Subjugator

285 million years PE, Serinarcta's new savannah woodlands are home to herds of hundreds of millions of grazers that feed on the grasses and water plants across the continent. And where there is prey, there can always be found predators.

Sawjaws remain among Serinarcta's most dominant predator guild - though far from its only one - and these bipedal tribbetheres have overcome the main limiting factor in their anatomy by transitioning to walk on their forelegs alone and raise their hind leg up into a new balancing tail. The first sawjaws and many living species were small predators, but this shift of anatomy now allows some sawjaws to grow bigger than any other land tribbetheres without sacrificing speed or agility, and now in this land of such abundant but large and well-armored meat, this gives them significant advantage over other tribbethere predators such as the foxtrotters in hunting on land. 

The largest sawjaw so far to evolve is the subjugator, a one-ton theropod-like apex predator descended from the swampsaw, and now one of the biggest carnivorous animals on land. The shoulders of this species have moved backward and downward into a hip-like arrangement, and so subjugators are fast and stable bipedal runners that are capable of endurance chasing to tire out prey even if it may run faster than they do for a shorter distance. Large trunkos are common prey, for these birds now can rival them in size and have few other enemies, and sometimes thorngrazers, even the fast-running forms, may fall on the menu if they manage a lucky catch, but the most frequently targeted animals by this hunter are the cygnosaurs, specifically the young and old. Greatly outsized by any single adult individual of this prey, it hunts in clans  - related groups of four to as many as twelve hunters, which use highly cooperative hunting tactics to outsmart their prey and separate a target from the herd. Though their jaws are their killing weapons, they also now exhibit a wicked slicing tail claw which lets them strike shallow, bloody blows at the flanks of their prey at a safer distance, and so seed chaos and panic and split apart the herd.

Subjagators, as with other social sawjaws, have a language of complex vocalizations used to communicate and to coordinate hunts, and different individuals can take adirections from the dominant leader(s) so that they hunt together as one. A herd of cygnosaurs is itself greatly cohesive and difficult to break up; a single animal must be targeted collectively for a hunt to succeed, and it takes the work of many to manage it. These huge herbivores have vicious defenses including whip-like tails, gut-ripping claws and incredible strength. Their great size makes even reaching the neck to deliver a debilitating bite a challenge in itself, and many must work to haul it down to the ground and gain the upper hand. Only a small percentage of hunts succeed, and almost always of animals somehow weakened. Truly fit adults in their prime are virtually without predators, yet there is no permanent haven: eventually all will become weak with age and be left behind by their herds into a lonely world where slicing teeth always lie waiting. Subjugators are powerful enough to eat the entire carcass of their giant prey, including its largest limb bones. Subjugators wear down the cusps of their teeth  quickly compared to smaller sawjaws by gnawing down these immense skeletons, and to keep them functional, they have evolved to periodically shed the outer layer of their teeth in layers every few weeks to reveal a new, sharp set beneath which has grown up from the beneath them and left unworn. This way of maintaining the sharpness of their teeth is unique to them among all molodonts, most of which have teeth that simply grow outward continuously to make up for gradual wear, but which means their teeth may never be completely sharp as a result of never getting a break from chewing. By regenerating a second set of fresh, new cusps as the older one is worn down, subjugators maximize the sharpness of their jaws and can maintain knife-sharp teeth almost all the time.

This unrivaled predator is very well-adapted to hunt on land and to run at a decent speed, and yet because the savannah woodlands it lives in were until comparatively recently a universally wet sogland habitat, it descends from ancestors which had acquired adaptations to facilitate better traversing water that have not yet been lost. The subjugator still exhibits a developed a fin of stiff cartliage along either side of their tails, which broaden its surface and allow them to paddle through water beaver-like and swim proficiently, and allow the subjugator to drive its victims into rivers and lakes where they become more vulnerable to its attacks - and where they float low in the water, with their heads and necks at a more accessible height to grab. With adaptable behavior and a broad diet, it can find other food along waterways too; many of the remaining larger thorngrazers such as the hadropotamus are semi-aquatic now too, having fled the cygnosaurs as they dominated the land. Even though they still swim poorly, they can walk along the bottom of these shallow waters, and so avoid detection by many of their enemies. Not so for the subjugator, though, which itself can dive well enough to catch them unaware even in deep, murky water, detecting them with an unrivaled sense of smell - one of Serina's most powerful - through a single large, fused nostril at the front of the snout. This specialized organ can detect scent even below the water, by holding air bubbles in a matrix of fine nasal hairs, through which underwater scent molecules diffuse.