Calyptosuchus was estimated to have been four metres long, or possibly larger, with a maximum carapace width of almost seventy centimetres. The
osteoderms were not entirely fused. Each row of the osteoderms corresponded to one
vertebra, and comprised four dorsal osteoderms. Two small squarish osteoderms formed the outside of the row (about 10 by 10 cm), and two much broader osteoderms (approximately 20 by 10 cm) formed the inside of the row and covered most of the back. Each of the lateral osteoderms have a raised boss towards the centre at the posterior end of the osteoderm, and are almost bent around the side of the creature, with a dorsal flange along the back contacting the paramedian (dorsal) osteoderms and a lateral flange running a little way down the side. This would probably have given it quite a boxy look. The paramedian osteoderms also have a raised boss, called a dorsal eminence, in the posterior centre of the osteoderm but do not bend around in the same manner. There are ventral osteoderms known, but they have not been preserved in the natural alignment as the dorsal and lateral osteoderms have and so we are uncertain how they were arranged. They appear to have been flat and rectangular. The only
skull fragment that is certainly
Calyptosuchus is a
dentary bone - no other cranial bones have been assigned to it with certainty. Only a middle part of the dentary is present, with an
edentulous patch to the anterior and nine
dental alveoli posteriorly. No
teeth are preserved except a few fragments of root. A
maxilla assigned with partial certainty to
Calyptosuchus has five dental alveoli, and probably contacted the external
naris at a point. The vertebrae have keels, unusually among aetosaurs, and the
axis vertebra has a noticeable concavity in the sides above which the
zygapophyses protrude. Most of these are broken. The centrum of the axis is slightly wider than it is tall, but those of the other
cervical vertebrae are taller than they are wide.
Neural spines and arches are elongated in all the vertebrae along the trunk, and their centra have a concave anterior face and a flat posterior face. They are
spool-shaped, typically for aetosaur vertebrae. Their
neural canals are large and deep. The
sacral vertebrae are very robust, and not fused unlike those of desmatosuchians. There are only two sacral vertebrae. The
caudal vertebrae number at least seventeen, with very tall neural spines (taller than the centrum is) and low-attached caudal ribs. The
holotype had all seventeen of the first caudal vertebrae articulated. Several
pelvic girdles are known, with ventral
acetabula and thickened peduncles. The
iliac blades are short, but very broad. The
ischia are short and quite curved, with thickened areas and rugosities near the ends. Much of the
pubis is slender, but the distal end expands until it is quite broad. The
femur is gracile, or more so than
Desmatosuchus, and has a pronounced crescent-shaped ridge near the proximal end. In a similar fashion, the
tibia is also quite gracile and shorter than the femur. The distal end bears a deep groove for articulation with the ankle bones. ==Classification==