Dushimys larsi, Zijlstra, Jelle S., 2012

Zijlstra, Jelle S., 2012, A new oryzomyine (Rodentia: Sigmodontinae) from the Quaternary of Curaçao (West Indies), Zootaxa 3534, pp. 61-68 : 62-65

Dushimys larsi , sp. nov.

Synonymy. Oryzomys sp. (Duivelsklip S.): De Buisonjé, 1974:185, 216

Holotype. RGM 592830, an isolated right m3 ( Fig. 1 f).

Paratypes. 3 M1s ( RGM 592814–592816); 2 M2s ( RGM 592817–592818); 1 M3 ( RGM 592819); 5 m 1s ( RGM 592820–592824); 3 m 2s ( RGM 592825–592827); 2 m 3s ( RGM 592828–592829).

Type locality. Cave-filling on the eastern part of Duivelsklip (coded C3-171), Curaçao, West Indies.

Diagnosis. As for the genus.

Etymology. Named after Lars W. van den Hoek Ostende, my mentor and supervisor at the Netherlands Centre for Biodiversity Naturalis, in recognition of his many important contributions to mammalian paleontology. For many years, Lars has supervised my research on rodents from the Antilles and elsewhere at Naturalis and helped me in numerous ways.

Description. M1 (n=3).— Cusps opposite. Anterocone complex, with distinct anterolabial and anterolingual conules divided by central anteromedian fossette and connected along anterior margin of molar. Anterolingual conule almost opposite to anterolabial conule. Anteroloph forms posterior border of anteromedian fossette, most distinctive at labial side. Anteroflexus present between anteroloph and anterolabial conule. Anterior mure connects middle of anteroloph to protocone. Paracone connected to anterior protocone and to middle of mesoloph (2). Median mure connects protocone to hypocone. Mesoloph long, reaching labial margin. Posteroloph strong, connected to hypocone. Metacone connected to middle of posteroloph (2/2). Labial cingulum present. One anterior, two posterior roots; accessory labial rootlet absent (3/3).

M2 (n=2).— Anteroloph present. Protoflexus present. Paracone connected to protocone and also to middle of mesoloph (1). Median mure connects protocone to hypocone. Mesoloph long, reaching labial margin. Posteroloph strong, connected to hypocone. Metacone connected to middle of posteroloph. Labial cingulum present but weak. One lingual, two labial roots.

M3 (n=1).— Anteroloph present. Paracone connected to anterior protocone. Median mure connects protocone to hypocone. Hypoflexus distinctive but small. Hypocone does not extend anteriorly at lingual margin. Mesoloph present. Metacone and posteroloph not distinct; a narrow ridge is present along the posterolabial margin from the hypocone to the labial end of the mesoloph. Labial cingulum strong. Two anterior, one posterior roots.

m1 (n=5).— Anteroconid bifid, with anterolabial and anterolingual conulids attached to diagonal ridges running toward anterior mure; anteromedian flexid reduced to fossettid by connection between anterolabial and anterolingual conulids at anterior margin (3) or present (2). Additional anterior-posterior ridge across anteromedian fossettid absent (4). Anterolabial cingulum present. Anterolingual cingulum present. Anterior murid connects middle of anteroconid to protoconid. Metaconid connected to anteroconid lingually of anterolingual cingulum, but not to protoconid (3). Median murid connects protoconid to hypoconid. Mesolophid present, reaching lingual margin. Ectostylid present. Posterolophid present, strong, connected to hypoconid. Entoconid narrowly (4) or broadly (1) connected to mesolophid and connected to hypoconid (3). Lingual cingulum present, but mesoflexid and posteroflexid (4) open. One anterior, one posterior root; accessory labial rootlet present.

m2 (n=3).— Anterolabial cingulum present. Anterolophid absent. Protoconid and metaconid connected at anterior margin. Median murid connects protoconid and hypoconid. Mesolophid present, reaching lingual margin. Ectostylid present. Posterolophid present, strong, connected to hypoconid, oriented at an angle of about 45° to axis of tooth. Entoconid connected to median murid slightly anterior to hypoconid and connected to mesolophid. Lingual cingulum present. Two anterior, one posterior roots.

m3 (n=3).— Anterolabial cingulum present. Anterolophid present (2). Protoconid and metaconid connected at anterior margin. Median murid connects protoconid to hypoconid via entoconid, mesolophid absent. Hypoflexid line-shaped, not distinctly broader at lingual margin than at middle of molar. Ectostylid present. Posterolophid present, strong, connected to hypoconid, continuous with lingual cingulum. Lingual cingulum present. At least one anterior and one posterior root; whether there are one or two anterior roots could not be determined.

Measurements. Holotype (m3): length 1.39 mm, width 1.17 mm. See Table 1 for further measurements.

Molar n Length Width

Min. Mean Max. SD Min. Mean Max. SD M1 3 2.39 2.42 2.44 0.03 1.47 1.55 1.61 0.07 M2 2 1.65 1.68 1.71 0.04 1.27 1.37 1.47 0.14 M3 1 1.21 1.12

m1 5 2.00 2.11 2.20 0.07 1.23 1.30 1.39 0.07 m 2 3 1.59 1.62 1.64 0.07 1.26 1.33 1.39 0.07 m 3 3 1.39 1.56 1.73 0.17 1.17 1.24 1.29 0.06 Comparisons and dicussion. Conditions in the taxa compared to are between parentheses. Among other oryzomyines from the ABC islands, Dushimys larsi differs from Oryzomys gorgasi ( Fig. 2 ) in having no accessory labial root on M1 (accessory labial root present; Voss and Weksler 2009); m2 three-rooted (two-rooted); m3 mesolophid absent (present); and having broader lower molars. The following measurements were obtained from specimens of O. gorgasi in the RGM (compare measurements of D. larsi in Table 1): length 2.02 mm, width 1.09 mm in an m1 from Savonet, Curaçao; length 1.52 mm, width 0.99 mm and length 1.42 mm, width 1.01 mm in two m3s from Tafelberg Santa Barbara, Curaçao. The difference in m3 width is statistically significant at the 95% confidence level (t = 5.0951; p = 0.0146). In the central lingual portion of the m3, O. gorgasi has two crests connecting the median murid with the lingual cingulum, corresponding to the entoconid and the mesolophid, but D. larsi has only one ( Figs. 1 , 2 ). On the basis of its position, the crest in D. larsi is most likely the entoconid; thus, I describe the m3 mesolophid as absent.

Dushimys larsi differs from “ Megalomys ” curazensis in having m1 with only a labial accessory root (with lingual and labial accessory roots); m2 with three roots (two roots); non-interpenetrating M1 and M2 flexi (interpenetrating); paracone connected to anterior part of protocone (to posterior protocone); anteroflexid absent on m2 and m3 (present); and in being much smaller (e.g., m3 length of 1.90 to 2.38 mm and width of 1.45 to 1.87 mm in a series of M. curazensis from Duivelsklip, the type locality). The new taxon differs from both species of Agathaeromys in lacking an anteromedian flexus on M1 (present) and in possessing an anterolophid and anterolabial cingulum on m3 (absent). In addition, it differs from A. praeuniversitatis in having m2 with three roots (two roots); m1 anteroconid with anteromedian fossettid (without anteromedian fossettid or flexid); and in being larger (m3 length is 1.12 to 1.16 mm and width is 0.82 to 0.91 mm in A. praeuniversitatis ; Zijlstra et al., 2010: table 4). It also differs from Agathaeromys donovani in lacking a metaloph on M3.

Among other oryzomyine genera recovered close to Dushimys in the phylogenetic analysis (see below), it differs from Oryzomys in lacking an accessory labial root under M1, an anterolophid on m2, and a mesolophid on m3. Differs from Cerradomys in having M1 without labial accessory root; m1 three-rooted (four-rooted); m2 threerooted (two-rooted). Differs from Sooretamys in having m2 three-rooted (two-rooted); M1 anterocone divided by anteromedian fossette (undivided); M1 protostyle absent; and m1 ectolophid and ectostylid absent (descriptions and figures in Weksler, 2006; Percequillo et al., 2008).

Figures

FIGURE 1. Type series of Dushimys larsi. All teeth are figured as if they were from the left. 1, M 1 (RGM 592814); 2, M 2 (RGM 592817); 3, M 3 (RGM 592819, reversed); 4, m 1 (RGM 592822); 5, m 2 (RGM 592825, reversed); 6, m 3 (RGM 592830, reversed; holotype).

FIGURE 2. Left lower dentition of Oryzomys gorgasi (LACM 96090).