posteriorly. The fourth infraorbital is located at the
posteroventral corner of the orbit, it extends into
the dorsal margin of the orbit and is expanded posteriorly
(the dorsal portion of this bone is not preserved
in MPEF-PV 1731). The posterior border of
the orbit is completed by one small and tubular
infraorbital bone and the dermosphenotic, which is
also small and tubular, and is almost dorsoventrally
oriented. Supraorbital bones are absent.
Jaws. The upper jaw is formed by very small premaxillae
and large maxillae (Figure 6, Figure 9,
Figure 10). The premaxillae are generally not preserved,
but MPEF-PV 1731 preserves a small and
very slender premaxilla articulating with the right
maxilla (Figure 10.1). This small premaxilla is
approximately five times longer than deep and
bears small conical teeth. The maxillae have a very
thin infraorbital portion and a widely expanded
postorbital portion. The infraorbital portion tapers
anteriorly and has posteriorly divergent slightly
convex ventral and slightly concave dorsal margins.
The postorbital portion of the maxilla is incompletely preserved in the studied specimens,
but it can be reconstructed. The dorsal portion is
best preserved in the disarticulated maxilla in
MPEF-PV 1496-5A (Figure 10.2). Behind the orbit,
the dorsal border of the maxilla bends abruptly
upwards, forming a rectangular postorbital plate,
which is almost 3 times higher than the maxillary
infraorbital portion at its maximal height. The dorsal
border is convex, curving in posteroventral direction,
and the posterior border is straight and
inclined posteriorly. The anterior and posterior borders
divert upwards, with the posterior border more
posteriorly inclined than the anterior border. The
ventral border of the postorbital portion is concave
and, thus, the ventral border of the maxilla taken as
a whole is sinuous, turning from convex to concave.
The lower jaw is poorly preserved in the studied
specimens. A coronoid process of the neopterygian
type is absent and the lateral surface is
mainly made up by the large dentary (Figure 7, Figure
9). The mandibular sensory canal runs veryclose to the ventral margin of the bone and exits
the dentary before the symphysis. The dentary and
maxilla bear two rows of conical teeth: a lateral row
of very minute conical teeth and a medial row of
larger and sharp conical teeth. Other bones or
details of the lower jaw are not discernable.
Palatoquadrate and parasphenoid. Of the palatoquadrate
only the very elongated and sharply
pointed dermopalatine bones are observable. The
anterior portion of the dermopalatines resembles
the anterior portion of the maxillae very closely and
bears a single row of conical teeth, which are similar
to the large medial maxillary teeth.
The parasphenoid is well preserved in several
specimens. Like in other chondrosteans, the orbital
portion of the parasphenoid is broad and presents