Antechinus bellus (Thomas, 1904)

Dyck, Steve Van, 2013, Taxonomy and redescription of the Fawn Antechinus, Antechinus bellus (Thomas) (Marsupialia: Dasyuridae), Zootaxa 3613 (3), pp. 201-228 : 219-225

Description of Antechinus bellus Holotype

Natural History Museum, London, BMNH 4.1.3.102. Adult male puppet skin with skull extracted—both skin and skull in good condition (refer Figures 16 and 17 ).

Type locality. South Alligator River , Northern Territory, Australia, approx. 12° 14'S 132° 24'E, altitude not supplied. Collector. J. Tunney, 25 May 1903 .

Pelage. Fur of the midback is up to 10 mm long with basal 6 mm Slate Colour, median 3 mm Pale Olive Buff and apical 1 mm black. The back appears as an overall speckled Light Greyish Olive. Guard hairs are interspersed thinly through the fur and are 12 mm on the rump and reduce to 5 mm where they terminate at the crown of the head. Fur on and below the shoulders, thighs, flanks and chin lacks black tips and these areas, and the belly, appear as Pale Olive Buff.

There is no distinct head-stripe but light areas immediately above each eye give the impression of a dark head ‘patch’. An eye-ring results firstly from an intense darkening of the skin of the eyelids and secondly from the dark hairs which surround the eye. A narrow band of short, black, eye-lash hairs completely encircles the eye. Above and under the anterior corner of each eye a small patch of dark hairs sweeps to one third of the way along the bottom and top of the eyelid, thereby making the area anterior to the eye-ring appear darker. The remainder of the fur above and under the eye is a light buff (Pale Olive Buff). The soft ventral fur (8 mm long on the belly) is Mouse Gray on the basal half and colourless to Pale Olive Buff on the apical half, and is interspersed by colourless medially-thickened guard hairs 14 mm long. The belly is thus an overall Pale Olive Buff. Forefeet are thinly covered with Pale Olive Buff hairs. Hindfeet are more thickly covered with lighter colourless hairs. The tail is thickly covered with hair and is strongly bicoloured dorsoventrally. Hairs average 3.5 mm along the tail length but increase to 10 mm right at the tip. Dorsally, the tail hairs are uniform Deep Olive Buff with Fuscous Black tips, but the distal third is covered with Olive Brown hairs which form a dorsal ‘crest’. Ventrally, the black tips are lost completely and the hairs are colourless.

Vibrissae. Approximately 22 mystacial vibrissae occur on each side, up to 22 mm long. The more dorsal mystacial vibrissae are Fuscous Black while those lower are colourless; supra-orbital vibrissae (Fuscous Black) number 1 each side; genals (Fuscous Black and colourless) number 3 (left) and 5 (right); ulna-carpals (colourless) number 3 each side; submentals (colourless) number 5.

Tail. The tail is shorter than the snout-vent length. It is thin, tapers toward the tip and has a weak dorsal crest.

Hindfoot. Interdigital pads are separate. The apical granule is elongate, enlarged and striate. An enlarged, fused hallucal/post-hallucal pad is present on each foot. Metatarsal granules are not present.

Ears. Ears are rounded with a ventral lobe defined by a shallow notch in the posterior margin. The supratragus has a pronounced thickened posterior margin and the distal end is reflected ventrally. The reflected tip is slightly concave.

Dentition (refer Figure 17 ). Upper incisors (left premaxilla is absent from skull along with LI 1-4). I 1 is narrow and peg-like, very procumbent and relatively uncurved; it is taller crowned than all other incisors and separated from I 2 by a diastema, thus I 1>I 2>I 3. All upper incisors have buccal cingula. I 4 carries no anterior or posterior cusp. Roots of I 4 are narrow, as in I 3 and I 2.

Upper Canines: C 1 is short, thick and slightly curved with an indistinct boundary between root and crown; very little of the root is exposed. There is a very weak buccal cingulum and no lingual cingulum. A minute posterior cusp is present.

Upper Premolar: Premolars are not crushed, and although no diastemata occur between teeth, a slight space occurs between the crowns of P 2 and P 3. All premolars are strongly cingulated buccally, and P 1 and P 2 have strong lingual cingulation (which is weak in P 3) such that P 3>P 2>P 1. Small, but clearly definable anterior cusps occur on P 1 and P 2. P 3 lacks an anterior cusp but has a strong posterior cusp. Postero-lingual lobes occur on P 2. Premolars are elliptical in occlusal view (with P 1 almost round).

Upper molars: The posterior tip of P 3 rests on the anterior cingulum of M 1 just lingual to and slightly below the prominent stylar cusp A. The anterior cingulum is very short, broad and incomplete. Stylar cusp B is absent and the paracone relatively unworn. There is no protoconule. The paracone on M 1 is approximately 1/3 the height of the metacone. Stylar cusps C and E are not present and M 1 lacks a posterior cingulum.

In M 2, the broad anterior cingulum which contacts the metastylar corner of M 1 tapers quickly as it progresses down and along the base of the paracrista and finally degenerates labially to the base of the trigon basin. No protoconule is visible. M 2 lacks stylar cusps A, C and E, and D is only slightly reduced in comparison to M 1. There is no posterior cingulum.

In M 3, the anterior cingulum is broader and longer than in M 2 but it becomes indistinct after covering 2/3 of the distance between stylar cusp B and the base of the paracone. Stylar cusp D is greatly reduced to a very small, blunt peak. Stylar cusps E and C are absent.

In M 4, the anterior corner is poorly developed. The broad anterior cingulum is slightly shorter than that of M 3. The protocone is greatly reduced and very narrow. There is no metacone development. In occlusal view, the angle made between the post-paracrista and the post-protocrista is close to 135°.

Lower incisors: The first lower incisor is much larger than I 2. I 1 and I 2 are paddle-like in anterolateral view and gouge-like in occlusal view. I 2 is subequal in crown height to I 3. I 3 is paddle-like but very long and narrow in lateral view, with a very weak posterior cusp; the lower canine rests against this posterior cusp. In occlusal view, a small notch separates the posterior cusp from the prominent posterolingual lobe, and crown enamel of primary and posterior cusps folds weakly so that the crest of the two cusps does not go so far as to bisect the tooth longitudinally.

Lower canine: C 1 is caniniform, short and thick and characterized by minimal curvature from root to crown tip. It has weak buccal and lingual cingulation and a very weak posterior cusp.

Lower premolars: P 1-3 are crowded and all in contact. They are weakly cingulated buccally and lingually and P 2>P 3>P 1. All are short-crowned and very thick. All possess low posterior cusps and P 1 possesses a weak anterior cusp. The bulk of each premolar mass is concentrated anteriorly to the line drawn transversely through the middle of the two premolar roots. Posterolingual lobes feature in P 1.

Lower molars: All are short and broad. The M 1 talonid is wider than the trigonid and the anterior cingulum is present but poorly developed. It terminates at the posterior base of the protoconid. There is no buccal cingulum. The narrow paraconid appears in lateral view as a small, broad shelf, the lingual edge of which makes a marked swelling on the endoloph and sets the paraconid out as a distinct cusp. The paracristid is almost 20° (to the horizontal) from the paraconid to the paracristid fissure and 45° from the paracristid fissure to the protoconid. The metacristid and hypocristid are roughly oblique to the long axis of the dentary. The cristid obliqua is very short and extends from the hypoconid to the posterior wall of the trigonid intersecting the trigonid directly below the tip of the protoconid. The hypocristid terminates 2/3 of the way between the hypoconid and the metastylid. A minute entoconid is present. From the base of the metaconid posteriorly, the talonid endoloph swings sharply lingually, finally returning buccally to the hypoconulid.

In M 2, the trigonid is slightly narrower than the talonid. The anterior cingulum is very poorly developed terminating lingually in a weak parastylid notch into which the M 1 hypoconulid is tucked. There is no buccal cingulum. A narrow, stronger posterior cingulum extends from the hypoconulid to the posterior base of the hypoconid. The paraconid is well developed and is the smallest trigonid cusp. There is a minute entoconid. The cristid obliqua extends from the hypoconulid to the posterior wall of the trigonid intersecting the trigonid at a point lingual to that point directly below the protoconid, but well buccal to the metacristid fissure. The hypocristid extends from the hypoconulid to the tip of the hypoconid. From the base of the metaconid, the endoloph shows a slight lingual incursion of enamel.

In M 3, the trigonid is wider than the talonid. A weak parastylid wraps around the hypoconulid of M 2 and there is a weak anterior cingulum on M 3 (which is stronger than in M 2). The posterior cingulum is as in M 2. A reduced cristid obliqua intersects the trigonid at a point well lingual to the longitudinal vertical midline drawn through the tip of the protoconid, but slightly buccal to the metacristid fissure. There is a minute entoconid. The endoloph of M 3 follows the line of the dentary axis. The rest of M 3 morphology is as in M 2 except that a small crest runs down from the hypoconulid to the beginning of the hypocristid.

In RM 4 (LM 4 is missing), the trigonid is wider than the talonid, which is greatly reduced. Of the three main trigonid cusps, the metaconid is slightly taller than the paraconid but slightly smaller than the protoconid. The hypoconid of the M 4 talonid is the only definable cusp. Between the hypoconid and the base of the metacristid, the cristid obliqua forms a low crest which contacts the trigonid wall just lingual to the metacristid fissure. There is a vaguely discernible entoconic bulge on the endoloph.

Skull. Antechinus bellus is a`Roman-nosed' antechinus - it has a deep rostrum and a premaxilla that is sharply inflected ventrally. The broad zygomata also give it a brachycephalic appearance. Sagittal and nuchal crests are not developed. The rostrum is grooved longitudinally by a depression running along the nasal sutures. The right and left alisphenoid tympanic bullae are narrowly separated and greatly enlarged. The foramen pseudovale are small and not bisected by the inner wing of the entocarotid canal. The eustachian canal opening is minute. The internal jugular canal foramina are large and the canals are raised and very prominent. The posterior lacerate foramina are also large and exposed as are the entocarotid foramina. The premaxillary vacuity extends from the level of the I 2 root back as far as the middle of the C 1 root. The very small maxillary vacuities extend from the level of the protocone root of M 1 back as far as the level of the protocone root of M 3. There are no palatine vacuities. The back of the cranium is smashed on the left side so that half the basioccipital is missing.

Additional diagnostic features. This highly differentiated antechinus is remarkable for the development of its very narrow interorbital width, broad rostrum, relatively wide zygomatic width, widely flaring jugals, short lower premolar row, short posterior palatal vacuities, large alisphenoid tympanic bullae and big ears.

Distribution. Antechinus bellus is restricted to the north wet-dry tropics of the Northern Territory where it is patchily distributed throughout open-forest and woodland of the lowlands ( Friend, 1985).

A. bellus specimens examined. FEMALES: Point Priest, Port Bremer, NT, 11° 13'S 132° 15'E (female CM1119 ) ; Smith Point, Port Essington , Cobourg Peninsula, NT, 11° 07'S 132° 08'E (female CM1136 ) ; West side of Bremer Bay , Cobourg Peninsula, NT, 11° 13'S 132° 15'E (female CM1151 ) ; East side of Bremer Bay , Cobourg Peninsula, NT 11° 13'S 132° 16'E (female CM1155 ) ; East side of Bremer Bay , Cobourg Peninsula, NT 11° 13'S 132° 16'E (female CM1158 ) ; Nourlangie Rock Area, Darwin and Katherine District , NT 12° 51'S 132° 49'E (female CM7088 ) ; 5km NNW of Nourlangie Rock, Darwin and Katherine District , NT 12° 49'S 132° 47'E (female CM7198 ) ; Upper Baroalba Ck , NT 12° 49'S 132° 48'E (female CM7735 ) ; 7km WNW of Koongarra Camp , NT 12° 42'S 132° 49'E (female CM8847 ) ; 9km SSE of Old Kapalga Homestead Site , NT 12° 44'S 132° 51'E (female CM11726 ) ; North side of Bremer Bay , Cobourg Peninsula 11° 08'S 132° 11'E (female CM1150 ) ; East side of Port Bremer , Cobourg Peninsula NT 11° 13'S 132° 16'E (female CM1153 ) ; East side of Port Bremer , Cobourg Peninsula NT 11° 13'S 132° 16'E (female CM1163 ) ; Victoria Settlement, Cobourg Peninsula NT 11° 22'S 132° 09'E (female CM1141 ) .

MALES: Jim Jim Falls , NT 13° 16'S 132° 49'E (male JM2028 ) ; Edward’s Point, Port Bremer , Cobourg Peninsula, NT 11° 11'S 132° 16'E (male CM1012 ) ; Smith Point, Port Essington , Cobourg Peninsula, NT 11° 08'S 132° 09'E (male CM1063 ) ; Victoria Settlement, Port Essington , Cobourg Peninsula, NT 11° 22'S 132° 09'E (male CM1144 ) ; West side of Bremer Bay , Cobourg Peninsula, NT 11° 13'S 132° 15'E (male CM1149 ) ; East side of Port Bremer , Cobourg Peninsula, NT 11° 13'S 132° 16'E (male CM1166 ) ; 6km North-west of Nourlangie Rock , NT 12° 49'S 132° 46'E (male CM7077 ) ; 5km North-west of Nourlangie Rock , NT 12° 50'S 132° 46'E (male CM7213 ) ; 3km North-west of Nourlangie Rock , NT 12° 50'S 132° 47'E (male CM7978 ) ; 7km WNW of Koongarra Camp , NT 12° 42'S 132° 49'E (male CM8846 ) ; 9km South-south-east of Old Kapalga Hospital Site, NT 12° 44'S 132° 51'E (male CM11730 ) ; Smith Point, Port Essington , NT 11° 07'S 132° 08'E (male CM1087 ) ; Port Bremer , Cobourg Peninsula, NT 11° 13'S 132° 15'E (male CM1159 ) ; Smith Point, Port Essington , NT 11° 07'S 132° 08'E (male CM1135 ) ; Port Bremer , Cobourg Peninsula, NT 11° 13'S 132° 15'E (male CM1113 ) ; Port Bremer , Cobourg Peninsula, NT 11° 13'S 132° 15'E (male CM1175 ) ; North side of Bremer Bay , NT 11° 08'S 132° 11'E (male CM1119 ) ; Smith Point, Port Essington , NT 11° 07'S 132° 08'E (male CM1016 ) ; Port Bremer , Cobourg Peninsula, NT 11° 13'S 132° 15'E (male CM1169 ) ; Port Bremer , Cobourg Peninsula, NT 11° 13'S 132° 15'E (male CM1161 ) ; Black Point, Port Essington , NT 11° 09'S 132° 09'E (male CM1025 ) .

Figures

FIGURE 16. Photograph of A. bellus holotype skin specimen: upper (a) and lower (b).

FIGURE 17. A. bellus holotype specimen stereo microscope photographs of skull and dentary: upper above (a), upper below (b), upper side (c) and lower side (d).