestors rose out of the ashes of the dinosaurs and ushered in the age of mammals.

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Brusatte, Steve. The Rise and Fall of the Dinosaurs: A New History of Their Lost World.New York: HarperCollins Publishers, 2018

Randall, David K. The Monster’s Bones the Discovery of the T. Rex and How It Shook Our World. New York: W.W Norton & Company, 2002.

Tyrannosaurus Rex, “Walter” and I. National Museum of Natural History Washington, D.C. (August 2022)

Meraxes Gigas.

Image Credit: Meraxes Gigas.

We have a new dinosaur! A theropod with short limbs like Tyrannosaurus Rex. Tyrannosaurus is not the only famous giant carnivorous dinosaur; meet Meraxes Gigas.

During the summer of 2022, researchers uncovered a previously unknown dinosaur from the Late Cretaceous, Meraxes Gigas. Meraxes belongs to the genus carcharodontosaurid theropods. The name, “Meraxes”, honors a dragon from the George R. R. Martin novel, A Song of Ice and Fire – Wikipedia The specific name, “Gigas”, derived from the Greek word meaning “giant”, in reference to the theropod’s large size.

Found in the Huincul Formation of Argentine Patagonia was a nearly complete skeleton. Meraxes Gigas is of pivotal importance because this discovery constitute a complete skull, partial forelimbs, complete hindlimbs, fragmentary ribs, and cervical and complete caudal vertebrae. 

The hand of theropods is imperative to determine whether the specimen is primitive or derived. Primitive in dinosaur terminology means an early stage in evolutionary development. Derived means most recent in dinosaurian evolution. To help this make sense, Coelophysis is a primitive ancestor of the derived Tyrannosaurus Rex.

Image Credit: Gignotosaurus skeleton, notice the longer arms and three digits on each hand. Giganotosaurus is more derived than the primitive theropod Coelophysis.

Primitive theropod dinosaurs have longer arms and digital formula I-IV. Derived theropods will have shorter arms and a reduced number of digits.

Image Credit: Coelophysis primitive theropod dinosaur. Notice that Ceolophysis has longer arms and 4 digits on each hand.

Coelophysis, the oldest known theropod, defined as a primitive Late Triassic theropod had longer arms and 4 digits on each hand.

Image Credit: Allosaurus

Allosaurus, more derived lived during the Middle-Late Jurassic and possess shorter arms and only three digits on each hand. Tyrannosaurus the Cretaceous apex predator had very short arms and only 2 digits on each hand.

Image Credit: Noelle K. Moser. Walter, Tyrannosaurus Rex located in Washington, D.C. has very short arms and only 2 digits on each hand.

As observed by these images, the skull, forearms, hands, and digits are gold in theropod discoveries. The hands of theropod dinosaurs tell us so much about the evolution of dinosaurs during the Mesozoic.

In addition to the forearms and digits, complete or near complete skulls found in new dinosaurs’ discoveries help us understand more about the creatures.

At first glance, the skulls of these giant theropods appear similar; massive jaws with numerous long serrated teeth. To the trained eye, the skulls of Giganotosaurus and Tyrannosaurus Rex are remarkably different.

Giganotosaurus has a long narrow skull that comes to a sharp point. The skull of Tyrannosaurus Rex is boxier and comes to a lateral line rather than a point. See the images below.

Another example of primitive and derived evolution is theropods, Allosaurus, Ceratosaurus, and, Tyrannosaurus. See the images below.

While these three theropods appear similar, Allosaurus and contemporary Ceratosaurus predate Tyrannosaurus by 80 million years.

Head Creasts:

Another feature present in theropod dinosaurs, specifically primitive species, is that of head crests. Many Late Triassic and Early Jurassic theropod species possessed head crests. It is thought that these crests were used as display features for mating and sexual dimorphism. In later derived theropod species, these crests disappear.

Image Credit:

The image above depicts Ceratosaurus nasicornis, the apex predator of the early Jurassic, displaying crests on the head can be seen. Ceratosaurus was driven to extinction by the Late Jurassic, succeeded by the more successful Allosaurus.

Image Credit:

Allosaurus, as mentioned above, is the most famous predecessor to Tyrannosaurus Rex. Living through the greater part of the Jurassic, Allosaurus was the apex predator of its time and possessed primitive features – three-digit hands, long forearms, and head crests. It is now known why derived theropods lose the head crests.

Image Credit:

By the time we traverse, the expansive amount of time between Ceratosaurus and Tyrannosaurus Rex (80 million years) head crests disappear from theropod anatomy.


In addition to reduced digits and head crests, as theropods evolve they get larger. Coelophysis at maturity was about 10 feet long and weighed 100 pounds. Compare that to the Jurassic theropod Ceraosaurus which grew to 20 feet long and weighed about 2,000 pounds. Allosaurus grew to be 12 feet long and 10 feet tall weighing 2.3 metric tons. Tyrannosaurus Rex, the largest land theropod to ever live grew to 43 feet long and weighed 6-8 tons.

Meraxes Gigas:

Now, that you have a better understanding of theropod dinosaurs, let’s take another look at Meraxes gigas. Meraxes is a crucial find in the world of dinosaur studies because the remains included key anatomical features, a complete forelimb, hand, a skull, and various other bones. The most important being that of the hand and skull.

According to the research, Meraxes Gigas had tiny arms like Tyrannosaurus with three digits on each hand like Allosaurus. Tyrannosaurus and Meraxies are not related as they are separated by about 20 million years, but it does suggest that as theropods evolved larger heads, the arms shrunk, no longer useful for hunting. Regarding size, Meraxes Gigas was 36 feet long and weighed 4 tons. To put this into perspective, Meraxies is smaller than Tyrannosaurus Rex but much larger than Allosaurus. Further noted, Meraxies does not appear to have head crests.

In terms of theropod evolution, Meraxies is more derived than Allosaurus but primitive compared to Tyrannosaurus. In terms of theropod evolution, this put Meraxies Gigas living about 90 to 100 million years ago, firmly in the Late Cretaceous. Meraxes Gigas and its close relative, Giganotosaurus died out in the Late Cretaceous, succeeding their position at the top of the food chain to the tyrannosaurids, and its famous member, Tyrannosaurus Rex.

Meraxes Gigas and the newly discovered theropod dinosaur were one of the last groups of giant carnivores to walk the Earth. While we often think of Tyrannosaurus Rex as being the lone giant carnivore stalking the Cretaceous, other large theropods competed with the tyrant dinosaurs. Although Meraxes Gigas never laid witness to the meteor that would ultimately bring the reign of the dinosaurs to an end, Tyrannosaurus Rex did.

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As always, thanks for reading Coffee and Coelophysis. Next time, we will take an in-depth look at the most famous theropod, Tyrannosaurus Rex.

~ Noelle ~

What is a Dinosaur?

Image Credit:

Before we advance in our discussion on Dinosaurs, it is imperative to define a dinosaur. Dinosaurs are unique creatures that ascended from the ashes left by the Permian Extinction. To fully answer this question, we must understand their origins. We often think of Dinosaurs as giants, but the truth is they came from animals that are smaller than a house cat (Thomas R. Holtz. 2007). In the beginning, dinosaurs were small, bipedal lizard-like animals. Coelophysis is one of the oldest and first theopod dinosaur. But before Coelophysis, another group inhabited the earth, the archosaurs.

Image Credit: Archosaurs Postosuchus and Desmatosuchus.

Archosaurs, the dinosaurian ancestor, were small with one adaptation, open hip joints with hind limbs positioned directly under their bodies. This adaptation would prove vital during the Jurassic when the Titanosaurs roamed the Earth. Without this very primitive but necessary anatomical adaptation, dinosaurs could not grow to the giant sizes that mesmerize us. Without open hip joints and legs positioned directly under their bodies, dinosaurs (such as the giant Sauropods and Giant Tyrant dinosaurs) could not assume an upright posture.

Open hip joint with hind legs positioned directly under the body with three or more sacral vertebrae fused to the pelvis is the first requirement to classify an animal as a dinosaur. 

Above are images of Walter, Tyrannosaurus Rex located at the National Museum of Natural History in Washington, D.C. Looking at his skeleton, the open hip joint of this large theropod is visible. Without a specialized hip joint positioning the hind legs directly underneath his body, Walter could not support his massive 6-ton weight.

Additionally, open hip joints provided yet another essential mechanism that aided dinosaurs, smooth locomotion and running. As bipedal locomotion organisms, we can relate to this efficient mode of movement. Without open hip joints connecting our legs to our pelvis, we would not be able to perform many feats that humans accomplish. Sports that require running, jumping, or aerial maneuvers we could not do without this vital anatomical modification.

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When looking at dinosaurs, there is another anatomical adaptation they possess. In Theropod such as Allosaurus, we notice “Big Al’s” hands. This anatomic trait is of much importance to the success of the dinosaurs. Hands complete with digits on the manas (hand) and pes (feet) allow the dinosaurs to grasp and carry objects. Bipedalism freed up the forelimbs to perform other functions that aided their survival. The incredibly tiny arms of Tyrannosaurs Rex are often the punch line of many jokes, but even T-Rex could use his hands. While small compared to the rest of the muscular bodies, it’s speculated that he could lift 100 lbs. with his forelimbs. More importantly, forelimbs unnecessary for locomotion proved to be a great asset to the success of the dinosaurs.

As habitual bipedal locomotion specialists, we appreciate our ability to have our hands free to perform other functions besides movement from one place to another. Just like the dinosaurs, the adaption of bipedal locomotion proves essential to our success as Homo sapiens.

The second requirement to classify an animal as a Dinosaur is hands complete with digits, both manus (hand) and pes (feet).

The drawing I did humorously demonstrate the possibilities available to T- Rex should he decide to take up berry picking. With adaptions of bipedal locomotion, T-rex and other dinosaurs had their hands free to carry and manipulate objects.

We often think of Dinosaurs as being extinct; they are not. Dinosaurs fly over our heads every day, and Avialians known as birds. Birds are not just related to dinosaurs; birds are dinosaurs, Coelurosaurs, a branch of theropod dinosaurs. I will revisit this in a later post. For now, understand that birds are dinosaurs because they are dinosaurs and possess a vital anatomical adaptation that all dinosaurs share.

The skull of an animal has many bones. We often think of the skull as one big bone, the head bone or cranium. However, a skull is a collection of many smaller bones that fuse, forming the cranium. In dinosaurs, one fundamental skull bone is missing, the postfrontal bone. In the image below, labeled are the bones of a dinosaur skull. Notice that the frontal bone (pink) is present, but the postfrontal bone is missing.

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Anapsids (line of descension for reptiles) and synapsids (line of descension for mammals, including humans) possess postfrontal cranial bones. Diapsids (the evolutionary line which contains the dinosaurs) lack postfrontal cranial bones. Ancestors of the dinosaurs, including the Archosaurs, retain this bone. This missing cranial bone in all dinosaurs present in dinosaurian ancestors assists their definition (Martin 2006).

All birds (heir of the dinosaurs) do not have postfrontal cranial bones. The postfrontal cranial bone fuse into the frontal bone during the later stages of embryonic development.

 The third requirement needed to classify an animal as a dinosaur; is the absence of a postfrontal cranial bone.

Cnemial crest is visible on Walter’s right left. This adaptation is related directly to the evolution of dinosaurs from reptilian ancestors.

The limb bones of dinosaurs, specifically if they are related to the appendicular skeleton (bones that attach or append to the axial skeleton). are vital because they provide information on how the dinosaur moved. In the posterior portion of a dinosaur, hind limbs are attached to the body by the pelvic girdle (hip socket) below the sacral vertebrae (fused vertebrae that attach the open hip joint to the spine).

Due to the evolutionary adaptation of an open hip socket, dinosaurs can support their weight directly over the hip joint. For this posture to be possible, dinosaurs require adaptions to facilitate this mode of locomotion. Attached to the hip joint by the acetabulum, the femur (thigh bone) terminates at the cnemial crest and the tibia. The cnemial crest is visible in the image above in Walter’s skeleton.

The tibia is key to two additional dinosaurian traits. The cnemial crest and the ascending process into the astragalus or anklebone. (Martin 2006). The astragalus (anklebone) and other small bones form a dinosaur’s tarsals (feet and toes). Dinosaurs walked with their metatarsals in contact with the ground. In other words, dinosaurs walked on thier toes. The digitigrade motion  is visible in the image above. Walter walks on his toes, heals never touch the gound when walking. This digitigrade locomotin can also present in dogs.

Contrast this with human locomotion. Humans walk with a relaxing stance in which most of the body weight in on the heels in a plantigrade stance. Human can only achieve a digitigrade when wearing high-heeles shoes or tiptoe. 

These adaptations relate directly to the evolution of dinosaurs from reptiles and archosaurs. Unlike reptiles which move with legs sprawled out to the side of the body like large lizards, dinosaurs walk upright with their legs directly underneath their bodies with digitigrade motion.

In addition to open hip joints and fused sacral vertebra, dinosuar locomotion requires the adaption of the cnemial crest, tibia, and astragalus to facilitate this upright smooth motion.

Finally, we come to the last requirement to classify an animal as a dinosaur; the femur that terminates into the cnemial crest, a tibia that ascends to the astragalus, and the astragalus which forms the metatarsals for digitigrade locomotion. Without these evolutionary adaptions, dinosaurs would not be able to support weight in an upward stance; dinosaurs would crawl in a sprawling posture like the reptiles that preceded them.

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I am a published author, multi-disciplinary writer, and blog contributor. If you like this blog, please visit my writing portfolio. The Works of Noelle Moser.

As always, thanks for reading. Next time, I will introduce a newly discovered theropod, Meraxes Gigas.

Welcome to Coffee and Coelophysis.

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They say that the best place to start is the beginning, with dinosaurs that is Coelophysis.

Dinosaurs are a unique biological group and were the most successful animals that evolution ever produced, and their reign as dominant creatures spanned millions of years. Compared to humans who have only been here for 6 million years. But dinosaurs did not spawn out of midair; dinosaurs were the inheritors of the Earth after the Permian Extinction or the Great Dying.

Approximately 251 million years ago, Earth suffered the most severe extinction. It is theroized that the Great Dying was the cause of increased volcanic activity that released large amounts of carbon dioxide into the atmosphere leading to increased ocean temperatures. The increased ocean temperatures disrupted the ocean conveyor belt responsible for breathing life into the oceans. As the seas became stagnant, hydrogen sulfide began to accumulate. Hydrogen sulfide is poisonous thus, all life in the oceans perished. As the gas escaped into the surrounding atmosphere, life on land began to die. The oceans experienced increased anoxia (depletion of oxygen) and acidification (reduction of Ph). As a result, many plants and animals that inhabited the oceans and surrounding land were wiped out. But life is resilient; over millions of years, life on Earth recovered. Only this time, out of the ashes of the Permian Extinction, new and more exciting life forms emerged.

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One of these life forms was the Stegocephalians. Stegocephalians developed unique adaptions of bones, jaws, and lungs. Most importantly, Stegocephalians evolved specialized fins with wrists and ankles helping push through the dense vegetation in swampy waters. They could also use these specialized fins to push along land if they needed to travel from one water source to another. Stegocephalians are very important to our discussion on dinosaurs because they are the pivotal key to the evolution of the dinosaurs. 

In terms of cladistics (classifying animals based on ancestral descent) throughout the course of evolution, three clades of animals are of importance: Anapsida, Synapsida and Diapsida

These three clades recognized by the diversification of the arrangement of skull bones, specifically the presence and position of temporal fenestrae (holes in the skull), a latch where skull bones fuse. In humans, we can feel our temporal fenestrae at either side of our skull behind our eye sockets. Most vertebrates possess temporal fenestrae, where and how many fenestrae various vertebrate organisms have can classify organisms into clades based on evolutionary lineage.

For example, below is a graphic of a Massospondylus Skull, labeled the temporal fenestra and another fenestra present in this animal’s skull.

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The anapsids, synapsids, and diapsids are three different clades of animals leading to various lineages. Anapsids are animals that lack temporal fenestrae. Fossil and modern turtles best represent this group of animals.

Synapsids and diapsids evolved from a common ancestor of anapsids during the later part of the Carboniferous period (Martin, pg.165). Synapsids during the Permian represented by herbivorous and carnivorous reptiles called Pelycosaurs. Dimetrodon is a perfect example of a Pelycosaur. Although not a dinosaur, Dimetrodon had a formidable appearance which causes many to assume it is a dinosaur.

Synapsids included lineages that later evolved into therapsids mammal-like characteristics and eventually into mammals. Dimetrodon is a very distant ancestor in our evolutionary lineage. Humans are Synapsids as are most mammals for which we share this evolutionary trait.

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That leaves Diapsids; dinosaurs are diapsids! Diapsids split into two clades; Lepidosauria and Archosauria. Lepidosauria are modern lizards such as geckos, iguanas, and Komodo dragons. Archosauria present adaption with special openings for air sacs in their skulls. Air sacs are one of the fundamental anatomical adaptations that birds possess. Air sacs aid the ability to fly by efficiently using oxygen. Since birds are related to dinosaurs, theropod dinosaurs, this means that dinosaurs descend from Archosaurs. Although all non-avian dinosaurs are extinct, Archosaurs are not. Archosaurs still exist today; we call them alligators and crocodiles. 

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Postosuchus is the poster child for Archosaurs. While traits that would eventually give way to the Tyrannosaurus Rex are apparent, Postoscuchus is a reptile, not a dinosaur. Postosuchus is a member of the clade Pseudosuchia, an Archosaur that includes modern crocodilians and descendent of the dinosaurs we call birds. While assumed that dinosaurs are extinct, they are not; they fly over our heads every day, and these are the Avialians or birds.

My backyard chicken flock. Chickens (as all birds) are theropods, descendents of Deinonychosaurs (better known as raptors) which are descendents of Archosaurs such as Postosuchus which are Diapsids.

How does this relate to Coelophysis?

You may be wondering how all of this relates to Coelophysis, the name of this dinosaur blog. Coelophysis is the first or oldest known dinosaur. Coelophysis lived approximately 228 to 201.3 million years ago during the latter part of the Triassic Period. Coelophysis is not an Archosaur. Coelophysis is a Diapsid on the same evolutionary line as Postosuchus except warm-blooded. Archosaurs are reptiles that are Ectothermic or cold-blooded animals that rely on the environment to regulate their body temperature. Dinosaurs are Endothermic or warm-blooded and maintain a constant body temperature independent of the environment. 

Dinosaurs are often associated with reptiles. The name dinosaur, coined by Richard Owen, meaning “Terrible Lizard” does not help this common misassociation. Dinosauria, the clade which contains all the dinosaurs, is a clade that is uniquely theirs. While dinosaurs have evolutionary relations to Archosaurs which are reptiles, Dinosaurs are in a class of their own. They are unique animals consisting of exclusive physiology. Coelophysis was simply the first, the beginning of the age of the dinosaurs.

I have been captivated by dinosaurs since I was a child. Astonished and memorized by these creatures, I still possess a child-like wonder about these animals. I never grew up, but today I am still fascinated by dinosaurs. More than just the immensity of their size, I seek to understand these amazing animals on a fundamental evolutionary level. To achieve this, I travel to Natural History Museums, stand at the feet of these beasts, look up, and work to learn about how they lived and died.

If you are like me, that is, you never grew out of your dinosaur phase from youth, grab a cup of coffee and let’s talk about dinosaurs. Coffee and Coelophysis is a journey through the Mesozoic, the great age of the Dinosaurs.

I am a published author, multi-disciplinary writer, and blog contributor. If you like this blog, please visit my writing portfolio.

The Works of Noelle Moser.

If you liked this post, chomp the subscribe button. As always, thanks for reading. Welcome to Coffee and Coelophysis.


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