Prenocephale

## PrenocephaleSloping Head

***Prenocephale*** (Sloping Head) is a genus of pachycephalosaurid dinosaur that lived in the Nemegt Formation, Mongolia, 70 million years ago, during the Maastrichtian stage of the Late Cretaceous Period.

## Paleobiology

### Size and Physique

*Prenocephale* is a small animal, merely 2.2 meters (7 feet, 2 inches) long, with a body mass of 40 kilograms (80 pounds). As indicated by its name, *Prenocephale* has a round, sloping head, surrounded by crown of small, bony spikes and knobs, the defining trait of pachycephalosaurs. It resembles *Stegoceras*, a closely-related pachycephalosaur that lived 77.5 - 74 million years ago in North America, with a few differences, like some closed-up openings on top of the skull as well as the absence of paired grooves above its eye sockets.

### Jaws and Dentition

On Prehistoric Planet, *Prenocephale* and its relative *Pachycephalosaurus* are depicted without cheeks, in sharp contrast with ceratopsians like *Triceratops* and *Pachyrhinosaurus*, which are depicted with cheeks. Using the works of Dr. Ali Nabavizadeh as justification, Dr. Darren Naish, lead consultant of Prehistoric Planet, brought up how pachycephalosaurs had simpler, more primitive teeth, and hence chewed food more like a lizard rather than doing so in the more complex manner in which ceratopsians and ornithopods chewed. Regardless of how this debate eventually gets resolved, current understanding has it that dinosaur cheeks aren't like those of mammals, since, contrary to popular belief, dinosaurs did not need cheeks to hold food, and one theory is that they may have had "cheeks" as a result of jaw muscles extending across the parts where true cheeks would be.

### Prehistoric Planet's Depiction

On Prehistoric Planet, the *Prenocephale* are countershaded, their back riddled with tiny osteoderms, with stripes running down across the body. The females have a dark gray back and light gray belly, while the males were intended to be depicted with brighter colors, including facial stripes and orange hindquarters, though this was ultimately darkened for the show and made even duller by dirt and ambient lighting.

Male *Prenocephale* are depicted with keratinized bristles running down their backs and tails (though concept art reveals that the females were initially planned to also have tail bristles). Tail bristles (determined in a 2016 study to be highly modified scales as opposed to feathers due to the different morphology and anatomy of these structures) are known in the primitive *Psittacosaurus*, a basal ceratopsian, and, though there is barely any evidence of such structures in others, some of the later, more advanced members of the ceratopsian clade are occasionally depicted with similar-looking filaments running down the back and tail (hence why the adult *Pachyrhinosaurus* males were depicted with such bristles in Ice Worlds). This speculative characteristic is sometimes extended to the other marginocephalian clade, pachycephalosaurs like *Prenocephale*. These keratinized bristles likely served as an additional means of display.

## Paleoecology

### Paleoenvironment

*Main: Nemegt Formation*

Main: Nemegt Formation

*Prenocephale* lived 70 million years ago in the Nemegt Formation, an area that would one day become the Gobi Desert in Mongolia. The formation shows evidence of a rich, humid environment with large river channels, tidal flats, and forests, with *Prenocephale* believed to prefer high upland wooded areas. However, the Nemegt Formation is also known to have undergone periodic droughts, and there is precedence for arid regions much like the Gobi Desert today existing in Mongolia during those times, thus somewhat justifying the depiction of *Prenocephale* living in a vast desert environment. Fittingly, *Prenocephale* is depicted as preferring to live around a small spring in the show, hidden within a canyon where they are less likely to be found and hunted by predators.

### Paleofauna

*Prenocephale* is one of the two pachycephalosaurs of the Nemegt Formation, the other being the smaller, flat-headed *Homalocephale*, which was previously theorized to be merely juvenile forms of their larger relative until actual young *Prenocephale* specimens were found with rounded domes, proving that both are different species. *Prenocephale* also coexisted with similarly-small creatures like *Mononykus* and at least eight oviraptorosaurs, and would have faced threats from hunters like *Adasaurus* and other indeterminate velociraptorine dromaeosaurids, as well as troodontids like *Borogovia*, *Tochisaurus*, and *Zanabazar*.

The Nemegt Formation is also home to medium-sized dinosaurs like *Gallimimus* and *Alioramus*, as well as significantly larger animals like *Barsboldia*, *Deinocheirus*, *Therizinosaurus*, and the apex predator of the region, the tyrannosaur *Tarbosaurus*. The largest inhabitants of the Nemegt Formation are titanosaurs like *Nemegtosaurus*, *Opisthocoelicaudia*, and other, larger titanosaurs that may potentially rival *Argentinosaurus* in size.

### Feeding Preferences and Adaptations

It is believed that *Prenocephale* is not a selective forager due to its mouth and premaxillary teeth not being as wide as its relative, *Stegoceras*. It is also suggested that they are omnivorous, feeding on plants and insects, like their relative, *Pachycephalosaurus* (which has theropod-like blade-shaped teeth in the front indicating a degree of omnivory, and, as shown in Swamps, feeds on some insects).

### Evasive and Defensive Tactics

***“ Long-necked Nemegtosaurs are joined by Mongolian titanosaurs. And with them, much smaller Prenocephale. ”***

― **David Attenborough**, *Badlands*
Given their small size, the *Prenocephale* are cautious, and hence travel with larger dinosaurs like *Nemegtosaurus* and the Mongolian Titan for protection from predators like *Tarbosaurus*. However, when panic rises within the herd, they may try to escape by using their small, agile form to escape to higher ground, though this, in turn, puts them in danger of being pursued by similarly agile predators like *Velociraptor*. Given how resources are limited in the desert, animals may be justifiably greedy and competitive over resources, explaining why the *Prenocephale* react with hostility when a juvenile *Tarchia* drinks from their oasis, growling, screeching, and nipping at the newcomer with their beaks as opposed to headbutting with their hardened skulls, though, given their small size, they were easily scared off when the *Tarchia* intimidated them by slamming its tail club on the ground, reminding them of its far greater size and power.

## Appearances

### Badlands

#### Segment 2

In the second segment of the episode, on the way to a temporary oasis hidden behind a plateau riddled with canyons that form a massive maze, a group of *Prenocephale* are seen traveling with a herd of *Nemegtosaurus* and Mongolian Titans for protection. Suddenly, the herd is thrown into panic by a trio of *Tarbosaurus*, scaring the *Prenocephale* into running up a canyon to escape to higher ground, an option the sauropods cannot take as they try to travel through the maze as quickly as possible.

***“ Only the Prenocephale can escape to higher ground. And this is what the Velociraptors have waited for. Now, the Velociraptors can finally spring their ambush. ”***

― **David Attenborough**, *Badlands*
Unfortunately, this means they ran right into the ambush of the *Velociraptors*, with one of the dromaeosaurs singling out one of the *Prenocephale* and pursuing it up a path where another *Velociraptor* is waiting. Upon reaching the ambush point, the other *Velociraptor* springs from behind the wall to kick the *Prenocephale* off the edge to its death. As the trio of *Tarbosaurus* feed on a *Nemegtosaurus* that died during the stampede, the two *Velociraptors*, along with their chicks, descend from the canyon to feed on the fallen *Prenocephale*, a meal secured for the whole family.

#### Segment 4

In the fourth segment of the episode, a juvenile *Tarchia* comes across a small spring hidden within a canyon, surrounded by seven *Prenocephale*. The ankylosaur walks through the group of pachycephalosaurs, which are surprised and displeased by the newcomer drinking some of their precious water. They growl, screech, and nip at the juvenile with their beaks, though the ankylosaur reminds them of its superior size and strength by slamming its tail club on the sandy ground, scaring the *Prenocephale* off and causing most of them to scurry behind a rock.

***“ Tensions often run high around an oasis. But a display of strength can prevent a dangerous battle. In the end, the Prenocephale are little more than annoying. ”***

― **David Attenborough**, *Badlands*
After the juvenile *Tarchia* and its companion get the adult *Tarchia* that owns the oasis to back off and let them have a share of the place, the *Prenocephale* watch the ankylosaur brothers drink from atop the rocks on the opposite side of the spring, unable to do anything about the situation.

## Trivia

* *Prenocephale* is the only Nemegt Formation species to debut in the second season of Prehistoric Planet, as all the other featured Nemegt Formation inhabitants already appeared in the previous season.
* *Prenocephale* is the only marginocephalian dinosaur featured on Prehistoric Planet that never got involved in intraspecific combat. On a more general note, it is also the only marginocephalian dinosaur never seen using its headgear at all, preferring to run from predators like *Velociraptor* (which is half the pachycephalosaur's weight) and nip at rivals with their beaks.
	+ However, given their conflict with a young *Tarchia* in the fourth segment of Deserts, *Prenocephale* is the only herbivore (as a member of a family that showed omnivorous traits, it still technically counts as a plant-eater) depicted fighting another herbivorous species (the same cannot be said for *Tarchia*, which didn't actually fight back, but managed to intimidate its foes). A close case involved one *Ornithomimus* trying to keep two *Edmontosaurus* away from his nest in the second segment of Ice Worlds, though both animals never actually contact each other, unlike the *Prenocephale*, which managed to nip at the young *Tarchia* until the juvenile scared them off by slamming its tail club on the ground.

## References

### General

1. ↑ 1.0 1.1 1.2 *The Princeton Field Guide to Dinosaurs*
2. ↑ Feathers or Scales?
3. ↑ Morphology and histology of new cranial specimens of Pachycephalosauridae (Dinosauria: Ornithischia) from the Nemegt Formation, Mongolia
4. ↑ Vegetarian dinosaur may have actually eaten meat, skull suggests

### Dr. Ali Nabavizadeh

1. ↑ New Reconstruction of Cranial Musculature in Ornithischian Dinosaurs: Implications for Feeding Mechanisms and Buccal Anatomy
2. ↑ Dinosaurs did not need cheeks to hold their food since they don't chew from side to side the way mammals do.

### Dr. Darren Naish

1. ↑ Pachycephalosaurs likely lacked cheeks because of their primitive teeth.
2. ↑ After basing off of Dr. Ali Nabavizadeh's works regarding pachycephalosaur chewing styles, the decision was made to depict pachycephalosaur anatomy as being more fit for lizard-style chewing as opposed to the more complex chewing styles of ceratopsians and ornithopods, further showcasing the anatomical diversity of ornithischians.

### Dr. Thomas Holtz

1. ↑ Lecture 17 Thyreophora Defense! Defense! DEFENSE!!

### Prehistoric Planet

1. ↑ Gabriel Ugueto, one of the designers who worked on Prehistoric Planet, shows *Prenocephale* concept art and confirms that the tail bristles of the females were removed on the show, making the bristles a male-exclusive feature.