Itaboraidelphys Marshall and Muizon, 1984

Tejedor, Marcelo F., Goin, Francisco J., Gelfo, Javier N., López, Guillermo, Bond, Mariano, Carlini, Alfredo A., Scillato-Yané, Gustavo J., Woodburne, Michael O., Chornogubsky, Laura, Aragón, Eugenio, Reguero, Marcelo A., Czaplewski, Nicholas J., Vincon, Sergio, Martin, Gabriel M. & Ciancio, Martín R., 2009, New Early Eocene Mammalian Fauna from Western Patagonia, Argentina, American Museum Novitates 3638, pp. 1-43 : 10-14

cf. Itaboraidelphys Marshall and Muizon, 1984 cf. Itaboraidelphys sp.

Figure 3F

All materials referred to this species are from Laguna Fría: illustrated is an isolated right m2 or m3 (LIEB-PV 1064), and additional referred materials include an isolated left metastylar area (M1 or M2; LIEB-PV 1066); isolated lower left premolar (LIEB-PV 1067); fragment of left upper molar (Mx; LIEB-PV 1110); and right metastylar fragment (LIEB-PV 1075).

In size and overall morphology, these specimens resemble the pattern seen in the Itaboraian-aged Itaboraidelphys , previously known from Itaboraí ( Brazil) and Las Flores ( Argentina). In the upper molars, the postmetacrista is well developed and trenchant; premolars are laterally compressed, and molars have unreduced talonids and well-developed paracristids.

‘‘Didelphimorphia’’ indet. Gen. et sp. indet. A

Three upper molars from Laguna Fría are difficult to assign. LIEB-PV 1042, possibly an M1, is completely preserved. This is a subtriangular tooth, canted anterolingually. The protocone is pointed anterolingually; paraconule and metaconule, respectively, are about half-way along the pre- and postprotocristae, and do not closely abut the lingual bases of the paracone and metacone; they do not appear to have been strongly winged. The preparacrista extends past the anterior base of the paracone to reach a small cuspule at the lingual base of StA. Paracone and metacone are well separated, about equally tall, but the metacone is somewhat more massive than the paracone. The centrocrista is linear, but weakly expressed. The talon basin is deep and separated by the centrocrista from the elevated stylar shelf. The stylar shelf is narrow and bears a complete complement of stylar cusps, all relatively small and much lower than the paracone or metacone. The ectoflexus is virtually absent. The postmetacrista is strongly crested and performed a shearing function. The elevation of the stylar shelf shows the derived nature of this tooth relative to a peradectian. Apparently the connection of the preparacrista to StB rather than to StA is a non-microbiotherian character.

Order Paucituberculata Ameghino, 1894 Family indet. Gen. et sp. nov. 4 Figure 3G

A left maxillary fragment with M2–3 and part of M4 (LIEB-PV 1135; fig. 3G) was collected in La Barda. The protocone is the lowest and widest cusp of the trigon; the paracone is small and lower than the metacone, the latter is pointed and has a metacrista posteriorly, longer than the paracrista in both molars. Paraconule and metaconule are developed.

Two additional specimens from La Barda are here referred tentatively to the same taxon. LIEB-PV 1137 is a well-preserved mandibular fragment with one lower molar and roots of an additional molar. The molar probably corresponds to an m2 or m3. Trigonid and talonid length is subequal; the paracristid is well developed and the metacristid has a deep fovea; paraconid and metaconid are close to each other, more than is expected for didelphimorphians. The anterobasal cingulum is narrow. LIEB-PV 1138 is almost identical to the former, but the metaconid is more separated from the paraconid, as occurs in m1s of Paucituberculata .

Gen. et sp. nov. 5

This taxon is represented by one upper and three lower molars from La Barda. The upper molar LIEB-PV 1151 shows a morphology similar to the above-described Paucituberculata , but larger in size and with cusps more inflated. The protocone and StB are the largest cusps and even more inflated; the metacone is subequal in size but taller than the paracone; the centrocrista is deep and its distal part is oriented labial and posteriorly. The metaconule and paraconule are more developed than in Gen. et sp. nov. 4, both winged, but the metaconule lacks the postmetaconular crest. The specimen LIEB-PV 1101 is a left lower molar that shows the paraconid and metaconid close to each other; talonid wider than trigonid; hypoconid is labially expanded. The specimen LIEB-PV 1136 is most probably a left m4. As in the lower molars of the Gen. et sp. nov. 4, the entoconid is compressed laterally.

Order? Paucituberculata Gen. et sp. indet. B

LIEB-PV 1108 is a left mandible from La Barda, with four alveoli and the root of a hypertrophied and procumbent i1. The mandibular ramus is low in comparison with Gen. et sp. indet. A, about half its height.

Order Sparassodonta Ameghino, 1894 Family Hathliacynidae Ameghino, 1894 Gen. et sp. nov. 6 Figure 3H

This new taxon is based on LIEB-PV 1036, a maxillary fragment with M?3 (fig. 3H), and LIEB-PV 1037, isolated metastylar portion of a right M?2, both from Laguna Fría. Although an additional specimen, LIEB-PV 1141, a fragment of a left M?2, was collected at La Barda, it is here assigned to the same taxon. LIEB-PV 1036 has a slightly reduced stylar shelf, with an StB still present, conical, and similar in size to the paracone; paracone and metacone are twinned, with the metacone much larger, resulting in a nearly absent centrocrista. The postmetacrista, although broken, appears to have been well developed. There is a small paraconule, but apparently the metaconule was absent or extremely reduced.

LIEB-PV 1036 is much larger than the oldest known hathliacynids ( Allkoquirus australis , from the early Paleocene of Bolivia, and the species of Patene , widely distributed between the late Paleocene and late Eocene of Patagonia and Brazil; Muizon, 1991; Marshall, 1978). The difference in height between paracone and metacone, and the reduction of the protocone are surprising in comparison with primitive hathliacynids. Also differing, the StB is not reduced and is subequal in size to the paracone.

A second aspect of major biostratigraphic significance is the fact that the upper molar LIEB-PV 1036 is very similar to a fragmentary upper molar assigned to Borhyaenidae indet. (MLP 79-I-17-5), held in the Museo de La Plata collection. Although it lacks the protocone, most of the tooth is well preserved and is comparable to the Laguna Fría molar in the StB dimensions, reduction of the other stylar cusps, width of the stylar shelf, and length of the postmetacrista. The major difference between the specimens is that, apparently, the Laguna Fría molar has a larger metacone. This difference, however, does not ‘‘invalidate’’ the potential attribution of both specimens to the same genus, and, probably, to the same species. Specimen MLP 79-1-17-5 was collected in 1979 at Bajo Palangana, Chubut Province, by M. McKenna and R. Turnbull, who tentatively correlated those levels with the ‘‘?Casamayoran’’ (McKenna and Turnbull, unpublished data). The stratigraphy of Bajo Palangana correlates almost completely with the Río Chico Group or Formation.

Family Borhyaenidae Ameghino, 1894 Subfamily Borhyaeninae Ameghino, 1894 cf. Nemolestes

LIEB-PV 1038 is an isolated left m?4 from Laguna Fría. The talonid is unicuspid and reduced, approximately 20% of the total length; the trigonid is formed exclusively by the paraconid and protoconid. Although partially broken, the paracristid seems to have been well developed. The anterobasal cingulum is present but weak.

The early representatives of the Sparassodonta are still poorly known. As an example, there is a citation of ‘‘cf. Nemolestes sp. ’’ from the Itaboraian of Brazil and Riochican of Argentina (see Marshall, 1978; Marshall et al., 1983). Also, indeterminate specimens are mentioned for Itaboraian levels of Itaboraí ( Brazil) and Las Flores (Patagonia) (Goin, personal obs.), as well as indeterminate borhyaenids from the Riochican of Cerro Redondo (see Simpson, 1935b).

Gen. et sp. indet. C

LIEB-PV 1093 is a right m?1 from La Barda. The trigonid is formed exclusively by the protoconid and the much lower paraconid; there is no keel basal to the paraconid. The anterobasal cingulum is vestigial and the preparacristid is short. The talonid is wider than the trigonid with only one central cusp and two labial and lingual slopes. The talonid ends in a small distal cuspule (hypoconulid?), with a lingual edge ending in a tiny crenulation (entoconid?). The presence of a central cusp in the talonid is a trait also seen in several borhyaenines, such as Plesiofelis and Pharsophorus , as well as in the proborhyaenids. The absence of a metaconid characterizes not only the m1 of proborhyaenids, but also all the lower molars of prothylacynines and m1 of borhyaenines.

Order Microbiotheria Ameghino 1887 Family Microbiotheriidae Ameghino 1887 Genus Eomicrobiotherium Marshall 1982 Eomicrobiotherium sp. Figure 3I

A single specimen of this taxon was found at Laguna Fría (LIEB-PV 1040, right m?3). It is robust, bunoid, with a short talonid which is relatively narrow, though slightly wider than the trigonid; large terminal but labially placed paraconid; protoconid and metaconid also large. The talonid is shorter than the trigonid; the cristid obliqua extends anterolingually to the rear of the trigonid posterior to the protoconid. The lingual half of the talonid is raised relative to the talonid basin, strongly blocking the lingual exit of that basin. The apically broken entoconid is a massive cusp. A broken wear surface suggests the former presence of a hypoconulid posterolingual to the entoconid, but another broken surface may show that this cuspid was present near the posterior midline of the tooth. A short anterior and posterior cingulum is present.

The massive nature of the cusps, the anterior projection of the low paraconid relative to the higher and more unified protoconid and metaconid, and the tall lingual margin of the talonid are all very distinctive features.

Gen. et sp. indet. D

This taxon is known from two specimens from Laguna Fría: LIEB-PV 1039 , a fragment of right dentary with the alveoli for i1-m2, and LIEB-PV 1041 , a right Mx. The alveoli for the incisors in LIEB-PV 1039 are not staggered as occurs in i2 of didelphimorphians. The four incisors appear to have been subequal in size, but i4 was probably smaller. The canine also was relatively small. LIEB-PV 1041 does not preserve the stylar shelf. The paracone and metacone are similar in size and height, and the centrocrista is linear, as in all other microbiotheriids. The protocone is robust and the trigon basin is wide; small paraconule and metaconule are present. Precise affinities of this taxon are difficult to assess, but the robustness of the molars suggests a possible relation with Pachybiotherium acclinum .

Family? Microbiotheriidae Gen. et sp. indet. E

LIEB-PV 1094 is an upper right molar lacking the protocone, probably an M4 because of the reduced metastylar area and absence of StD, that was collected at La Barda. Paracone and metacone are similar in size, but the paracone is slightly taller. The centrocrista is linear; the precingulum is short and narrow. StB and StA are subequal and a tiny StC is placed behind the posterior crest of the StB.

Order? Microbiotheria Ameghino, 1887 Gen. et sp. indet. F

Two lower molars from Laguna Fría and two uppers from La Barda are included in this taxon. The uppers show a linear centrocrista and short postmetacrista. The metaconule is much larger than the paraconule; neither is winged. The protocone is not wide, as seen in Caroloameghiniidae . These upper molars differ from microbiotheriids in having a welldeveloped metaconule and short postmetacrista. On the contrary, the short postmetacrista and relative size of the metaconule suggest affinities with Caroloameghiniidae . The lower molars are twice the size of Gen. et sp. indet. E. In the specimen LIEB-PV 1043, probably an m1, the metaconid is small and placed posterior to the protoconid; the trigonid/ talonid width is similar; the entoconid is laterally compressed and close to the metaconid; and the hypoconid is robust and does not project labially; and the hypoconulid is very small and nearly centrally placed.

Order Polydolopimorphia Ameghino, 1897 Suborder Hatcheriformes Case et al., 2004 Family Glasbiidae Clemens, 1966 Palangania cf. P. brandmayri Goin et al., 1998

Two lower molars from La Barda (LIEB- PV 1089 and 1090) and one from Laguna Fría (LIEB-PV 1051) are here assigned to this taxon. Trigonid and talonid lengths are similar, but the talonid is wider. The labial side is clearly twice the height of the lingual side. The trigonid shows a distinctively low protoconid and a small crest joining lingually the paraconid and metaconid; thus the trigonid basin is closed. The hypoconid is broad and the hypoconulid is relatively central; the anterobasal cingulum is absent, as is the postcingulum.

These molars resemble Palangania brandmayri in having low trigonid cusps, similar in height; metacristid is not vertical but forms an inclined surface toward the talonid; hypoconulid reduced and separated from the entoconid; entoconid large and bulbous. These molars are nearly the same size as those of the type species of Palangania .

Figures

Fig. 3. Marsupials from Laguna Fría (LF) and La Barda (LB). A, Peradectidae gen. et sp. nov., LIEB- PV 1031 (LF); B, Caroloameghiniidae gen. et sp. nov., LIEB-PV 1098 (LF); C, Peradectoidea gen. et sp. nov., LIEB-PV 1097, left M3 (LB); D, Protodidelphis sp. nov., LIEB-PV 1091, left M?3 (LB); E, Pauladelphys sp. nov., LIEB-PV 1123, m2 in a fragment of right dentary (LF); F, cf. Itaboraidelphys sp., LIEB-PV 1064, an isolated right m2 or m3 (LF); G, Paucituberculata gen. et sp. nov. 1, LIEB-PV 1135, a left maxillary fragment with M2–3 and part of M4 (LF); H, Sparassodonta, Hathliacynidae, gen. et sp. nov. LIEB-PV 1036, M?3 in a maxillary fragment (LF); I, Eomicrobiotherium sp., LIEB-PV 1040, a right m?3 (LF); J, Palangania sp., LIEB-PV 1106, left M?3 (LB); K, Gashternia ctalehor, LIEB-PV 1132, a right M4 (LB).