Here's my original sketch of what would eventually be my fursona: Hyenasaurus aegypticus, a half-spinosaurid/half-spotted hyena beast. The major changes to my personal character were the theropod tail as opposed to the short hyena tail seen here, and the addition of neural spines. This is just a general example of the species, so the colors aren't my personal character's or anything.

Another thing that's interesting is the sexual dimorphism in spotted hyenas, as the females are larger and tougher than the males (thanks to a generous wash of testosterone in utero) which is rather uncommon in mammals.
Furthermore, paleontologists have found that in many theropods the female is usually larger than the male of most species (much as in modern day birds), so that means female hyenasaurs would be friggin' massive. :3

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Species: Hyenasaurus aegyptiacus (H. aegyptiacus)
lit. "Hyena Lizard from Egypt"

Appearance: A large-sized terrestrial carnivore falling under a group of proto-mammals known as reptile-like synapsids (reptiles with mammalian qualities, which would eventually give rise to today's true mammals), H. aegyptiacus (or 'hyenasaurus' as it is more commonly known) would've been an impressive animal to see hunting prey across its native marshlands of Cretaceous South Africa. So named by paleontologists for its striking skeletal similarities to Crocuta crocuta, the African spotted hyena. At the time of its discovery, it was considered to be a 'missing link' of sorts between mammals and reptiles, though given the scarcity of found specimens it appears to have been an aberrant specie whose genetic legacy was self-condemning. While most therapsids ruled through the early and into the late Triassic and died off to be replaced by the dominant land, ocean, and air archosaurians (dinosaurs, pterosaurs and the like), H. aegypticus was somewhat of an anomaly in that it easily rivaled many early theropod dinosaurs of its time in size when the only other remaining members of its clade were wolf-sized at best.

The closest therapsid in genetic relation to the comparatively massive H. aegyptiacus was the cat-sized Pristerognathus: https://upload.wikimedia.org/wikipe.....gnathus_DB.jpg
Hyenasaurus was estimated to have stood at an imposing thirteen feet at the shoulder and fossil findings indicate it would've reached upwards of twenty three feet in length from the tip of the snout to the tail. It is thought to have weighed in at 2.3-3.0 tons at adult size, with the females being slightly larger than males as an example of sexual dimorphism.

It moved about bipedally, though the elongate forelimbs would have allowed it to transition and lope on all fours as a modern grizzly bear does when the need for faster locomotion arose.

A striking display of elongated neural spines running from the cervical vertebrae down to the sacral vertebrae would've given the illusion of added size to intimidate possible rivals, and was thought to have acted as a sort of cooling system on particularly hot days, the spines being packed with blood vessels so that the animal need only rest near a breeze to cool itself down.

The skull has an odd combination of features, with differentiated teeth including large crushing molars to take advantage of bony remains that other predators would have no interest in consuming, as well as peg like canines, incisors and premolars that would've been used to skewer fish or other prey.
The lower jaw is powerful and contains a jaw joint connecting further back into the skull, a feature seen on other early synapsids but not on transitional mammals. The snout is elongate but lacks the air sacs of earlier proto-mammals, suggesting with such a heavy skull it could add impact to its bite force when pursuing prey.

Skin impressions indicate Hyenasaurus had a generous coat of fur-like hairs across the majority of its body, allowing for it to survive in colder climes and thus to adapt to the steadily cooling temperatures of the late cretaceous. The only places it appears to have lacked this hair appear on the distal portions of the forelimbs and hind limbs, the elongate spine, as well as the snout. It is unknown why the animal lacked hair in these locations.

Of the few complete skeletons discovered, it seems the majority of animals surviving into adulthood appear to have sustained bite and gouge wounds on the neural spines and the ribs of the ventral abdomen, giving rise to the idea that these animals could be fighters where food came into play and were sometimes the victim of larger, dominant predator theropod species if they fell into competition with one another, though its size would've put it at an advantage against smaller theropods such as Ceratosaurus.