The holotype skull of
Brazilichthys is made up of most of the skull that is anterior to the opercular series with what is present measuring long and deep. The
skull roof of
Brazilichthys is poorly preserved with fragmentary bones suggested be the
frontal and
parietal bones being the only parts of the material suggested to be that part of the skull roof. The front of the skull is generally more well preserved with a large
nasal bone being present. Small notches are located at the anterior and posterior edges of the bone which would have been where the nasal openings would have been positioned. The circumorbital series is generally well preserved outside of what has been interpreted as the dermosphenotic by more recent authors. Though partially hidden by the nasal an
premaxilla, the
sclerotic ring of the fish is preserved. The ring is comparably large compared to the orbit though does generally have the same shape. Though the
braincase of
Brazilichthys is not preserved, bones associated with it such as the
parasphenoid are found in the specimen. This bone was long with an inflated anterior end that would have most likely been in articulation with the
ethmoid region of the braincase along with the
vomers. The vomers would have been a part of the roof of the mouth but would not have possessed any teeth. The most notable features of the skull of
Brazilichthys are the upper and lower jaws along with the
dentition. The
maxilla and
dentary are the largest bones that make up the upper and lower jaws respectively. The maxilla, as the size would suggest, a long bone with it going far past the eye which it changing shape as it passes the
orbit. The premaxilla is much smaller than the maxilla, though still robust. Though not preserved, it can be assumed that the rostral bone would have made contact with the premaxilla. Under the orbit, the maxilla bends downwards only to expand when passed the opening. The dentary, similar to the maxilla, is very long with ornamentation similar but overall more robust towards the front of the bone. Other than the dentary, the
angular and
surangular are the only other external elements of the jaw that are present in the holotype though both are at least partially covered by the dentary. The
endoskeletal bones such as the articular are only partially
mineralized. Both the upper and lower dentition are organized into two rows which are even present were the bones overlap one another. The inner tooth row would have been much larger than the smaller ones and were more widely spaced. Outside of the much larger size, the teeth of the inner row also differ due to them being curved with them being described as
fangs in papers describing the dentition. These larger teeth are only seen on the maxilla and dentary bones with only the outer row being present in other teeth that make up the jaws. When the mouth of the fish would close, the upper fangs would overlay the dentary whereas the fangs on the lower dentition would fit into
fenestrae found on the interior surface of the maxilla. Not every one of these fenestrae would have been inline with a fang, instead only every other fenestrae would be filled by a fang from the lower dentition when the mouth would close. Evidence of tooth replacement on the upper dentition can be seen through depressions present between the fangs which this being similar to what is seen in not only extinct genera but also modern day
bichir and
cutlassfish. The placement of the depressions along with the patterns of fenestrae on the maxilla suggests that the teeth would have been replaced in an alternate pattern both within the one side of the dentition but also between the sides. This meaning that the teeth would have been alternatively replaced on one side of the mouth and then the other rather than it happening on both sides at the same time. Similar styles of tooth replacement is also seen in some modern fish, namely in the family containing
pacus and piranhas. The gular bones present under the front half of the lower jaw were all around the same size though the median gulars are the only ones to possess a pit line on their surface. Behind the gulars, there are seven or more pairs of
branchiostegal rays though they are largely poorly preserved. Similarly, the opercular series of
Brazilichthys are also poorly preserved with the only bone present being the left
opercle.Due to this bone, along with the rest of the series, being so poorly preserved, nothing can be said about the exact anatomy of the region. The
hyoid of the fish is only partially preserved with only the left
hyomandibula and the hypohyals being preserved. A number of bones part of the branchial arches are preserved with the
epibranchials being short. In contrast to this, the
ceratobranchials and
hypobranchials are much longer with the
ceratobranchials being U-shaped in cross section. == Paleobiology ==