Premaxilla.—

Rostrum is laterally compressed forming a middorsal ridge anterodorsally, with its summit being upraised to form a bulbous boss (Fig. 2.3). Premaxillary symphysis exceeds half the total anteroposterior extension of the premaxilla and is enlarged relative to the condylobasal skull length. It is strongly downturned, forming an angle between 55° and 60° with the occlusal plane. Anteroventralmost end of the maxillopremaxillary suture is on the vertical level of (i.e. perpendicular to) the symphyseal summit. Mesorostral fossa is not indented anteriorly, but retracted and enlarged, reaching posterior to the level of the anterior margin of the orbit (Fig. 2.1, 2.2). Nasal process is thin and tapers at its posterior end. Alveoli for the first incisor tusks are preserved; those for I2 and I3 are absent (Fig. 3.1, 3.2). A dentiform process as in hydrodamalines is not developed. Masticating surface is lanceolate in shape, reaching its maximum transversal dimension at the level of the posterior end of the foramen incisivum. The latter opens anteriorly without distinct demarcation. Anterior palatal roof in front of the infraorbital foramina is distinctly narrower than the posterior palate.

Nasal.—

Internasal area is thin and often broken, but its full extent is observable in the specimens LS RLP PW 2005/5042-LS and PMN SSN12WD14. Nasals are small, with the internasal suture being shorter than half the length of the interfrontal suture (Fig. 2.1, 2.2). They extend anterolaterally almost up to the level of the anteriormost extension of the supraorbital process in adults, extend even farther in juveniles (FMD SRK Eck 124; Fig. 4.3), and then slope backwards to form a shorter median tip. Nasals meet in the midline and are separated by a nasal process from the frontals. A nasal incisure is present at the posterior end of the mesorostral fossa, but it is small, not extending posterior to the supraorbital processes.

Ethmoidal region.—

Mesethmoid forms a distinct perpendicular plate of 15 mm in maximum width, but becomes narrower and is constricted dorsally and ventrally. Becoming narrower also posteriorly, this vertical wall extends below the nasals and along the narial passages to fuse with the presphenoid. Crista galli is triangular in cross section, projecting upward from a broad base and becomming thinner towards the roof of the cranial cavity. The often not well-preserved cribiform plates of the exethmoids are deeply grooved and perforated for the passage of the olfactory nerves. Usually, a large ethmoturbinal, or concha maxima ethmoidalis (Kaiser, Reference Kaiser1974), is visible as a thick, vertically flattened plate on each side below the nasals and medial to the frontal. A thin lamina papyracea is sometimes preserved, but broken on the ventromedial side of the supraorbital process in all available specimens. Other ethmoturbinals are either not developed or not preserved.

Vomer.—

Exposed on the damaged anterior medial wall of the temporal fossa (Fig. 2.3) and on the ventral side of the holotype, forming the anterodorsal extension of the presphenoidal crest (Fig. 3.1, 3.2). It passes along most of the internal narial passage and contacts the maxilla and palatine before it runs out in a longitudinal groove on the dorsal side of the maxilla. Only the right lateral border of this maxillary groove is visible through the mesorostral fossa in the holotype (Fig. 2.1, 2.2), the vomer itself is not preserved there.

Lacrimal.—

Not completely preserved in any available specimen, but its extent can be judged from the imprints on the adjacent jugal and maxilla. This bone is arranged in an oblique dorsoventral axis and fills a space of ~20 mm in height between the jugal and frontal. Lacrimal contacts premaxilla anterodorsally, which is best preserved in the holotype and can be also traced in FIS M8002 and M2597. Nasolacrimal canal, which extends into the nasal cavity, is clearly discernible in BSPG 1956 I 540 (Fig. 2.3).

Frontal.—

Frontal roof is flat and delimited by the temporal crests, which form distinct keels that are as prominent on the frontal as on the parietal (Fig. 2.1, 2.2) and vary between types C, D, and E (Domning, Reference Domning1988, p. 405). A knoblike boss is not developed posteromedial to the temporal crests. Internasal process can be differently developed, but it is generally short and does not exceed half the length of the internasal suture (Figs. 2.1, 2.2, 4.3). Supraorbital process is dorsoventrally flattened with its dorsal surface gently inclined ventrolaterad (Fig. 2.3). Its lateral margin is smooth and oriented along an anteromedial-posterolateral axis, ending in a prominent posterolateral corner. Orbitotemporal crest is weak. Lamina orbitalis has a thin falciform anterior edge, contributing to the medial wall of the temporal fossa.

Parietal.—

Parietal roof is flat between lyriform temporal crests (Fig. 2.1, 2.2). In adults of advanced age (e.g., FIS M8002), these crests can rise high above the parietal roof that, in consequence, becomes slightly concave. Intertemporal constriction is distinct, reaching its maximum at about the center of the skull roof, and producing parietals, which bulge laterally. Frontoparietal suture is V-shaped and the frontal processes do not exceed half of the interfrontal length. Of all studied specimens, the parietal is longer than the frontal and the cranial roof is elongated relative to the width of the supraoccipital; the ratio l_FP/w_SO varies between 2.07 in BSPG 1956 I 540 and 2.6 in FIS M8002. In endocranial view (Fig. 4.1, 4.2), the parietooccipital suture is detectable as a slight transverse sulcus or at least as deep dorsolateral pits. Posterior margin of the parietal can be either convex as in ALMD-JBH A92 (Voss, Reference Voss2008, fig. 9B) or double-curved, forming a median tip as in NMDU-Geo 0001 (Voss, Reference Voss2008, fig. 4B). Tentorium osseum is well developed, and the internal occipital protuberance forms a prominent projection at the intersection of the bony falx and the tentorium. Bony falx cerebri is distinct and gradually flattens out before reaching the frontoparietal suture. Below the internal protuberance, a roughly triangular bone is present. Endocranial surface shows wide grooves and traces of vessels.

Supraoccipital.—

Intercalated between the parietals, following the angle of the lambdoid suture (Fig. 2.1, 2.2). Parietal and supraoccipital form an angle that varies between 120° (e.g., BSPG 1956 I 540 [Fig. 2.3], ALMD-JBH A92) and 140° (e.g, FIS M2597, MNHM PW 1991/66-LS). It is wider than high (Figs. 3.3, 4.4–4.7), with a width-to-height ratio that exceeds 1.5. Nuchal crest is pronounced and broadly convex, extending downwards to about half the height of the supraoccipital. Greatest width of the bone is at this level, and is greater than its width more ventrally at the supraoccipital-exoccipital sutures. External occipital protuberance is caudally prominent in all specimens, even in the juvenile FMD SRK Eck 124 (Fig. 4.3, 4.4). It either remains approximately at the level of the parietal roof (e.g., NHMUK PV M9415 [Fig. 4.5], NMDU-Geo 0001 [Fig. 4.7], BSPG 1956 I 540 [Fig. 3.3]) or rises slightly above it (e.g., IRSNB unnumbered [Fig. 4.6], HLMD-WT Az 174 and 177, MCZ 8830). External occipital crest exceeds half the height of the supraoccipital and sometimes even reaches its ventral margin (ALMD-JBH A92; see also Voss, Reference Voss2008, fig. 9). In some specimens (FIS M2715 and IRSNB unnumbered [Fig. 4.6]), a nutrient foramen penetrates the upper part of this crest. Two shorter ridges (i.e., the medial edges of the semispinalis capitis muscle insertions) accompany the external occipital crest. They are usually distinctly developed, but behind the level of the median crest, giving a crown-shaped appearance to the external occipital protuberance. This feature is observable to a less distinct degree in BSPG 1956 I 540 (Fig. 3.3) and FMD SRK Eck 124 (Fig. 4.4). Insertion areas for the semispinalis muscles are rugose and irregularly shaped depressions, which are defined ventrally by more or less prominent ridges that meet the nuchal crest laterally, giving the depressions a roughly triangular form. Internal lamina show paired bulges that can either be ovoid (Voss, Reference Voss2008, figs. 4B, 9B) or terete. A more or less pronounced furrow is present medially (FIS M2597; Fig. 4.1, 4.2), which accompanies a ridge extending up to the parietooccipital suture in NMDU-Geo 0001(Voss, Reference Voss2008, fig. 4B) instead of a triangular bone as described above. Other specimens (ALMD-JBH A92; Voss, Reference Voss2008, fig. 9B) have a nutrient foramen at the base of this furrow. Sutural surfaces for the exoccipitals have an irregular relief and intersect medially at an angle that varies between 140° (BSPG 1956 I 540 [Fig. 3.3], NMDU-Geo 0001 [Fig. 4.7], ALMD-JBH A92) and 150° (IRSNB unnumbered; Fig. 4.6).

Exoccipital.—

Meet in a suture of 10 mm dorsal to the foramen magnum (Fig. 3.3). Dorsolateral borders are rounded, more or less smooth and not flange-like. Paroccipital processes are long, reaching as far ventrally as the occipital condyles. Foramen magnum has a triangular outline with its dorsal peak surpassing the level of the occipital condyles. Supracondylar fossae are deep and extend across the entire widths of the condyles. A hypoglossal (condyloid) foramen completely surrounded by bone is present (Fig. 3.1, 3.2).

Basioccipital.—

Firmly fused with the basisphenoid in adults, so that the suture between the two elements is obliterated (Fig. 3.1, 3.2, 3.4). Sphenooccipital eminences for the longus capitis muscles form bilateral rugosities that are convex and separated by a slight furrow.

Presphenoid, basisphenoid, orbitosphenoid.—

Well preserved in the holotype (Fig. 3.1, 3.2), with the basi- and presphenoid firmly fused and in obliterated contact with the orbito- and alisphenoid, and pterygoid. Basi- and presphenoid have a flat ventral surface with a slight anterodorsad slope. Presphenoid forms a median crest that projects out cranially to join the vomer. Orbitosphenoid is not completely preserved, but partially exposed on the right lateral side of the skull (Fig. 2.3). It contributes to the anterior medial wall of the temporal fossa.

Alisphenoid

wing-shaped pterygoid processes originate ventrolateral to the basisphenoid; their posterolateral sides are each formed by the alisphenoid (Fig. 2.3). Outer surface is flat to slightly uneven. An alisphenoid canal is no longer discernible and the foramen ovale forms a distinct incisure. This is excellently visible laterally and also ventrally in the holotype (Figs. 2.3, 3.4), where the foramen ovale opens into the foramen lacerum.

Pterygoid.—

Pterygoid processes are posteromedially formed by the pterygoid (Fig. 3.1, 3.2). Pterygoid fossa extends above the level of the roof of the internal nares. Distal end builds up ventromedially a hook-shaped hamular process.

Palatine.—

Anterior parts are dorsoventrally flattened and anteroposteriorly elongated, extending beyond the posterior edge of the zygomatic-orbital bridge of the maxilla up to the anterior margin of DP5 in subadults (FIS M2597; Fig. 4.1, 4.2) or even to the level of P4 in adults (BSPG 1956 I 540; Fig. 3.1, 3.2). Posterior border has an incisure that does not surpass the level of M2 even though it is broken posteriorly in some specimens. Small and paired foramina can occupy a position more or less medial to M3 (BSPG 1956 I 540; Fig. 3.1, 3.2) or to M1 (FIS M2597; Fig. 4.1, 4.2). In BSPG 1956 I 540, a larger foramen is also present medial to the left M2. Posterior parts contribute to the anteromedial margins of the pterygoid processes as well as to the posterior wall between the internal nares and the temporal fossa. Sutures with the surrounding bones are still visible.

Maxilla.—

Infraorbital foramen is small, does not exceed 200 mm² and is oval in cross section, distinctly higher than wide (Fig. 3.1, 3.2). Infraorbital canal is not obstructed. Zygomatic-orbital bridge is elongated anteroposteriorly and has a concave, smooth surface. Its ventral side is nearly level with the palate or slightly above the alveolar margin, ranging between 10 mm and 15 mm in adults and subadults. Anterior margin of zygomatic-orbital bridge is very thin, 2 mm on average, while the posterior margin is thickened, between 10 mm and 20 mm. Tooth arcades are lyriform, broadly convex between the molars, tapering at the level of the premolars and widening again towards the foramen incisivum. Palate is thin at the level of the penultimate cheek tooth. Posterior opening of the maxillopremaxillary canal can be detected through the orbit.

Squamosal.—

Extends to the temporal crests and forms conspicuous indentations in the posterior corners of the parietal, causing the separation of the temporal and nuchal crests (Figs. 2, 4.3). Delimits the mastoid foramen anteriorly together with the exoccipital posteriorly and the supraoccipital dorsally. Sigmoid ridge is prominent and relatively straight, extending to the level of the ventral margin of the supraoccipital and onto the rostrad-projecting ventral tip of the posttympanic process. The latter is roughened and serves as attachment for the sternomastoid muscle. External auditory meatus is short mediolaterally and about as wide anteroposteriorly as high. Zygomatic process is strongly developed, triangular in lateral view with a rounded posterior and a tapering anterior end, often with a slightly dorsad-rising tip. Its outline is straight to concave posterodorsally and nearly straight anterodorsally and ventrally. Lateral surface is generally smooth, with a horizontal concavity in the anterior half. Medial side of the zygomatic process is flat to concave and defined dorsally by a sigmoidally curved dorsal edge. Zygomatic root shows a distinct notch posteriorly. Processus retroversus is moderately inflected (Fig. 3.1–3.3). Mandibular fossa is deep, tuberculum is broad and prominent, both being transversely directed. Postglenoid process forms a prominent knob, defining the mandibular fossa posteriorly.

Jugal.—

Preorbital process is thin and does not reach the premaxilla (Fig. 2.3). Ventral rim of the orbit is not overhanging. Ventral extremity lies approximately under the posterior edge of the orbit. A postorbital process is present dorsally, but distant from the supraorbital process. Unless broken as in BSPG 1956 I 540, the zygomatic process of the jugal extends posteriorly on the ventral side of the zygomatic process of the squamosal to the anterior margin of the tuberculum. Its length exceeds the diameter of the orbit.

Ear region.—

NHMUK PV M9415, MNHM PW 1991/66-LS, MB.Ma. 52010, and BSPG 1956 I 540 (Fig. 3.4) preserve the periotic completely or in parts, comprising the mastoid, petrosal, and tegmen tympani. Periotic is set in a closely fitting cavity of the squamosal, not fused with the alisphenoid or any other skull bone. It is often broken, lacking the petrosal, and then reveals the characteristic density of sirenian bones. Mastoid is fused anteriorly with the petrosal and tegmen tympani; its transition to the latter is smooth and continuous. Processus fonticulus forms an oval and roughened protuberance that fits into the mastoid foramen (Figs. 2.3, 3.3). Tegmen tympani is convex, kidney-shaped, and adjacent to the lateral side of the cranium, forming the roof of the tympanic chamber. Anteromedially, it tapers into a blunt end. Tegmen tympani and the mastoid are of similar size. Petrosal extends far into the foramen lacerum (Fig. 3.4), is nearly circular in cross section and bears a smooth-surfaced, knoblike promontorium on its ventral side. Promontorial ridge extends posterolaterad up to the level of the squamosoexoccipital suture. Oval window (fenestra ovalis or fenestra vestibuli) opens anterolaterally and is (contrary to what its name suggests) rounded. A large, oval perilymphatic foramen opens posteromedial to the promontorium. Medial to the posterior attachment surface of the tympanic, a distinct, mediolaterally elongated concavity for the origin of the musculus stapedius is present. Endocranially, the endolymphatic foramen forms a narrow and slit-like opening. Tympanic is asymmetrical, bulbous, and smooth-surfaced, with a blunt medioventrally directed tip. Its anterior branch is shorter than the posterior one and attached to the tegmen tympani. Posterior branch expands into a rounded and flat plate, facing the anteromedial side of the posttympanic process, and is preserved in the holotype (Fig. 3.4). Lumen of the tympanic arch is spanned by the malleus, which is present in situ in HLMD-WT 420 on the left side as the only preserved auditory ossicle. It is a massive and stout element, with a sharp vertical ridge on its lateral side.

Hyoid apparatus.—

Not known from any available specimen assignable to Kaupitherium gruelli n. gen. n. sp.

Mandible.—

Symphysis is distinctly higher than long. Principal mental foramen, accompanied dorsoposteriorly by several accessory mental foramina (Fig. 5.1). Horizontal mandibular ramus is slender, moderately concave ventrally and sharply downturned anteriorly and not tangent to the angle posteriorly. Below the condyle, the posterior outline is broadly convex, lacking a processus angularis superior. Although broken or replaced by plaster in most specimens, the coronoid process of the ascending ramus has a slight anterior slope. Condyles occupy a position below the level of the coronoid processes, which is erroneously reconstructed in the holotype (Fig. 5.1). In ventral view, the mandibular symphysis is broad and bulging laterally (Fig. 5.2). Mandibular foramen is undivided and exposes the dental capsule of m3 posteroventrally. Condyles are elliptical, with the medial and lateral edges having the same anteroposterior length (Fig. 5.3). Coronoid foramen is enlarged, with 7 mm in average diameter. Masticating surface is narrow, scarcely wider than the two rows of tooth alveoli it bears, without a furrow in the median plane.

Dentition.—

Complete cheek tooth series including DP5/dp5 is preserved in the upper and/or lower jaws of NHMUK PV M9415, MNHM PW 1949/157, and BSPG 1956 I 540 (Fig. 3.1, 3.2), the latter preserving also the antemolar dentition. Besides a pair of tusks, the dental formula included three permanent premolars, a persistent deciduous fifth premolar and three molars (I1/i0, C0/c0, P2/p2–4, DP5/dp5, M1–3/m1–3).

Incisor tusks (I1) are preserved in BSPG 1956 I 540 (Figs. 2, 3.1, 3.2), LS RLP PW 2005/5042-LS, and PMN SSN12EC55 (Fig. 5.5). They extend about half the length of the premaxillary symphysis, are slightly curved along their longitudinal axis, and protruded ~2.0 cm from the premaxillae. Crown is distinct from the root and composed of enamel on all sides, being suboval or subelliptical in cross section. Its ventral tip is often slightly worn.

P2–P4 are single-rooted (Figs. 3.1, 3.2, 4.1, 4.2). In BSPG 1956 I 540, P2 is heavily worn, which causes a pencil-shaped appearance of it, indicating that this tooth occluded with its lower counterpart. P3 and P4 are moderately worn, but still reveal a high central cusp that is surrounded mesially, lingually, and distally by accessory cuspules, whose number apparently increases distad within the tooth arcade. Crowns of the left P3–4 are nearly unworn and preserved in situ in PMN SSN12WD14. This specimen is on display in the position in which it was found in the rock, and therefore the teeth were not fully accessible, but only visible from their smooth and convex labial side. DP5 crown is heavily worn in all available specimens (Fig. 3.1, 3.2), but it can be clearly identified as a three-rooted molariform tooth, indicating that no replacement occured at this locus. DP5 is heart-shaped in outline, but smaller than M1. Proto- and metaloph and an anterior cingulum are usually observable.

Upper molars show the highest degree of tooth wear on M1 and the lowest degree on M3. Only in very old individuals like BSPG 1956 I 540 are the occlusal surfaces of M1–3 uniformly flattened and concave (Fig. 3.1, 3.2). Size of the molars is not reduced relative to the skull, but increases in the distal direction within the tooth arcade, M3 being the largest molar. Molars are morphologically similar with roughly heart-shaped crowns, whose lingual sides are pointed. Roots always consist of a mesiolabial, distolabial and lingual part. Enamel is smooth and ~2 mm thick. M1 is heavily worn in all specimens, but both M2s of FIS M2597 (Fig. 5.4) and NHMUK PV M9415 still reveal the cusp pattern. Protoloph forms a transverse row of paracone, protoconule, and protocone. Metaloph shows the metacone and hypocone at the same level, with the metaconule shifted towards the protoloph, obstructing the transverse valley. Transverse valley, separating both lophs, is deep and V-shaped where it opens at the lingual and labial sides. Sometimes, its lingual and/or labial terminations bear an accessory cuspule, as on the left M2 of FIS M2597 (Fig. 4.1, 4.2). Pre- and postcingula form strong ridges that are attached lingually to the proto- and metaloph. They decrease in height and open to the labial (or buccal) side. Postcingulum is usually bicuspate. Anterior and posterior basins are about equal in size and do not exceed the maximum length of the transverse valley. On M2, the protoloph is slightly larger than the metaloph, a condition that is developed to a marked degree on M3, which has a rather elongated form. FIS M2597 (Fig. 5.4) and NHMUK PV M9415 preserve nearly unworn M3s, which are not yet fully erupted, indicating the subadult age of both individuals. M3 morphology does not strikingly differ from that of M2. Distolabial to the paracone, one or two accessory cuspules can close the transverse valley. Precingulum is cuspate, attached to the paracone, and open lingually. Anterior basin is narrow and deep. Metaconule, obstructing the transverse valley, is not a small cusp between the usually larger metacone and hypocone, but it is about as large as the adjacent cusps. Its apex slopes lingually towards the hypocone. A distinct furrow separates the hypocone and metaconule. Hypocone is somewhat set back and not on the same level with the metacone, causing a convex arrangement of the metaloph. Posterior basin is larger than the anterior one and generally enclosed by two to three cingular cusps. Postcingulum is attached to the hypocone and opens labially.

Lower dentition is best known from mandibles of NHMUK PV M9415 and MB.Ma. 52010 (Fig. 5.3). Masticating surface of the mandibular symphysis is marked by four closely spaced and shallowly concave pairs of alveoli filled with spongy bone tissue. These depressions presumably represent the former positions of three incisors and one canine on each side, which are no longer developed in this taxon.

Presence of p2–4 is indicated by their single alveoli, which are broken out in some specimens and, therefore, not always clearly determinable. Although collections like the HLMD and the MNHM house numerous isolated premolars, such teeth associated with any of the investigated specimens are not known to date.

NHMUK PV M9415 preserves dp5–m3 on both sides, with dp5–m2 worn. Molars and the molariform dp5 are two-rooted with mesiodistally elongated crowns, which slightly increase in size distad within the tooth arcade. Crowns show an equally sized protolophid and hypolophid, separated by a deep transverse valley, and are higher lingually than labially. Metaconid and an accessory cuspule, connected mesiolingually to the hypoconid and obstructing the transverse valley, can be still detected on m2. A slight precingulum is visible at least on m1–m2. Hypoconulid lophule is bicuspate and encloses a distinct talonid basin. Lower m3 is not yet fully erupted in NHMUK PV M9415 and in a moderate state of wear in MB.Ma. 52010 (Fig. 5.3). Protolophid is slightly larger than the hypolophid. Proto- and metaconid and hypo- and entoconid are subequal in size. Anterior cingulum is indistinct anterolabially. Hypoconulid has one large cusp in NHMUK PV M9415; in MB.Ma. 52010 (Fig. 5.3), an additional and smaller cusp is present lingually. Talonid basin is variable in width. Otherwise, m3 resembles the preceding molars.

Vertebral column.—

Fourteen vertebrae from the thoracic, lumbar, and caudal segments were already described and illustrated for NMDU-Geo 0001 (Voss, Reference Voss2008), now assigned to Kaupitherium gruelli n. gen. n. sp. Therefore, the following description is kept generalized and complemented by data obtained from (nearly) complete skeletons like NHMUK PV M9415 and BSPG 1956 I 540.

NHMUK PV M9415 most likely preserves a complete series of 55 vertebrae: seven cervicals, 19 thoracics, three lumbars, and 26 caudals. Atlas broken and attached to the occipital region. Remaining column comprises two series of articulated vertebrae separated between T17 and T18. Vertebrae are compressed and partially broken up to the level of T8.

Atlas, completely preserved in BSPG 1956 I 540, has kidney-shaped and concave cranial and caudal articular facets. Transverse processes are aliform and slope posterodorsad, bearing the foramen transversarium at their base. Articular surface for the odontoid process of the axis extends caudad and forms an oval concavity. Upper arch is broadly convex with a slight median keel and a posterior indentation for the neural spine of the axis. Axis has a prominent odontoid process, which bears a flattened and rounded facet ventrally and a roughened rostral tip. Transverse processes are hook-shaped and the foramen transversarium is oval. Anterior articular facets are suboval, higher than wide, and flat to slightly convex. Neural spine is rounded and massive, with a median keel anteriorly that terminates into a pointed rostral tip for the atlas. Spine has a median cleft posteriorly. Postzygapophyses are flattended ventrally, facing ventrolaterad. In BSPG 1956 I 540, the axis and C3 are fused in their dorsal half, so that both vertebrae are visibly separated only in lateral view. This ankylosis is a peculiar characteristic of this specimen and a deviation from the normal condition in this species, which normally comprises seven clearly distinguishable cervical vertebrae. C3–7 have anteroposteriorly flattened centra, slender and dorsally keeled neural arches, and large vertebral foramina. Transverse processes are short and hook-shaped, often with small and irregular protuberances ventrally. Foramen transversarium is opened in C7 lacking a dorsolateral bony bar. Pre- and postzygapophyses lie at the same level. Articular facets are directed dorsomediad in the first and ventrolaterad in the latter.

Thoracics have knob-like transverse processes with a ventrolateral facet for the tuberculum of the corresponding rib. Neural arch surrounds a keyhole-shaped vertebral foramen in the majority of thoracics. On T1–3, it is distinctly larger, resembling those of the preceding cervicals. Neural spines are keeled anteriorly and concave posteriorly, sometimes with a thin median crest, and have roughened summits, forming a more or less triangular tuberosity. Those of T1–3 are narrower craniocaudally than in the following thoracics, strongly elongated dorsoventrally, and pointed. A distinct caudad inclination of the neural spines starts from T6. Caudad slope slightly decreases from T15 onwards, where the neural spines also reach their maximum craniocaudal extension. Prezygapophyses are dorsally flat and horizontally directed. Mammillary processes are short, but distinct. Postzygapophyses are backward-pointed and flat ventrally.

Except for the mammillary processes, the neural arches of the lumbars do not differ from the posterior thoracics. Neural canals are suboval, wider than high. Neural spines are keeled anteriorly and posteriorly. Third lumbar is interpreted as sacral vertebra, because its transverse processes are roughened ventrally and have a thickened, blunt distal end for the attachment of the pelvic ligaments.

Anterior caudals are slightly heart-shaped, the more posterior ones are either elliptical or hexagonal. Starting with Ca9, the transverse processes no longer originate from about the middle of the centrum, but from its upper third. Transverse processes of Ca1–4 are similar to the lumbars in transversal length and horizontal extension. From Ca5 onwards, they progressively sweep back, extending up to or passing the level of the caudal epiphysis, become nearly parallel to the midline between Ca9 and Ca13, straighten again at Ca14 and are perpendicular to the horizontal body axis from Ca16 to Ca23. Transverse processes are slight lateral extensions on Ca24–26. Neural spines are moderately high, with a mid-cranial keel and a slight cleft posteriorly in the more anterior caudals. Otherwise, the spine descends straight downward or forms a mid-caudal keel. Distinct inclination of the neural spine begins with Ca4 and increases continuously caudad. Ca20–26 lack a neural arch and a real vertebral canal. Ca1–2 still bear short and pointed postzygapophyses that are absent on the remaining ones.

Chevrons.—

Complete series not preserved in any specimen. Four isolated halves, which may have been articulated, but not fused with their counterparts, and one pair are known from HLMD-WT 420. They are roughly Y-shaped or U-shaped. Ventral edges are broader than the dorsal ones, and both are thickened and rugose.

Ribs.—

Do not significantly differ from NMDU-Geo 0001 (Voss, Reference Voss2008). Complete series is preserved in BSPG 1956 I 540 and NHMUK PV M9415, including 19 left ribs and most of their right complements. Overall shape either can be slender, with wide intercostal spaces (NHMUK PV M9415) or thick and nearly touching along their shafts (BSPG 1956 I 540, NMDU-Geo 0001). Cranial- and caudalmost elements differ from the otherwise uniform morphology. R1 (Fig. 6.1, 6.2) articulates with C7 and T1 and bears a protuberance below the capitulum for the origin of the musculus longus capitis. Distal end is extended mediolaterally, in some specimens (BSPG 1956 I 540) to a remarkable degree, and has a rugose concavity for cartilage attachment to the sternum. R2–R3 are medium-sized, truncated and concave distally, and probably were also connected to the sternum. From R4 onwards, the ribs are convex and smooth distally and most likely had no sternal connection. Capitulum and tuberculum are distant from each other on R1–6, reflecting the significant length of the collum (i.e., the neck of the rib). R1–6 also show a distinct angle that is kept in R4–6 through the total length so that their shafts are strongly bent inward. Capitulum and tuberculum come progressively closer on R7–18. Their angle is less distinctly developed and the shaft is mediolaterally compressed about midlength. Ribs are elliptical in cross section and reach their maximum craniocaudal width and mediolateral thickness in their distal third. R19 is the shortest of all ribs, with its capitulum and tuberculum virtually fused.

Sternum.—

Only the manubrium is known and preserved in LS RLP PW 2005/5042-LS (Fig. 6.4) and FMD SRK Eck 124. It is elongated anteroposteriorly and flattened to slightly concave dorsally. Ventral side is slightly convex and sometimes has a knoblike convexity anterocentrally, but a real median sternal keel is not developed. Lepsius (Reference Lepsius1882, pl. 6, fig. 63) figured a manubrium (HLMD-WT Az12) that was found in the same deposits as Kaupitherium gruelli n. gen. n. sp. and shows ventrally a distinct median keel. However, this find is isolated and looks distorted, or probably is asymmetrical, as sirenian sterna sometimes are, and therefore is not further considered here. In the juvenile FMD SRK Eck 124, the cranial half is somewhat narrower than the caudal one, ending in a bluntly rounded and straight anterior margin. Manubrium of LS RLP PW 2005/5042-LS keeps a more or less constant mediolateral width along its length and has a smoothly convex cranial end (Fig. 6.4). In either case, an anterior tongue-shaped process as outlined by Furusawa (Reference Furusawa2004) is not developed. Articulation facets for R1 are large and rugose laterocentrally in LS RLP PW 2005/5042-LS, where the bone reaches its greatest width. Posterolaterally, the articulation (demifacet) for R2 is preserved on the right side. Caudal margin is straight to concave and thickened for the cartilaginous attachment to the supposed corpus, indicating that the sternum of K. gruelli n. sp. is definitively composed of more than one element. Most likely, it resembles that of K. bronni, comprising also a compact corpus and an elongated xiphisternum.

Scapula.—

Slender and sickle-shaped with a smooth lateral surface divided by a short and straight scapular spine (Fig. 6.3). A proximal rugosity (tuber spinae) is not developed and the spine is slightly caudad-inflected, running diffusely out about half the length of the blade. Spine is either low and smoothly rounded (NHMUK PV M9415), or it is more elevated above the outer surface and somewhat sharpened (MNHM PW 1991/66-LS; Fig. 6.3). Acromion is missing in most specimens and broken in MNHM PW 1991/66-LS, but still attached to the spine, extending up to the level of the neck (i.e., the collum scapulae), and ending in a smoothly convex tip. Supraspinous fossa is smoothly concave and wider than the infraspinous fossa. Coracoid process is blunt and moderately sized, inflected mediad, and not separated from the anterior apex of the articular glenoid. Glenoid cavity is large, moderately concave, and oval. Costal surface is flat to smoothly concave.

Humerus.—

Compact element with distinctly developed epiphyses and preserved in NHMUK PV M9415 (Fig. 7.1–7.4), HLMD-WT 420, and MNHM PW 1991/66-LS. Greater tubercle is elevated above the caput and continues distad into the deltoid crest (Fig. 7.1, 7.2). Deltoid crest overhangs laterally (Fig. 7.3), forming a marked deltoid tuberosity, and tapers into a narrow deltopectoral crest at about half the length of the shaft. Caput is rounded and flanked distomedially by the lesser tubercle. Articulation facet for the radius and ulna is bisymmetrical and nearly perpendicular relative to the proximodistal axis. Coronoid and olecranon fossae are distinct and deep (Fig. 7.3, 7.4).

Radius and ulna.—

Right elements of HLMD-WT 420 are incompletely preserved (Fig. 7.5, 7.6). Both are fused proximally and distally. Radial and ulnar distal epiphyses are separated from the diaphyses by visible sutures. Epiphyses are trapezoidal and bear the articular facets for the adjacent carpals. Shallow grooves for extensor digiti quinti and extensor carpi radialis tendons are present on the laterodistal end of the ulna and anterolaterally on the distal end of the radius, respectively, as well as on the adjacent epiphyses. Diaphysis of the ulna does not extend as far distally as that of the radius, but the ulnar epiphysis is longer than that of the radius, so that both bones terminate at the same level. Anteroposterior thickness of the ulnar diaphysis exceeds that of the radius, but the transversal length of both is similar below the level of the proximal ends.

Manus.—

Rarely preserved and only known from HLMD-WT 420. Neumann (Reference Neumann1936) described the incomplete autopodium of two lower Oligocene specimens from Flörsheim (western Germany). While his “skeleton II” (Neumann, Reference Neumann1936, p. 258) was no longer available for personal investigations in the FIS due to its presumed loss in WWII, his “skeleton I” was in part accessible in Mainz (MNHM PW 1910/1). Identification of the latter as belonging to K. gruelli n. sp. is not certain due to distortion and damage by fire, however, it gives a benchmark for the following description. Kaiser’s (Reference Kaiser1974) terminology is applied here in order to avoid confusion in the use of different terms for the same parts. HLMD-WT 420 preserves 17 elements from the right side, comprising four carpals, five metacarpals, and eight phalanges (Fig. 8). Carpals are arranged in a proximal and a distal row, each consisting of originally three single elements, of which the fused trapezium-trapezoid, scaphoid, and pisiform are missing as well as four phalanges.

Triquetrum (Fig. 8.6) is discoid and articulates with the ulna proximally, hamate and metacarpal V distally, pisiform posteriorly (on the ulnar side) and lunate anteriorly (on the radial side). Ulnar facet is triangular and saddle-shaped and smaller than the one for the hamate, which is nearly flat and subtriangular. The latter is continuous with the facet for metacarpal V, which is narrow and suboval and overlaps on the lateral side. Strip-shaped area of 7–9 mm is present laterally. Ulnar side bears an irregularly shaped concavity for the pisiform. Anterodistally, a narrow, mediolaterad-extending ridge articulates with the lunate.

Lunate (Fig. 8.8) resembles a cuboid. Proximal facet for the radius is nearly flat and delimited by roughly parallel-extending edges. Attachment for the capitate is kidney-shaped, with a smooth s-shaped flexure, slightly convex laterally and concave medially. Ulnar side is trapezoid and bears distally a narrow and elongated facet for the triquetrum, which is continuous with that for the capitate. A less-distinct facet for the scaphoid is present proximally on the radial side and is continuous with that for the radius. Medial or volar side is smoothly convex, whereas, the lateral side has a smooth, but uneven surface.

Hamate (Fig. 8.5) is wedge-shaped and essentially articulates with the triquetrum proximally, capitate anteriorly, and metacarpals III, IV, and V distally. Proximal facet is the largest of all, roughly triangular and slightly concave; a very small articulation for the lunate is present anteromedially. On the distal side, three continuous facets meet each other at angles between 130° and 135°, all being slightly concave. Articulation for metacarpal IV is the largest and roughly rectangular. Facet for metacarpal III is mediolaterally elongated and that for metacarpal V is trapezoid and the smallest of all facets. Radial side bears proximally a mediolaterally elongated and irregularly shaped facet for the capitate; a second, distal, facet forms a slight ridge for metacarpal III. Medial and lateral sides are convex, with the first being knob-like and uneven and the latter smooth-surfaced.

Capitate (Fig. 8.7) is overall trapezoid and articulates with the lunate proximally, metacarpal III distally, trapezium-trapezoid and metacarpal II anteriorly, and hamate posteriorly. Proximal facet is nearly flat. Distal articulation is slightly concave, having a weak ridge for the hamate posteriorly. Radial surface is tripartite, with a 4mm wide band for the trapezium-trapezoid extending along the proximal margin, and distally, a larger lateral and smaller medial semicircular facet for metacarpal II, which are continuous with that for metacarpal III. Ulnar side bears a proximal and distal facet for the hamate. Lateral side is flat to slightly convex, the medial side is knob-like and uneven.

Metacarpals (Fig. 8.4) are elongated with simple facets for the phalanges distally, except for metacarpal I, which terminates in a blunt conical tip and appears to have not been attached to a phalanx. It measures 39 mm in total length, is curved in the ulnar direction forming a distinct ridge anteriorly, and is triangular in cross section. Diaphysis and proximal epiphysis are fused, with the suture still visible on the volar side. Metacarpal II is 56 mm long, smooth-surfaced, but moderately rugose on its proximal end. Lateral side is less concave than the medial side. Radial side shows a longitudinal ridge that rises distally into a blunt tuberosity. Ulnar side forms a gentle, distad-extending keel at about half the length of the diaphysis. Proximal end is triangular in cross section and articulates with metacarpals I and III, the trapezium-trapezoid, and capitate. Metacarpal III measures 65 mm in length and differs only slightly from metacarpal II in that it is rectangular to trapezoid in cross section proximally, and elliptical centrally and distally. Two proximal and continuous articulation surfaces meet at an angle of ~120°; they are nearly rectangular and flat. Distal epiphysis is connected with the diaphysis by a clearly visible suture. Metacarpal IV is 58 mm in preserved length lacking the distal epiphysis, which is reconstructed in Figure 8.4 and was most likely shorter than it appears, considering the epiphyseal length in metacarpals II and III. It resembles metacarpal III as supposedly does the size, considering the distal epiphysis to be included. Metacarpal V also lacks its distal epiphysis and is 55 mm long. It is mediolaterally flattened, suboval in cross section, and bears posteroproximally an extension for the pisiform.

Eight of originally 12 phalanges are preserved (Fig. 8.1–8.3). Digits II–V each preserves the distal phalanx forming a small, plate-like bone. Digit II has a 19mm long middle phalanx with a nearly flat lateral and a concave medial side. Facets for the adjacent proximal and distal phalanges are small and subcircular. Distal phalanx is the smallest of all, measuring 9 mm in length. Proximal articulation surface is oval. It is somewhat shorter anteriorly than posteriorly, producing an oblique distal margin. Phalanges of digit III only differ in size from those of digit II, with the middle phalanx 20 mm long and the distal one about as long as wide, measuring 11 mm in maximum dimensions. Proximal phalanx of digit IV is 29 mm long, but otherwise resembles the latter. Distal phalanx is wider than long (15 mm×11 mm) and terminates in a more or less straight margin. Digit V preserves a 29mm long distal part of the proximal phalanx, indicating that it is the largest of all the phalanges. This is in accord with Neumann (Reference Neumann1936, p. 273), who gave a maximum length of 41 mm for it. Bone is semicircular in cross section and mediolaterally flattened. Laterally, the distal epiphyseal suture is visible. Facet for the distal phalanx is flat and semicircular. Distal phalanx is slightly longer than wide (17 mm×15 mm) and longer anteriorly than posteriorly, causing an inclination of the distal margin. Both phalanges of digit V have flat volar and slightly convex lateral sides.

Innominate.—

Known from NHMUK PV M9415 (Fig. 9.1), BSPG 1956 I 540, MB.Ma. 52010 (Fig. 9.2), PMN SSN12EC55, and HLMD-WT 420 (Fig. 9.3, 9.4). The latter are also illustrated in Schmidtgen (Reference Schmidtgen1912, pl. 29, figs. 4, 5). This sample reflects a uniform morphology lacking distinct intraspecific variation. Ilium, ischium, and pubis are firmly fused in adults, but loosely connected with each other in juveniles, as can be inferred from an isolated ilium in FMD SRK Eck 124. Ilium is elongated, slender, and rounded in cross section. Proximal end is slightly swollen with a 20–30mm long depression dorsomedially that serves as attachment of the ligaments for the sacral vertebra. Pubis is short and triangular, with a moderately rugose ventral tip. Acetabulum is round and distinctly concave. Ischium is transversally flattened, plate-like, and the widest element due to its oblique dorsoventral expansion. Distal end is somewhat thickened with a rugose area. Pubis is inflected mediad while the ischium inclines laterad. Foramen obturatum is generally not developed, but present ventroposterior to the acetabulum in HLMD-WT 420 (Fig. 9.3, 9.4), indicating individual variation and an observation reminiscent of Metxytherium krahuletzi (Domning and Pervesler, Reference Domning and Pervesler2001, pl. 19, fig.1). Anteroventral margin of both foramina is broken out, but its maximum dimensions amount to about 5 mm×7 mm.

Femur.—

A number of isolated femora are known from different collections (e.g., HLMD, MNHM, IRSNB), but none of these is associated with skeletal remains enabling a clear taxonomic assignment to K. gruelli n. sp. Femora are slender with rounded proximal epiphyses and tapered distal ends lacking any articulation for the zeugopodium. This is in accordance with the pelvic morphology and the acetabulum size allowing the indirect determination of a vestigial femur.

Premaxilla.—

Nasal processes are thin and taper at their posterior ends, with lengthy overlap of the frontals and nasals, but, in contrast to K. gruelli n. sp., do not contact the lacrimal (Figs. 10.1, 10.2, 11.2). Symphysis is strongly downturned forming an angle with the horizontal plane of ~57°.

Nasal.—

Krauss (Reference Krauss1858, pl. 20) depicted the nasals of the holotype in a more complete condition than they are preserved at present. While both elements are now separated in the midline (Fig. 11.3, 11.4), they are shown to have met in the midline posteriorly in Krauss (Reference Krauss1858). This is in accord with the condition visible in MB.Ma. 52009 (Fig. 10.1, 10.2), indicating an internasal suture that extends less than half the length of the interfrontal suture.

Ethmoidal region.—

Ethmoidal region is comparable to the conditions in K. gruelli n. sp. and quite well preserved in the holotype specimen (SMNS 1539; Fig. 11.4). Mesethmoid forms a prominent perpendicular plate that measures 10 mm to 15 mm in width, becoming narrower dorsally, ventrally, and posteriorly. Cribiform plates of the exethmoids are clearly visible on the holotype and deeply recessed from the cranial cavity, forming oval depressions for the olfactory bulbs. Ethmoturbinal is large and flanks the frontal medially below the nasal. A thin lamina papyracea is preserved on the lateral side of the ethmoturbinal and also on the ventromedial side of the supraorbital process of the frontal.

Vomer.—

Clearly visible on the ventral side of the holotype (Fig. 11.4), though incompletely preserved. It forms a V-shaped bone as in other sirenians and is firmly fused with the ethmoid dorsally. Contact with the presphenoid can be judged from specimen MB.Ma. 52009, where the vomer is visible through the orbit (Fig. 11.2) due to damage of the lateral frontal wall. Dorsal longitudinal groove of the maxilla that housed the anterior extension of the vomer is competely preserved in MB.Ma. 52009 and clearly visible through the mesorostral fossa (Fig. 10.1, 10.2).

Lacrimal.—

Both elements preserved in MB.Ma. 52009, with a maximum anteroposterior length of 33 mm and a lacrimal foramen of 3.7 mm in maximum diameter (Fig. 11.2). It is not in contact with the premaxilla because the maxilla is interposed, reaching up to the anterior tip of the supraorbital process of the frontal. This condition is best visible on the left side in specimen MB.Ma. 52009 (Fig. 10.1, 10.2), where the lacrimal is completely preserved including a distinct nasolacrimal canal.

Frontal.—

Internasal process is small and slightly projects between the nasals posteriorly (Fig. 10.1, 10.2). Temporal crests vary as in K. gruelli n. sp. between types C, D, and E (Domning, Reference Domning1988, p. 405). Intertemporal constriction is also variable, but strong (i.e., the cranial roof is distinctly narrower than the cranial cavity) and reaches its maximum at about the center of the skull roof (i.e., on the parietal portion).

Parietal.—

Parietal roof usually flat between the prominent and lyriform temporal crests (Fig. 11.3, 11.6); in specimens of advanced age, such as MB.Ma. 52009 (Fig. 10.1, 10.2) and SMNS 47736, the parietal roof tends to be concave between high temporal crests. In contrast to K. gruelli n. sp., the frontal processes of the parietal are long and exceed half the length of the interfrontal suture. Overall proportions of the cranial roof indicate a slight brachycephaly according to the ratio l_FP/w_SO, which is 1.93 in the holotype and MB.Ma. 52009. Internally (Fig. 11.4, 11.7), the tentorium is prominent, with a triangular bone element always present in the median plane, but a median ridge crossing the transverse sulcus as in K. gruelli n. sp. has not been observed in the investigated sample.

Occipital region.—

Supraoccipital bears a convex nuchal crest that terminates in thickened dorsolateral ends. Nuchal crest has a distinct notch medially, but without the supraoccipital projecting onto the cranial roof (Figs. 10.1, 10.2, 11.1, 11.3, 11.5, 11.6, 11.8). External occipital protuberance is weakly developed, never rises above the level of the parietal roof, and is not differentiated from the external occipital crest. The latter forms a median ridge that can be either distinct (SMNS 1539; Fig. 11.5) or low (e.g., MCZ 8829; Fig. 11.8), and diffusely flattens out about halfway down the external lamina. Both the external protuberance and crest are distinctly indented (e.g., MCZ 8829 [Fig. 11.6, 11.8], IRSNB 8289), though to a lesser extent in the type specimen (SMNS 1539; Fig. 11.3, 11.5) due to the rostrad notching of the nuchal crest and usually do not exceed the level of the medial edges of the muscle insertions. Comparable to the observations in some representatives of K. gruelli n. sp., a nutrient foramen is visible at about mid-length of the external occipital crest in MCZ 8829 (Fig. 11.8) and QB 4/12.721 (Voss, Reference Voss2012, fig. 3). Ventral margin of the supraoccipital is slightly pointed medially, forming an angle of ~140° between the sutural surfaces for the exoccipitals (SMNS 1539 [Fig. 11.5], MB.Ma. 52009 [Fig. 11.1], and MCZ 8829 [Fig. 11.8]). Endocranially (Fig. 11.4, 11.7), the parietooccipital suture is indicated as a deep transverse sulcus. Relief below the sulcus is relatively flat, with a narrow furrow in the median plane and terete bulges dorsolateral to it. Exoccipital and basioccipital like those of K. gruelli n. sp.

Presphenoid, basisphenoid, orbitosphenoid, alisphenoid, pterygoid, palatine.—

Do not appear to differ from K. gruelli n. sp. Pre- and orbitosphenoid are not completely preserved in any specimen. Otherwise, the sphenoidal, pterygoid, and palatine regions are well displayed in MB.Ma. 52009 (Figs. 11.2, 10.3, 10.4). Similar to K. gruelli n. sp., a small foramen is present medial to the right M3 of MB.Ma. 52009 (Fig. 10.3, 10.4).

Maxilla.—

Zygomatic-orbital bridge of the maxilla (Fig. 10.3, 10.4) is anteroposteriorly long and nearly on the level of the palate. Its posterior end is thickened in comparison to the very thin anterior margin. Infraorbital foramen is small as in K gruelli n. sp., but contrasts in having a round shape.

Squamosal.—

Similar to K. gruelli n. sp., but strikingly particular, the sigmoid ridge rises prominently and nearly vertically up to the ventral margin of the supraoccipital as it can be seen in MB.Ma. 52009 (Fig. 11.2) and FMD SRK Eck-Rat 43. Zygomatic process shows a straight to concave posterodorsal end, which is best visible in dorsal and caudal views of MB.Ma. 52009 (Fig. 10).

Jugal.—

Does not differ from that in K. gruelli n. sp.

Ear region.—

Is best preserved in MCZ 8829 (Fig. 12) and MB.Ma. 52011, both comprising the whole periotic, whereby MB.Ma. 52011 additionally shows the tympanic and auditory ossicles. Periotic does not differ morphologically from K. gruelli n. sp. In endocranial view (Fig. 12.2), the pars canalicularis of the petrosal bears an inflated and rounded pyramid, which corresponds to the cerebral part (Robineau, Reference Robineau1969) that continues with the endocranial surface of the tegmen tympani. The remaining cerebellar part is plane and rather square. Two foramina open near the anteromedial edge of the cerebellar surface, providing passage for the facial (VII) and auditory (VIII) nerves, and lie in an oval and concave area corresponding to the internal auditory meatus. The most anteromedially facial foramen is delimited by a distinct suprafacial commissure. Towards the mastoid region, in the posterolateral wall of the pyramid, a narrow and slit-like endolymphatic foramen is situated.

An isolated right tympanic with the anterior and posterior branches broken is preserved in MB.Ma. 52011, whereas MB.Ma. 52009 preserves both tympanics in situ, showing the anterior branch to be distinctly shorter than the posterior one (Fig. 10.3, 10.4). Its posterior attachment is still connected to the anteromedial side of the posttympanic process. Whole extent of the attachment surface is visible, revealing a large, oval plate that faces the mastoid posterodorsally and the top of the external auditory meatus of the squamosal anterodorsally. Imprints of the smaller and rounded anterior attachment are visible on the anteroventral side of the tegmen tympani. A ridge and groove along the proximolateral edge of the anterior branch most likely served as attachment area for the tympanic membrane.

Malleus is also preserved in situ in MB.Ma. 52009, filling the lumen of the right tympanic arch (Fig. 11.2). Laterally, a sharp vertical ridge is visible that rises from the otherwise smooth surface. Right malleus from MB.Ma. 52011 is isolated and a stout element. Its posterior end bears a convex orbicular apophysis. Processus muscularis is enlarged and massive, forming a rounded protuberance. Tip of the process appears to be separated from the anterior branch of the tympanic only by a few millimeters in MB.Ma. 52009, indicating a short musculus tensor tympani. Sharp vertical ridge on the lateral side of the malleus originates from the dorsal end of the manubrium and extends ventrad. Its anterior and posterior surfaces are flat, and the dorsal and ventral margins converge, producing a heart-shaped outline of this ridge. External edge of the manubrium is slightly convex. Articulation surface with the incus comprises two facets, a larger anterior and a smaller posterior facet, both being roughened and raised above the body of the malleus. In MB.Ma. 52011, the right incus and stapes are preserved in situ. Incus is only visible in ventromedial view, protecting the crus breve from sight, but revealing the concave articular facets for the malleus. Surface of the incudal body bears anteroventrally two slight concavities. Crus longus is short and stout. Its medial end is formed by the processus lenticularis that sharply curves inward just a few millimeters behind the corpus incudis and articulates with the head of the stapes. Visible length of the stapes measures about 8 mm. Stapedial foramen is well developed just lateral to the basal end, which is attached to the oval window.

Hyoid apparatus.—

Not known from any available specimen assignable to K. bronni.

Mandible.—

Mandibular morphology (Fig. 13) resembles that in K. gruelli n. sp.

Dentition.—

Although heavily worn, FIS M8385 preserves the complete upper cheek tooth series, which appears not to differ morphologically from K. gruelli n. sp. Dental formula in the upper jaw was most likely I1, C0, P3–4, DP5, M1–3. I1 is best preserved in MCZ 8829 (Fig. 14.2), is ~10 cm long, and extends approximately half the length of the premaxillary symphysis (Fig. 11.2). It resembles that in K. gruelli n. sp. and, judging from the crown length, it protruded most likely ~20 mm from the premaxillae.

Subadult MWNH-TER-1 (Fig. 14.3, 14.4) still has a vestigial alveolus, supposedly that of DP3, mesiolingual to both P3. That reflects the opposite of Luckett’s (Reference Luckett1993) observation that successional teeth develop only lingual to their deciduous predecessors in a wide range of therians. Sirenia that are not included in Luckett’s (Reference Luckett1993) ontogenetic assessment of dental development might represent an exception, at least in the developmental pattern of the maxillary dentition. A further, vestigial alveolus is clearly visible ~10 mm anterior to the left P3; an indistinctly preserved one is on the right side. Both are interpreted here to represent the locus for DP2, which unlike K. gruelli n. sp., is no longer replaced in this species.

MB.Ma. 52009 (Fig. 10.3, 10.4) shows the alveoli for DP5 in the state of resorption, which is best visible on the right side and in accordance to its advanced age. While the distolabial and lingual alveoli are clearly identifiable, the mesiolabial alveolus is barely present. Roots of M3 are also particular in MB.Ma. 52009, which are strongly developed with the distolabial root jutting out far from the maxilla. Upper molars (Fig. 14.1) are usually worn to such an extent that no detailed description of their cusp pattern is possible, but their preserved morphology resembles that in K. gruelli n. sp.

Most complete mandibles, providing information on the tooth morphology and the lower dental formula (i0, c0, p3–4, dp5, m1–3), belong to MNHM PW 1984/37-1, SMNS 47736 (Fig. 13), MAz GP 1000, and FMD SRK Eck-Rat 43. In regard to preservation, the teeth are heavily worn and their presence is mainly indicated by their alveoli. As in K. gruelli n. sp., the mandibular symphysis bears a spongy and roughened masticating surface with irregularly formed and shallowly concave alveoli that seem to represent the former loci of three pairs of vestigial incisors and one pair of vestigial canines. Alveoli of p3 and p4 are clearly determinable in most cases. Numerous isolated and single-rooted premolars from the lower Oligocene of Germany are housed in the collections of HLMD and MNHM, but no premolar is known to have been associated with the individuals and partial skeletons assigned to K. bronni. SMNS 47736 (Fig. 13.3, 13.4) shows a further alveolus on the right side at the beginning of the masticating that is small and has no left counterpart and is interpreted here as being vestigial. Specimen MAz GP 1000 preserves dp5 to m3 from both tooth arcades, which do not appear to differ morphologically from K. gruelli n. sp. Usually, the bipartite alveoli of dp5 are discernible (MNHM PW 1984/37-1, MB.Ma. 52009), but some specimens show the alveoli of this unreplaced premolar in the state of resorption (FMD SRK Eck-Rat 43, SMNS 47736). In SMNS 47736 (Fig. 13.3, 13.4), the special case of irregular resorption can be observed, because the two dp5 roots are still preserved on the right side, whereas the corresponding alveoli on the left side are already coalesced. Only the remains of the lingual bony interseptum and, deep inside the alveolus, also the interseptum from the labial side indicate that this alveolus was once divided. Indistinct remains of a precingulum are discernible at least on m2 and m3 of SMNS 47736, as well as a postcingulum enclosing a moderately wide talonid basin on m2 and forming a distinct hypoconulid lophule on m3.

Vertebral column.—

A partial vertebral column is already known from QB-4/12.721 (Voss, Reference Voss2012), which is now assigned to K. bronni, and therefore the reader is referred to the description of it. No significant morphological differences are discernible between K. gruelli n. sp. and K. bronni, and the following data complement the knowledge of K. bronni.

A putative nearly complete column is known from SMNS 47736, comprising seven individual cervicals, 20 thoracics, three lumbars, and 17 caudals. However, some postcranial elements were replaced from a second specimen and it is not certain which ones exactly (R. Ziegler, personal communication, 2013). Thus, it cannot be ascertained if the number of vertebrae, especially from the thoracic and lumbar segments, was correctly determined.

Complete cervical columns of MB.Ma. 52009 and MAz GP 1000 show the special feature of a fused axis and C3, as was already described for K. gruelli n. sp., supporting the observation that this fusion occurs occasionally throughout the Sirenia (e.g., Petit, Reference Petit1928; Domning, Reference Domning1978, p. 86).

In contrast to 20 thoracic vertebrae assessed for SMNS 47736, specimen MAZ GP 1000 reveals only 16 thoracics. Even if 19 thoracics are taken to be generally present, as is seen in K. gruelli n. sp., this indicates intraspecific morphological variation comparable to the observations in extant Trichechus species (Domning and Hayek, Reference Domning and Hayek1986).

Number of lumbar vertebrae varies, too. In specimen MAZ GP 1000, four lumbars with the caudalmost one serving as sacral vertebra are identified, which seems to differ from K. gruelli n. sp. and SMNS 47736, but is in accordance with the observations in QB-4/12.721 (Voss, Reference Voss2012).

Caudals 1–3 still have long and nearly horizontally directed transverse processes resembling those of the lumbar region. The lack of markedly roughened distal ends on their transverse processes and the presence of articulation facets for chevrons on the ventral side of the centrum distinguish those caudals from the preceding lumbars and sacral. From Ca4 onwards, the caudad inclination of the transverse processes begins. Considering the total number of 26 caudal vertebrae in K. gruelli n. sp., the caudal series in K. bronni is not completely known.

Chevrons.—

A number of isolated chevron bones are known from MB.Ma. 52009; they do not differ from K. gruelli n. sp. (HLMD-WT 420).

Ribs.—

Do not differ morphologically from those described for K. gruelli n. sp. and reference is made to Voss (Reference Voss2012), who already described and illustrated the ribs of QB-4/12.721. Ribs either are compact and voluminous with a great anteroposterior width (MB.Ma. 52009), or they are overall slender (QB-4/12.721). First rib (Fig. 15) has a ventral protuberance and a remarkable width of its distal extremity in all investigated specimens.

Sternum.—

In contrast to K. gruelli n. sp., the sternum is completely known by three elements, though not from a single individual. Specimen MCZ 8829 preserves the manubrium, which is similar to that of MB.Ma. 52009, where the corpus is also present (Fig. 16.1). MNHM PW 1984/37-1 includes the corpus and the xiphisternum (Fig. 16.2). Overall morphology resembles that in K. gruelli n. sp. Manubrium of MCZ 8829 is flat to slightly concave dorsally and convex ventrally with a ventromedial knob on its anterior half, whereas MB.Ma. 52009 is double-curved in lateral views with the dorsal surface being concave anteriorly and flat to slightly convex posteriorly. Otherwise, the surfaces are smooth. Manubrium reaches its greatest mediolateral width at about half its length, whence the large and deep rugosities for articulation with the first ribs extend laterodistad. A smaller and less concave pair of facets lies at the junction of the manubrium and the corpus, as indicated by chamfered posterolateral edges of the former. Corpus is compact and roughly octagonal, and is a small element intermediate between the much larger manubrium and xiphisternum. Its dorsal and ventral surfaces are smooth and flat. All edges are rounded and chamfered for the appropriate rib articulation that it forms together with the adjacent sternal elements. Xiphisternum has a paired articulation only at its anterolateral corner, indicating that, in total, three pairs of the anteriormost ribs articulated with the whole sternum, which is consistent with the rugose distal texture of R1–3. Anterior part of the xiphisternum resembles the corpus in shape and size, but it tapers distad to form a long posterior process. Although its distal end is broken in MNHM PW 1984/37-1, this process is clearly divided, and asymmetrical.

Scapula.—

Does not significantly differ from that in K. gruelli n. sp. A tuber spinae is minor (MB.Ma. 52009; Fig. 16.3, 16.4) or not (MCZ 8829) developed. Distal end of the acromion is broken in all specimens, but its position at the collum scapulae is clearly determinable.

Humerus.—

Left humerus is preserved in the partial skeleton MAz GP 1000 (Fig. 16.5). As in K. gruelli n. sp., it is a compact bone. However, the suture between the proximal epiphysis and humeral shaft is not obliterated, indicating that this animal was not very old. Deltoid crest is separated from the greater tubercle by this suture and overhangs only slightly laterally.

Radius and ulna.—

Right articulated radius-ulna complex is known from MNHM PW 1945/233 (Fig. 16.6) and similar to K. gruelli n. sp. Both lack their distal epiphyses, but are otherwise completely preserved. Ulnar shaft is ~10 mm shorter than that of the radius. Articulation surface for the humerus has a semilunar shape on the ulna, but is flat on the radius. Anterior margin of the olecranon is tilted back and forms an angle of ~50° with the axis of the ulnar shaft. Proximally, the olecranon is thickened and bears a tuberosity.

Manus.—

Autopodium elements unquestionably referable to K. bronni are known by two middle phalanges (QB-4/12.721-PH), which were already described by Voss (Reference Voss2012). Further, a single distally broken metacarpal, measuring 62 mm in preserved length, is known from IRSNB Reg. 4006. It most likely represents the left metacarpal III, according to its congruent morphology with that in K. gruelli n. sp.

Innominate.—

Pelvic remains associated with partial skeletons of K. bronni are known from QB-4/12.721 (Voss, Reference Voss2012) and MB.Ma. 52009, the latter of which preserves the complete pelvis of the right side (Fig. 16.7–16.10). Posterior end of the ischium is neither markedly thickened nor flaring laterad. According to Domning (Reference Domning1991), this animal could therefore be interpreted as a female. A rugose protuberance is present on the dorsal edge of the ischium directly across from the ventralmost pubic extension. Another protuberance occurs on the ventromedial edge of the acetabular region ~20 mm from the ventral tip of the pubis. A foramen obturatum is missing.

Femur.—

Specimen IRSNB Reg. 4006 includes the left femur lacking its distal end and measuring 88 mm in preserved length. Femur is an overall gracile element, with its proximal end distinctly thickened. Femur head is rounded and flanked laterally by the greater trochanter, which forms an oval tuberosity well below the top of the head. Femur neck is indistinct. A slight prominence is present anteroventral to the neck, which corresponds to the lesser trochanter. Femoral shaft is slender, transversally rounded and tapering distad.