Agathumas

Agathaumas was a large horned dinosaur that lived during the Late Cretaceous period, about 68 to 66 million years ago. It lived in what is now Wyoming, in North America. At that time, the area had rivers, forests, and a warm climate. As a ceratopsian, Agathaumas would have been a plant-eater, using its beak-like mouth to feed on low-growing plants.

Tier: 4

Dimorphism: Males feature bolder, more striking colors, sharper and more prominent dermal spikes, taller and thinner frills, and taller, more impressive horns.

Habitat: Redwoods and Cedrus Forest

Diet: Herbivore

Active Time: Agathaumas, like most large plant-eating dinosaurs, was active during the daytime (diurnal).

Group Limit: 6 individuals

Defense: 4 individuals

Nesting Season: Spring & Summer

Adoption: ✅

Behavior

Agathaumas is highly aggressive, even more so than other ceratopsians. It does not back down from fights, often battling rivals or even apex predators to the death, even when alone. Most charge without warning and are fiercely protective of their own, attacking immediately without hesitation or question to defend themselves or their herd from any perceived threat. Herds are led by one dominant bull who will tolerate his sons until they come of age or longer, as long as they do not attempt to court the herd’s females. The females were more affectionate within the herd, communicating through low vocalizations and often resting close together. During large seasonal migrations, they tolerated the presence of other herbivores moving alongside them, but outside of those periods, they are openly hostile and territorial toward other plant-eating species.

Courting and Nesting

Each herd is led by a dominant bull. Challengers are often his grown sons or a lone bull seeking to take over the herd. Males engage in fierce battles, clashing with horns and frills in contests of strength, usually stopping just short of death. Females keep very hidden nests and are typically very moody during this time, even toward the bull. If he gets too close to the nest or their young, the females aggressively call at him as a warning that he is much too close. Females only tolerate other females nearby.

However, in times of danger, the female allows the bull to come closer if it means increased protection for her offspring. Females can also choose to leave after a new bull is chosen and follow an older bull if they have been with him for multiple seasons and he has proven himself a strong and capable protector. In rare cases, the female decides to leave the herd if the bull isn’t up to her standards (poor protector).

Mandatory Behavior

Never Back Down, Never What?

Agathaumas are extremely aggressive ceratopsians that rarely back down, even when the odds are against them. A lone Agathaumas stands its ground, even if the danger it is facing is an apex carnivore like a T. rex, preferring to fight to the death rather than flee. Due to their relentless fighting nature, many bulls are heavily scarred and worn from countless battles, their frills and horns bearing the marks of previous confrontations. These scars serve as a warning to rivals and a testament to their resilience and dominance. (This is mandatory only for battle-worn subspecies like Broken Horn and or Hole in the Crest, for other subspecies, it is optional)

Thwack Norris

Agathaumas love to fight and often seek out other dinosaurs to spar with, using loud calls and aggressive displays to provoke challengers. These battles are rarely fatal but often leave one or both combatants with deep, permanent scars, visible reminders of their skill and toughness. Even outside of dominance disputes, Agathaumas engage in these fights for practice or challenge, showing their relentless drive to assert themselves and prove their strength among other dinosaurs.

Danger A – Foot

Agathaumas has always despised Deinocheirus, not just out of jealousy, but because of the constant rivalry over water. Sturdy and armored, proud of his sharp horns and heavy frill, Agathaumas fiercely guards the watering holes within his territory. When the towering Deinocheirus lumbers in with its enormous claws and awkward frame, wading into the shallows as if it owns the place, Agathaumas sees red. He hates sharing what he has claimed. With snorts and pounding steps, he charges, forcing the long-armed giant to retreat from the water’s edge. Again and again, Agathaumas chases Deinocheirus away, determined to keep both his territory and his pride untouched.

Frill at the Fill

Agathaumas are rarely found far from water, preferring to anchor their territory around rivers, lakes, and deep watering holes. They typically move only when a source begins to dry or competition becomes too intense, traveling with purpose from one claimed basin to the next. However, when heavy rains fall and temporary pools spread across the land, this aggressive ceratopsian seizes the opportunity. With fresh water no longer limited to the shoreline, Agathaumas ventures inland, expanding its range and asserting dominance over newly formed watering grounds before the dry season returns. In rare cases, if an inland watering hole proves large enough, rich in vegetation, and defensible from rivals and predators, the herd attempts to claim it permanently. Only after holding and defending that territory through four full seasons, enduring drought, storm, migration pressure, and predator threats, does Agathaumas consider it secure enough to establish nesting grounds and raise its young there.

Optional Traits

Females may adopt other ceratopsian hatchlings or juveniles if they find them. Despite the species’ aggressive nature, females show a soft spot for young ceratopsians, but only until they reach late adolescence or sub-adulthood. Once the young begin to look noticeably different from the herd, the female usually chases them out, though in rare cases she continues to tolerate her unusual “adopted” offspring.

Mother Knows Best

When Agathaumas have hatchlings or juveniles, the herd becomes extremely protective. The females are the first to confront and kill any young apex carnivores they encounter, while the bulls join in to lend their strength and size. By eliminating these potential threats before they mature, the herd greatly increases the chances of survival for their young, showing just how far they go for their herd.

Calm Beneath The Crest

Agathaumas show a surprising tolerance toward smaller ceratopsians. The younger and lighter-framed horned dinosaurs are not seen as threats, nor as serious competitors for territory. In fact, their presence often brings a sense of familiarity, shared frills, shared horns, shared instincts. At the water’s edge, Agathaumas stands watchful but calm as the smaller ceratopsians drink nearby, accepting them as distant kin rather than rivals. The little horned cousins are allowed to linger, moving through the territory under the quiet protection of their larger, more armored relatives.

No Crocs Allowed:

Agathaumas view crocodilians with open disdain, insulted that such low, sliding beasts dare enter waters they claim. Their sudden, snapping jaws and scaly hides only fuel their outrage, and none of them tolerate their presence. With snorts, stomps, and threatening charges, they drive them away from the shoreline/water, making it clear that these intruders are neither welcome nor respected. To Agathaumas, the waterholes are his domain, and any crocodilian foolish enough to wade into them challenges not just his space, but his pride.

Credits : Littlered with support from KushalaDarora

Sources:
https://en.wikipedia.org/wiki/Agathaumas https://extinctanimal.fandom.com/wiki/Agathaumas

Last updated: 2/17/2026