Pachycephalosaurus (Thick-headed Lizard) is a genus of pachycephalosaurid marginocephalian dinosaur that lived in western North America 70 - 66 million years ago, during the Maastrichtian stage of the Late Cretaceous Period. It is named for its most distinctive feature, a skull roof 36 centimeters (1 foot, 2 inches) long, and 25 - 30 centimeters (10 - 12 inches) thick, providing it the thickest skull of any dinosaur.[PhP 3][PhP 2]
Pachycephalosaurus is the type species of the pachycephalosaur family, a group of small, bipedal dinosaurs related to ceratopsians, recognized for their thickened, highly ornamented skulls that were likely used for a variety of purposes ranging from display to physical combat, as indicated by numerous head lesions found in some specimens.[11][9]Pachycephalosaurus is the last and largest known pachycephalosaur, though it still stood no taller than the average human, reaching around 1.5 - 1.8 meters (5 - 6 feet) in height, 5 - 7 meters (16 - 23 feet) in length, and 370 - 488 kilograms (816 - 1,076 pounds) in mass,[4][5][TH 1][6][PhP 2] well within the upper weight range of mainland North American grizzly bears.[TH 1][12]
David Attenborough opens up the mystery surrounding the bizarre, dome-shaped heads of pachycephalosaurs
“ This is the skull of a pachycephalosaur, a 16 foot-long plant-eater. Despite years of research, we're still trying to understand why it had this bizarre-shaped head. ”
The most durable part of the skeletons of marginocephalians like pachycephalosaurs and ceratopsians are their bony heads, making them more likely to survive various destructive natural forces and degradation even after the animal has long died and the rest of its body has decayed. Due to this, most of what is known of Pachycephalosaurus is inferred from several well-preserved skull elements, with examples including AMNH 1696 (the holotype specimen, providing the most complete Pachycephalosaurus endocast), USNM 264304 (though not as complete as AMNH 1696, it is believed to preserve the olfactory system of Pachycephalosaurus more accurately), and BMRP 2001.4.5 (which bears 23 head lesions, brought up as evidence that their domes were used for fighting).[11][9]Pachycephalosaurus possessed large optic nerves and large, rounded eye sockets that faced forward, giving the animal good binocular vision. Moreover, as indicated by the endocast of specimen USNM 264304, Pachycephalosaurus (and other pachycephalosaurs in general) had a well-developed olfactory system consisting of large, divergent olfactory lobes with large nerves, deep and robust olfactory bulbs, and short, thick olfactory tracts, serving as evidence that they had a decent sense of smell compared to other dinosaurs.[13][14]
A female Pachycephalosaurus, possessing a less vivid (but still vibrant) coloration compared to males
As with most pachycephalosaurs, the post-cranial remains of Pachycephalosaurus are poorly known, for the bodies of marginocephalians like pachycephalosaurs and ceratopsians are not as tough as their heads, therefore making the rest of their skeletons less susceptible to fossilization, especially for smaller animals. But based on the fossils of relatives and the few fragments that were found, Pachycephalosaurus is believed to have a short, thick neck, short arms that ended in hands with five fingers (of which only the first three have claws), broad hips, long legs, and a thick, heavy tail made rigid by tendons that were ossified (turned to bone), though this bundle of solidified bony rods does not necessarily make the tail especially bulky.[DN 3]
Skull Dome, Ornamentation, and Growth[]
The younger male (left) blocks the attack of the dominant male
“ The surface was marked with a mesh of tiny fibers. Perhaps they supported brightly colored skin used to attract a mate. ”
The most prominent feature of Pachycephalosaurus is its helmet-like skull roof, surrounded by a crown of spikes, knobs, and horns that travel around the head all the way down to the dinosaur's snout. These domes are formed by a fusion of its frontal and parietal bones (and further thickened by bone deposits),[15] able to grow approximately 36 centimeters (1 foot, 2 inches) in length (comprising 60% of the entire skull, which is 60 centimeters or 2 feet in total length),[7] and reach 25 - 30 centimeters (10 - 12 inches) in thickness.[PhP 2][PhP 3] The way pachycephalosaurs used their domes is still not completely understood. The Uncovered segment "Was Pachycephalosaur Really A Headbutter?" brings up traces of a mesh of fibers on the dome that may indicate the presence of brightly-colored skin to serve as a display, though this could not have been its only purpose, as a mere display structure would not have justified its evolution in the form of a heavy dome several inches thick, and, unlike the head ornaments of hadrosaurs and ceratopsians, pachycephalosaur domes are not as varied, making them quite unsuitable for species recognition (with this similarity in domes causing paleontologists to sometimes incorrectly consider several distinct pachycephalosaur genera as one and the same).[16] Many studies and several lines of evidence clearly point to the dome's constant, physical use as a battering ram, like a study in 2008 supporting the theory that pachycephalosaur skulls could deliver and withstand tremendous headbutting forces, with possible keratinous covering and probable dense connective tissue cushioning the blows to protect their brains.[4]
The dominant male (right) strikes the younger male in the flank
“ Ten inch-thick skulls enable them to survive powerful head-on collisions. ”
Some studies argue that, even if the heads of pachycephalosaurs can resist powerful impacts, the force of headbutting would break their necks, and they resorted to striking each other's flanks, or swinging their heavy skulls sideways like clubs. However, the likelihood that they adopted proper postures specific for ramming, coupled with constant evidence of multiple lesions on the domes (with one specimen, BMRP 2001.4.5, bearing 23 dome scars),[11][9] injuries that quickly healed, eventually lead to a reanalysis of pachycephalosaur domes, with their CT scans compared to those of modern-day headbutting artiodactyls.[PhP 2][17] Currently, with this evidence, the idea that pachycephalosaurs butted heads is more acceptable than it once was. Aside from being used for intimidation and combat, the pachycephalosaurs can also use their heads for other, more mundane tasks during peacetime, as demonstrated by the dominant male striking and pushing a tree down in order to force out the insects within.
Pachycephalosaurus wyomingensis "Sandy" specimen, Royal Ontario Museum
“ The most distinctive feature about the pachycephalosaurs, of course, is this really weird dome that they have on their head. All around it is a series of very odd tubercles and knobbles and bobbles. They look quite dragon-like. ”
― Dr. Susannah Maidment, Natural History Museum
The Pachycephalosaurus on Prehistoric Planet is based on the "Sandy" specimen, which has pointed horns as opposed to blunt knobs. The taxonomy of Pachycephalosaurus is, to this day, subject to continuous debate, with conflicting views regarding the relationship of the spike-crowned form with the more familiar knob-crowned type. Although the former is still officially considered a growth stage of the latter, forming the sole species P. wyomingensis, some experts (including Dr. Darren Naish, Prehistoric Planet's lead consultant) theorize that the horned type is distinct enough to be considered a second species known as P. spinifer (previously interpreted as a distinct genus known as Stygimoloch, which means "Styx Demon"), for it is found in rock layers above the knobbed P. wyomingensis specimens, indicating that it lived later and may have in fact descended from the knob-crowned form. A 2025 study even suggests that Stygimoloch might be valid as a distinct taxon, given how it supposedly only appeared within the last 500,000 years of the Mesozoic Era before the Cretaceous-Paleogene Extinction Event.[1] Hence, the identity of the species on Prehistoric Planet depends on the validity of the spiked Pachycephalosaurus, which may be a subadult P. wyomingensis, a distinct species called P. spinifer, or a separate genus referred to as Stygimoloch.[DN 1][DN 2]
Similar to their ceratopsian cousins,[18] pachycephalosaurs have skulls that are composed of fibrolamellar bone which contains fibroblasts that rapidly deposit bone for the purposes of replacing or reshaping old and damaged bone tissue with new bone tissue, for the process of healing bone is important to animals that frequently use their heads for purposes that inevitably lead to wear and tear, though, as indicated by the numerous lesions on pachycephalosaur domes, even the quick-healing properties of fibrolamellar bone would not be able to perfectly mend all the injuries that the animals sustain. Uniquely, the fibrolamellar bone seen in pachycephalosaurs resembles periosteal bone (refer to "periosteum", the membrane that covers the outer surface of all bones except the articular surfaces, the parts by the joints, of long bones), albeit without canaliculi (microscopic canals between the lacunae, spaces containing osteocytes in bones).[8][7][9] These features also give their skulls the extreme plasticity needed to change in size and shape as the animal grew and adopted a different lifestyle; the squamosal (head rear) horns, which may start out
4.8 - 11 centimeters (4.33 - 1.9 inches) long and 2.5 - 3.4 centimeters (1 - 1.34 inches) thick, eventually shrink down to 3.6 centimeters (1.42 inches) in length and 4.2 - 5.3 centimeters (1.65 - 2.1 inches) in thickness, diminishing in importance as the skull dome is developed as the more prominent feature.[7]
This can be seen on Prehistoric Planet, where, compared to the old, dominant male, the young male appears to have a flatter, less-developed dome, resembling that of Dracorex hogwartsia (Dragon King of Hogwarts), which, unlike P. spinifer, is now fully acknowledged not as a separate dinosaur, but as a less mature form of Pachycephalosaurus. These age-related features, coupled with an individual's scars (ranging from chipped horns to head lesions), help further establish a pachycephalosaur's maturity, prowess, and rank in social hierarchy. Similar cases can be seen in both extinct and living animals, with the fourth segment of North America depicting this with the 30 year-old veteran male Triceratops, his asymmetrical horns and uneven frill setting him apart from the others in the mating season, making him an intimidating, well-seasoned rival in the eyes of other males, and, for the females, an attractive, hardened fighter with considerably preferable genes.
The dominant male Pachycephalosaurus feeding on insects
Pachycephalosaurus possesses a short muzzle with a pointed beak, filled with small, rigid teeth with leaf-shaped crowns. These teeth are sharp and serrated, not meant for tough, fibrous plants like the flowering shrubs of its time, but rather for shredding through leaves, seeds, and fruits,[14][19] though one lower jaw was discovered to have serrated, blade-like front teeth resembling those of carnivorous theropods, indicating a degree of omnivory,[10] which is seen on the show when the pachycephalosaurs fed on insects from a dead tree.
On Prehistoric Planet, Pachycephalosaurus and its relative Prenocephale are depicted without cheeks, in sharp contrast with ceratopsians like Triceratops and Pachyrhinosaurus, which are depicted with cheeks. According to paleontologist and anatomist Dr. Ali Nabavizadeh, pachycephalosaurs and other basal ornithischians had features consistent with those of lepidosaurs (lizards and tuataras), like short coronoid processes (the blade-like protuberances on either side of the mandible), similar buccal emarginations (the raised ridges that run along the outer side of the teeth next to the cheeks, defining the cusp tips and guiding chewing forces), foramina (blood vessel pits) concentrated rostrally (near the front), and thin, rounded, rostrally elongated labial dentary ridges (bone ridges lateral to the teeth). Their retroarticular processes (the bony walls that form the back of the temporomandibular joints, which connect the mandible to the skull) are noticeably long, and their pterygoid bones (which form part of the palate) have large flanges, indicating that their medial pterygoid muscles (important for mastication, the act of chewing) are hypertrophied, heavily developed compared to those of ceratopsids, stegosaurs, and ankylosaurs, which have retroarticular processes that are small or almost nonexistent. Overall, the idea is that pachycephalosaurs had simpler, more primitive teeth and a more basic lizard-like chewing style compared to the complex manner in which ceratopsians and more derived ornithischians chewed using their comparatively more advanced dental batteries. These basal ornithischians would have likely had lizard-like "lips" formed by large scales, but no cheek-like flaps connecting the upper and lower jaws.[AN 1][AN 2] Regardless of whether they had cheeks or not, current understanding has it that dinosaur cheeks are not like those of mammals given how, contrary to popular belief, dinosaurs did not need cheeks to hold food since they did not chew from side to side like mammals.[AN 3] Although at least some dinosaurs had skin covering the adductor muscles extending across their upper and lower jaws (some birds like condors do indeed have flaps of skin stretching across the sides of their mouths, while the nodosaurid Panoplosaurus of the Campanian Dinosaur Park Formation in Canada shows evidence of buccal flaps), no sauropsid (what is understood to be "reptiles", including avian dinosaurs) possesses cheeks or lips that are analogous to the more complex facial muscle anatomy of mammals.[AN 1][AN 2][TH 2]
Citing Dr. Ali Nabavizadeh's works as justification, Dr. Darren Naish had the show's pachycephalosaurs depicted without cheeks, instead only possessing large scales lining their jaws, resembling those seen forming the "lips" of lizards,[DN 4] fit for chewing food more like a lizard rather than engaging in the more complex mastication styles of ceratopsians and ornithopods.[DN 5]
Vocalizations[]
The large, dominant male calls for a herd meeting
The exact vocalizations made by pachycephalosaurs are unknown, though it is plausible to believe that, as with other dinosaurs, they made sounds reminiscent of various modern-day reptiles and birds. As with the aforementioned animals, non-avian dinosaurs like Pachycephalosaurus may not have needed to open their mouths in order to vocalize, as vibrating and amplifying the sound of air within the body is sufficient.
Prehistoric Planet uses the singing voice of a black grouse (albeit lowered in pitch to match the animal's larger size) to provide their warbling coos during peacetime, while the calls of herons and hornbills are added to provide harsher, rougher grunts and bellows whenever they engage in aggressive, more intimidating behavior.
The younger male (left) defies the authority of the dominant male
“ In a drought-stricken basin where much has perished, an old Pachycephalosaurus bull defends his leadership against a young challenger. ”
― The official Apple TV+ episode synopsis for Swamps
On Prehistoric Planet, the pachycephalosaurs are depicted with a yellow and brown color combination, with their domes partly covered in dark scales that may be battle scars and long-healed lesions, gashes, and bruises from previous battles, and blade-like bony protrusions jutting from the sides of their lower jaws. The females have paler scales compared to the males, which have prominent markings in the form of green and black speckles and stripes across the body, orange highlights by the throat area, and domes that come in a vibrant shade of red. The dominant male is noticeably larger and more heavily-built than the other members of his herd, with a tall, prominent dome and large back horns with some of the tips chipped off, serving as proof of his fighting experience. By contrast, the younger male's dome seems less prominent, less rugged, and not as heavily-marked with dark scales, given his age and lesser experience. Dr. Darren Naish designed the facial features of Pachycephalosaurus based on the skeletal reconstructions of Dr. Scott Hartman,[DN 1][DN 5] while the color variants were worked on by David Krentz, ensuring that, while the males have more vibrant coloring, the females were, to a degree, also striking in looks.[DN 6]
David Attenborough introducing Pachycephalosaurus as one of the spectacular animals of the Mesozoic Era
“ During the age of the dinosaurs, spectacular species like this pachycephalosaur attract the most attention. But the prehistoric world was also home to a wide variety of other quite different species. ”
Pachycephalosaurus is the main focus of the fourth, penultimate segment of Swamps, which centered around an old bull facing off against a young upstart in his herd. The species was also further discussed in "Was Pachycephalosaur Really A Headbutter?", an Uncovered segment which presents evidence of its headbutting capabilities and concluded that the dome of Pachycephalosaurus was useful as a display and as a weapon. The skull of a Pachycephalosaurus also briefly appears in the opening of the Uncovered segment "What Else Lived Alongside The Dinosaurs?", where it is used as an example of a spectacular species that attracts the most attention during the age of the dinosaurs.
Pachycephalosaurus herd searches for sustenance in a dry basin within the Scollard Formation
Pachycephalosaurus lived 70 - 66 million years ago in Laramidia, an island continent that would one day become western North America, which, by that time, was split in half by an inland sea. Fossils have been excavated mostly from the Hell Creek Formation in Montana and South Dakota, the Lance Formation in Wyoming, while indeterminate remains have been uncovered from the Denver Formation in Colorado,[3] but evidence of its presence further north indicates that it was cosmopolitan, not confined to certain faunal provinces. In fact, the fourth segment of Swamps, which is focused on Pachycephalosaurus, is confirmed by official press notes to have taken place in the Scollard Formation, located in what is now southwestern Alberta, Canada,[PhP 1] with the animal's presence indicated by a domed parietal found in the area.[2] Following the discovery of specimen UW 26525 (a partial yet diagnostic left squamosal considered by the study to be Stygimoloch) in the Ferris Formation in southern Wyoming (100 kilometers or 62.14 miles south of the Lance Formation in eastern Wyoming), a 2025 study states that the degree of the animal's palaeobiogeographic range is challenged by the fact that, despite extensive searches in Utah, Colorado, New Mexico, and Texas, no trace of Stygimoloch (which is considered a rare dinosaur to begin with) can be found south of Wyoming. The study does, however, consider the factors of poor preservation for the pachycephalosaur's scarcity as well as imprecise dating (as the study asserts that Stygimoloch is distinct from Pachycephalosaurus based on how it can only be found half a million years before the Cretaceous-Paleogene Extinction Event), and that available evidence does support (but not conclude) the hypothesis that Laramidia's dinosaurs were cosmopolitan by the end of the Cretaceous.[1] In any case, the aforementioned formations show that Pachycephalosaurus lived by the the eastern edge of Laramidia, where rivers, forests, and coastal plains were kept constantly humid by ample rainfall and a subtropical climate warmer than those areas are today, rendering those regions devoid of a cold season.
Three Pachycephalosaurus running through the fields of the Scollard Formation
“ This inland basin in North America was, in the past, several feet deep in water. But after a decade of drought, it's now bone-dry. Nonetheless, some dinosaurs still linger here. ”
Due to how little of their bodies have fossilized, it was once believed that pachycephalosaurs dwelled in areas of high elevation like mountains, where the conditions needed for the fossilization process are poor, with their heavy skulls rolling down to lower regions where they can be preserved. Prehistoric Planet depicts the pachycephalosaurs as running through a dry, open inland basin said to have once been several feet deep in water, rendered bone-dry by a decade of drought. However, Dr. Darren Naish clarified that such an environment would not have been appropriate for Pachycephalosaurus (it was only shown in such an area because of filming constraints). Instead, Pachycephalosaurus would have more likely thrived in wetter, more heavily forested lowlands like the one shown in the fifth and final segment of Swamps.[DN 7]
Paleofauna[]
A selection of non-avian dinosaurs that lived in the Hell Creek, Lance, and Scollard Formations (Pachycephalosaurus on the right side, in teal)
Pachycephalosaurus coexisted with other well-known dinosaurs like Ankylosaurus, Edmontosaurus, Triceratops, and Tyrannosaurus rex, which served as the apex predator of the regions where Pachycephalosaurus lived in, with the juveniles filling in the niches between those occupied by the adults and smaller predators like Acheroraptor and Pectinodon.[DN 7]Pachycephalosaurus also lived alongside two smaller pachycephalosaurs, Sphaerotholus and Platytholus.
In a 2011 study that estimated the proportions of large-bodied dinosaurs in the Hell Creek Formation, it was revealed that Pachycephalosaurus made up only 1% of the dinosaurs found in Hell Creek, though many other dinosaurs (e.g.) were just as rare, if not even more so, with some not even included in the breakdown of Hell Creek's paleo-population.[20] However, several factors known as taphonomic biases can also affect these population estimates, making various species appear to be more or less common than they actually were during their time. Some of the most common sources of bias include an animal's physical traits, the characteristics and conditions of the organism's habitat (especially its final resting place), the accessibility of the fossils in question, and human errors. In the case of Pachycephalosaurus, it is possible that some of the isolated theropod teeth in its habitat may in fact belong to it, which could, in turn, indicate that it might have been less rare than it first appeared to be.[10]
As one of the last non-avian dinosaurs, Pachycephalosaurus, along with most of the animals it coexisted with, would have bore witness to the Cretaceous-Paleogene Extinction Event 66.043 million years ago,[21] a catastrophe that ultimately wiped out three-quarters of all life on Earth, including all non-avian dinosaurs.
Feeding Preferences and Adaptations[]
The dominant male tries to knock a tree down
“ They prefer to feed on fruit and leaves. But now, they're forced to make do with roots and insects. ”
While usually viewed as plant-eating dinosaurs, pachycephalosaurs possess serrated, bladed teeth much like those of theropods, indicating that they may have eaten and processed just enough meat to be considered omnivorous rather than mostly herbivorous.[10] Given their omnivorous diet, the pachycephalosaurs are shown to be resilient, able to adjust their dietary habits by subsisting on roots and insects in the absence of their preferred food, fruits and leaves. A 2013 study of various Laramidian dinosaurs suggested that most plant-eating dinosaurs, regardless of mass, would have been restricted to feeding on plants and other forms of food around a meter (3 feet, 4 inches) in height,[22] though this limitation can be circumvented by the animal either rearing up past its default height, or by bringing down food just out of reach through various means, as shown when the dominant male Pachycephalosaurus headbutted a tree to the ground to feed on the insects within it. Members of the Pachycephalosauria clade have a very wide ribcage and a large gut cavity that extends to the base of their tail, suggesting that they relied on fermentation to digest food.[14]
Social and Agonistic Behavior[]
Young male bullies another member of the herd
“ The herd is lead by a large male. He keeps order, so everyone is able to search for food in peace. But trouble is brewing within the herd. The young male is throwing his weight around. It's time for the dominant male to put him in his place, or kick him out. ”
Nothing is known about pachycephalosaur social lifestyle, but based on their ceratopsian relatives and similar modern-day analogues, the adults likely had a social hierarchy, and parents took care of their young, at least, until the young males, upon reaching maturity, try to gradually assert their dominance by bullying more submissive members of the herd. In response, the large male leading the herd would confront the troublemakers to prevent further disruption of order within the herd, since, if these younger males are allowed to continue disregarding the herd's social hierarchy, they may gain enough courage and strength to eventually challenge and even overthrow the leader himself. Such potential contenders are left with two choices; they can either submit to the dominant male's authority and keep their place within the herd, or face the leader in a duel, with the consequence of their defeat being their eviction for disrupting peace and order within the herd.[DN 8]
The dominant male (right) tries to intimidate the younger male
“ He flaunts his colorful headgear, trying to intimidate the youngster. But he's not going to back down that easily... ”
As with most animals, the pachycephalosaurs try to intimidate their rivals first with a vigorous display of their prominent features. Given the greater prominence of domes over horns in more mature specimens, a larger dome size is likely a better indicator of power and experience, as not only would larger domes appear to be clearly more capable of delivering and resisting hits, these domes would also have a larger area of colorful skin to display, as well as more scars to show, proof of the individual's ruggedness and extensive experience. With all this, pachycephalosaurs with larger domes, more colorful heads, and more scars are more likely to intimidate lesser rivals and attract females, which would help avoid the need to fight. However, warning and mating displays are not guaranteed to work at all times, provoking rivals to prove their dominance through more physical and more violent means.
The dominant male (left) and the younger male headbutt each other
“ When they first saw these very thick, domed skulls - and these domes could be up to 30 centimeters in thickness - they were thought to be very strong. It was thought that maybe they were using them for headbutting each other in contests over social hierarchy. ”
― Professor Paul Barrett, Natural History Museum
A study in 2008 determined that a Pachycephalosaurus weighing around 488 kilograms (1,076 pounds) can have a closing speed of 6.7 meters (22 feet) per second, considered the reasonable maximum final velocity for pachycephalosaurs given their likely hip heights and limb proportions, on par with the highest observed speed of collisions between American football players. At this speed, Pachycephalosaurus would have received an average rebound (negative impact force) of 16,600 - 66,400 newtons or 1,700 - 6,780 kilograms (3,750 - 14,950 pounds) while decelerating at 16.5 - 66 centimeters (6.5 - 26 inches). This would result in 127.3 megapascals of pressure suddenly being imparted on the animal's entire dome (as opposed to being gradually applied) at the given point of impact, which is below the 200 - 300 megapascals that the dinosaur's thick skull can withstand. Point force application (which calculates more consistent, gradual force exertion) also suggests that a stress magnitude of 14,660 megapascals would have been focused on one square centimeter (0.4 square inches) at the top of the pachycephalosaur's dome, the very point of impact (while this method is not strictly correct, this calculation is done in order to cover any potential underestimates in the study). Whatever the case, this stress would have been cushioned by a likely keratinous covering and probable dense connective tissue, then dissipated throughout the skull before reaching the neurocranium (braincase).[4] Overall, biomechanical analysis supports the theory that pachycephalosaurs can engage in headbutting behavior.
The younger male (left) fails to block his rival, who glances off against his flatter dome and strikes him in the neck
“ What they've shown is that pachycephalosaur domes could actually have withstood an enormous amount of force. The sort of force that goes through American footballers when they hit each other. ”
― Dr. Susannah Maidment, Natural History Museum
The rate of a pachycephalosaur's sudden deceleration (and therefore, the resulting force) is consistent with the range at which American football players experience concussions.[4][PhP 2] Pachycephalosaurs would have been able to withstand forces beyond human tolerance, and the fibrolamellar bone that makes up their skulls contains fibroblasts that rapidly deposit bone to quickly repair damages that they sustain.[8][7][9] Even so, for safety reasons, pachycephalosaurs would have probably still preferred to ram each other at lower speeds around 3 meters (10 feet) per second, resulting in a rebound of 3,600 - 14,500 newtons, or 370 - 1,430 kilograms (816 - 3,150 pounds) while decelerating at 16.5 - 66 centimeters (6.5 - 26 inches).[4] Pachycephalosaurs would have only likely resorted to greater collision speeds and maximum striking power during high aggression justified by high stakes, like herd leadership. As shown by osteomyelitis (bone infection resulting from penetrating trauma or trauma to tissues over the affected bone) on pachycephalosaur skulls (for the fibrolamellar bone making up their skulls cannot perfectly repair all the injuries that they suffer),[9] the Dreadnoughtus males fighting in the first segment of Deserts (resulting in the death of the older male), musk oxen killing each other during the mating season,[23] and several cases of deer continuing to attack their long-dead rivals or getting their antlers stuck with each other (sometimes resulting in the deaths of both combatants),[24][25][26] animals are willing to use lethal force and risk their own lives in the process several times (regardless of whether they are aware of the risks or have their better judgment clouded by testosterone-fueled rage) just to emerge victorious in battles against their own kind. Hence, while pachycephalosaurs may have exhibited caution during fighting, evidence and comparison with other animals suggest that, in more intense battles, they would have been willing to deliver and sustain grievous, life-threatening injuries in order to win, with the scars that remain serving as solid evidence of an individual's experience as a strong fighter and survivor, making them more intimidating to enemies (predators and rivals of the same species alike) and more attractive to members of the opposite sex.
Males would rely on any tactic to win, including wrestling like monitor lizards, locking horns, and even faking defeat.
“ The older male is heavier. But the younger is more agile and has more stamina. And that tips the balance in his favor. ”
Given all these findings, while they did headbutt as indicated by evidence and research, Prehistoric Planet did not depict the pachycephalosaurs rushing at each other at the same time, head lowered, in the same way as musk oxen do. Instead, rushing is done by the aggressor within a shorter distance (while the opponent goes on the defensive by bracing for impact), the combatants prefer to bash and shove each other up-close, swing their heads like clubs (which the dominant male attempts to do in order to knock his retreating opponent off-balance), and even lock the horns on the back of their head in an attempt to stab each other. It is shown that the older, more powerful, and more experienced male is more willing to go on the offensive from the start, initiating most of the headbutts, recovering from collisions quicker, and continuing to push his adversary even when blocked, allowing him to slam through the defensive efforts of his enemy and maintain the pressure on him.[DN 9] When a fight goes on for long enough, rivals would resort to wrestling with each other much like monitor lizards, doing anything to force the duel in their favor.
The dominant male (right) forces his defeated rival to leave his herd
“ A bellow of victory... but, too soon. The loser has to pay a heavy price. Exile. Alone, it will be a struggle to fend for himself. But life here will not be easy for the winner either, unless the water returns to this land, and soon. ”
The younger male also showed some inexperience by failing to confirm if his older rival was indeed unable to continue the fight, allowing the older male to exploit his premature celebration, knock him down to the ground, and have him evicted from the herd for his transgressions and insubordination. Without the company of a herd, a lone pachycephalosaur is vulnerable not just to predators, but also to other problems, from weather conditions to, ironically, nothingness, a lack of resources, which could in turn cause health deterioration and death. Living in groups may inevitably lead to competition between its members, but herds also provide safety in numbers, as well as cooperative foraging, where herd members scout and search for resources faster than a solitary animal can, and across a range greater than what any one of them can cover on their own. Thus, through the efforts of many, the members of such a group can increase their chances of finding something that most - if not all - of them can benefit from. Living in herds also allows for the passing of knowledge. Prehistoric Planet demonstrates this in the sixth and final segment of Deserts, where older members of a Secernosaurus herd, knowing alternate sources of food and water, get the rest of their herd to endure long walks through the desert to arrive to these sources, in turn teaching a vital survival lesson for the next generation. Most importantly, herding behavior may even help prolong the life of members afflicted with ailments of all sorts, as demonstrated by two ceratopsians, Centrosaurus specimen TMP 1989.018.0108 (suffering advanced bone cancer in its right leg) and Pachyrhinosaurus specimen TMP 89.55.1234 (which has a massive hole stretching across the right side of its face). Despite their debilitating conditions, both animals survived longer than expected because they lived in herds. They were able to keep up with the rest of their companions rather than falling behind, and they both ultimately met their ends, not due to their illnesses and injuries, but due to catastrophic events (likely flash floods) that wiped out their entire herds.[27][28] It is reasonable to believe that, being relatives of ceratopsians, similar advantages may also apply to pachycephalosaurs that engage in herding behavior. Exiled and denied of all of the benefits of living in a group, the young, evicted member of the pachycephalosaur herd may end up being targeted by hunters, or left wandering aimlessly in an even harsher place devoid of food, water, and proper shelter. The remaining members of the herd, on the other hand, may potentially die together due to unfortunate circumstances, or finally come across solutions (temporary or otherwise) to the hardships they are facing (e.g. hidden sources of water, or an area unaffected by the decade-long drought of their land), thus saving them all.
Gallery[]
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While David Attenborough used the more common soft "c" pronunciation for "pachycephalosaur" on Prehistoric Planet, Professor Paul Barrett and Dr. Susannah Maidment pronounced it with a hard "c", which matches the original ancient Greek term for head, "kephalē". Nevertheless, both pronunciations are currently considered acceptable.
↑ 8.08.18.2Reid REH (1997) Histology of bones and teeth. In: Currie, PJ and Padian, K, editors. Encyclopedia of Dinosaurs. Academic Press, San Diego, CA. 329–339.
↑ 14.014.114.2Maryańska, Teresa; Chapman, Ralph E.; Weishampel, David B. (2004). "Pachycephalosauria". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press
↑Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300.
