Sparassocynus maimarai, Abello, María Alejandra, Reyes, Martín De Los, Candela, Adriana Magdalena, Pujos, Francois, Voglino, Damián & Quispe, Bernardino Mamani, 2015

Abello, María Alejandra, Reyes, Martín De Los, Candela, Adriana Magdalena, Pujos, Francois, Voglino, Damián & Quispe, Bernardino Mamani, 2015, Description of a new species of Sparassocynus (Marsupialia: Didelphoidea: Sparassocynidae) from the late Miocene of Jujuy (Argentina) and taxonomic review of Sparassocynus heterotopicus from the Pliocene of Bolivia, Zootaxa 3937 (1), pp. 147-160 : 151-156

Sparassocynus maimarai new species

Fig. 5 , Tables 1–2

Etymology. “ maimarai ” in reference to the locality of Maimará where the new species was discovered. Holotype. JUY-P-48, left mandibular fragment with a complete p2–m4 series.

Locality and Horizon. The type specimen was collected in the Maimará Formation (late Miocene-early Pliocene), near the Locality of Maimará, Jujuy Province, Argentina ( Fig. 1 C).

Diagnosis. Sparassocynus maimarai differs from S. bahiai and S. derivatus by its smaller size, the relatively longer m1 with respect to the m4, its more robust and conical entoconids, and the presence of a lingual cingulum extended between para- and metaconid on the m1–3.

Comparative description. Considering the mean of m1–3 length as a proxy of species size, S. maimarai is 9% smaller than S. bahiai and S. derivatus ( Tables 2 and 3 ). The horizontal ramus of the dentary is short and deep as in S. bahiai and S. derivatus , and about a 40% deeper than Hesperocynus ( Tables 2 and 3 ). The mandibular symphysis is long, ending posteriorly behind to the p3–m1 boundary ( Fig. 5 A–C). The ventral border of the horizontal ramus between p2 and m4 is not preserved ( Fig. 5 A–B) and the possible presence of a well-developed notch mark for the geniohyoid muscle, a diagnostic character of sparassocynids ( Goin, 1991), could not be evaluated. On the labial side of the dentary two mental foramina are present, one located below the p2 and the other below the posterior root of m1. The anterior end of the mandible is broken in front of the p2 ( Fig. 5 A–B). Behind the root of the canine is the posterior alveolus of p1, which was oblique to the dentary row ( Fig. 5 C). The p2 is labiolingualy compressed, and has a small posterior cusp; the p3 is narrow posteriorly with a small lingual talon (Fig. C, E). Premolars are slightly imbricated, without diastema between them such as some specimens of S. derivatus (e.g., MMP 1088).

Molars increase in length, and have a proportionally longer and wider trigonids, from m1 to m4. First lower molar is relatively longer with respect to the m4 than it is in S. bahiai and S. derivatus ( Tables 2 and 3 ). Talonids of S. maimarai are shorter and narrower than the trigonids as occur in the remaining Sparassocynus species ( Fig. 5 C; Tables 2 and 3 ). The talonid of m4 is, in the contact with the trigonid, as wide as that of S. derivatus and S. bahiai ( Figs. 5 C and 3A–B), and wider than in H. dolgopolae ( Fig 3 D; Tables 2 and 3 ). Similarly to the remaining Sparassocynidae , trigonids are higher than talonids ( Reig & Simpson, 1972; Goin, 1991). The paraconid is lower than proto- and metaconid; metaconid is reduced compared to the protoconid and partially fused to this cusp ( Fig. 5 D–E, G). The paraconid is slightly larger than that of S. bahiai and S. derivatus . Lingually, a basal cingulum is located between para- and metaconid ( Fig. 5 D, F–G). Anterobasal cinguli are narrow and become anteriorly wider along the paraconid where they form deep hypoconulid notchs. The hypoconids are lingual to the protoconids and do not project labially ( Fig. 5 C, F). The entoconids are robust and rounded in section (i.e., are not labiolingually compressed; Fig. 5 C, F) compared to that of other Sparassocynus species. The hypoconulids are well developed, especially on m2–3, and locked in the deep hypoconulid notchs of the respective posterior molars.

‘ Sparassocynus ’ heterotopicus MNHN-BOL- 011896 0.9

continued.

Taxon Lm3 Wtrigm3 Ltrigm3 Wtalm3 Ltalm3 Lm4

Sparassocynus maimarai 3.4 2.2 2.4 2 1 3.5 Sparassocynus derivatus 3.7 2.3 2.7 2.2 1 4.2 Sparassocynus derivatus 3.8 2.6 2.8 2.4 1 4.3 Sparassocynus derivatus 3.4 2.2 2.5 2.2 0.9 4 Sparassocynus derivatus 3.5 2.4 2.4 2.3 1.1 3.9 Sparassocynus derivatus 3.7 2.6 2.7 2.3 1 4.4 Hesperocynus dolgopolae 3.4 2.2 2.3 2.1 1.1

Hesperocynus dolgopolae 3.6 2.25 2.4 2 1.2 3.8 Sparassocynus bahiai 4 2.5 2.9 2.3 1.1 4.4 Sparassocynus bahiai 3.7 2.5 2.8 2.35 0.9 4.2 Sparassocynus bahiai 4 2.3 2.9 2.1 1.1 4.4 ‘ Sparassocynus ’ heterotopicus 3.6 2 2.5 17.5 1.1 3.6 LM2 WM2 LM3 WM3 LM4 AM4 ‘ Sparassocynus ’ heterotopicus 3.25 2.8 3.5 3.2 3.7 3.4 continued.

Taxon Lm1/Ltal Lm2/Ltal Lm3/Ltal Wtrigm4/wtal The assignation of the specimen JUY-P-48 to the Sparassocynidae is based on the presence of the following diagnostic characters of the family (according to Reig & Simpson, 1972; Goin, 1991): (1) high dentary, (2) long symphysis, (3) premolars without diastema, (4) lower molars with high trigonids and low talonids, (5) short and narrow talonids, and (6) metaconid small and partly fused with protoconid.

In the context of the Sparassocynidae specimen JUY-P-48 shared several characters with Sparassocynus species. Like them it has a deeper dentary, talonids of m1–3 relatively shorter, and talonid of m4 proportionally wider than that of Hesperocynus dolgopolae ( Figs. 3 and 5 A; Tables 2 and 3 ). Forasiepi et al. (2009) have considered that two characters mentioned previously as diagnostic of the Sparassocynidae ( Reig & Simpson, 1972; Goin, 1991) are actually diagnostic of Sparassocynus : an extremely reduced metaconid fused with the protoconid and slightly imbricate premolar tooth row. Unfortunately, the first of these traits could not be evaluated in the specimen JUY-P-48. It is hard to establish if the size difference between metaconid and protoconid was similar to that in S. bahiai and S. derivatus because of worn degree of molars ( Figs. 3 A–B and 5A). In relation to the second character, we observed that the imbrication degree of the premolars shows intraspecific variability, at least in one species of this genus; therefore, we considered that this trait is not diagnostic of Sparassocynus . All studied specimens of S. bahiai have slightly imbricate premolars, but in S. derivatus specimens premolars could be not imbricated (e.g., MMP 1379) to slightly imbricated (e.g., MMP 412).

Compared with S. derivatus and S. bahiai , specimen JUY-P-48 is characterized by its smaller size, the m1 relatively longer with respect to the m4, the proportionally robust and conical entoconids, and the presence of a lingual cingulum extended between para- and metaconid on the m1–3 ( Tables 2 and 3 ). These characters indicate that the new specimen from Maimará locality represents a new species of Sparassocynus : S. maimarai sp. nov.

Figures

FIGURE 1. Map showing geographical positions of localities mentioned in the text. A, boxed area in map of South America showing central and southern Bolivia, and central and northern Argentina. B, fossiliferous localities: (1) Umala, (2) Arroyo Lobería, (3) Monte Hermoso, (4) El Guanaco, (5) Quehué, (6) Caleufú, (7) Puesto Arroyo Seco de la Frazada, and (8) Chiquimil. C, area of Jujuy Province with the location of the type locality of Sparassocynus maimarai n. sp.

FIGURE 3. Lower dentition of Sparassocynus and Hesperocynus in occlusal view (anterior towards top). A, Sparassocynus derivatus, MMP 412 M, right m 1 – m 4; B, Sparassocynus bahiai, MLP 11 - 119, right m 1 – m 4; C – D, Hesperocynus dolgopolae, C, FMNH 14469 (holotype), right p 2 – m 3; D, MLP 86 - VII- 10 - 1, right p 2 – m 1, talonid of m 2, and complete m 3 – 4.

FIGURE 5. Sparassocynus maimarai sp. nov. (holotype JUY-P- 48). A – C, mandible in lingual (A – B) and occlusal (C) views (arrow indicates the posterior extent of the mandibular symphysis); D, detail of m 3 – 4 in lingual view (anterior towards right); E, p 2 – m 4 series in labial view (anterior towards left); F – G, schematic drawings of the m 4 in occlusal (F) and lingual (G) views. Abbreviations: Ac, anterobasal cingulum; Ed, entoconid; Hy, hypoconid; Hyd, hypoconulid; Lc, lingual cingulum; m 1 – m 4, lower molars; mas, mandibular symphysis; Me, metaconid; p 1 – p 2, lower premolars; Pa, paraconid; Pr, protoconid.

Tables

TABLE 2. Mandibular and dental ratios of Sparassocynidae species and ‘ Sparassocynus ’ heterotopicus estimated from measurements in Table 1. Upper values are means and lower values are ranges; sample size (n) is given in taxon column.

Taxon	Wtrigm4	Ltrigm4	Wtalm4	Ltalm4	Lm1-3	Lm2-3
Sparassocynus maimarai	2.2	2.5	1.5	1	9	6.4
Sparassocynus derivatus	2.5	3.1	1.5	1.1	9.7	6.9
Sparassocynus derivatus	2.6	3	1.8	1.3	9.8	7
Sparassocynus derivatus	2.2	2.6	1.5	1.4	9	6.4
Sparassocynus derivatus	2.5	2.9	1.7	1	9.2	6.5
Sparassocynus derivatus	2.5	3	1.9	1.4	10.1	7.1
Hesperocynus dolgopolae					9	6.3
Hesperocynus dolgopolae	2	2.8	0.6	1	9	6.2*
Sparassocynus bahiai	2.5	3	1.8	1.4	10.2	7.5
Sparassocynus bahiai	2.5	3	1.7	1.2	9.5	7
Sparassocynus bahiai	2.4	3	1.6	1.4	10	7.4
‘ Sparassocynus ’ heterotopicus	2	2.3	1.5	1.3		6.8

TABLE 3. Compared mandibular and dental characters diagnostic of Sparassocynid species.

Character	Hesperocynus dolgopolae	Sparassocynus bahiai
horizontal mandibular ramus (Lm1-3/MH)	shallow	deep
m1-3 talonid relative length (Lm1/Ltal; Lm2/Ltal; Lm3/Ltal)	long	short
relative width of talonid and trigonid of m4 (Wtrigm4/wtal)	narrow m4 talonid	wide m4 talonid
entoconid shape	gracile and labiolingually compressed	gracile and labiolingually compressed
lingual cingulum between para- and metaconid	absent	absent
relative length of m1 and m4 (Lm1/Lm4)	relatively longer m1 with respect to the m4	relatively longer m1 with respect to the m4
continued.
Character	Sparassocynus derivatus	Sparassocynus maimarai sp. nov.
horizontal mandibular ramus (Lm1-3/MH)	deep	deep
m1-3 talonid relative length (Lm1/Ltal; Lm2/Ltal; Lm3/Ltal)	short	short
relative width of talonid and trigonid of m4 (Wtrigm4/wtal)	wide m4 talonid	wide m4 talonid
entoconid shape	gracile and labiolingually compressed	robust and conical
lingual cingulum between para- and metaconid	absent	present
relative length of m1 and m4 (Lm1/Lm4)	relatively longer m1 with respect to the m4	relatively longer m1 with respect to the m4