Nectomys saturatus Thomas, 1897

Chiquito, Elisandra Almeida & Percequillo, Alexandre Reis, 2019, The taxonomic status of Nectomys saturatus Thomas, 1897 (Cricetidae: Sigmodontinae), Zootaxa 4550 (3), pp. 321-339 : 327-330

Nectomys saturatus Thomas, 1897

Nectomys saturatus Thomas, 1897a:546 . Type locality “Ibarra, N. Ecuador, alt. 2225 metres.”

Nectomys squamipes saturatus: Hershkovitz, 1948:51 . Name combination.

Nectomys apicalis: Musser & Carleton, 2005: 1132 . part.

Holotype: BMNH 97.11 .7.40, a sub-adult male collected by W. F. H. Rosenberg in May 19, 1894 under field number WR90, preserved in skin and skull at The Natural History Museum, London. The skin is well preserved, with the right pinnae with the top broken, the dorsum of the right forefeet damaged, and the tail screwed up in the proximal part and lacking the apical end. The skull and mandibles are also well preserved, with the anterior part of the nasals broken, the left lacrimal is broken, the hemimandibles were separated and glued posteriorly, the angular process and inferior notch are broken in the both hemimandibles, and the right coronoid process broken.

Paratype: BMNH 3.1 .8.3, a sub-adult female collected by W.F. H. Rosenberg in May 19, 1894

Type locality: “Ibarra, N. Ecuador, alt. 2225 metres”, 00° 21’ N; 78° 07’ W (Payter JR, 1993). Ibarra is located in northern Ecuador, at the Ibarra Inter-Andean Basin, where vegetation is characterized by Forest and semideciduous bushland north of the Valles ( Aguirre & Medina-Torres, 2013). According to holotype label, the specimen was “caught in meadow close to city”, and its “native name [is] Piza”.

Distribution: This species is known only for the type locality.

Diagnosis: Mystacial vibrissae long, surpassing the pinnae when laid back; ventral keel of the tail composed only by white hairs; ungual tufts of pes white; hypothenar pad small and fleshy; rostrum very robust (long and wide); interorbital region with supraorbital margins tending to be parallel-sided; interparietal semicircle shaped; molar series very long (8.42 – 8.55 mm); M1 with distinct paralophule.

Morphological description: Head and body large and robust (table 1, figure 6); tail length longer than head and body (105%–116% of head and body length; table1); hindfeet long and robust (26% of head and body length; table 1); pinnae rounded and small (10%–11% of head and body length; table 1). Dorsal pelage long, soft and dense, consisting of short and dense underfur (wool hairs; thin, wavy, short; range 10–11 mm) and longer and lax overfur (guard and cover hairs; thick, long; cover hairs long, range: 13–14 mm; guard hairs sparse and long, range: 19–20 mm). Dorsal body color dark grayish brown finely grizzled with pale yellow. Flanks brown grizzled with pale yellow. Ventral color dark gray orangish, slightly grizzled, and subtly lighter than dorsal pelage. Mystacial vibrissae entirely black, long, surpassing pinnae when laid back. Tail slightly bicolored, covered with brown and short hairs on dorsal surface, and white and long hairs on ventral surface, forming a distinct white ventral keel on the tail; tail scales larger and squares, with about 12 scales/centimeter. Dorsal surface of hind feet gray, covered with short hairs with ½ distal portion white and basal ½ brown; ungual tufts white, absent on digit I and shorter than claws on digits II to V; interdigital webbing present; natatory fringes present on the external lateral margins of pes; ventral surface naked with evident scales, unpigmented, with four small interdigital pads and two tarsal pads (thenar and hypothenar).

Skull large, heavy and robust (table 2; figure 7). Rostrum long, broad, tapering anteriorly, with inflated capsular projection of nasolacrimal foramen; rostrum flanked by wide and moderately deeply excavated zygomatic notches; lacrimal small, mainly contacting the maxillary; interobital region wide, almost parallel sided, with dorsolateral margins with well-developed supraorbital crests, which do not reach the frontal/parietal suture; parietal expanded laterally, with a crest in the suture with squamosal; braincase elongated; interparietal long and wide, semicircle shaped. Zygomatic plate (in lateral view) slightly projected forward, with dorsal free margin straight and anterior margin also straight, inclined anteriorly; zygomatic spine absent. Zygomatic arch robust; jugal welldeveloped. Posglenoid foramen small and narrow; tegmen tympani laminar, do not reach the squamosal; hamular process of squamosal wide and robus, defining a small subsquamosal fenestra; mastoid small and compressed antero-posteriorly, without fenestra. Incisive foramina medium sized, occupying about 64% of length of diastema (table 2), with lateral margins slightly concave and diverging posteriorly, wider posteriorly; posterior margins do not reach the alveolus of M1. Palate long and wide (sensu Hershkovitz, 1962); posterolateral palatal pits numerous and complex, recessed in moderately deep palatal fossae; mesopterygoid fossa wide, with anterior margin squared with a medial notch, reaching the maxillary, but not the alveolus of M3; roof of mesopterygoid fossa perforated by small and narrow sphenopalatine vacuities. Parapterygoid plates wide and robust; posterior opening of alisphenoid canal wide; foramen lacerum medium narrow. Auditory bullae moderately inflated, with Eustachian tube short and wide. Mandible long and deep (figure 7); coronoid process large, triangular; superior notch deep; angular process short, not surpassing the condyloid process posteriorly; inferior notch shallow; capsular process of lower incisor as a small and rounded process.

Upper incisors opisthodont. Molar series (figures 7 and 8) slightly divergent; labial and lingual cusps arranged in opposite pairs; labial flexi, paraflexus and metaflexus, and lingual flexi, protoflexus and hypoflexus, overlap in the median line of the molars; paraflexus and metaflexus oriented obliquely posteriorly. Upper molar range 8.42– 8.55 mm, M1 width range 2.31–2.54 mm.

Anterocone of M1 not divided by the anteromedian flexus, anterocone slightly divided by a shallow and discrete medial valley; anterocone connected posteromedially by the anterior mure and connected postero-labially to the anteroloph by anterostyle; anterostyle well developed. Anteroloph posterior and parallel to anterocone, connected medially to anterior mure. Paracone connected antero-medially by a transversal ridge to protocone and to the median mure, forming a long paraflexus, and connected postero-labially to mesoloph by the mesostyle, mesostyle well developed. Protocone connected anteriorly to anterior mure ans apart from anterocone by protoflexus and from paracone by paraflexus. Mesoloph long, connected medially to median mure and labially to mesostyle; mesoloph separated from paracone by mesoflexus and from metacone by metaflexus; when worn, mesoloph fuses to paracone forming a long and distinct mesofossete. Metacone joining hypocone anteromedially, forming a long metaflexus (or metafosset), and joining posteroloph medially, defining a small posteroflexus (or posterofosset). Hypocone connected anteriorly to median mure and separated from protocone by hipoflexus and from metacone by metaflexus; hypocone connected postero-medially to posteroloph, reaching up to the labial margin of the molar. Posteroloph long. M2 resembling M1, but without anterocone; anteroloph present (unique structure remaining of procingulum). Anteroloph connected anteriorly to protocone, anterior mure absent. M3 with distinct anteroloph, connected to protocone antero-medially. Anterolingual cíngulum absent. Paracone connected antero-medially to protocone and median mure, forming the paraflexus; paracone connected to protocone by median mure, forming medial parafosset. Mesoloph fused to median mure and to paracone. Metacone reduced. Hypocone reduced, hypocone apart from protocone by hypoflexus well excavated. Posteroloph reduced, connected to hypocone.

Lower incisors narrow and long. Lower molar (figure 8) series with lingual and labial cusps positioned in opposing pairs. Anteroconid of m1 undivided by anteromedian flexid, anterior margin of anteroconid rounded. Anterolophid parallel to anteroconid and separated from this by anteroflexid. Anterolabial cingulum well developed, connected to anterior murid. Metaconid and protoconid joined antero-medially to anterior murid; metaconid apart from anterolophid by short metaflexid, and apart from anterolophid by long mesoflexid; metaconid connected to anterolophid. Protoconid separated from anterolabial cingulum by shallow protoflexíd, and from hypoconid by wide and deep hypoflexid; ectostylid absent. Mesolophid connected to median murid and apart from metaconid by deep mesoflexid and joined to entoconid on lingual surface, entofossetid small. Entoconid and hypoconid connecting antero-medially to median murid, and apart by deep posteroflexid. Posterolophid starts from posterior end of hypoconid, and extend to lingual margin of the molar. m2 resembling m1; anteroconid and anterolophid absent. m3 resembling m 2 in size. Anterolabial cingulum present; metaconid and protoconid distinct, apart by mesoflexid; enamel island positioned medially to the hypoconid, possibly remaining from posteroflexid (posterofossetid).

Karyology: There is no information about diploid or fundamental number for this species.