Cardiatherium patagonicum, Vucetich & Deschamps & Olivares & Dozo, 2005

Vucetich, María G., Deschamps, Cecilia M., Olivares, A. Itatí & Dozo, María T., 2005, Capybaras, size, shape, and time: A model kit, Acta Palaeontologica Polonica 50 (2), pp. 259-272 : 262-265

Cardiatherium patagonicum sp. nov.

Figs. 4–6 and Table 1.

Synonym: Kiyutherium cf. orientalis Pascual and Bondesio, 1985 ; cf. Kiyutherium, Dozo et al. 2002 .

Holotype: MPEF−PV 740 /1, right mandibular fragment with m1–m2. Figs. 4 and 5A .

Hypodigm: The holotype and MPEF−PV 740 /9 and 26, left p4s ; MPEF−PV 740 /10 and 41, anterior fragments of right p4 ; MPEF−PV 740 /27, right p4 ; MPEF−PV 740 /11, 12, and 34, anterior fragments of left p4 ; MPEF−PV 740 /2, 3, 4, 5, 24, 25, 30, and 36, isolated right m1 or m2 ; MPEF−PV 740 /29, 31, and 39, isolated left m1 or m2 ; MPEF−PV 740 /6, small right mandibular fragment with m2 ; MPEF−PV 740 /7, fragment of left m3 ; MPEF−PV 740 /20 and 40, fragment of right m3 ; MPEF−PV 740 /22, fragment of palate with left P4 ; MPEF−PV 740 /28, isolated left P4 ; MPEF−PV 740 /14, isolated right P4 ; MPEF−PV 740 /8, damaged right M1 or M2 ; MPEF−PV 740 /13, isolated right M1 or M2 ; MPEF−PV 740 /15 and 16, left M1 or M2 ; MPEF−PV 740 /17, small fragment of left palate with M1 ; MPEF−PV 740 /19, fragment of lower incisor ; MPEF−PV 740 /23, isolated left M1 or M2 ; MPEF−PV 740 /18, isolated right M3 ; MPEF−PV 740 /33, fragment of right M3 ; MPEF−PV 740 /32 and 38, fragments of left M3 ; MPEF−PV 740 /35, isolated left M3 ; MPEF−PV 740 /37, fragment of a juvenile palate with right M3 ; MPEF−PV 740 /21, right mandibular fragment with p4−m1 probably of an unborn specimen, and MJG 22−IV−1976, anterior fragment of p4 .

Locality and age: All the specimens labeled as MPEF−PV 740 / were found at the marine cliffs between Punta Delgada and Punta Lobo (about three kilometers west from Punta Delgada ; 42 ° 47’ S, 63 ° 40’ W; Fig. 1 ), Estancia Rincón Chico , southeastern Peninsula Valdés, Chubut Province, Argentina; upper levels of the Puerto Madryn Formation (late

Miocene; Dozo et al. 2002); MJG 22−VI−1976 was found at Bahía Creek, Río Negro Province, Río Negro Formation “capa d” ( Angulo and Casamiquela 1982), late Miocene ( Marshall et al. 1983).

Etymology: patagonicum in reference to its Patagonian distribution.

Diagnosis.—The new species differs from “ Procardiatherium ” chasicoense , Cardiatherium isseli , and C. talicei in having a p4 with h.sn.i. It differs from C. paranense (and its synonyms, see below), “ Kiyutherium ” orientalis , and “ K ”. rosendoi in that the h.sn.i. overlaps the lingual end of h.1e. It differs from all the mentioned species in having (1) a very deep h.1e. reaching the lingual wall, forming a c.sn.i., which is lingually leveled with c.2i and c.3i.; (2) h.2e. bifurcate at the lingual end in adults, and with isthmus joining pr.I, and pr.s.a. globose; (3) m1–m2 with deeper h.s.i. and h.t.i. (up to 40% and 72% of the MW respectively) for equivalent sizes, and h.s.i. labiolingually oriented. It shares with C. paranense and “ K ”. orientalis the arched pr.I of m3, but differs in having a very deep h.t.i. also in young individuals. It differs from “ Kiyutherium ” octolaminatum, Anchimysops villalobosi , and? A. dubius in having higher number of laminae in M3 (10 or 11 versus 6 or 8).

Description.—The sample consists almost exclusively of isolated cheek teeth of different sizes, interpreted as representatives of individuals of different ages within a single population. Cheek teeth are gracile, somewhat longer than wide, with elongate joined prisms, and with deep flexids. The mandible MPEF−PV 740/21 is considered an unborn specimen because its preserved teeth are only slightly worn ( Kraglievich 1941), and the bone shows incomplete ossification. In addition it is the smallest specimen of the sample.

The p4: as in all hydrochoerids p4 has 3 prisms; Pr.II lingually bears a long h.1i. and a shorter h.sn.i. In some specimens (MPEF−PV 740/27, 9, and 34; Fig. 5B, E , and H), the h.1i. is very deep and forms a protrusion of the posterior margin of the h.1e. The h.sn.i. is longer than in other cardiatheriines, and its labial end exceeds the lingual end of h.1e. Pr.I has two lingual flexids, h.2i. and h.3i. As the h.sn.i., the h.2i. overlaps the lingual end of the h.1e. However, this middle lingual portion of p4 is very variable, and part of this variation depends on size. For example, in MPEF−PV 740/27 ( Fig. 5B ) both h.2i. and h.sn.i. are scarcely outlined in the occlusal surface, but on the basal surface they exceed slightly the bottom of h.1e. In MPEF−PV 740/10 ( Fig. 5C ) the h.sn.i. is scarcely developed and h.2i. is not yet outlined on the occlusal surface, but it can be seen on the basal surface. Instead, in MPEF−PV 740/26 ( Fig. 5D ), which is somewhat larger than the former two teeth, both flexids already exceed the bottom of the h.1e. in the occlusal surface. In most specimens the h.3i. is deeper than h.2i. and h.sn.i., but in MPEF−PV 740/12 ( Fig. 5G ) it is slightly shorter than the h.2i., which is very long in this specimen. Instead, in MPEF−PV 740/41 h.3i. is only slightly longer than h.2i. One of the largest specimens (MPEF−PV 740/34; Fig. 5H ) has a single flexid in pr.II (h.3i.?), which is very deep and bifurcate at the end. The c.3 (limited by h.2i. and h.3i.) is variable in shape and size, depending on the development and orientation of h.2i. In large specimens (MPEF−PV 740/9,11, 12, and 34; Fig. 5E–H ) there are outlines of h.4i. and h.5i. The h.1e. penetrates up to the lingual border of the tooth, placing the c.sn.i. at the lingual margin of the tooth. The pr.s.a is separated from pr.1 by a deep h.2e. This is bifurcate at the labial end, with a deep anterior ramus anteriorly oriented, and a less developed posterior ramus, slightly backwardly oriented. Both rami are separated by a widened portion of the isthmus that joins internally pr.s.a and pr.I. In the three smallest specimens (MPEF−PV 740/10, 26, and 27; Fig. 5B–D ) the h.2e. is not bifurcate and the isthmus is not widened. In the unborn specimen the p4 lacks h.sn.i., h.2i. and h.3i., the h.1e. traverse the entire width of the tooth and the h.2e. is nearly labially closed.

The m1–m2: as in the other hydrochoerids, m1 is probably smaller than m2, as suggested by the holotype ( Figs. 4 , 5A , Table 1). The h.s.i. is narrow and encompasses from 24% up to 46% of the molar width with increasing AP. The h.t.i. extends more than half the occlusal surface, from 57% to 78% of the molar width with increasing AP. The h.f.e. and h.p.i. are deep and reach the opposite side of the tooth. The h.s.e. is wide, deep and reaches up to 30% the width of pr.Iib. In the unborn specimen, m1 has the h.t.i. already formed although very short, h.s.i. is only hinted, while the h.s.e. is only barely developed.

The m3: the anterior wall is very curved and the h.t.i. very deep, reaching almost the external margin of the tooth ( Fig. 5P–Q ), as in the m3 of Cardiatherium paranense and C. isseli . The anterior wall of h.f.e. is S−shaped, with a middle sector wider than the rest, like that of C. isseli . The h.s.i. is deeper than in the m1–m2. and the h.t.i. reaches the labial border of the tooth. In MPEF−PV 740/ 40, the h.t.i. also reaches the labial portion of the tooth, although it is a small tooth in which the occlusal surface is still smaller than the base.

The i1: slightly wider than high, with its anterior face gently curved, the enamel extends slightly on each side.

The P4: two of the isolated upper cheek teeth (MPEF−PV 740/14 and 22; Fig. 6A and B ) are considered P4 because the anterior side is more curved than in the other specimens, and the external side of the posterior lobe of Pr. I (between H.P.E. and H.S.E.) is long and anteroposteriorly oriented. Consequently, the longest anteroposterior diameter of this lobe lies on the labial side and not in the middle as in molars. Except for these characters, the structure is very similar to that of M1–M2, but with wider lobes, especially the anterior of Pr.I.

The M1–M2: assignment to tooth locus is difficult, but one specimen (MPEF−PV 740/17) included in a small left palate fragment, is considered M1 because it lies just behind the beginning of the zygomatic arch as in other cardiatheriines. The rest are considered M1–M2 ( Fig. 6C–F ). The H.P.E. penetrates into the Pr.I more than 50% of the width, while the H.S.E. is shorter, but deeper than in Kiyutherium orientalis , K. scillatoyanei , K. rosendoi , and Cardiatherium paranense . In one of the specimens (MPEF−PV 740/15; Fig. 6D ) the H.S.E. is superficial. In the largest specimens, the enamel disappears in the postero external apices of the posterior lobe.

The M3: there are two complete M3; the largest (MPEF−PV 740/35) has 10 long laminae plus a shorter posterior one; the other (MPEF−PV 740/ 37) is a juvenile specimen with nine long laminae plus a shorter one with a posterior projec− + tion on the labial side. Another large but incomplete specimen (MPEF−PV 740/18; Fig. 6G ) has 9 long laminae and the remains of another broken lamina also long. According to the structures of the M3 of all Hydrochoeridae , it may be assumed that this specimen had at least 10 complete laminae plus another shorter one. The Pr.I is split by a deep H.P.E., which encompasses approximately 70% the prism width. Pr.II, Pr.III, and Pr.IV have a conspicuous external flexid, while more posterior ones only have a smooth depression. In MPEF−PV 740/18 the internal flexid that separates Pr.III from IV (H.3I.) is bifurcated at the bottom, limiting a short lobe as wide as the laminae, and rising from the external wall. The lingual end of each prism is pointed and curved backward up to Pr.VIII, while from Pr.IX on, the ends are rounded and have no torsion. The lobes are joined by the external wall as in all cardiatheriines, but the enamel seems too thin in the external column of each prism.

Mandible: the only fragment of an adult, the holotype, is quite damaged. The diastema is elongate, slightly concave on the upper side, and rises anteriorly (diastema length> 22.75 mm; height in front of p4 = 19.95 mm). The mental foramen is placed in front of p4 and at half height of the ramus. The angular region rises below the m2 and from this point it is oriented downward. The bottom of the i1 alveolus is placed internally to the anterior half of the m2. In the unborn specimen the upper margin of the diastema is gently concave in front of the p4 and slopes upward anteriorly (diastema length 8.90 mm, height in front of p4 = 7.3 mm); the symphysis is very smooth and the chin is almost undeveloped; the fossae for the masseters are very shallow.

Figures

Fig. 4. Cardiatherium patagonicum sp. nov. Puerto Madryn Formation, Punta Delgada, Chubut. Holotype, right mandible with m1–m2, MPEF−PV 740/1. Stereopair in occlusal view (A); schematic drawing in occlusal view (B) showing m1–m2; schematic drawing in labial view (C) showing the roots of m1–m2; photograph in lingual view (D).

Fig. 5. Cardiatherium patagonicum sp. nov. occlusal surfaces of the lower cheek teeth: right m1–m2 (A, J–O), right p4 (B, C), left p4 (D–I), right m3 (P), left m3 (Q). A. MPEF 740/1 (holotype, m1–m2). B. MPEF 740/27 (inverted). C. MPEF 740/10 (inverted). D. MPEF 740/26. E. MPEF 740/9. F. MPEF 740/11. G. MPEF 740/12. H. MPEF 740/34. I. MJG 22−IV−1976.J. MPEF 740/25.K. MPEF 740/4.L. MPEF 740/3. M. MPEF 740/5. N. MPEF 740/24. O. MPEF 740/2. P. MPEF 740/20. Q. MPEF 740/7 (inverted). I, modified from Pascual and Bondesio (1985).

Fig. 6. Cardiatherium patagonicum sp. nov. occlusal surfaces of the upper cheek teeth: right P4 (A), left P4 (B), left M1–M2 (C, D, F), right M1–M2 (E), right M3 (G). A. MPEF 740/14. B. MPEF 740/22 (inverted). C. MPEF 740/16 (inverted). D. MPEF 740/15 (inverted). E. MPEF 740/13. F. MPEF 740/23 (inverted). G. MPEF 740/18.

Fig. 1. Map showing the localities (black dots) and provinces yielding cardiatheriines. White squares—the capitals of Argentina and Uruguay.