Microcavia jayat, Teta & Ojeda & Lucero & D’Elía, 2017

Teta, Pablo, Ojeda, Ricardo A., Lucero, Sergio O. & D’Elía, Guillermo, 2017, Zavreliella shidai Han & Liu & Luo & Tang 2021, sp. n., Zoological Studies 56 (29), pp. 1-18 : 12-14

Microcavia jayat n. sp.

( Figs. 3-6 , 9-10 ) LSID: urn:lsid:zoobank.org:pub:7582C06E-83EB-4458-BA58-F19E092ACE67

Microcavia australis salinia : Cabrera, 1953:29; part, not Thomas, 1921.

Microcavia australis salinia : Cabrera, 1961:571; part, not Thomas, 1921.

Microcavia australis : Quintana, 1996:67; part, not Thomas, 1921.

Holotype: An adult female [f] preserved as skin and skull ( MACN-MA 17331 ; figures 9 and 10), and collected on 21 October 1969 by Abel Fornes and Merle L. Kuns (original field number CAF 3070 ).

Paratype: An adult male [m] preserved as skin and skull ( MACN-MA 17333), and collected on 21 October 1969 by A. Fornes and M. Kuns (original field number CAF 3072).

Type locality: Argentina: Santiago del Estero, Pellegrini, Santa Isabel (26°20'S, 64°20'W).

Additional material (localities arranged by increasing latitude): MACN-Ma 17330 [f], MACN- Ma 17332 [f], MACN-Ma 17334 [f], MACN-Ma 17335 [f], MACN-Ma 17336 [f], MACN-Ma 17337 [f], MACN-Ma 17338 [f], MACN-Ma 17339 [f], MACN-Ma 17340 [f], MACN-Ma 17341 [f], MACN- Ma 17342 [f], MACN-Ma 173441 [f], skins and skulls from Santa Isabel, Santiago del Estero; MACN-Ma 36.957, fluid preserved specimen from Cañada de La Costa, Santiago del Estero (27°33'S, 64°52'W); MACN-Ma 28.157 [f], skin and skull from Herrera, Santiago del Estero (28°23'S, 62°20'W); and MACN-Ma 42.96 [f], MACN-Ma 42.97 [f], fluid preserved specimens from Tacañitas, Santiago del Estero (28°37'S, 62°36'W).

Etymology: This species is dedicated to J. Pablo Jayat, a close friend and colleague that in an ongoing productive career is the author of important contributions towards the characterization or the mammal fauna of northern Argentina. The name is a noun in apposition.

Measurements of the holotype (in mm): Total length, 195; hindfoot length (with claw), 32; ear length, 18; TLS 45.22; CIL, 41.04; IOC, 10.50; ZB, 27.54; BB, 20.26; NL 13.56; NW, 6.73; FL, 18.00; DL, 11.6; BIF, 2.94; LIF, 5.98; TRL, 10.42; PL, 19.22; BPP, 15.95; BPM 3, 11.12; TBL, 11.25. Body mass of the holotype, 60 g.

Diagnosis: A medium-size species of Microcavia (length of head and body ca. 187 mm, condiloincisive length ca. 40 mm) having the following unique combination of characters traits: dorsal coloration is yellowish brown, whereas ventral coloration is grayish with patches of pure white hairs on throat, and inner sides of the fore and hindfeet, and the inguinal region; skull strongly built, wide and relatively short; dorsal profile moderately bowed; outer borders of nasals almost parallel-sided; zygomatic arches widely expanded and angled towards its middle portion and with a conspicuous paraorbitary process; jugals posteriorly extended behind the border of the glenoid fossa; suture between palatines occupied by heart-shaped palatal cristae that surpass the posterior border of the palate which is nearly trapezoidal; small sphenopalatine vacuities and relatively broad presphenoids; incisors slightly proodont to orthodont although not visible from above.

Distribution: Microcavia jayat is restricted to the thorn-scrub forests of the Dry Chaco ecoregion in the province of Santiago del Estero in north-central Argentina. However, it is likely that the range of M. jayat extends to the dry Chacoan forests of the nearby provinces of Salta, Chaco, Cordoba and Santa Fe. Moreover, it is possible, that the specimens referred by Contreras (1966) to M. a. salinia, from Tostado, Santa Fe (29°14'S, 61°46'W), for which no vouchers are available, as well as other populations from Santiago del Estero (e.g., Choya; 28°29'S, 64°51'W; see Quintana 1996), are also referable to this species.

Morphological description: Microcavia jayat is smaller than M. maenas and comparable in size with M. australis . Its pelage is fine and slightly hispid; individual hairs are yellowish at the base and brownish at the tip on the dorsum and head and yellowish with two or three brownish bands on the flanks, giving a general yellowish brown appearance, darker and brownish on the midline and head; ears are small and covered by short grayish hairs; a patch of whitish hairs is found behind the ears; eyes are large and are surrounded by a ring of whitish hairs; vibrissae are brownish and fine; manus and pes are covered by yellowish brown hairs; ungual tufts are short on frontclaws and large on hindclaws, but do not surpass the tip of claws; ventral hairs have brownish gray to dark gray bases and whitish distal tips; a “tie” of dark gray hairs is present on the neck; patches of pure white hairs, more or less conspicuous, are present on throat and the internal side of forelegs and sometimes in hindlegs and the inguinal area; palmar and plantar surfaces are dark brownish; plantar surface is squamated, covered by three large, partially fused, interdigital pads and one large thenar pad.

The skull is strongly built, its dorsal profile is moderately bowed; the rostrum is short and relatively narrow; the nasals are slightly vaulted anteriorly, with their outer margins nearly parallel; the naso-frontal suture forms a “ V ” widely open; the fronto-parietal suture is straight; the interorbital constriction is broad and flat; the orbits are large and rounded; the upper zygomatic process of the maxilla is extended as a plate over the rostrum; the lachrymals are partially interposed between the maxilla and premaxilla; the masseteric fossa of the zygomatic arch is deep and well defined; a conspicuous paraorbitary process is present; the jugal is posteriorly extended beyond the border of the glenoid fossa; the posterior process of the squamosal is straight; the posterior margin of the upper diastema is not vertical; the incisive foramina are nearly triangular in outline, with rounded margins in its posterior border; the palate is concave, with the palatine bones occupying the posterior half of the palate; the suture between palatines is occupied by heart-shaped palatal cristae that surpass the posterior border of the palate; the posterior margin of the palate is nearly trapezoidal in outline; the parapterygoids are large; the roof of the mesopterygoid fossa is well ossified, with small sphenopalatine vacuities along the presphenoid; the limit between the mastoid and paraoccipital process is at the same level of the auditory meatus; the occipital condyles are ovate and large and positioned above the ventral surface of the auditory bullae; the tympanic bullae are voluminous, with its external auditory meatus relatively short; the paraoccipital apophyses are short.

The mandible is low and slender; in labial view, the notch for the insertion of the tendon of the masseter medialis pars infraorbitalis muscle lies between the p4 and m1; this notch is continued by a horizontal crest that extends anteriorly to the level of the anterior lobe of m1; the dorsal fossa of the horizontal crest is deep; the lateral crest originates at the level of the m1 and is horizontal; the coronoid process is small and triangular and is oriented backwards; the condyloid process is level with or slightly higher than the coronoid.

The upper incisors are orthodont to proodont, with white enamel; the upper toothrows are anteriorly convergent, with the P4s almost in contact by its medial side; the P4 and M1-M2 are constituted by two lanceolated prisms of dentine, surrounded by a continuous wall of enamel and linked by small enamel isthmus; the lingual apex of each prism is slightly turned backwards; those lobes of the P4 are narrow than those on M1- M2 which are subequal in size; the hipoflexus on M1-M3 is long, with its borders nearly parallel along most of the teeth and slightly divergent to the lingual portion; the primary external flexus on M1-M3 is short and wide; the M3 has a rounded to drop-shaped enlargement, attached to the second prism; the p4 is smaller than m1-m3 both anteroposteriorly and transversely. The anterior lobe of p4 is obliquely oriented and heart-shaped, with a well developed anterior projection; the posterior lobe is more narrow and shorter than the posterior lobe of the molars; the anterior lobe on m1-m3 is more lanceolate than the posterior lobe; hypoflexid on m1-3 is funnel-shaped and wide, with a rounded lingual apex; primary internal flexids are wide and slightly oriented posteriorly.

Variation: Ventral coloration is variable among individuals, with a gradient from dark gray to whitish. At least two individuals (MACN- Ma 28.157, MACN-Ma 17340) have a markedly brownish dorsal coloration, as is usually seen in M. australis . White patches on throat, internal side of the fore and hindfeet and inguinal region are very conspicuous in some specimens (e.g., MACN-Ma 17332, 17334, 17338), but weakly expressed in others.

Morphological comparisons: Morphological differences between M. jayat n. sp. and M. australis and M. maenas were discussed under the results section. In M. niata the skull is strongly bowed, with a very short and high rostrum (upper diastema length <upper toothrow length), and has a curved posterior process of the squamosal. M. shiptoni has proportionally smaller tympanic bullae, with proportionally larger external auditory meatus and the additional prism in the upper third molar is smaller. Both in M. niata and M. shiptoni the upper incisors are proodont and visible from above. M. jayat n. sp. differs from the fossil species M. chapadmalensis , M. criollensis , M. reigi , and M. robusta by its much smaller size (length of tootrow ca. 11 mm vs. 12-18 mm in fossil species; q.v., Ubilla et al. 1999) and less robust cranium.

Natural History: We know very little about the natural history of this species. The specimens referred to M. jayat were collected in the Dry Chaco ecoregion. The Dry Chaco is characterized by thorn scrub xerophytic forest vegetation dominated by Aspidospermum quebracho-blanco and Schinopsis quebracho with a subcanopy made up of several species of Fabaceae and arboreal cacti. Wooded areas are intermixed with open savannas, mostly dominated by grasses, shrubs, and trees. The weather is subtropical, strongly seasonal, with a dry season during winter months and high temperatures during the entire year; the mean annual temperature is 21.5°C, with maxima reaching 50°C; precipitation are in the order of 700 mm per year ( The Nature Conservancy 2005).

Conservation: Given the current knowledge, this species could be listed as Data Deficient, since it is only known from <10 localities and most of the aspects of its natural history are unknown. The Dry Chaco has been under severe perturbation due to logging and livestock grazing and during recent agricultural expansion (mostly due to increased soybean crops; Vallejos et al. 2015). For example, deforestation in Argentinean Dry Chaco amounted to an average of 100,000 hectares per year between 2001 and 2007. As a corollary of all of these activities, the Dry Chaco faces severe problems of desertification and erosion of its soils ( The Nature Conservancy 2005).

Figures

Fig. 3. Dorsal (A-C) and ventral (D-F) views of the skull of three species of Microcavia: M. australis (A, D; MACN-Ma 14.543), M. maenas (B, E; MACN-Ma 34.116) and Microcavia n. sp. (C, F; MACN-Ma 17333). Scale bars = 5 mm.

Fig. 4. Lateral views of the skull and right dentaries in labial views of three species of Microcavia: M. australis (A; MACN-Ma 14.543), M. maenas (B; MACN-Ma 34.116) and Microcavia n. sp. (C; MACN-Ma 17331). Scale bars = 5 mm.

Fig. 5. Selected anatomical traits of three species of Microcavia (A, MACN-Ma 16379; B, MACN-Ma 34.81; C, MACN-Ma 17331; D, MACN-Ma 16379; E, MACN-Ma 36.72; F, MACN-Ma 17333; G, MACN-Ma 28.51; H, MACN-Ma 36.84; I, MACN-Ma 17331), depicting the relative position of inferior process of the jugal (marked by the arrow) relative to the glenoid cavity (a-c) and size and shape of the palatal cristae (d-i). A, D, G = M. australis; B, E, H = M. maenas; C, F, I = M. n. sp. Abbreviations: gc = glenoid cavity; jf = jugal fossa; mpp = medial process of the palate; pc = palatal crista; sq = squamosal. Photographs are not in scale to facilitate comparisons among proportions.

Fig. 6. Selected anatomical traits of three species of Microcavia (A, MACN-Ma 14543; B, MACN-Ma 36.72; C, MACN-Ma 17331; D, MACN-Ma 25.51; E, MACN-Ma 36.84; F MACN-Ma 17333), depicting the contour of the posterior border of the palate and size of sphenopalatine vacuities (epv). Abbreviations: fo = foramen oval; pc = palatal crista; ps = presphenoid; pt = pterygoid. Photographs are not in scale to facilitate comparisons among proportions.

Fig. 9. Dendrogram of unweighted pair-group method of averages of Mahalanobis distances among 10 geographic samples of Microcavia. For the acronyms see Materials and Methods.

Fig. 10. Holotype of Microcavia jayat n. sp., from Santa Isabel, Santiago del Estero, Argentina (MACN-Ma 17331): skull in right lateral (above), dorsal (below, left) and ventral (below, right) views, and left dentary (reversed) in labial view. Scale bars = 5 mm.