Antechinus argentus, Baker, Mutton & Hines, 2013

Baker, Andrew M, Mutton, Thomas Y & Hines, Harry B, 2013, A new dasyurid marsupial from Kroombit Tops, south-east Queensland, Australia: the Silver-headed Antechinus, Antechinus argentus sp. nov. (Marsupialia: Dasyuridae), Zootaxa 3746 (2), pp. 201-239 : 228-231

Description of A. argentus holotype QMJM19966

Pelage: Fur over the whole body is bicoloured with the base approx ¾ of each hair being dark mouse grey and the apical ¼ being the colours described as follows. The fur on the head is pale gull grey, and some hairs are black at the very tip; there are longer guard hairs on the head which are entirely black; thus the overall impression of the colour of the head (and neck) is a grizzled silver. There are some olive-buff hairs introduced on the back of the head and deep olive-buff / fuscous black hairs in front of the ears. The chin hairs are pale gull grey and thus the impression of the head and chin is silver / whitish (and this distinction is particularly obvious in museum specimens stored in spirit). The fur colour on the back changes gradually from grizzled silver on the head and neck, through olive-buff to deep olive-buff on the flanks, rump and upper surface of the tail base. The belly is fur is tilleul-buff; the ventral fur is 5–8 mm long with 7–10 mm long guard hairs. The fur on the upper hands and feet is pale olivebuff to olive-buff. The tail fur colour is bicoloured, darker on top and lighter underneath: the fur on the upper base of the tail is mostly deep olive-buff, changing gradually to mostly fuscous black towards the tip, such that the tail appears to darken noticeably along the length, particularly in the last third. There appears to be a mid-dorsal strip of darker colour that extends along the entire upper tail length and this is caused by a scattering of completely fuscous black and also fuscous black tipped hairs that extend from the rump and along the length of the upper dorsal surface of the tail. The underside of the tail is predominantly light greyish olive at the base, gradually darkening to deep greyish olive at the tail tip; again, on the underside of the tail there is a sparse scattering of fuscous black tipped hairs, slightly darkening the overall appearance, but these are much sparser than the upper tail surface. Thus, the general impression of the tail is that it is subtly bicoloured: at the base deep olive-buff on the top and light greyish olive on the underside and at the tip mostly fuscous black on top and deep greyish olive on the underside. The hairs at the base of the tail are about 3mm long, gradually lengthening to 5–6 mm towards the tip. Guard hairs are 10–15 mm long on the rump and reduce to 6mm on the crown of the head; guard hairs vary in colour from almost entirely fuscous black, to the basal half fuscous black and an almost colourless apical half. Fur of the mid-back is about 9mm long but varies in colour, from the basal band being 6mm long and mouse grey, the medial band olive buff and 2 mm long, and the apical band 1mm long and fuscous black, to other hairs with the basal band being 6mm long and mouse grey and the apical band 3mm long and light greyish olive color. There are striking pale eye rings, broken only at the front and rear of the eye. This is formed by strips of fur above and below the eye that are pale smoke grey at the base and mid length of the hair; some of these hairs are tipped in pale smoke grey and others are tipped in fuscous black. The hairs on the dorsum of the snout and in front of, at rear, and around the eye (surrounding the lighter eye ring) are strongly tipped with fuscous black, thus giving a vague impression of a ‘dark mask’ in these regions.

Vibrissae: there are approximately 25 mystacial vibrissae on each side, the more dorsal fuscous black, ranging to the more ventral almost colourless. Supraorbitals (fuscous black) number 2 and 2; ulna-carpals (colourless) number 2 and 2; genals (fuscous black and colourless) number 4 and 4; submentals (colourless) number 2.

Hindfoot: the interdigital pads (2.20 mm) are separate, enlarged, elongate and striate. The striate hallucal pad is not fused to, and slightly separated from, the elongate, striate post-hallucal pad on each foot, with the appearance of two oval pads, the post-hallucal (3.90 mm) being about 1.5 times the length of the hallucal pad (2.50 mm). The metatarsal pad (3.00 mm) is enlarged, elongate and striate, longer than the hallucal pad, but shorter than the posthallucal pad. Terminal pads of digits are weakly striate on toes 2–5 and more strongly striate on toe 1. Hair on the foot covers the heel and extends diagonally partially across the foot. Granules of varying size (0.2–0.6mm) cover the undersurface of the foot.

Ears: the ears are large with a simple, uncurled supratragus.

Tail: the tail is thin and tapers towards the tip, and is about 10.5mm longer than head-body length.

External Measurements: Body weight 28.90g; head-body length 96.86mm; tail-vent length 107.53mm; hindfoot length 18.41mm; ear length 18.76mm.

Dentition: The skull is intact and in good condition, with only minor tooth wear; the mandibles and their teeth are in similarly good condition, although the right mandible is broken at the point of the posterior P 1 and anterior P 2 junction.

Upper incisors: I 1 is sturdy, procumbent and high-crowned. It is curved and separated from I 2 by a diastema. Left and right I 1 are well separated, but the tips of both teeth are worn. In crown height, I 2 and I 3 are subequal; they are higher than I 4. All upper incisors have buccal cingula, which is more subtle in I 2 than in I 3 and I 4. Of the upper incisors, I 1 and I 3 have weak lingual cingula and there is a posterior lingual cingulum in I 4. I 4 carries no anterior or posterior cusp and its root is narrow, subequal in width of roots of I 2 and I 3.

Upper canines: C 1 is narrow and caniniform with a distinct boundary between root and crown. The buccal cingulum is stronger than the lingual. There is no anterior cusp, but a minute posterior cusp is present.

Upper premolars: A minute diastema occurs between C 1 and P 1, P 1 and P 2, P 2 and P 3. All upper premolars carry strong buccal and lingual cingula. In crown size: P 3>P 2>P 1. Small anterior cingular cusps and posterior cusps occur on P 1 and P 2; P 3 lacks an anterior cusp but exhibits a strong posterior cusp. In occlusal view, P 1 and P 2 crowns are roughly oval in shape; both teeth possess a small post-lingual lobe and P 3 carries a slightly larger medial-lingual lobe.

Upper Molars: M 1: The posterior tip of P 3 touches the parastylar corner of M 1 anterior to, and against, the base of stylar cusp A, which is small. The anterior cingulum below stylar cusp B is short, narrow and complete. Stylar cusp B is moderately well-developed. Stylar cusp C is a worn rudiment. A minute protoconule is present at the base of the paracone apex. The paracone itself is low and worn, about subequal to stylar cusp B. Stylar cusp D is large and rounded, about three times the height of stylar cusp B. Stylar cusp E is a worn rudiment. M 1 shows a very weakly developed posterior cingulum.

M 2: In M 2, the broad anterior cingulum, which contacts the metastylar corner of M 1, tapers abruptly as it progresses down and along the base of the paracrista and degenerates labially, at about the base of the paracone apex. A small protoconule is present at the base of the paracone apex. All stylar cusps A–E are present, but both C and E are minute and rounded and B is small and rounded. Stylar cusp D is moderately well-developed and broadly peaked, but worn at the tip and lower than in M 1. There is a poorly developed posterior cingulum that degenerates at the base of the post-protocrista. The post-protocrista is well developed and peaked.

M 3: In M 3, the broad anterior cingulum, which contacts the metastylar corner of M 2, tapers abruptly as it progresses down and along the base of the paracrista and degenerates labially, just buccal to the base of the paracone apex. A very small and rounded protoconule is present at the base of the paracone apex; the protoconule in M 3 is smaller than in M 1 which in turn is smaller than in M 2. Stylar cusps A–D are present, but C is minute and broadly rounded; stylar cusp E is absent. Stylar cusp D is well-developed and peaked, about 2/3 size of cusp D in M 2, which in turn is slightly smaller than cusp D in M 1. The posterior cingulum is very weakly developed. The post-protocrista is well developed and broadly rounded.

M 4: In M 4, the metastylar corner shows no development. The broad anterior cingulum is just complete and tapers gradually such that it degenerates labially, about level with the base of the paracone apex. There is no posterior cingulum. The protocone is reduced and moderately narrow, less than half the width of that in M 3. The post-protocrista is weakly developed and broadly rounded.

Skull: The dorsal surface of the rostrum is not entirely flat but exhibits some longitudinal mid-line swelling halfway along the length of the nasals. The left and right alisphenoid tympanic bullae are moderately widely separated and only moderately enlarged. The foramen pseudovale is large and not bisected by a bridge of the alisphenoid. The eustachian canal opening is moderately large. The internal jugular canal foramina are relatively large, the canals are slightly raised. The posterior lacerate foramina are much larger and exposed, and the entocarotid foramina are small. The anterior palatal vacuities extend from the posterior end of the I 2 root and terminate at the level of the posterior root crown of the upper canine teeth. Posterior palatal vacuities originate at the M 1 paracone and terminate at the level of the M 4 metacone.

Dentary: Lower Incisors: I 1 is greater in crown height than I 2. I 1 and I 2 are oval in anterolateral view and gougelike in occlusal view. I 2 is taller in crown height than I 3. I 3 is incisiform in lateral view with a small posterior cusp at the base of the crest, which descends posteriorly from the apex of the primary cusp; there is a posterior-lingual lobe. There is a narrow gap between the I 3 posterior cusp and the lower canine.

Lower Canines: C 1 is caniniform, broad and characterized by erect projection and curvature from root crown to tip. It has moderate buccal and lingual cingulation and a small posterior cusp.

Lower Premolars: The premolar row is relatively crowded, all premolars are touching each other in the left mandible (in the right mandible, P 3 does not contact M 1 and the condition of contact in RP 1 and RP 2 is uncertain because the mandible is broken at this point): P 1 and P 2 are broadly in contact, such that the anterior edge of P 2 forms a wedge in the posterior of P 1; C 1 just touches P 1, as does P 3 with M 1. P 1-3 are moderately cingulated buccally and lingually. In crown height, P 2 is taller than P 1; P 1 and P 3 are subequal in crown height. Left and right P 3 are double rooted and not transversely aligned in the tooth row. The crown of P 3 possesses a small posterior cusp; P 1 and P 2 possess a broader posterior cusp. All premolars are without anterior cusps. Both P 1 and P 2 are broad, with broadly rounded posterolingual lobing, which is particularly pronounced in P 1.

Lower Molars: M 1: The M 1 talonid is wider than the trigonid. The anterior cingulum is present but only moderately developed, not uniting to form a complete buccal and posterior cingulum. There is a weak buccal cingulum, but it is incomplete at the base of the protoconid. A greatly reduced paraconid appears in occlusal view as a small sub-horizontal spur. The metacristid and hypocristid are roughly oblique to the long axis of the dentary. The cristid obliqua extends from the hypoconid to the posterior wall of the trigonid, intersecting the trigonid at a point well buccal to the point directly below the tip of the protoconid. There is a small, broadly rounded entoconid. From the base of the metaconid posteriorly, the talonid endoloph follows the line of the dentary to the entoconid, but with a buccal orientation, until reaching the base of the hypoconulid.

M 2: In M 2, the talonid is slightly wider than the trigonid. The anterior and posterior cingula are moderate as in M 1 and the moderate buccal cingulum is incomplete at the base of the protoconid. The paraconid is well developed but is the smallest main trigonid cusp, smaller than the metoconid, which in turn is smaller than the protoconid. The entoconid is moderately developed and blade-like, about twice as tall as in M 1. The cristid obliqua extends from the hypoconulid to the posterior wall of the trigonid, intersecting the trigonid at a point directly below the tip of the protoconid but well buccal to the metacristid fissure. The hypocristid extends from slightly anterior and buccal to the hypoconulid to the tip of the hypoconid. From the base of the metaconid posteriorly, the endoloph follows a line of the dentary as in M 1.

M 3: In M 3, the trigonid is just wider than the talonid. A prominent parastylid wraps around the hypoconulid of M 2. The anterior cingulum on M 3 is slightly stronger than that in M 2, and the buccal cingulum is incomplete and posterior cingulum moderate. The paraconid is well developed but the smallest main trigonid cusp, slightly smaller than the metaconid, which in turn is dwarfed by the prominent protoconid. The entoconid is moderately developed and slightly smaller than the entoconid of M 2. The cristid obliqua extends from the hypoconulid to the posterior wall of the trigonid, intersecting the trigonid at a point directly below the tip of the protoconid but well buccal to the metacristid fissure. From the base of the metaconid posteriorly, the endoloph of M 3 follows a line of dentary with no lingual swelling.

M 4: In M 4, the trigonid is wider than the talonid. The anterior cingulum is as in M 2; the buccal cingulum is absent; the posterior cingulum is absent. The metaconid is slightly taller than the paraconid, and both are much shorter than the prominent and sharply peaked protoconid. The weak hypoconid of the M 4 talonid is greatly reduced and a barely definable hump. The entoconid is present but minute and broadly rounded. The cristid obliqua forms a low, weak crest which contacts the trigonid wall directly below the metacristid fissure. A notable feature of M 4 morphology is the reduction of the talonid crown enamel and absence of buccal cingulum below the cristid obliqua, which causes the talonid to appear as a relatively narrow spur jutting off the trigonid wall. From the base of the metaconid posteriorly, the endoloph of M 4 exhibits greater buccal orientation away from the line of the dentary compared with any other lower molar.