Overall, the cranium of
Colossosuchus appears dome-shaped when viewed from the side. The tip of the elongated upper jaw, known as the terminal rosette, is strongly turned downward at a 70° angle. The rosette is large and bulbous, with its front flattened and the downward curvature is much steeper than in most other phytosaurs. A series of parallel crests run exclusively along the left side of the
premaxilla and
maxilla. The
nares are located just before the eyes like in other phytosaurs and unlike in crocodiles. Just before the opening of the nares a pair of prenarial fossa are present, which
Colossosuchus shares with
Diandongosuchus. The naris themselves are not elevated above the eyes, but the
septum is located above the rim of the narial openings. This too is similar to
Diandongosuchus, as well as
Ebrachosuchus and several species of
Parasuchus, while setting it apart from most
leptosuchomorphs. The nares overlap with the
antorbital fenestra for over 50% of their length, a condition also seen in all mystriosuchines other than
Volcanosuchus. The
nasal bone is covered in band-like ornamentation, which is replaced by
dendritic (branched) ornamentation on the skulltable. Where the nasal bone meets the
frontal bone a U-shaped depression can be found. The
supratemporal fenestra open dorsolaterally, meaning to the top and side of the skull, and are located below the skulltable. The
postorbital-
squamosal bar is depressed and oriented down and to the sides, while the
parietal-squamosal bar is convex and positioned so that it descends beneath the skull table. The shaft of the
mandible is broad, about 59% of the width of the mandibular
symphysis. The
dentition consists of three parts and is tripartite, meaning several sets of teeth are present. These consist of the large teeth found in the terminal rosette and the distinct premaxillary and maxillary tooth sets. This sets
Colossosuchus apart from other basal mystriosuchines and draws parallels to leptosuchomorphs, the only mystriosuchines besides
Colossosuchus to feature tripartite dentition. Four teeth were located on either side of the terminal rosette, the first three of which were large and of roughly equal size. The first two tooth pairs are firmly located at the bottom of the snout tip, while the third and fourth pair originate on the side of the bone and are angled slightly outward. The final pair was smaller and followed by three small anterior premaxillary teeth. In general,
Colossosuchus had a very high tooth count, with around 57 teeth being present on either side of the upper jaw. The
neural arches possess well-developed laminae and fossae, which are similar to those seen in
Angistorhinus and both
Smilosuchus adamanensis as well as
Smilosuchus gregorii. The
sacrum consists of three vertebrae, like in
Smilosuchus adamanensis and
Redondasaurus cf. gregorii.
Size The body size of
Colossosuchus was determined through the use of multiple different methods. According to prior publications, including Heckert
et al. (2021), head to body proportions changed among phytosaurs in their evolutionary history. According to them, basal taxa such as
Parasuchus had larger heads, with
P. hislopi having a head that makes up 21% of the total length. Later phytosaurs are then hypothesized to have had proportions more similar to modern crocodilians like the
saltwater crocodile, only accounting for 13-15% of the total length. Based on this Datta and Ray propose that
Colossosuchus would have had more derived proportions which, assuming that the skull makes up 13% of the body length, would yield a maximum length of over . To prevent overestimating the size, two additional regression equations were used, one based on the length of the femur and the other based on skull length. The former yielded a maximum length of only , considered to be an underestimate, while the latter resulted in a maximum length of over . The estimate is favored by Datta and Ray, who argue that it is most in line with the body size seen in other derived phytosaurs including
Smilosuchus. This would consequently mean that
Colossosuchus was among the largest known phytosaurs discovered. These estimates, however, only apply to the largest known individuals and do not represent the average size attained by
Colossosuchus. The fact that the fossils were discovered in a mass death site instead provides a wide range of sizes for the 21 known individuals, which range from juveniles to fully mature adults. Skeletally immature members of this species are generally smaller than and characterized by their comparably big eyes, lacking ornamentation, unfused bones and poorly developed muscle scars. Subadults and transitional individuals are thought to occupy a size range between while skeletal maturity appears to have been reached at a length greater than . ==Phylogeny==