Phyllotis andium Thomas, 1912

Rengifo, Edgardo M. & Pacheco, Víctor, 2015, Taxonomic revision of the Andean leaf-eared mouse, Phyllotis andium Thomas 1912 (Rodentia: Cricetidae), with the description of a new species, Zootaxa 4018 (3), pp. 349-380 : 363-366

Phyllotis andium Thomas, 1912

Andean Leaf- eared Mouse

Phyllotis andium Thomas (1912: 409) Phyllotis melanius Thomas (1913:407) Phyllotis fruticicolus Anthony (1922:1)

Holotype. Adult male, British Museum 99.9.9.68 collected 18 April, 1899 by Perry O. Simons.

Type locality. Cañar, [Cañar,] Ecuador. Alt. 2600 m

Distribution. From Baños, Tungurahua, Ecuador throughout the Andes to Ambo, Huánuco, Peru, 870–4388 m elevation (see Fig. 13 ).

Measurements. External and craniodental measurements are presented in Table 2 .

Emended diagnosis. Phyllotis andium is a medium sized rodent (average = 226.84 mm in total length) with relatively short ears (21.30 mm) in comparison to other congeners; tail slightly longer than head and body length, with a poorly developed pencil; pectoral streak present, but barely conspicuous; the condyle-incisive length is 25.40 mm in average; short rostrum; fronto-nasal suture aligned with the fronto-premaxillary suture; interorbital region narrow, with a supraorbital margin that is sharply edged; orthodont upper incisors; maxillary palatal pits close to the incisive foramen, or at the middle of the maxillary portion of the palatine; small and undivided procingulum on M1 ( Fig. 9 ).

Description. The dorsal pelage is composed of rich-brow hairs that have neutral grey at the base, the dorsal band on the dorsum is inconspicuous; the hairs are dense and long and average 13 mm over the rump; the ventral pelage is whitish with a short grey basal band followed by a white band; a pectoral streak is present but barely conspicuous. The pinnae are comparatively short in comparison to congeners; the auricular patch is inconspicuous; an orbicular ring is absent. The genal, superciliary, submental, interramal and mystacial vibrissae are present; the mystacial vibrissae reach the posterior border pinna when laid back against head. The tail is barely longer than the head and the body together (± 119.86 mm). It is dimly bicolored, dark above and pale neutral gray below and both the dorsum and venter are furred; the hair along the shaft extends over more than 2 rows of scales. The dorsal surface of the manus is covered with fine white hairs and the ungual tuft is present but not very dense. The margin of the ventral surface of the claws is closed at the base. The III pad is above the II and IV pads and the hypothenar is longer than the thenar. The metacarpal patch is absent. The pes is slender and elongate, with white hair on the dorsal surface, and a scarce ungual tuft; the heel is furred. Six small plantar pads are present. The hypothenar is behind IV pad and it is smaller than the thenar, though both are separated by a gap; the plantar surface among the pads is squamated. The metatarsal patch is absent. Digit I is the shortest and digit V is smaller than II, III and IV digits.

The skull profile is convex and slightly more swollen in the interorbital region ( Fig. 9 ). The rostrum is short. The nasolacrimal capsule is moderately broader than the anterior portion of the rostrum (in the dorsal view). The nasal is conical and long and anteriorly it is broad; in the lateral view it projects anterodorsally beyond the premaxillae and the anterior border of the incisors. The fronto-nasal suture is aligned to the fronto- premaxillary suture; the premaxillary-naso-frontal joint is anterior to the maxillary-fronto-lacrimal joint. The premaxillary is short and narrow; it projects slightly anteriorly to the plane of the incisors. The zygomatic plate is moderately broad with a vertical dip and the anterodorsal spinous process is absent; the zygomatic notch is deep; the infraorbital foramen is narrow; the superficial masseteric origin is small but conspicuous; the antorbital bridge lies below the dorsal surface of the rostrum and it overlaps slightly and is connected to the lacrimal. The zygomatic arch has parallel-sides, which are slightly convergent anteriorly; the zygomatic process of the maxillary is narrow; it is barely wider than the antorbital bridge; the jugal is long and very thin. The interorbital region is narrow and moderately concave, the molar bases are visible from the dorsal view; the supraorbital margin has sharp edges; the lacrimal is large and projects over the antorbital bridge. The frontal bone is moderately narrow (in the dorsal view) and slightly swollen (in the lateral view) and it doesn't have have a medial depression. The braincase is rounded and the fronto-parietal suture is slightly serrated and convex; the parietal edge (on the squamosal-parietal suture) is smooth; the interparietal is small with a trapezoid-shape and both the interparietal-parietal and interparietalsupraoccipital sutures are dentate. The palatal region is long and narrow. The incisive foramen is long and narrow with parallel margins, extending to the M1 alveolus. The premaxillary portion of the septum builds a medial ridge overlapping on the vomer; the maxillary portion of the septum is moderately thin. The bony palate is moderately wide and long, extending behind the posterior plane of M3. The maxillo-palatal suture is dentate. The palatal lateral grove is shallow. The maxillary palatal pit is placed close to the incisive foramen or in some cases at the middle of the maxillary portion of the palatine. The posterior palatine foramen is very small. The posterolateral palatal pit is small and placed anterior to the mesopterygoid fossa. The mesopterygoid fossa is narrow and square-shaped with parallel sides. The palatal process is absent. The sphenopalatine vacuities are large and reach halfway to the basisphenoid. The presphenoid is present but thin. The parapterygoid fossa is triangular and wide, but with inconspicuous or absent vacuities. The parapterygoid process is long and projected outside. The middle lacerate foramen is moderately open. The alisphenoid strut is absent. The anterior opening of the alisphenoid canal is smaller than the buccinator-masticatory and foramen ovale joint. The ethmoid foramen is small and is placed dorsal to M2. The ethmoturbinals are moderate in size and smaller than the sphenopalatine foramen. The sphenopalatine foramen is large with an ovoid shape and bounded by the palatine bone; the optic foramen is very large with a halfmoon shape. The orbitosphenoid is large and overlaps M3 barely or borders M3. The carotid circulation corresponds to the “primitive” condition (sensu Voss 1988) with a large stapedial foramen, a distinct squamosalalisphenoid grove, and a wide sphenofrontal foramen; the internal carotid is large and bounded by both the basioccipital and the ectotympanic portion of the auditory bulla. The auditory region is formed by moderate-sized ectotympanic bullae. The tegmen tympani overlaps the posterior suspensory process of the squamosal, it has a sinuous groove; the ectotympanic ring is closed and the dorsal margin of the ectotympanic extends to make contact with the petrosal. The bony Eustachian tube is long; it exceeds or is at same level of the anterior margin of the middle lacerate foramen, in some cases it contacts the parapterygoid process. The anterior process of the ectotympanic (stapedial spine) is moderate-size. The malleus and incus are exposed in the lateral view. The lamina of the malleus is square shaped with a long and thin manubrium parallelly orientated, and it has a well-developed and large orbicular apophysis. The processus brevis of incus is conspicuous have a rounded base and knob-like tip. The cephalic process of the malleus exhibits a thin crest. The postglenoid foramen is smaller than the subsquamosal fenestra; the hamular process of the squamosal is moderately broad and reaches the mastoid bone. The lambdoid ridge is absent. The basioccipital is narrow with a trapezoid-shape; it shows a medial spine that extends to the basioccipital—basisphenoid suture. The mastoid (the periotic capsule of the petrosal) is squared-shape with an open mastoid fenestra and a conspicuous mastoidoccipital opening. The occipital condyle is not evident in the dorsal view; the paraoccipital process is small.

The ventral margin of the mandible is slightly concave; the diastema is short with a weakly acute angle formed by the root of m1. The superior and inferior masseteric crests converge anteriorly forming a smooth crest that extends to the anterior edge of m1. The mental foramen is high and positioned on the dorsal surface of the diastema. The capsular process is present but small. The coronoid process is small but is level with the condyle process, forming a shallow sigmoid notch. The condylar process is rounded and is level with the angular process which has a deep angular notch.

The Upper Incisor has an orthodont orientation; the tips are rounded without incisor groves; the wear surface of the upper incisor face is flat and faces backwards. The tooth topography is determined as having a tetralophodont dental pattern; it has a flat crow (lightly hypsodont); the cusp arrangement on M1 is intermediate and on m1 it is alternate; the toothrow has a parallel orientation. The alveolus of M1 is placed anterior to the incisive foramen and slightly behind the posterior margin of the zygomatic plate. The procingulum of M1 is small and undivided; the paraflexus has a triangular shape, and it is sunken in to cover half of M1; the paraflexus and metaflexus are wider than the protoflexus and hypoflexus; the paracone and metacone are slightly narrower than the protocone and hypocone. The M2 has an “S” shape; the hypoflexus is slightly deeper and narrower than the metaflexus; the paraflexus is distinctly deep (viewed in juvenile specimens, so superficial wear is not evident). The M3 is smaller than the M2. The m1 has a procingulum that does not show an anteromedian flexid and is smaller than the metaconid, and equal to or larger than the protoconid; the metaflexid is small or slightly deep. The m2 has an inconspicuous protoflexid. The m3 is smaller than the m2.

Variation. In general P. andium preserves the same phonotypic characteristics throughout its all distribution, but as many widely distributed species, we found s ome variability in morphological characters among populations; the maxillary palatal pit in all specimens from Ecuador and in some specimens (less than 50%) from northern Peru is located close to the incisive foramen whereas all specimens from the reaming of distribution it is located in the middle of the maxillary portion of the palatine; the bony Eustachian tube is long in almost all of the individuals (more than 90%), but it is very long and makes contact with to the parapterygoid process in all specimens from La Libertad, Peru; the metaflexid of M1 is small in specimens from Ecuador and northern Peru (Piura-Lambayeque) but it is deeper in specimens from southern Huancabamba. Additional genetic and molecular studies are needed to interpret this variation.

Natural history. The knowledge about this species is scarce; it inhabits the Andean Paramos and the Andean subtropical forest and appears to be common ( Tirira 2007).

Remarks. Two names are synonymous of P.andium : melanius and fruticicolus . P. melanius was described by Thomas (1913), however, this name was erroneously assigned to the skull of P. andium and the skin of Akodon aerosus . We reviewed the type of P. fruticicolus of Anthony, 1922 and confirmed that it corresponds to young specimens mentioned by Pearson (1958) in his revision.

Figures

FIGURE 9. Dorsal, ventral and lateral views of the cranium and the mandible of Phyllotis andium (MUSM 24754).

FIGURE 13. Illustration map showing the distribution range of Phyllotis andium, Phyllotis. stenops, and Phyllotis occidens sp. nov.