The skull roof is partially preserved in specimens, JME-ETT1, JME-ETT2, and JME-ETT18 (Figs. 2, 4, and 5). The premaxillae taper into an acute rostrum, which projects beyond the lower jaw for approximately one seventh of the total length of the skull, and are ornamented with small longitudinal striations.

The anterior extremities of the premaxillae are united along the dorsomedial line of the skull giving the impression of a single “rostrum”. The posterior part of each premaxilla is covered by the rostral, forming a kind of “tube” which extends, caudally into the ethmoidal region of the braincase, as in the other members of the family [8]. Each premaxilla bears a row of teeth that increases in size caudally.

The rostral bone is unpaired, deeply convex and twice as long as wide. It inserts, in front, between the posterior part of the premaxillae and caudally, overlies the anterior margin of the frontals. The ethmoidal commissure is found at the anterior third of the bone; from it, several canalicules are directed anteriorly. The ethmoidal commissure has no contact with the supraorbital canal backwards.

The frontals, as in other aspidorhynchids, are fused to the parietals and the dermopterotics during the ontogeny [8] (Fig. 4 and Fig. 5). These bones have an equal width throughout their lengths, extending from the rostral bone posteriorly to the extrascapulars. A single pair of extrascapulars is present; they are slightly longer than wide, asymmetrical, tapering medially and containing the extrascapular comissure.

The supraorbital canal finishes close to the middle point of the fronto-parieto-dermopterotic (probably in what should be the posterior margin of the frontal) and does not join the otic canal. Anteriorly, this canal goes through the nasal.

Two remnants of infraorbitals are preserved in specimens JME-ETT2 and JME-ETT18 (Fig. 4 and Fig. 5); so we assumed that there are about three small and rectangular infraorbitals. The first infraorbital lies in ventral contact with the posterior part of the lamellar expansion of the maxilla that is located at the anterior third of the bone and joins the nasal dorsally. The posteroinferior part of the first infraorbital overlies the entopterygoid. The other infraorbitals overlie the anterior border of the postorbital bones.

The dorsal circumorbital bones are the supraorbital and the dermosphenotic. The supraorbital, forms the anterodorsal margin of the orbit contacting the dermosphenotic. Anteriorly, the lateral margin of this bone forms part of the orbital margin and dorsally it is tightly sutured to the frontal. Posteriorly it articulates with the large postorbital bone. The dermosphenotic is pierced by the infraorbital canal.

The sclerotic ring consists of two sclerotic plates.

Depending on the specimen, and as described for other aspidorhynchid species [8], there are two or three large postorbital plates. They cover the anterior margin of the preopercle. The preopercle presents two well-defined parts: a vertical dorsal ramus and an expanded ventral part. The preopercular canal follows the posterior border of the bone. There is individual variation with respect to the number of canalicules branching from the main preopercular canal (Fig. 4 and Fig. 5).

The opercle is hypertrophied and forms the majority of the opercular series. It is almost one and a half times deeper than long, bearing a ventral part which is more developed than the dorsal. The anterior border is straight, perpendicular to the head axis, and partially covered by the preopercle. Its posterior border is strongly convex and overlays widely the supracleithrum. The dorsal linear border is inclined ventrally at the rear, and rides over the dorsal margin of the subopercle. The triangular subopercle is reduced in size. Seven incomplete branchiostegal rays are preserved in specimen JME-ETT2.

The upper jaw consists of the premaxilla, described above with the skull roof, maxilla and supramaxilla (Fig. 4 and Fig. 5).

The maxilla is elongated, divided into an expanded ventral part, that increases in depth posteriorly, and a somewhat rounded lamellar expansion projecting from the dorsal border at its anterior third. The oral border of the maxilla bears a row of teeth, all of similar size.

The supramaxilla is a small oval bone whose length is about one fifth of the maxillary length. It is located above the posterodorsal angle of the maxilla.

An unpaired predentary, a pair of dentaries, splenials, and angulars have been identified in the lower jaw.

The predentary is short, triangular, and toothed. It is linked to the rest of the mandible by a vertical suture. The predentary is much shorter than the premaxilla, and its length is equal to about one quarter of that of the dentary. The oral border of the predentary bears a row of median large teeth, that increase in size rearward, and a row of small, lateral teeth (Fig. 6); this disposition seems to be different from what is known in other species of Aspidorhynchus.

The dentary constitutes the major part of the mandible, being low at its symphysis with the predentary, and increasing in height posteriorly to form the coronoid process. The teeth of the dentary are large, increasing in size caudally. The posteriormost bone of the lower jaw is the angular. The lateral surface of this bone is ornamented with small tubercles. The mandibular canal is contained within the dentary and the angular.

Only the orbital part of the parasphenoid can be observed; it is a fragile, thin bone. The parasphenoid presents a thin shagreen of tiny teeth on its anterior part.

The palatal complex is not well preserved and only the ectopterygoid and the entopterygoid can be differentiated. The ectopterygoid is a thin and elongated bone, bearing an oral row of small teeth. The entopterygoid presents an internal surface with tiny villiform teeth.

The quadrate is a fan-shaped bone, lacking the posteroventral process. The bone is characterized by a thickening of its posterior border which leans against the symplectic. The ventral end of the symplectic does not reach the lower jaw, and only the quadrate is involved in the jaw articulation.

The hyomandibula is observed on specimen JME-ETT18, in where the dermal bones are displaced. The bone is stocky, being expanded and strengthened in the middle-part by a vertical rod-like ridge.

The hypohyal appears to be a single nodular element. The anterior ceratohyal is long and thin, approximately three times longer than deep. The borders of this bone are slightly concave. The bone is devoid of fenestra or groove for passage of the efferent hyoid artery.

The posttemporal bone is somewhat oval and located behind the skull; the posterior edge overlies the dorsal end of the supracleithrum. The supracleithrum laterally overlaps the dorsal end of the cleithrum. The cleithrum has an elongated lower arm which seems to be equal or longer than the upper arm. We note a well ossified bone, similar to that found in other aspidorhynchids that is here interpreted as a scapulocoracoid (Fig. 4 and Fig. 5).

The pectoral fins are well developed and comprise eight or nine rays. The first ray is not fused with the propterygium.

Both the dorsal and the anal fins are triangular and located posteriorly in the body, at the level of the 55th and 51st transversal row of scales, respectively. The dorsal fin has three unbranched and 10 branched rays. The anal fin is larger than the dorsal fin; and is formed by three unbranched and about 15 branched rays.

The caudal fin of A. sanzenbacheri has previously been discussed and figured, but not assigned to a specific taxon [3]. The caudal fin is forked; the ventral lobe is longer than the dorsal, a character of the genus Aspidorhynchus among aspidorhynchids [10].

Small epaxial and hypaxial fringing fulcra are placed between the basal fulcra and the first and last principal rays.

The dorsal lobe is composed of nine basal fulcra (including the procurrent rays plus the first transverse segmented rays), and eight principal rays. The ventral lobe comprises eight basal fulcra (four procurrent rays and four transverse segmented rays) and nine principal rays.

The total number of principal rays (= 17) is lower than in other species of the genus where the caudal skeleton has been described: 19 to 22 in A. acutirostris and 18 in A. antarcticus [10] and [19].

The scale rows consist of thick ganoid-type scales. The flank scales are arranged in three rows of similar size. The scales have well-developed peg and socket articulations. Dorsal to the flank scales there are three rows of small ornamented scales The dorsalmost scale rows are ornamented by longitudinal parallel ripple-like ridges, separated by narrow intervals. Ventral to the flank scales, there are five or six rows of small, rectangular, smooth scales.

As in the other species of the genus [11] and [23], the histology of the scales showed the complete absence of ganoin in A. sanzenbacheri.