Javier N. Gelfo

Persistence of a Mesozoic, non-therian mammalian lineage (Gondwanatheria) in the mid-Paleogene of Patagonia

We describe two isolated molariforms recovered from early–middle Eocene (early Lutetian) levels of northwestern Patagonia, Argentina. Comparisons with major lineages of therian and non-therian mammals lead us to refer them to a new genus and species of Gondwanatheria (Allotheria). There is a single root supporting each tooth that is very short, wide, rounded, and covered by cementum; the steep sidewalls, lack of a neck between the crown and root, and the heavily worn stage in both molariforms suggest that they were of a protohypsodont type. Both teeth are strongly worn at their centers, all along their length, with the labial edge less worn than the lingual; they show strong transverse crests that alternate with lingual grooves. The protohypsodont aspect of the teeth, as well as the strong, transverse crests, are suggestive of sudamericid affinities; on the other hand, the thin enamel layer and the occlusal pattern formed by the crests and grooves shows more similarities to molariform teeth of the Ferugliotheriidae. The new taxon adds evidence regarding the (1) extensive radiation of the Gondwanatheria throughout the Southern Hemisphere, (2) persistence of several lineages well after the Cretaceous/Paleogene boundary, and (3) early evolution of hypsodont types among South American herbivorous mammals.

A New Xenungulata (Mammalia) from the Paleocene of Patagonia, Argentina

Abstract A new form of Xenungulata Paula Couto, 1952 from red levels of the Peñas Coloradas Formation in a locality near Puerto Visser (45°17′S, 67°01′W), Chubut province, Argentina, is represented by a fragmentary left jaw with the m3 (MPEF-PV 1871). Notoetayoa gargantuai n. gen. and n. sp. is the first ever found in direct association with Carodnia feruglioi Simpson, 1935a which characterizes the incompletely known homonymous zone of the late Paleocene of Patagonia. A preliminary phylogenetic analysis, including representatives of “Condylarthra,” Litopterna, Notoungulata, Pyrotheria, Xenungulata and Astrapotheria, plus the characters that could be scored in the new taxon, was performed using TNT software. A single most parsimonious tree was obtained. Notoetayoa gargantuai has a closer phylogenetic relationship with the Xenungulate Etayoa bacatensis Villarroel, 1987 from the ?middle Paleocene of Colombia than with any other Tertiary ungulate group of South America. Notoetayoa gargantuai fills an important gap in the knowledge of the mammalian faunas from the Paleocene of Patagonia, particularly of the poorly known pre-Itaborian times.

A mitogenomic timetree for Darwin’s enigmatic South American mammal Macrauchenia patachonica

The unusual mix of morphological traits displayed by extinct South American native ungulates (SANUs) confounded both Charles Darwin, who first discovered them, and Richard Owen, who tried to resolve their relationships. Here we report an almost complete mitochondrial genome for the litoptern Macrauchenia. Our dated phylogenetic tree places Macrauchenia as sister to Perissodactyla, but close to the radiation of major lineages within Laurasiatheria. This position is consistent with a divergence estimate of ∼66 Ma (95% credibility interval, 56.64–77.83 Ma) obtained for the split between Macrauchenia and other Panperissodactyla. Combined with their morphological distinctiveness, this evidence supports the positioning of Litopterna (possibly in company with other SANU groups) as a separate order within Laurasiatheria. We also show that, when using strict criteria, extinct taxa marked by deep divergence times and a lack of close living relatives may still be amenable to palaeogenomic analysis through iterative mapping against more distant relatives.

The youngest non-lepidosirenid lungfish of South America (Dipnoi, latest Paleocene–earliest Eocene, Argentina)

The first lungfish tooth plate from the Las Flores Formation, Chubut, southern Argentina, is described. This is the youngest ceratodontid known from the continent. In Africa, ceratodonts disappeared in the Eocene. Afterwards, they are only known from Australia until their extinction during the Pleistocene. The Las Flores tooth plate also represents the southernmost lungfish known since the Coniacian (early Late Cretaceous).

The condylarth Raulvaccia peligrensis (Mammalia: Didolodontidae) from the Paleocene of Patagonia, Argentina)

Abstract The Paleocene locality of Punta Peligro (Hansen Member of the Salamanca Formation) in Argentina has yielded not only ‘condylarths’ but also an extraordinary assemblage of therian mammals derived from Laurasian immigrants and non-therian mammals, relicts of the Mesozoic Gondwanan radiation. The materials, a left jaw fragment with the talonid of the second molar and the third molar, and an isolated upper molar, allow the revalidation of Raulvaccia peligrensis considered previously as a junior synonym of Escribania chubutensis. In addition to other characters, Raulvaccia strongly differs from E. chubutensis in its lesser size, the development of the m3 talonid, the presence of a hypocristid, and a postcristid. Originally Raulvaccia and Escribania were considered as Mioclaenidae, Kollpaniinae, together with other ungulates from the Santa Lucía Formation, from the early Paleocene locality of Tiupampa in Bolivia. In contrast to the Tiupampan ‘condylarths,’ Raulvaccia shares derived characters with E. chubutensis, particularly in the upper molars, such as a strong parastyle and the presence of hypocone located close to, but well differentiated from the protocone. These characters support a previous hypothesis which argues for the removal of the Peligran ‘condylarths’ from the more primitive Kollpaniinae, and sustains its relationship to the exclusively South American Didolodontidae. The revalidation of Raulvaccia peligrensis shows that the diversity of placental mammals during the earliest known Paleocene in Patagonia was greater than previously thought, and supports for the early differentiation of the Didolodontidae.

A new Megadolodinae (Mammalia, Litopterna, Protherotheriidae) from the Urumaco Formation (Late Miocene) of Venezuela

Synopsis A new genus and species of Proterotheriidae Megadolodinae, Bounodus enigmaticus, from the Upper Miocene Urumaco Formation of Venezuela, is described on the basis of a poorly preserved right maxillary fragment with brachydont cheek teeth. Teeth and alveoli preserved are interpreted as part of the alveolus of P3 and P4‐M3. The new taxon differs from Megadolodus, the only other known genus of the subfamily, in having a proportionally smaller P4 and M1, the latter elongated antero‐posteriorly and with the protocone root more mesial than that of the hypocone. Bounodus enigmaticus gen. et sp. nov., reinforces the hypothesis that the Megadolodinae represent a distinct radiation within the Proterotheriidae, the two other major clades being the Anisolambdinae and Proterotheriinae.

Cranial Morphology of the Late Oligocene Patagonian Notohippid Rhynchippus equinus Ameghino, 1897 (Mammalia, Notoungulata) with Emphases in Basicranial and Auditory Region.

“Notohippidae” is a probably paraphyletic family of medium sized notoungulates with complete dentition and early tendency to hypsodonty. They have been recorded from early Eocene to early Miocene, being particularly diverse by the late Oligocene. Although Rhynchippus equinus Ameghino is one of the most frequent notohippids in the fossil record, there are scarce data about cranial osteology other than the classical descriptions which date back to the early last century. In this context, we describe the exceptionally preserved specimen MPEF PV 695 (based on CT scanning technique and 3D reconstruction) with the aim of improving our knowledge of the species, especially regarding auditory region (petrosal, tympanic and surrounding elements), sphenoidal and occipital complexes. Besides a modular description of the whole skull, osteological correlates identified on the basicranium are used to infer some soft-tissue elements, especially those associated with vessels that supply the head, mainly intracranially. One of the most informative elements was the petrosal bone, whose general morphology matches that expected for a toxodont. The endocranial surface, together with the surrounding parietal, basisphenoid, occipital, and squamosal, enabled us to propose the location and communication of main venous sinuses of the lateral head wall (temporal, inferior and sigmoid sinuses), whereas the tympanic aspect and the identification of a posterior carotid artery canal provided strong evidence in support of an intratympanic course of the internal carotid artery, a controversial issue among notoungulates. Regarding the arrangement of tympanic and paratympanic spaces, the preservation of the specimen allowed us to appreciate the three connected spaces that constitute a heavily pneumatized middle ear; the epitympanic sinus, the tympanic cavity itself, and the ventral expansion of the tympanic cavity through the notably inflated bullae. We hope this study stimulates further inquires and provides potentially informative data for future research involving other representatives of the order.

Eocene ungulate mammals from West Antarctica: implications from their fossil record and a new species

Abstract Here we describe a new terrestrial mammal from the Eocene of Seymour Island (Isla Marambio) represented by a lower left third molar and assigned to a new species of Sparnotheriodontidae, an ungulate family with a broad palaeobiogeographical distribution in South America. The specimen was found in the Cucullaea I allomember of the La Meseta Formation, in a new mammalian locality (IAA 2/16). Notiolofos regueroi sp. nov. shares a brachyodont, lophoselenodont and bicrescentic molar pattern with N. arquinotiensis, recorded for a stratigraphic sequence of 17.5 Ma in Antarctica. The criteria for the species differentiation are the absence of mesial and labial cingulids, the larger paraconid, the wider talonid basin, the accentuated distal projection of the hypoconulid, the centroconid development and the smaller size. Together with the astrapotherian Antarctodon sobrali, they represent the medium to large terrestrial mammals of the early Eocene Antarctic landscape that was mostly dominated by closed forests of Nothofagus. Dental wear facets and differences in their body mass are inferred and discussed as possible evidence of niche differentiation. Additionally, the presence of land mammals with Patagonian affinities in the Eocene of Antarctica reinforces the Cretaceous–Palaeocene presence of the Weddellian Isthmus, a functional land corridor between Antarctica and South America.

Considerations about the Evolutionary Stasis of Notiolofos arquinotiensis (Mammalia: Sparnotheriodontidae), Eocene of Seymour Island, Antarctica

Abstract. Notiolofos arquinotiensis is the most abundant terrestrial placental mammal in the Paleogene of the Antarctic continent. Evidence suggests a South American origin of Sparnotheriodontidae, and an allopatric speciation event for the appearance of N. arquinotiensis. It was recorded exclusively on Seymour Island, through most of the La Meseta and Submeseta formations. Isotopic and paleomagnetic calibration of the units indicate a relatively continuous fossil record of at least 17.5 Ma. The stasis hypothesis is tested here as opposite to the possibility of a wider and previously non-identified specific diversity of Antarctic sparnotheriodontids. The material of N. arquinotensis available was compared in preservation, characters and dental occlusal areas to the more complete phylogenetic relative Sparnotheriodon epsilonoides and the North American Meniscotherium chamense. Despite there being no close phylogenetic relationship between Notiolofos and Meniscotherium, the morphological dental similarity between them suggests they could be interpreted as ecologically equivalent taxa. The analysis allows the reassignment of some N. arquinotensis teeth to other dental loci. The results indicate that there are no reasons to justify the presence of different species through the stratigraphic sequence or to refute the morphological stasis in N. arquinotensis. Stasis among Antarctic Eocene vertebrates is also recorded among Eocene penguins. The “Plus ça change” model indicate that morphological stasis and punctuated equilibrium were detected as the usual responses to widely fluctuating physical environments such as those characteristic of temperate regions and shallow waters. This model fits well with inferences on Antarctic paleoclimate and paleogeography and the land fossil record.

Procellariiform remains and a new species from the latest Eocene of Antarctica

Abstract New remains from the La Meseta (Thanetian – Lutetian) and Submeseta (Lutetian – Rupelian) formations (Seymour Island, Antarctica) are tentatively assigned to Diomedeidae and Procellariidae (Procellariiformes). Based on the fossil record and several analyses that attempt to explain the evolutionary patterns of Diomedeidae, Notoleptos giglii gen. et sp. nov., based on a small tarsometatarsus, was an ancestral form that lived in Antarctica before the rise of large-sized albatrosses. Subsequent environmental cooling since the late Oligocene could have selected against small body size, to the detriment of small-sized albatrosses like Notoleptos, thus favoring large body size and setting the stage for the development of the specialized albatross flight. ZooBank ID (LSID): urn:lsid:zoobank.org:pub:C8D9C862-1536-4EA3-8A76-70903AA75639