Negodiaetictis rugatrulleum, Smith & Czaplewski & Cifelli, 2016

Smith, Kent, Czaplewski, Nicholas & Cifelli, Richard L., 2016, Middle Miocene carnivorans from the Monarch Mill Formation, Nevada, Acta Palaeontologica Polonica 61 (1), pp. 231-252 : 243-246

Negodiaetictis rugatrulleum sp. nov.

Fig. 7 .

Etymology: From Latin ruga, wrinkled; trulleum, basin—in reference to the talonid basin of the m1.

Holotype: OMNH 54974 , right partial dentary with p3–m1 and alveoli for c and p2.

Type locality: OMNH V972 (UCMP V70147), Eastgate, Churchill County, Nevada, USA.

Type horizon: Basal-most unit of the Monarch Mill Formation ( Axelrod 1985), Barstovian (Miocene).

Material.— OMNH 54888 , right m2 from type locality .

Diagnosis.—Unique among mustelids in having crenulated enamel on all known lower teeth (p3–m1), especially pronounced on the talonid basin of m1.

Measurements (in mm).—p3: AP, 5.6; T, 3.3; p4: AP, 5.8; T, 4.0; m1: AP, 9.4; TRL, 5.8; TAL, 4.1; TRW, 4.5; TAW, 4.5; m2: AP, 4.1; T, 3.5; p2–4: alveolar length, 15.9; p2–m1: alveolar length, 23.6; p3–4: length, 12.3; p3–m1: length, 20.7. Depth of dentary bone beneath protoconid of m1 9.0.

Description.— Dentary: This element is short and moderately deep (slightly less deep than the length of m1), with a curved ventral margin. The preserved part shows two small mental foramina, one below the p2 and one below the posterior root of p3. The posterior edge of the mandibular symphysis is preserved and reaches a level below the middle of the p3.

Lower premolars: The p1 is absent, the anterior alveolus for p2 being directly adjacent to that for c. The existing premolars, p2–4, are crowded together between c and m1, indicating a shortened rostrum. The p2 is represented only by two empty alveoli set at an oblique angle to the axis of the lower toothrow ( Fig. 7A ). The anterior alveolus, placed against the posterior border of the c alveolus, is the smaller of the two sockets that held p2. Similarly, p3 is also two-rooted, with the anterior root smaller than the posterior, and the two roots and crown oriented at an angle oblique to the axis of the dentary. The crown of p3 is of robust construction, is wider posteriorly than anteriorly, bears one main cusp, and is covered with crenulated enamel. No posterior accessory cusp is present. The anterior and posterior cingulids are strong but lack cingular cusps, though the posterior cingulid bears a continuous series of tiny cuspules. The labial and lingual cingulids are weak. The crown and roots of p4 are aligned with the axis of the lower toothrow and dentary. Two roots are present, of which the posterior is larger. The crown is wider posteriorly than anteriorly, is covered with crenulated enamel, and bears a strong, posterolabially placed accessory cusp in addition to the main cusp. The labial and lingual cingulids are weak; the anterior and posterior cingulids are strong but lack cingular cusps. The posterior cingulid bears a series of very small cingular cuspules.

Lower molars: The m1 has a relatively low, open trigonid with an oblique protoconid-paraconid (paracristid) carnassial blade and a relatively high talonid, and is covered with crenulated enamel. A very short but distinct lingual cingulid is present below the anterior portion of the trigonid valley. Labially, a thin cingulid extends posteriorly from a point below the paraconid, becoming weak below the protoconid, then becoming disjunct posteriorly, with short, strong, crenulated segments labial to the notch between the protoconid and hypoconid and the notch between the hypoconid and hypoconulid. No accessory roots are present, only large anterior and posterior roots. The metaconid is well developed, taller than the paraconid, and positioned slightly posterior to the protoconid. The protoconid and metaconid are joined by a V-shaped crest (protocristid) with a median notch like that in the carnassial blade. The talonid is slightly shorter and slightly wider than the trigonid, and is expanded lingually. The talonid is basined but the basin is partly filled by an internal, crenulated low mound that extends basinward from the hypoconid. The hypoconid is moderately large and is separated from the posterior margin of the protoconid by notches and two low, small accessory cuspules, which might represent a modified protostylid. The hypoconid is connected through a basin-ringing posterior and lingual rim composed of a continuous series of small cuspules separated from one another by notches to a point just posterior to the postmetacristid. Here the talonid rim is separated by a tiny notch from the ridge running down the posterior face of the metaconid. There is no distinct entoconid.

The m2 is lacking from the type specimen and is represented only by the partial anterior rim of an alveolus that is filled with rock matrix. Due to the condition of the specimen ( Fig. 7 ) it cannot be determined whether a second root or additional lower molar was present. However, an isolated m2 ( OMNH 54888 ) was found. We believe that it may belong to the holotype jaw because: (i) the two specimens were discovered in the same quarry in the same field season; (ii) the two are identical in preservation and color; iii) the m2 ( OMNH 54888 ) has a small anterior interdental contact facet matching the size and shape of the facet on the posterior face of m1 on the holotype ( OMNH 54974 ); (iv) the slight degree of occlusal wear is consistent between the specimens; and (v) OMNH 54888 has crenulated enamel, as would be predicted for m2 of this species .

The isolated m2 is single-rooted with the strongly tapering root slanting posteriorly from the crown. The occlusal surface of the crown would have been tilted forward slightly from the horizontal and relative to the occlusal surface of m1. The crown is small with an ovate outline in occlusal view, and is slightly longer than broad. The paraconid is absent. The low protoconid and metaconid join to form a transverse crest (protocristid) just behind the middle of the crown, dividing the crown into anterior (trigonid) and posterior (talonid) portion, of which the former is larger. Both the anterior and posterior basins have heavily crenulated enamel like that of the m1.

Remarks.— Negodiaetictis rugatrulleum gen. et sp. nov. resembles various taxa of Mustelidae , especially some Galictini and Lutrini . Definitions of these and other mustelid subclades vary among authors but continue to be refined, and placement of mustelid genera into infrafamilial groupings is unavoidably inconsistent due largely to the incompleteness of the group’s fossil record. The family requires revision, beyond the scope of the present article, which compounds the problem of making comparisons with additional poorly represented but presumably distinct and related taxa. Negodiaetictis rugatrulleum gen. et sp. nov. most closely fits Baskin’s (2011: 2) diagnosis of Galictini ; it shares with galictins small size, a relatively deep jaw (dentary depth is 95% of m1 length), crowded premolars, p1 absent, m1 with an open bladelike trigonid, m1 with a lingually expanded and basined talonid with a posterolingual cingulum extending from the base of the reduced metaconid to the hypoconid, and hypoconid separated from the protoconid by a small notch. Based on specimens in hand, Negodiaetictis differs from Baskin’s (2011) diagnosis of Galictini in only a few features, including unreduced metaconid, presence of a small cuspule in the notch separating the protoconid from the hypoconid, and heavier degree of enamel crenulation.

Based on our own comparisons and on what we have gleaned from the literature, Negodiaetictis gen. nov. differs from Brevimalictis gen. nov., Cernictis Hall, 1935 , Eira Smith, 1842 , Enhydrictis Stefani, 1891 , Galictis Bell, 1826 , Grisonella Thomas, 1912 , Lartetictis Ginsburg and Morales, 1996 , Limnonyx , Lutravus Furlong, 1932 , Mionictis , Pannonictis Kormos, 1931 , Sminthosinis Bjork, 1970 , Trigonictis Hibbard, 1941 , and Trochictis Meyer, 1842 , in having crenulated enamel on lower cheek teeth, rugose enamel on the m1 talonid (especially on the hypoconid, hypoconulid, and talonid basin), and m1 talonid rim consisting of a beaded series of cuspules separated from one another and from the protoconid, metaconid, hypoconid, and hypoconulid by small notches. Negodiaetictis gen. nov. further differs from Enhydrictis (a Eurasian genus) in having p2 large and two-rooted, having p4 with a posterior accessory cusp, having m1 lacking a distinct entoconid, and having the m1 metaconid posterior crest separated by small notch from the adjacent internal rim of the talonid (fide Pilgrim 1932; Baskin 2011). It further differs from Pannonictis in having p4 with a posterior accessory cusp ( Baskin 2011).

Negodiaetictis gen. nov. is comparable to certain Eurasian taxa in some respects. One example is the Eurasian genus Trochictis , which is often placed in Melinae, but variously in Gulolinae (e.g., by Ginsburg 1999), and said to be referable possibly to Galictinae by Baskin 2011. The species Trochictis depereti Major, 1903 shows some similarities to Negodiaetictis gen. nov., such as an m1 talonid with a large basinward-sloping expansion of the hypoconid and rimmed with a posterior cingulid having a series of small cuspules ( Thenius 1949a: fig. 3). Pilgrim (1932: 854) also noted “crenulation of the entoconid” of m 1 in Eurasian Trochictis? pusilla Major, 1903 and T. taxodon Gervais, 1852 . However, N. rugatrulleum gen. et sp. nov. differs in general from Trochictis as noted above, and further differs in lacking p1, having crowded p2—p4, having the m1 protoconid taller than the metaconid, having the m1 talonid base higher than the trigonid base, and having the m1 lacking a distinct entoconid. Helbing (1927) noted a resemblance between Eurasian Trochictis and North American Mionictis . In addition to the differences noted above, Negodiaetictis rugatrulleum gen. et sp. nov. further differs from Mionictis in having the p4 with a prominent posterior accessory cusp. For further discussion of species sometimes referred to Mionictis , see below.

Relative to extinct North American members of the Galictini , Negodiaetictis rugatrulleum gen. et sp. nov. differs from Cernictis (see also Baskin 2011) in having m1 with a relatively longer talonid (more than half the length of the trigonid), anterior end of labial cingulid not extending upward on the anterior border of paraconid, hypoconid not trenchant, talonid basin partly filled by basal expansion of the hypoconid, posterior face of the metaconid bearing a ridge and separated from a high lingual margin of talonid by a metastylid, posterior talonid cingulid of m1 composed of a series of connected small cuspules, tooth enamel crenulated, and smaller size ( Cernictis has an m1 length that ranges from 10.6–11.5 mm; measurements from Baskin 2011). Some specimens of Trigonictis show the m1 talonid rim with a series of beaded cuspules (e.g., Ray et al. 1981: fig. 3, but less pronounced than in N. rugatrulleum gen. et sp. nov.), but otherwise Negodiaetictis gen. nov. differs from Trigonictis in having a strong posterolabial accessory cusp on p4, carnassial paraconid-protoconid blade (paracristid) shorter and more obliquely oriented, with the trigonid less open; m1 talonid longer relative to length of trigonid, m1 talonid basin partly filled by expanded base of hypoconid, tooth enamel crenulated, and smaller size. Negodiaetictis gen. nov. further differs from Brevimalictis chikasha gen. et sp. nov. in much larger size, p4 with posterior accessory cusp, metaconid nearly equal height to protoconid, and m1 talonid with rugose rim, basin, and cusps. Negodiaetictis gen. nov. differs from Sminthosinis in having p4 with strong posterolabial accessory cusp, m1 metaconid positioned slightly posterior relative to the protoconid, m1 posterior cingulid composed of series of small connected cuspules, and strongly crenulated enamel on all known teeth, especially m1 talonid. Negodiaetictis gen. nov. differs from Lutravus in having p4 with a strong posterolabial accessory cusp, m1 with a large metaconid separated from the internal cingulid of the talonid by a metastylid, hypoconid separated from the protoconid by a small accessory cuspule rather than a narrow notch, posterior cingulid composed of a series of connected small cuspules, crenulated enamel on all teeth, especially pronounced on m1 talonid basin and on hypoconid. Negodiaetictis gen. nov. differs from the extant galictin genera Eira and Galictis in having a two-rooted p2, and having the p4 with a posterior accessory cusp, and from Grisonella in having the m1 with a stronger metaconid.

Regarding Baskin’s (1998) characteristics for Lutrini , Negodiaetictis rugatrulleum gen. et sp. nov. differs in lacking a p1 (although p1 is only primitively present in members of the tribe and many have short muzzles and crowded premolars) and in having m1 with a relatively short trigonid and long, narrow talonid and crenulated enamel on the teeth. However, allowing for notches associated with the rugose enamel and beaded rim of the m1 talonid, Negodiaetictis rugatrulleum gen. et sp. nov. resembles lutrins in having m1 with an accessory cuspule (protostylid?) on the posterior margin of the protoconid (partly separated by a small notch) and a strong metaconid connecting to a broad, basined talonid (with the connection interrupted by small notches). The Eastgate taxon differs from the Eurasian lutrin Limnonyx (as illustrated by Willemsen 1992: pl. 5: 5, 23) in having m1 with much larger, especially longer, talonid relative to trigonid, talonid basin largely filled by basinward expansion of hypoconid, and smaller size than the two known species ( Willemsen 1992). It differs from the Eurasian genus Cyrnaonyx Helbing, 1935 in having the m1 talonid about the same width as the trigonid, not lingually expanded, and without a strongly developed external talonid cingulum ( Willemsen 1992). Negodiaetictis gen. nov. differs from North American Satherium species in having dentary depth below m1 less than m1 length, m1 relatively narrower for its length, with slightly more open trigonid; m1 talonid posterior cingulid composed of a series of small connected cuspules, m1 talonid basin partly filled by basinward expansion of base of hypoconid, strongly crenulated enamel, and much smaller size ( Gazin 1934). Negodiaetictis gen. nov. differs from Lutra Brisson, 1762 in having the m1 with a relatively more open trigonid, the talonid narrower than the trigonid and longer relative to the trigonid length, and lacking an anteroposteriorly elongate hypoconid. It differs from Lontra Gray, 1843a in having a relatively more open m1 trigonid and narrower talonid lacking an expanded labial cingulum. It differs from Aonyx Lesson, 1827 in having the m1 talonid the same width as the trigonid, entoconid absent, and the external cingulum of the talonid weakly developed. It differs from Pteroneura in having the m1 with a more open trigonid, a relatively longer talonid, and the talonid about the same width as the trigonid. Negodiaetictis gen. nov. differs from European Paralutra Roman and Viret, 1934 in having a relatively much longer m1 talonid. It differs from Enhydritherium in having a shallower dentary beneath m1, a much more open m1 trigonid, m1 taller and much narrower relative to its length, m1 talonid shorter than trigonid, talonid basin partly filled by basal expansion of hypoconid, crenulated enamel, and smaller size ( Berta and Morgan 1985).

Negodiaetictis rugatrulleum gen. et sp. nov. resembles the lutrin Mionictis in most characters at the generic level such as having premolars that are robust and crowded, with sharp posterior crests but no cingular cusps; and a stout m1 with open trigonid, with the trigonid low but somewhat larger than the talonid, a semibasined talonid that is broadly expanded internally, a well-developed metaconid situated posterior to the protoconid and bearing a strong, sloping posterior crest extending downward and backward, the hypoconid prominent with a flat, gently sloping internal surface, and the hypoconid separated from the protoconid by a notch and a small accessory cusp posterior to the protoconid ( Matthew 1924; Baskin 1998). However, the Eastgate taxon differs from all named species of Mionictis (as listed and characterized by Baskin 1998) in having a strong posterolabial accessory cusp on p4, crenulated enamel on all known lower teeth, especially the talonid basin of the carnassial, and in having the posterior cingulum of the p3, p4, and talonid of m1 broad and composed of a series of closely connected, small cuspules. Negodiaetictis rugatrulleum gen. et sp. nov. differs from M. incertus Matthew, 1924 , the type species for the genus, in having the m1 with a high talonid, with a posterior ridge of the metaconid that is not continuous with the internal cingulid or posterior cingulid (the metaconid of Negodiaetictis gen. nov. is instead separated by a notch that is partly filled with a cuspule, which in turn is separated by another small notch from the posterior cingulid), with the posterior cingulid formed by a series of small cuspules, and with the hypoconid internal surface and talonid basin much crenulated. It further differs from M. incertus in having the other surfaces of the known teeth moderately crenulated, p4 with a large posterior accessory cusp, and in smaller size. Negodiaetictis gen. nov. differs from M. elegans Matthew, 1924 in having premolars less compressed and in smaller size. Negodiaetictis rugatrulleum gen. et sp. nov. is about the same size as, and most closely resembles M. letifer Cook and Macdonald, 1962 in premolar alveoli and crowding, and in p4 morphology, but differs from that species in having the posterior ridge of the metaconid separated by a notch containing a small cuspule from the rest of the lingual talonid cingulid, most of the talonid cingulid composed of a series of closely-connected small cuspules, posterobasal cuspule of protoconid smaller, and enamel crenulation on all known teeth. Negodiaetictis rugatrulleum gen. et sp. nov. differs from Mionictis pristinus (originally placed in Lutra by Matthew and Gidley 1904], later in Brachypsalis [ Cope, 1890] by Webb [1969a], and most recently referred to Mionictis by Baskin [1998]) in having p4 with a large posterolabial accessory cusp, m1 without a hypoconulid but with talonid cingulid composed of a series of connected small cuspules, crenulated enamel, and much smaller size. Baskin (1998) tentatively assigned the taxon previously known as Brachypsalis angustidens Hall, 1930 to Mionictis? angustidens ; the uncertainty is due in part to the type specimen being heavily worn, especially the carnassial. The Eastgate species differs from M.? angustidens in having p4 with a much stronger posterolabial accessory cusp, p4 broader posteriorly than anteriorly, crenulated enamel, and smaller size.

Negodiaetictis rugatrulleum differs from Eurasian Lartetictis dubia (Blainville, 1842) (as illustrated under the name Mionictis dubia by Thenius 1949a: figs. 1, 2) in having p4 with a large posterolabial accessory cusp, m1 with an accessory cusp posterior to the protoconid, posterior cingulid of talonid with series of small cuspules, and crenulated enamel on all known tooth surfaces, especially in the m1 talonid basin.

Virtually all previous North American specimens of Mionictis spp. are from the early Barstovian to late Hemphillian of the Great Plains, with one possible early Hemphillian occurrence (of M.? angustidens ; Baskin 1998) from Kern River, California. Negodiaetictis rugatrulleum gen. et sp. nov. closely resembles the late Hemingfordian M. letifer of the middle Sheep Creek beds, northwestern Nebraska; and early Barstovian to late Clarendonian M. pristinus from Little White River (type locality) and several other localities, Nebraska ( Baskin 1998).

Negodiaetictis rugatrulleum gen. et sp. nov. differs from the non-aquatic lutrine Teruelictis riparius Salesa, Antón, Siliceo, Pesquero, Morales, and Alcalá, 2013 from the late Miocene of Spain in lacking a p2 and in having an m1 with crenulations and a protoconid that is noticeably higher than the paraconid, and an m1 with a tall, large talonid basin ( Salesa et al. 2013). However, these taxa are similar in having a large metaconid that is nearly as high as the protoconid. Both taxa have a metaconid that is adjacent to the protoconid. The configuration of the metaconid, protoconid, and distal cristids arising from these cusps in Teruelictis riparius forms an M-pattern on the occlusal surface of the distal wall of the trigonid, which is not seen in N. rugatrulleum gen. et sp. nov.

Mustelids are well known for their opportunistic feeding habits. The crenulated enamel on the teeth of Negodiaetictis rugatrulleum gen. et sp. nov. is unique among Mustelidae . The presence of crenulations may indicate a diet of plant materialsuchasseeds(seeDiscussion).Whether Negodiaetictis rugatrulleum is a galictin or lutrin (or lutrine) or a member of some other clade of mustelids, it apparently had a unique dietary specialization, possibly including plant matter.

Stratigraphic and geographic range.—Western Nevada, USA; Monarch Mill Formation, Barstovian (Miocene).

Figures

Fig. 7. Mustelid carnivoran Negodiaetictis rugatrulleum gen. et sp. nov. from the Eastgate LF, basal-most unit of the Monarch Mill Formation, Barstovian (Miocene), Churchill County, Nevada, USA. OMNH 54974, holotype right dentary (posteroinferior margin cropped from images) with p3–m1 and alveoli for c and p2 in occlusal (A, stereopair), labial (B), and lingual (C) views.