Ennatosaurus is known by several adult skulls (PIN 1580/14, 17 (
holotype), 122, 4543/1), as well as by a juvenile skull (PIN 1580/24) associated with many postcranial elements from several individuals. All these elements allowed the reconstruction of a composite skeleton. Unlike all other derived caseids that have a tiny skull relative to the body size,
Ennatosaurus is peculiar by the small size of its postcranial skeleton compared to that of its skull. However, almost all of the postcranial material in
Ennatosaurus belongs to juvenile individuals, and the unusual proportions of this composite skeleton could be explained by the mounting of an
adult skull on a juvenile skeleton. However, the existence of some bones of subadult and adult individuals suggests that
Ennatosaurus did indeed have a proportionally smaller body than that of other derived caseids. The largest adult skull of
Ennatosaurus (the holotype PIN 1580/17) is approximately 17 cm long, a size similar to the skull of
Cotylorhynchus romeri, while the few adult bones of
Ennatosaurus are half the size of the corresponding adult elements in
C. romeri. As in other caseids,
Ennatosaurus has a very short skull with a snout sharply sloping forward and very large external nares.
Ennatosaurus is distinguished, however, by its proportionally longer facial region than in
Casea and
Euromycter. The dorsal ramus of each
premaxilla contributes to a narrow intranarial bar, narrower than that of
Euromycter, but of width similar to that of
Cotylorhynchus romeri. The skull roof is distinguished by the very large contribution of the
frontal to the dorsal margin of the
orbit. It occupies about 50% of the length of the latter while in
Euromycter and
C. romeri the frontal represents less than 10% of the margin of the orbit. The
jugal is very characteristic in having a thick and very elongated anterior ramus creating an area of extended contact with the
lacrimal. In other caseids, the anterior ramus is very thin and ends in narrow vertical contact with the lacrimal.
Ennatosaurus also differs from all other caseid in its
temporal fenestrae significantly larger than the nostrils and orbits, its
palate with a narrower
parasphenoid, and its upper dentition more reduced in number. In
Ennatosaurus, each premaxilla and
maxilla only have two and eight teeth respectively against 4 and 11 teeth respectively in
Euromycter and 3 and 15 or 16 teeth in
C. romeri. The premaxillary teeth are conical in shape, the following teeth are spatulate with five to seven cuspules arranged longitudinally. . The postcranial skeleton also shows many original characters. The
vertebral centra of all regions of the body are characterized by the presence of two well-developed ventrolateral pits, deep and elongated anteroposteriorly. The neural spines of the vertebrae show a diamond-shaped section along its entire length, a condition similar to that observed in
Ruthenosaurus. The vertebrae of the "lumbar region" are characterized by the absence of fused or co-ossified ribs (a characteristic to be taken with caution given the juvenile condition of the specimens). The
humerus has a robust
ectepicondyle and a not completely closed ectepicondylar foramen. A deep and well marked fossa is present immediately behind the
acetabular buttress of the
ilium. The
femur is very characteristic, its
proximal articular surface is much wider dorsoventrally than anteroposteriorly and an elevated and robust bony crest extends from the narrowest part of the
shaft to the top of the posterior
condyle with which it merges to form a single support structure. The intertrochanteric fossa is much more developed mediolaterally than anteroposteriorly in relation with the conformation of the proximal articular surface. The
tibia is distinguished by its flattened shaft with a subelliptic and non-circular cross section, as is the case in most caseids which have not undergone
diagenetic deformation. The
manus is not fully known and the preserved elements indicate a
phalangeal formula 2-2-3-?-2. It was probably similar to that of the
foot, more complete, whose formula is 2-2-3-3-2. The
toes are short and terminated by small
unguals similar to blunt
claws. ==Geographic and stratigraphic range==