Antechinus arktos, Dyck, 2014

Dyck, Steve Van, 2014, The Black-tailed Antechinus, Antechinus arktos sp. nov.: a new species of carnivorous marsupial from montane regions of the Tweed Volcano caldera, eastern Australia, Zootaxa 3765 (2), pp. 101-133 : 122-124

Description of A. arktos Holotype QMJM20009

Description. HOLOTYPE Queensland Museum JM20009, Female from Best of All Lookout, Springbrook NP (skull and frozen).

Pelage (see Figure 4 ): Colours for the A. arktos holotype are as follows: fur of the mid-back, up to 15 mm long with basal 12 mm Dark Gull Gray, median 1 mm Prout’s Brown and apical 1 mm Fuscous black. The back appears overall to be Prout’s Brown changing markedly to a rich Brussels Brown to Raw Umber on the rump. Guard hairs (medially-thickened) are Fuscous black fading to Sepia; they are very prominent giving an overall shaggy appearance, and up to 25 mm long on the rump, reducing to 8 mm where they terminate at the crown of the head. The head, shoulders and neck are mottled deep olive, dark olive and chaetura black, such that the head and shoulders are distinctly less vibrant than the back and especially the rump. The holotype lacks a head-stripe but there are patches of lighter coloured Dresden brown fur above and below the eye. Above the eye this fur is reduced to a thin line but under the eye it is more extensive extending under the eye, back towards the cheek and to the tips of the hair in front of the ear, on each side of the head. The soft ventral fur, up to 10 mm long on the belly is Dark Gull Gray on the basal 8.5 mm and Pale olive Grey on the apical 1.5 mm. It is interspersed by medially-thickened spines up to 11 mm long. Forefeet and hindfeet are very dark; fuscous black on the upper and lower surface; the underside of both fore and hindfeet are covered in fuscous black pigmented granules, which give it its overall dark appearance. The claws on the forefoot are very long, up to 4.3mm, and slightly longer than the claws on the hindfoot (up to 3.9mm). The tail is very dark, markedly contrasting the rich umber rump; the dorsal surface of the tail is black with a lighter fuscous Black on the underside. The tail hairs are dense, fine and evenly short (2–3mm); at the rump, the Brussels brown / raw umber hairs on the rump are dense, long with long guard hairs and these extend just onto the tail base, but then abruptly terminate after covering 5mm of tail base into the very short-haired, evenly dark tail .

Vibrissae. Approximately 24 mystaceal vibrissae occur on each side and these are up to 22 mm long. All are Fuscous Black in colour. Supra-orbital vibrissae (Fuscous Black) number 2 on the right and 2 on the left; genals (Fuscous Black and colourless) number 6 right and 6 left; ulna-carpals (colourless) number 4 left and 4 right; and submentals (all colourless) number 4.

Tail. The tail is shorter than the head and body. It is thick at the base (6mm) and tapers gradually towards the tip.

Hindfoot. Interdigital pads are separate. The elongate hallucal and post-hallucal pads are separate on both feet. The metatarsal pad is long and oval shaped; all the foot pads are heavily striate. Claws are very long (longest on hindfoot measures 3.9mm; longest on forefoot measures 4.3mm).

Ear. For a large antechinus, the ears are smallish (16.29mm); the supratragus is uncurled.

Dentition (refer Figure 5 ). Upper Incisors. I 1 is broad, triangular with a curved anterior plane, almost two times taller-crowned than all other incisors and is not separated by a diastema from I 2. The flaring crown of I 1, spreading posteriorly as well as anteriorly, does not quite meet the slightly flared I 2 so that the I 1 and I 2 do not quite touch. Left and right I 1 contact to form a cutting "V" and are not markedly procumbent. In crown size I 3 =I 4>I 2. All upper incisors, but for I 4, lack buccal cingula and in I 4 the cingulum is positioned to the mid-posterior of the tooth. There is no lack of differentiation between root and crown. All crowns are long antero-posteriorly and low. I 4 carries no anterior or posterior cusp. The roots of I 4 are wide, slightly wider than I 3 and I 2.

Upper canines: C 1 is fairly slender and caniniform with a slight boundary between the root and crown. There is a very weak buccal cingulum at the anterior of the tooth and no lingual cingulum. There is a minute anterior cusp and a large posterior cusp.

Upper premolars: All premolars are fairly narrow and slender. Diastemata occur between C 1 and P 1, P 1 and P 2 (diastemata equally sized at 0.3mm), P 2 and P 3 (diastema measures 0.05mm) and P 3 contacts M 1. All premolars carry very weak buccal and lingual cingula. In crown size (right and left) P 3>P 2>P 1; P 3 is 1.3 times larger than P 2 but P 1 is only 2/3 height of P 2. Large posterior cusps occur on P 1-3. No upper premolars possess posterolingual lobes, but there is a medial lingual lobe on P 3 formed at the posterior root of the tooth.

Upper molars: The posterior tip of P 3 is positioned in the parastylar corner of M 1 but lingual to and slightly below the minute stylar cusp A. The anterior cingulum below stylar cusp B is short, broad and incomplete. Stylar cusp B is moderately large but smaller than the paracone and there is a small, rounded protoconule present; the paracone is smaller than stylar cusp D, which in turn is much smaller than the metacone. Stylar cusp C is small and stylar cusp E is a worn rudament. M 1 possesses a weak posterior cingulum formed at the base of the postprotocrista and tapering posteriorly to a point level with the base of the post-metacrista; thus the protocone appears subtly broad. The metacone is immediately lingual to, and 1.5 times larger than, stylar cusp D. The line from the metastylar corner of M 1 to the tip of the protocone is slightly indented and the post-protocrista is moderately swollen.

In M 2, the very broad anterior cingulum which contacts the metastylar corner of M 1 tapers quickly as it progresses down and along the base of the pre-paracrista and finally degenerates before meeting the trigon basin. Stylar cusp B is smaller than stylar cusp D, which is slightly smaller than the paracone, which in turn is much smaller than the metacone; the protocone is well defined and about the same height as in M 1; there is a small, rounded protoconule present. Stylar cusp A is low and rounded, stylar cusp C is present, small and rounded but stylar cusp E is a rounded nubbin. M 2 possesses a weak posterior cingulum formed at the base of the postprotocrista and tapering posteriorly to a point level with the base of the post-metacrista; thus the protocone appears slightly broad.

In M 3, the anterior cingulum is subequal in breadth and slightly longer than in M 2. It becomes indistinct after covering 2/3 of the distance between stylar cusp B and the lingual base of the paracone. The protoconule is very low and broadly rounded. Stylar cusp A is very small; stylar cusp B is slightly lower and more rounded than D; these two cusps are smaller than the paracone, which in turn is smaller than the metacone; stylar cusp C forms a clear peak and is slightly larger than the equivalent cusp in M 2 and M 1; stylar cusp E is very small and rounded. M 3 possesses a very weak posterior cingulum formed at the base of the post-protocrista and tapering posteriorly to a point lingual with the base of the post-metacrista.

In M 4, the ectoloph between stylar cusps B and D is fairly straight. The narrow anterior cingulum tapers, forming a very narrow shelf that continues all the way to the base of the pre-protocrista; a posterior cingulum is absent. The protocone is greatly reduced and very narrow; the metacone forms a large and obvious rounded lobe at the posterior of M 4.

Lower incisors: All lower incisors project horizontally from the tip of the dentary. In crown height: I 1>I 2>I 3. I 3 is incisiform in lateral view with a distinct posterior cusp at the base of the crest which descends posteriorly from the apex of the primary cusp. The lower canine rests against this posterior cusp. In occlusal view, I 3 has a very small notch separating the posterior cusp from the prominent posterolingual lobe, and the crown enamel of the primary and posterior cusps fold lingually such that the crest of the two cusps bisects the tooth longitudinally. I 3 has a weak posterior buccal cingulum.

Lower canines: C 1 is premolariform. There is moderate curvature from root to crown tip and the tooth is shortcrowned, only slightly larger than P 2. C 1 has weak buccal and moderate lingual cingulation and a moderate posterior cusp.

Lower premolars: All premolars are elongate and narrow and there are clear diastemata separating P 1 from both C 1 and P 2 only. In crown height: P 2>P 3>P 1, such that P 2 is about 1.2 times the height of P 3 and about twice the height of P 1. All premolars possess distinct posterior cusps, which in P 2 is very long. No premolars possess anterior cusps. The bulk of premolar mass is concentrated anteriorly to the line drawn transversely through the middle of the two premolar roots. Postero-lingual lobes are not features of the lower premolars but a narrow cingulum surrounds each tooth.

Lower molars: All molars are moderately narrow. In M 1, the talonid is wider than the trigonid and no anterior cingulum is present. A narrow, weak posterior cingulum extends from the hypoconulid to the posterior base of the protoconid, with a very narrow posterior buccal shelf. The very narrow paraconid appears in occlusal view as a small, steeply sided spur with an appreciable shelf. The paraconid makes little contribution to the bulk of the ectoloph enamel. The metacristid and hypocristid are oblique to the long axis of the dentary. The cristid obliqua is moderate, about 45 0 and extends from the hypoconid to the posterior wall of the trigonid, intersecting the trigonid at a point slightly buccal to that point directly below the tip of the protoconid. The hypocristid terminates at the buccal base of the hypoconulid. The entoconid is moderate and rounded on the left mandible but worn to a nubbin on the right mandible. From the base of the small, peaked metaconid posteriorly, the talonid endoloph roughly follows the line of the dentary until the base of the hypoconulid, albeit with a slight lingual bulge.

In M 2, the trigonid and talonid are about subequal in width. The anterior cingulum is moderate, originating lingually in a weak parastylid notch into which the hypoconulid of M 1 is tucked. A small buccal cingulum occurs between the trigonid and the talonid; a narrow, weak posterior cingulum extends from the hypoconulid to the posterior base of the hypoconid. The paraconid is well developed, but is the smallest trigonid cusp, with the metaconid larger and protoconid largest. The protoconid is well developed and subequal with the protoconid on M 3. The entoconid is a moderate, well-developed peak. A fairly steep (60 0) cristid obliqua extends from the hypoconid intersecting the posterior wall of the trigonid at a point directly below the tip of the protoconid, which is well buccal to the metacristid fissure. From the base of the metaconid posteriorly, the endoloph roughly follows the line of the dentary axis, with a slight lingual bulge due to the entoconid swelling.

In M 3, the trigonid is wider than the talonid. A very weak parastylid wraps around the hypoconulid of M 2, and the M 3 anterior cingulum is moderate, similar to that in M 2. A small buccal cingulum occurs between the trigonid and the talonid; the weak posterior cingulum is as in M 2. The fairly steep (60 0) cristid obliqua intersects the trigonid at a point slightly lingual to the tip of the protoconid, which is buccal to the metacristid fissure. The entoconid is a moderate, well-developed peak, slightly smaller than that in M 2. From the base of the well-developed metaconid posteriorly, the endoloph of the M 3 talonid takes a slightly more buccal orientation than that seen in M 2.

In M 4, the trigonid is much wider than the talonid. The anterior cingulum is moderate, slightly narrower than in M 3, but the posterior cingulum is absent. A small buccal cingulum occurs between the trigonid and the talonid. Of the three main trigonid cusps, the metaconid is slightly taller than the paraconid but both are markedly smaller than the protoconid. The cristid obliqua forms a shallower (30 0), smaller crest which contacts the trigonid wall directly below the metacristid fissure. Of the talonid cusps, the small hypoconid is the largest cusp. The hypoconulid is very weakly formed and the entoconid is a low, rounded nubbin.

Figures

FIGURE 4. (a–b) Photograph of live A. arktos paratype specimen; (c) underside hindfoot of the holotype specimen; note the dark pigmentation around the granules. Photographs (a–b) are Copyright Gary Cranitch (Qld Museum); photograph (c) is Copyright Harry Hines.

FIGURE 5. A. arktos holotype specimen photographs of skull and dentary (a–f): a. skull, top view; b. skull, bottom view; c. skull, side view; d. dentary, top view; e. dentary, bottom view; f. dentary, side view. Photographs are Copyright Andrew Baker.