Propalorchestes novaculacephalus Murray, 1986 , pp. 195– 211

Trusler, Peter W. & Sharp, Alana C., 2016, Description of new cranial material of Propalorchestes (Marsupialia: Palorchestidae) from the Middle Miocene Camfield Beds, Northern Territory, Australia, Memoirs of Museum Victoria 74, pp. 291-324 : 295-315

Propalorchestes novaculacephalus Murray, 1986, pp. 195– 211 , figs. 1–6: Murray 1990, pp. 39–51, figs 1-3: Black, 2006, pp. 351–361, figs. 1–2.

Holotype. NTM P8552-10 : left and partial right side of neurocranium including most of the zygomatic arch and latex endocast.

Type locality. “Top Site” quarry in the Camfield Beds, Bullock Creek tributary of Camfield River, north central Northern Territory ( Plane and Gatehouse 1968; Murray, 1986).

Distribution and Age. Bullock Creek LF, Camfield Beds, Northern Territory middle Miocene (Woodbume et al., 1985), Riversleigh WHA Faunal Zone B–C, middle Miocene (Black, 2006; Travouillon et al., 2006; Woodhead et al., 2015; Arena et al., 2015).

Paratypes. NTM P862-27 , right maxilla with M 1-2, Bullock Creek LF; NMVP 187282, right dentary with M 2-4, HW site, Bullock Creek LF, Camfield Beds, Northern Territory ( Murray, 1990)

Referred material. QMF12429, isolated right M 2, Henk’s Hollow LF, Riversleigh, northwestern Queensland (Archer et al., 1989, 1991); QMF50605, left maxilla with dP 3, P 3, M 1-3, Jim’s Carousel LF; QMF51399, left M 1, Henk’s Hollow LF; QMF30883, right partial maxilla with P 3, M 1 (broken), Wayne’s Wok LF; and QMF30884, right M 1, Camel Sputum LF (Black, 2006); QMF537310, Cadbury’s Kingdom LF (Arena et al., 2015).

Additional material described herein. QMV2000GFV459, near complete cranium with right M 1-4, left P 3, M 1-4, M 2-4 crowns sheared off, Top site, Bullock Creek LF, Camfield Beds, Northern Territory; NMVP 179093 isolated M 4 fragment, posterior moiety of crown, Top site, Bullock Creek LF; NMVP 249851 isolated P 3 fragment, lingual half of crown, Horseshoe West Site, Bullock Creek LF; QVM 2000GFV406, right dentary fragment with M

2-4

, Top site, Bullock Creek LF.

Description

Preservation. QVM 200GFV459, near-complete splanchnocranium with partial neurocranium: missing tip of nasal, ventral extremities of masseteric processes, mid region of the left zygomatic arch, pterygoid wings, (incl. rim of choana), nuchal plate, most of basicranium, mastoid processes, paraoccipital processes, associated auditory osteology and occipital condyles. All incisors, except the right I 1 root and crown base, are lost. Cheek teeth well worn, highly fractured with considerable crown enamel losses; right M 2-4 crowns sheared off, left P 3 missing.

Cranial overview. The preservation and preparation of the external surface is excellent for the most part. Some of the suture lines and damaged occipital morphology are slightly over-etched. Much of the internal structure of the skull is evident including the thin septa between sinuses and residual parts of the bony nasal septum, nasal conchae and cribiform plate. Some limestone matrix remains supporting this delicate osseous anatomy and occupies fully enclosed sinuses. The neurocranium is rotated 2° to the right with respect to the splanchnocranium. The slight torsion of the skull, (about the narrow mid-region), probably results from the loss of the left zygomatic arch and fracture of the right arch. The basicranium has been sheared-off, abraded and the bone weathered, indicating that this aspect of the skull had been exposed for some time either prior to complete burial or through subsequent weathering of the limestone rock.

In dorsal view, the skull form is narrowly waisted dividing an ovoid, (approx. 90 mm long, 65 mm wide) crested neurocranium from a wedge-shaped splanchnocranium. From the “waist,” the central region of the skull broadens anteriorly to form a trapezoidal prism, (approx. 72 mm long, 72 mm wide at the frontal). The anteriorly facing surface of this prism connects perpendicularly with the anterior roots of the zygoma to form a transverse, flat facial plane with small, forwardly directed orbits. A narrow rostrum, approximately half the width of the facial plane, projects abruptly from this transverse surface. The entire dorsal rostral surface is excavated forming a 100 mm long, nasal cavity; widest sub-proximally, 45 mm from the facial plane, where it forms a heart-shaped aperture (figs. 2A, 3A).

In anterior view, the dorsal skull outline is strongly crested with broadly convex frontals separated by the shallow frontal depression. The orbits are positioned well below the level of the nasals, within the dorsal one third of the facial surface. The infraorbital foramina are prominent and the wide proximal part of the nasal aperture is oval-shaped in this view (figs. 4A, 5A).

In lateral view, the dome of the neurocranium is accentuated by the sagittal crest and the rostrum (approx. 123 mm long from the orbital rim), deflected 24° below the plane of the cheekteeth (figs. 4B, 5B).

Although broken at the free rostral nasal process, the sutured portion of the nasals are short and highly retracted. The lateral maxilla-premaxilla walls are highly excavated with the premaxilla ascending processes surmounting their entire extent. The anterior portion of the nasal cavity is a narrow slot defined by thinly crested lateral premaxilla walls. A strong premaxilla midline eminence surmounts a shallowly concave, but rounded rostral tip. The incisor alveolar arcade is arcuate. The rostral diastema is flat and gently re-curved, with sharp diastemal crests and well-defined sulci on each side of the ventral midline. The sulci are deepest where they accommodate incisive foramina and continue posteriorly for two thirds of the external palate. The maxilla tooth rows are proportionately small for the size of the skull, flat in the frontal plane, straight and parasagittal. The zygomatic arch is deep, but proportionately thin; the lateral surface of the jugal portion is concave, curves gently downwards to the masseteric process while maintaining a vertical orientation and is defined by a dorsal crest along the jugal. The crest becomes anteriorly directed at the masseteric process; the masseteric jugal crest would have delimited the dorsal and anterior extent of the m. masseter superficialis. The zygomatic process of the squamosal also projects perpendicularly, to form the squamosal sulcus and concave posterior floor of the temporal fossa. The posterolateral edge of the temporal fossa is angled approximately 125° to the midline before flattening to form the lambdoid crests. These crests form a distinctive arc that projects over, and restricts, the small occipital plate. The posterior face of the occiput is deeply excavated and though concave, slopes posteriorly at approximately 125° from the cheektooth plane for the part that has been preserved. The postglenoid fossa is clearly defined posteriorly by an extensive, but thin ventral crest that curves anterolaterally. The jugal contributes a slight curvature that provides lateral confinement of the glenoid articular surface. There is a sharp medial limit to the glenoid, but most of this feature is not preserved. The remainder of the basicranial surface-features are not preserved (figs. 2–6, supplementary 3D interactive pdf).

Supraorbital region and Splanchnocranium. The approximately 5.5 mm high sagittal crest gradually decreases in sharpness anteriorly and diverges to form frontal crests at the parietal-frontal suture to a maximum angle of 30° either side of the midline. The frontal crests are well rounded: form a V-shaped crease at their median edge along the dorsal surface of the frontal to define the posterior edge of the frontal depression, and a gentle ridge along each posterolateral edge that probably delimited the anterior extent of the m. temporalis. The postorbital process of the frontal is weak and ill-defined. The frontal crests broaden and weaken anteriorly, but form the frontal eminence as a gently rounded boss over each orbit.

The frontal eminence curves downwards to contribute to the supraorbital region by a complex suture with the lacrimal to form a moderately rugose, frontolacrimal tuberosity. The frontal contributes the largest proportion to the structure; thus the lacrimal does not form an independent “lacrimal tuberosity.” The frontolacrimal tuberosity continues the curving form of the frontal eminence. Each tuberosity contains two irregular pits at the dorsolateral extremity, but damage from acid-etching appears to have exaggerated the pitted texture. A dorsally directed groove extends from the left lacrimal foramen on the medial orbital wall. At the corresponding region of the right medial orbital wall, the form of the right lacrimal foramen is obscured by matrix residue, but is possibly represented by two small apertures. The lacrimal contributes only a small amount to the vertical facial plane at its dorsal extent. Its anterior edge sutures with the maxilla along the medial orbital rim before uniting with the jugal near the ventral border of the orbit and curving posteriorly down its internal surface. Posteriorly, the lacrimal-frontal suture runs vertically down the lateral cranial wall from the frontolacrimal tuberosity.

The nasal-frontal suture diverges at 45° from the midline on the dorsal surface of the skull and assumes the anterior edge of the frontal eminences at their anterolateral extent. At this point the nasals form a small lateral process to narrowly contact the maxilla ascending process that in turn, precludes nasal contact with the lacrimal. The nasal suture then turns medially to contact the flared dorsal extent of the premaxilla ascending process and traverses anteriorly before turning posteroventrally to continue along the internal roof of the nasal cavity. The nasal-premaxilla suture forms a slightly rugose, flattened ridge to the retracted dorsal rim of the nasal aperture at either side of the nasal spine, but is separated from the spine by a smooth, shallow parasagittal groove or narial notch ( Woodburne, 1967). The narial notch is analogous to the nasal incisure seen in Tapirus , but the groove does not extend to form a sulcus (diverticular meatus) on the dorsal surface of the nasals (Boas & Paulli, 1908, 1924; Witmer et al., 1999).

Unfortunately, the rostral process of the nasal in QVM 2000GFV459 has been fractured and lost, leaving little indication of its extent or morphology. The nasal process was narrow at its base; approximately one third of the maximum width of the nasal bones and one half the width of the anterior nasal roof. It may have formed a “nasal spine” with a weakly arched transverse profile at its base. It cannot be ascertained if this continued as a curved spine when seen in lateral profile, as in Palorchestes painei ( Woodburne, 1967; Murray, pers. comm.) or as a flattened shelf with a small terminal spike as in P. azael (Trusler, in prep.). The former seems more likely in Propalorchestes and has been suggested by dotted outline in figures 3A, 5B.

The term “nasal spine” has been strictly applied here to the morphology of the nasal bone. This term is often used for the vertical midline projection of the premaxilla at the anterior of the nasal cavity. We have preferred the term premaxilla midline eminence for this feature, as suggested by Murray (pers. comm.), because it relates functionally to similar eminences or midline crests formed by the premaxilla or maxilla in other taxa with retracted nasal anatomy (see description p.6). Both features are common in taxa with retracted nasals or laterally excavated premaxilla and maxilla nasal walls. The nasal spine and premaxilla midline eminence both act as extended structural support for the free portion of the cartilaginous nasal septum at its dorsal and anteroventral extents respectively ( Witmer et al., 1999).

An inverted trapezoid suborbital fossa (approx. 32.25 mm in height) is formed between the masseteric crest along the anterolateral edge of the jugal, the ventral orbital rim, and a vertical ridge formed by the maxilla-jugal suture line of the face; approximately 6.25 mm lateral to the infraorbital foramen. The fossa is smooth and shallowly concave. The maxilla-jugal suture then deflects laterally to join the lowest part of the jugal masseteric crest. This junction forms a sharp U-shape above the ventral edge of the maxilla root of the zygoma. This slightly concave region forms the dorsal extent of the subzygomatic sulcus that re-curves ventrally. The tip of each masseteric process is abraded to a point just dorsal to the level of the M 1 crown base. The tapering form suggests that the masseteric process of this specimen may not have projected below the base of the molar crowns, (figs. 5A–B).

Infraorbital foramina appear proportionally small compared to Palorchestes and smaller than those described by Murray (1990) for the Propalorchestes novaculacephalus paratype, NTM P862-27 (tables 1, 2). Slightly higher than wide (average maximum diameter 5.97 mm; average minimum diameter 5.47 mm), the rounded rectangular infraorbital foramen possesses a thin, horizontal baffle that projects from its medial wall. A facial fossa extending anteriorly along the lateral maxilla surface from the infraorbital foramen is only weakly evident in this specimen. Anteroventral to this is a long, shallow premaxilla lateral fossa. The ventral limit of this lateral fossa accentuates the line of the diastemal crest.

The premaxillary ascending processes that cap the long lateral nasal walls are expanded proximally with a convoluted suture to the nasals and maxilla as described above. A second ‘flat’ surface originates on the medial side of the distal half of the nasal wall. It becomes rounded as it rolls onto the lateral surface, but not as sharply as the narial notch above it. Proximally, this forms a sharp dorsal rim along the premaxilla ascending process at the widest part of the nasal aperture. Distally, this anteriorly directed surface forms a broader, rounded dorsal edge on the premaxilla as it becomes confluent with the lateral wall of the nasal aperture. In so doing, it effectively restricts the width of the nasal aperture. Between this second feature and the projecting root of the maxilloturbinate on the medial surface of the nasal wall, a third flat surface arises to run anteriorly. This surface becomes a shallow groove that also rotates onto the dorsal edge of the premaxilla to become confluent with the lateral nasal wall. The medial edge of this groove is raised into a sharp, thin, subnasal crest that forms a convex profile (approx. 24.7 mm long) to the proximal nasal rim when seen in lateral view. In dorsal view the subnasal crests are parasagittal and delimit the narrow anterior part of the nasal aperture (width 11.5 mm). At the anterior termination of each crest, the profile curves further ventrally to form a more rounded, but concave rim; defining the distal extent of the nasal cavity and rising to form the premaxilla midline eminence. The anterior of the nasal aperture is semicircular in dorsal view. The midline eminence is abraded, but enough remains to indicate it formed a higher, paired transverse peak across the midline. The posterior wall of the eminence bears two small pits. The premaxilla-maxilla suture forms a straight, oblique passage as it traverses anteroventrally from the dorsolateral edge of the nasal along the lateral rostral wall to the diastemal crest. On the ventral surface of the diastema, the premaxilla-maxilla suture turns sharply posteromedially before abruptly running anteromedially to the incisive foramen within the palatal sulcus. On the lateral wall of the sulcus the premaxilla projects posteriorly to form each incisive foramen and the incisive process that separates them. The incisive process also forms a rounded midline ridge that deeply divides the palatal sulci along the ventral premaxilla. Ventrally, the maxilla contributes only to the posterior end of the incisive foramen. Dorsally, the morphology is the converse; the maxilla forms an incisive process that projects anteriorly to form the medial walls of the incisive foramena and expands slightly over the midline within the nasal cavity for a further 6.4 mm. Posteriorly from this point, the maxilla forms the sharply raised sulcus that would have accommodated the vomeronasal (Jacobson’s) organ, the ventral insertion for the nasal septum and the vomer (see below). The palate is flat, except for the palatal sulcus that shallows and narrows from a point opposite the anterior moiety of M 1. The midline suture forms a slight ridge in this region. Two anterior palatal foramina are positioned slightly asymmetrically lateral to the edge of the palatal sulcus, adjacent to the M 1. Minor foramina are similarly laterally sited posterior and anterior to these. The maxillapalatine suture is highly convoluted, commences at the midline opposite the interloph valley of M 3 and arcs anteriorly before running posteriorly beside the posterior moiety of M 3 and the M 4. On the right, the suture meanders increase in lateral-medial amplitude before descending into the posterior palatine foramen. The foramen lies immediately posterior to, and aligned with, the medial edge of M 4 and opens into a slightly anteromedially directed trough that extends to a position level with the M 4 metaloph. The remaining posterior surface morphology and posterior palatine rim is not preserved.

The premaxilla rostral tip contained three pairs of incisors in a semicircular arc with the incisive portion of the palatal sulci extending anteriorly to the I 1 alveoli. The I 3 alveolus is the largest, av. 12.07 mm diameter, and forms a lateral subterminal swelling that widens the rostrum. Some surface is lost at the premaxilla tip and about the alveoli, but the curved, anterior face preserves a shallow concave fossa above the right incisor alveoli. This would also have been a paired feature of the rostral tip. The root and crown base of the right I 1 remains; the left I 1 alveolus is 5.76 mm in diameter. The I 2 alveolus is intermediate, av. 6.58 mm diameter.

Cranial roof. In lateral view, the dorsal profile of the neurocranium is high and strongly convex due to a prominent sagittal crest (maximum height approximately 5.5 mm, horizontal length approximately 100 mm, circumference length, approximately 120 mm). The crest is formed entirely by parietal; there is no indication of an interparietal, but the posterodorsal region of the skull is well fused. Woodburne (1967b) was unable to define the cranial sutures in the occipital region for P. painei . The crest reduces sharpness posteriorly as it divides at the occipital to form the laterally curving, lamboidal crests.

Cranial walls. There are several irregularly positioned foramina on the dorsolateral parietal and squamosal surfaces that follow the line of the lamboidal crests. Murray (1986, figs. 2–4A, C) identified similar foramina on the left of holotype NTMP 8552- 10, but they are highly asymmetric on QMV2000GFV459. The parietal and squamosal contribute equally to the swollen ovoid form of the posterior part of the neurocranium. Murray (1986, pp. 202–3) remarked that the general morphology of the neurocranium of Pr. novaculacephalus was didelpid-like with respect to its crested, narrowly waisted and ovoid character, but added this was likely a derived state in Propalorchestes and not a plesiomorphic condition.

The glenoid region is well characterized by Murray’s description of the holotype ( Murray, 1986, p. 199). It is consistent with the morphology of QVM 2000GFV459, particularly the more complete, right side of the specimen. The roughened surface irregularities of the jugal and its lateral glenoid process confine the anterolateral extent of the articular surface. The glenoid fossa is essentially a transverse groove along the posterior boundary of the shallowly concave anterior articular surface. It is bounded mesially by the oblique ventral projection of the medial glenoid process and opens laterally between the transversely oriented postglenoid process and the lower ventral plane of the anterior articular surface. A pair of fine creases on the anterior articular surface of the squamosal, delimit the transverse boundary between the two. These creases are very slightly curved anterolaterally towards the jugal, as Murray (1986) detailed, and form a very shallow groove between them (fig. 3B). The lateral half of the postglenoid process preserves a more ventral and distinctly anteriorly rolled crest. The rim of the crest is rugose and further confines the articular region. Murray (1986) did not mention this distinctive morphology, presumably because, if present, it was lost through damage.

Only small anterior portions of the pterygoids remain of the basicranial region and are sheathed anteriorly by the extensive vomerine surface within the choanal orifice. The median septal plate of the vomer is partly preserved. The squamosal-alisphenoid suture cannot be followed posteriorly from the medial glenoid process due to breakage and loss.

The zygomatic arch projects directly anteriorly from the posterior zygomatic root in both the holotype and QVM 2000GFV459 whereas it arcs anterodorsally in P. painei and the curvature continues to the ventrally extended tip of the masseteric process. The excavation of the lateral jugal surface of the zygomatic arch is pronounced and covers a greater proportion of its surface than in P. painei . The anterior extremity of the squamosal on the dorsal edge of the zygoma has been damaged. The frontal process of the zygoma cannot be seen in this thin region and was probably relatively slight. The damage and some over-etching of the squamosal-jugal suture has resulted a highly convoluted extension of the suture that continues along each orbital rim, almost to the lacrimal suture. The medial surface of the arch bears four shallow depressions.

Cranial rear. The proportion of the occipital region preserved in QVM2000 GFV459 is similar in area to that of the Pr. novaculacephalus holotype, but represents the dorsal half only, compared to the near complete left half in the holotype. Furthermore, the new specimen has lost most of the remaining external occipital surface. This prevents reconstruction of the occipital region in QVM2000 GFV459 and restricts comparison with the taxonomically significant basicranial and condylar anatomy of the holotype. The general proportions and plane of the occipital plates in both specimens compare favourably (occipital plane of QVM2000 GFV459 96.5° posterior to occlusal plane; NTMP8552-10 estimated to be 100.0°) and the right suboccipital fossa was strongly concave and well separated by a midline ridge (figs. 7, 9) .

Endocranial Sinuses. Using the CT data, some auditory and most non-auditory sinuses can be examined and compared with the original holotype description and illustration of Murray (1986, fig. 4). A graphic overlay is provided (fig. 7C).

The paired epitympanic sinuses that lay immediately dorsolateral of the cerebellar region of the endocranium are exposed by posterior breakages (figs. 3B, 7B, C, 8A, B, C, E). They appear to not extend as posteriorly as those in the holotype partly for this reason. The posterior parietal sinus location indicated by Murray (1986, fig. 4b, d) is also more posterior to that of QVM 2000GFV459. Several irregular vacuities can be seen in this location (mostly right of the midline), but some represent damage and losses. The graphic comparison presented in figure 7C indicates that there is a slight discrepancy in the angle of view between that of Murray (1986) and our own, which has resulted in the relative posterior displacement of all sinus features of the holotype in respect to those of QVM 2000GFV459. The parietal sinus was an extensive volume that occupied all of the dorsal and dorsolateral expansion about the endocranium. In dorsal outline it was slightly asymmetric and paired. The broad lateral sinus expansions only relate in part to those figured by Murray(1986,fig.4D)(fig.7C). The sinus schema he elucidated for the endocranial cavities aligns with the new material, but the scan provides insights permitting an alternative interpretation of the anatomy. The large sinus that shrouds the endocranial cavity of the brain beneath the parietals, is the parietal sinus and not the frontal sinus as originally designated by Murray (1986), but accords with anterior and posterior views of the natural breakage of the holotype in Murray (1992, figs. 2A, B). The sinus volume includes a large posterior lobe along the midline and posterolateral flanges that correlate to the “posterior-” and “anterior parietal sinuses” respectively of Murray’s (1986) holotype description. These do not appear to be independent in QVM 2000GFV459. The lateral expansion within the parietal extends beneath the parietal-squamosal suture line on the lateral surface of the skull and the sinus floor closely abuts the anterior epitympanic sinus (figs. 7C, 8, 9).

A paired anteroventral chamber of the parietal sinus closely abuts the posterior portion of the frontal sinus. It is united via a sagittal passage from the mid point of the main parietal chamber floor to its ventral half. The floor of this passage forms the very thin roof of the cerebral portion of the endocranial chamber. The anteroventral parietal sinus lies dorsal to the olfactory bulbs and is aligned with the serial divisions of the frontal sinus above the cribiform plate (fig. 9A, supplementary 3D interactive pdf).

Only the dorsal parts of the auditory sinuses remain in QVM2000 GFV459. Dorsal to these, a small horizontal supraoccipital sinus surmounts each epitympanic sinus and runs anterolaterally to contact the posterolateral end of the parietal sinus with its anteromedial corner. The supraoccipital sinus identified in the holotype is depicted entirely medial to the epitympanic sinus, but in the new specimen, a, large posterior epitympanic sinus projects posteriorly from beneath it. A vertical strut incompletely partitions the posterior portion of the epitympanic from a more voluminous anterior epitympanic sinus. These are partially exposed by the loss of the basicranium. The most anterolateral extensions of the sinuses, including the glenoid hypotympanic sinus, are preserved within the posterior root of the zygoma .

The frontal sinus is chambered. Its asymmetry is pronounced, but does not obscure the basic pattern of paired transverse divisions of the volume that extends from a point level with the frontal-parietal suture at the cranial “waist” to the midline point of the frontal-nasal suture. The most posterior chamber lies ventral to the main parietal sinus, separated from it by irregularly thick, bony walls. A large lateral frontal sinus diverges anterolaterally from beside the second anterior frontal chamber to occupy the volume beneath the frontal crests and frontal eminence. Thus, the lateral frontal sinus extends well forward of the midline chamber series to terminate posterior to the frontolacrimal tuberosity.

In addition to the frontoparietal sinuses, maxillary sinuses are also evident (figs. 8D, E). They are highly asymmetric; the right side is three times the volume of the left and extends to the maxilla-jugal suture. Their volume is subdivided (or isolated) and appears to represent a lateral elaboration of the maxillary sinus. Structurally, this relates to the vertical expansion of the anterior root of the zygoma and facial surface. This is similar to the lateral squamosal sinus elaboration above the glenoid with the widening (horizontal expansion) of the posterior zygoma (see p. 14). The degree of sinus development shown in Propalorchestes is strong and significant in relation to the allometric trends and specializations of later and larger Vombatomorphia (Murray, 1992; Sharp, 2016). An indication of the evolutionary development of the sinus system and corresponding increase in skull size can be gained by the comparative outline featuring P. azael (fig. 9). The volume of the endocranial cavity has remained reasonably constant despite the five fold increase in skull volume, indicating the extreme degree of negative allometry of the brain.

Nasal cavity – The voluminous cavity is divided by a stout ethmoidal nasal septum. A thick and osseous dorsal pedestal attaches to the ventral surface of the nasals. Bony lateral expansions are preserved on the medial lateral walls of the maxilla, midway between the premaxilla midline eminence and the base of the nasal spine. These served as the attachment sites for the extensive maxilloturbinates ( Fig. 9A ). The ventral edge of the septum was located in an elevated median trough on the cavity floor and the anteroventral extent of the septum, whether ossified or cartilaginous, was confined by the base of the premaxillary midline eminence. Fragments of the ethmoturbinates remain against the cribiform plate. The location of the nasoturbinate scroll can be seen bridging the nasal and dorsomedial surface of the proximally flared premaxilla process. The dorsal outline of the cavity is proportionally wider than P. painei both with respect to the parallel-sided anterior part and the expanded, heart-shaped proximal portion of the cavity. The cavity is slot-like in P.painei where the proximal portion is more triangular, the central region slightly laterally curved and the distal third parallel-sided. The nasal cavity length proportions for both Pr. novaculacephalus and P. painei represent one third of their skull length. Propalorchestes novaculacephalus has a gently concave profile to the lateral wall of the nasal cavity because the subnasal crest and the narial notch (lateral to the nasal spine) is less incised.In dorsal aspect, Pr. novaculacephalus is morphologically similar to P. azael , but proportionally, the nasal cavity is half the skull length in P. azael . In anterior view Pr. novaculacephalus has proportionally the widest oval-shaped aperture, P. azael is intermediate in being narrowly triangular and P. painei the narrowest and more parallel-sided.

Dentition. Cusp nomenclature for Propalorchestes follows Rich and Archer (1979) and Murray (1990) wherein: the protoloph is composed of buccal stylar cusp C and the lingual protocone; and the metaloph is composed of a buccal stylar cusp D and a lingual metaconule. Both the paracone and metacone are subsumed into the protoloph and metaloph respectively (Black, 2006). Note that the hypocone described by Woods (1958) and Woodburne (1967) for Palorchestes is probably homologous to the metaconule (Murray and Wells, pers. comm.) (See fig. 13 for Propalorchestes upper dentition showing terminology).

A composite description for the Propalorchestes dentition will be provided drawing upon the QMV2000GFV459 skull and QMV2000GFV406 mandible (figs. 12, 13A–B & 16).

dP 3: not expected for the age of the QMV2000GFV 459 specimen and an isolated dP 3 has yet to come from the Bullock Creek LF. Refer to Black (2006) for a detailed description of the dP3 from a juvenile maxilla, Pr. novaculacephalus QMF 50605, Jim’s Carousel LF, Riversleigh WHA.

P 3: sub-triangular in occlusal view; bicuspid crowned; trirooted; and wider than long. The crown bears a large central parametacone and a large lingual protocone. The moderately worn QMV2000GFV459 left P 3 occlusal morphology (fig. 13A) compares favourably with the unworn Pr. novaculacephalus P 3 QMF50605 from Riversleigh.

Three crests extend from the parametacone of QMV2000GFC459: 1) a short anterobuccal crest, which fades down the steeply sloping buccal face and provides a lateral lobe on the parametacone occlusal wear facet outline; 2) A short anterolingual crest produces an anterolingual lobe of wear; and 3) A prominent posterobuccal crest, descends steeply to the base of the crown, produces a large posterior lobe to the wear outline. The occlusal wear from the posterobuccal and anterolingual crests is aligned with the steep-sided valley separating the parametacone and protocone.

The protocone apex shows a small wear facet that incorporates two crests in outline: 1) a weak anterobuccal crest opposes the anterolingual crest of the parametacone in the interloph valley; 2) a posterobuccal crest runs parallel to the posterobuccal crest on the parametacone. A posterolingual cingulum extends from the base of the posterobuccal parametacone crest to the lingual base of the protocone, forming a posterolingual cleft from which the posterobuccal protocone crest decends. A weak posterobuccal ridge extends from the base of the posterobuccal parametacone crest, confluent with a posterobuccal cingulum that curves anteriorly around the tooth margin and fades into the base of the crown opposite the parametacone apex. This cingulum forms a broad cleft on the posterobuccal face of the parametacone that separates its two buccally directed crests. Black (2006) described a sub-apical crest on the anterobuccal face of the parametacone that curves lingually around the base of the tooth. This is strongly indicated on QVM2000GFV459 by a sharp extension of the parametacone wear facet that extends to the base of the anterobuccal corner of the parametacone. From this point a short ridge extends posterobuccally, while a faint precingulum wraps posterolingually on the anterior tooth base. The pre- and postcingulum morphology is more extensive than QMF50605, but this may be indicative of the under developed, un-erupted condition of the QMF50605 P 3. The crown of P 3 extends well below the occlusal line of the upper molars and it’s degree of wear is significantly less than M 1; (the occlusal area of the P 3 wear facets are closer to the wear extent on the M 4 metaloph).

Upper molars are roundly sub-rectangular to trapezoidal in occlusal outline and bilphodont, consisting of a protoloph (connecting the protocone, paracone and stylar cusp C) and a metaloph (connecting the metaconule, metacone and stylar cusp D). (figs. 13B, 16). The protoloph and metaloph are slightly crescentic, recurved posteriorly, but to differing extents. Stylar cusp C is posterior to the paracone and stylar cusp D is sharply deflected posteriorly. There is posteromedial buttressing of the protocone and metaconule. The interloph valley is deep, V-shaped in profile and partially bridged by a “proto-midlink,” corresponding to the midlink that connects paracone to metacone in Palorchestes ( Mackness, 1995) . Precingulum, postcingulum and lingual cingulum are present, but there is no buccal cingulum. A weak to moderate forelink (or preparacrista) extends from a weak stylar cusp B towards the paracone and a postlink (or postmetacrista) extends from a stylar cusp E towards a point between the metacone and metaconule. All “links” are positioned buccal of the crown midline to varying extents. Both the fore- and postlinks confer slightly extended, less rounded corners to the buccal face of the crown in occlusal view; these correspond with stylar cups B and E, respectively. The presence of a lingual cingulum gives a straighter, less “waisted,” outline to the lingual face in occlusal view and squarely confines the interloph valley in medial view. By comparison to the crown ornament of Palorchestes species, wrinkled to pustular ornament is only weakly present in the clefts of the cingula and interloph valley in Propalorchestes (fig 12).

The morphological progression of the upper molars is as follows: 1. The size gradient for length and width is sub-equal from M 1 -M 3, but the M 4 of QVM2000GFV459 is longer and narrower. 2. The length of the protoloph compared to metaloph near the crown base increases from sub-equal for M 1 to approximately 125% of the metaloph on M 4. 3. The width of protoloph usually greater than metaloph. 4. The extent of occlusal wear is always greatest on the “thicker” protoloph. 5. The anterior face of both lophs is more steeply inclined than the corresponding posterior face. 6. The length of the interloph valley increases slightly from M 1 -M 4. 7. The prominence of all “links” (or cristae) generally decreases from M 1 -M 4. 8. Crown outline in occlusal view for M 1 is trapezoidal with buccal side longest, M 2 more rectangular, M 3-4 increasingly trapezoidal with the lingual side increasingly the longest (fig. 16).

The degree of wear on QVM2000 GFV459 M 1 precludes an indication of original relative cusp heights. The morphology compares most closely with the Pr. novaculacephalus paratype NMTP862-27 ( Murray 1990, fig. 3); (figs. 12B, 13). In regard to the individual cristae on the crown, the “forelink” or preparacrista is prominent and extends to the anterolingual margin of the crown as in QMF50605. The “postlink” or postmetacrista also compares well with QMF50605, QMF51399 and QMF30844, but is more extensive and further buccally directed than in these Riversleigh specimens. In the QMF51399 and QMF30844, the “postmetacrista” is incipient and not confluent with stylar cusp E. In all specimens, a postparacrista extends posteriorly into the interloph valley where it meets a weak, short, anterior crest at the base of the metaloph at a point opposite the metacone apex. This “proto-midlink” is prominent in the new material and the paratype NTMP862-27 , but less developed in the Riversleigh specimens. On QVM2000 GFV459, the loph wear facets almost unite across this structure on the right M 1, whereas it does bridge the loph wear on the left M 1. There is a second incipient bulge, medial to the metacone, on the anterior metaloph face, that is also present on NTM682-27 , but is either less developed or not evident in the Riversleigh material (fig. 13, refer also to the M 2 description below). Pre-, post- and lingual cingula are strongly developed and of sub-equal size for all specimens .

M 2 is similar to M 1, but has a narrower and less steeply sided metaloph that ultimately wears to produce a parasagittaly wider wear facet than M 1. The interloph valley is also less steeply sided and forms a broader cleft with the lingual cingulum. The right QVM2000GFV459 M 2 has an equally pronounced, second anterior bulge, medial to the first, at the base of the metaloph and a slightly weaker one opposing it on the posterior surface of the protoloph. This closely matches the morphology in the paratype NTM682-27 M 1 for which Murray (1990, p. 41) described the structure as a centrocrista and a pair of bulges separated by a rhomboidal fossa in the interloph valley. QMF50605 M 1 and M 2 also have a less pronounced version of this morphology and together both features are probably the precondition for the double midlink developed in later Palorchestes . The combination of this structure and the less inclined interloph valley ultimately produces M 2 loph wear facets with a double connection and a circular to rhomboidal fossa between them (fig. 13). This is commonly seen in the wear conditions in Palorchestes dentition. The second Pr. novaculacephalus paratype, QMF12429 comparesleastfavourablywithQVM2000GFV459, QMF50605 or NTM682-27, because there is no indication of the second bulge on the anterior face of the metaloph and the postparacrista is weak and not well aligned with the single crest at the anterior base of the metacone (fig. 13). This constitutes the weakest indication of a “proto-midlink” of all the Propalorchestes material. If it is regarded as an M 3, the identity of QMF12429 remains questionable.

The preserved right M 3 continues to show a small proportional reduction in the metaloph by comparison to the protoloph and a slightly reduced steepness to the posterior faces of both lophs. The postmetacrista is reduced in size, descends only half way to the metacone and is less markedly directed towards the posterobuccal corner of the crown. Although the specimen is broken in this region and the remaining morphology has a more prominent relief, it compares favourably with the proportional changes seen in the QMF50605 tooth row and indicates that the postmetacrista, stylar cusp E and the “protodoublelink” morphology are all positioned less buccally than M 2 and M 1. The postcingulum is reduced in proportion to the reduction of the M 3 posterior moiety. Due to breakage, the lingual cingulum is missing. The precingulum, stylar cusp B and “forelink” remain well developed and the latter cusp and crista retain the anterobuccal position.

M 4 continues the proportional reductions in crown morphology, but the remaining right tooth on QMV2000GFV459 has lost the buccal 1/3 of the protoloph and the posterior surface of the metaloph has been sheared off. The postparacrista is a distinct, high crest; the interloph valley is wider, its cleft is more crenulate and it features incipient double bulges at the anterior base of the metaloph. The lingual cingulum is longer with a wider, shallower, forked cleft. The buccal side of the interloph valley may also be slightly enclosed, but the fractured surface precludes determining the possible presence of a weak buccal cingulum.

Re-examination of the prepared material from Bullock Creek held by MV has revealed two further isolated dental fragments. The first specimen, NMV P249851 (No. 2329) from HW, appears to be a slightly worn (less than QVM2000GFV459) lingual moiety of a right P 3 crown. It consists of the interloph valley and part of the lingual side of the missing main loph. It is significantly larger than Ngapakaldia bonythoni P 3 in Black (2010, fig. 2a-a’). The second specimen NMV P179093, is a crown from the posterior moiety of an M 4 from Top Site. It preserves sufficient features recognised more easily in Pr. novaculacephalus M 1 morphology, but in the correct proportion to the regression of form in the QVM2000GFV459 right M 4.

Figures

Figure 9. Propalorchetes novaculacephalus reconstructed cranial sinus outline compared with Palorchestes azael as revealed in parasagittal section taken immediately left of midline to exclude sagittal septa: a, Propalorchetes novaculacephalus QVM2000GFV459 based of CT scan data; scale bar represents 5 cm: b, Palorchestes azael NMVP216490 represented at the size of Pr. novaculacephalus 9a, based on exposures of cranial fragments and CT scan data; scale bar represents 10 cm: c, Propalorchetes novaculacephalus QVM2000GFV459 represented to scale of P. azael NMVP216490 in 9b; scale bar represents 10 cm.