A new archaic homodont toothed cetacean (Mammalia, Cetacea, Odontoceti) from the early Miocene of Peru

Apart from a few exceptions, extant odontocetes (toothed cetaceans) exhibit a roughly homodont dentition. The transition from basilosaurid-like double-rooted cheek teeth with accessory denticles to single-rooted conical teeth occurred during the late Oligocene-early Miocene. At that time, several clades of now extinct, homodont and predominantly long-snouted odontocetes appeared in the fossil record. Among them, members of the genera Argyrocetus Lydekker, 1893 and Macrodelphinus Wilson, 1935, from the early Miocene of the Northeast Pacific and Argentina, were tentatively attributed to the family Eurhinodelphinidae. However, due to the fragmentary state of the specimens, unambiguous apomorphies of the family could not be detected. Based on two well-preserved skulls with associated mandibular elements, discovered in early Miocene layers of the Chilcatay Formation (Pisco Basin, Peru), we report on a new genus and species of long-snouted homodont odontocete, Chilcacetus cavirhinus n. gen., n. sp. Characterized by, among others, the presence of alveoli on the anterior premaxillary portion of the rostrum, the lack of a lateral groove on the rostrum, anterodorsally elevated nasals, a possibly autapomorphic cavity between nasals and mesethmoid in the posterior wall of the bony nares, a high temporal fossa, and the absence of ankylosis along the mandibular symphysis, C. cavirhinus n. gen., n. sp. does not fit in any of the known odontocete families, but shares several morphological features with Argyrocetus spp. and Macrodelphinus. Our phylogenetic analysis, based on 77 characters for 35 odontocete taxa, suggests the existence of an early Miocene Eastern Pacific long-snouted homodont odontocete clade (with an hypothetical South Atlantic member, the poorly known Argyrocetus patagonicus Lydekker, 1893), distinct from the only superficially similar eoplatanistids and eurhinodelphinids. Furthermore, our consensus tree indicates an early branching of this new clade compared to other homodont odontocete lineages. Unfortunately, the results of the cladistic analysis presented here are not well supported; a reappraisal of Argyrocetus and Macrodelphinus is needed to more clearly define the new clade and bolster its phylogentic position

Neogene and Quaternary fossil remains of beaked whales (Cetacea, Odontoceti, Ziphiidae) from deep-sea deposits off Crozet and Kerguelen islands, Southern Ocean

Although a high number of extant beaked whale species (Cetacea, Odontoceti, Ziphiidae) live in the Southern Ocean and neighbouring areas, only little is known about the past occupation of the region by these highly specialized, deep diving and echolocating cetaceans. Recently, longline fishing activities along the seafloor at depths of 500-2000 m off the sub-antarctic Crozet and Kerguelen islands, Indian sector of Southern Ocean, resulted in the accessory "capture" of tens of ziphiid fossil cranial remains. Our description and comparison of the best-preserved and most diagnostic crania from this sample lead to the identification of more than eight species in at least seven genera: the hyperoodontines Africanacetus ceratopsis, Khoikhoicetus kergueleni n. sp., Hyperoodontinae indet. aff. Africanacetus, and Mesoplodon sp. aff. Mesoplodon layardii, the ziphiines lzikoziphius rossi and Ziphius sp., and the ziphiids indet. Nenga sp. aff. Nenga meganasalis and Xhosacetus hendeysi. Unsurprisingly, with at least four species in common (A. ceratopsis, lzikoziphius rossi, X. hendeysi, and Ziphius sp.), the assemblage displays high similarities with assemblages described from deep-sea deposits off South Africa, providing thus new data on the palaeogeographic distribution of several extinct species and indicating a roughly similar geochronological age for at least a part of the assemblages. The limited amount of data available points to a pre-Pliocene age for a large part of the Crozet-Kerguelen assemblage, suggesting a relatively early, Miocene colonization of the Southern Ocean by crown ziphiids. Contrastingly, C-14 radiometric dating of two specimens of Mesoplodon sp. aff. Mesoploden layardii yielded latest Pleistocene-earliest Holocene ages. These results reveal the presence either of an extinct species of Mesoplodon in the Southern Ocean only a few thousands years ago, or of an up-to-now unidentified extant species closely related to the strap-toothed whale M. layardii

EURHINODELPHINIDS FROM THE EARLY MIOCENE OF PERU: FIRST UNAMBIGUOUS RECORDS OF THESE HYPER-LONGIROSTRINE DOLPHINS OUTSIDE THE NORTH ATLANTIC REALM

Among the many hyper-longirostrine dolphins (Odontoceti) from the Miocene, members of the family Eurhinodelphinidae bear two highly distinctive cranial features: a long and edentulous premaxillary portion of the rostrum and a mandible that is significantly shorter than the rostrum. Until now, unambiguously attributed members of this clade were only recorded from early to middle Miocene deposits of the North Atlantic realm (east coast U.S.A., North Sea Basin, and Mediterranean). In this work we describe and compare two partial skulls of longirostrine dolphins from late early Miocene (Burdigalian, 19.25-18 Ma) marine deposits of the Chilcatay Formation, in the East Pisco Basin (southern coast of Peru), preserving rostral and mandibular material, as well as ear bones. Based on these specimens we report diagnostic remains attributable to this family for the first time for the whole Southern Hemisphere and the whole Pacific Ocean. This major expansion of eurhinodelphinids' palaeogeographic distribution contrasts with their proposed shallow-water, coastal environments; it suggests a new dispersal route for members of the family across the Central American Seaway; and it further highlights the similarities between the odontocete faunas of the southeastern Pacific and North Atlantic realm during the Miocene. Better-preserved eurhinodelphinid specimens from the odontocete-rich Chilcatay Formation will allow for a more detailed comparison with North Atlantic members of the family

A new large squalodelphinid (Cetacea, Odontoceti) from Peru sheds light on the early miocene platanistoid disparity and ecology

The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78±0.08Ma (Burdigalian, EarlyMiocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the EarlyMiocene radiation of crown odontocetes

A new platyrostrine sperm whale from the Early Miocene of the southeastern Pacific (East Pisco Basin, Peru) supports affinities with the southwestern Atlantic cetacean fauna

Contrasting with their suction feeding modern relatives in the families Kogiidae and Physeteridae, Miocene physeteroids display a broad range of feeding strategies. Despite the continuous improvements of the fossil record, the transition from the earliest sperm whales to suction feeding forms as well as the once prominent macroraptorial forms remains poorly understood. In the present work, we investigate a partial sperm whale skull from Lower Miocene (Burdigalian) strata of the Chilcatay Formation of the East Pisco Basin, along the southern coast of Peru. Based on this specimen, we describe a new species in the genus Diaphorocetus Ameghino, 1894, which was previously known only by the holotype of Diaphorocetus poucheti (Moreno, 1892) from a roughly synchronous unit in Patagonia (Argentina). Differing from the latter in its smaller cranial dimensions, higher tooth count, and minor differences in the position of facial foramina, the new species Diaphorocetus ortegai n. sp. confirms a key character of D. poucheti, the marked dorsoventral flattening of the maxillary portion of the rostrum. Such cranial proportions suggest that, compared to other physeteroids, D. poucheti and D. ortegai n. sp. were more efficient at performing fast lateral sweeps of their rostra to capture small- to medium-sized prey items with their proportionally small teeth. Recovered as stem physeteroids in our phylogenetic analysis, these sister species contribute to the ecomorphological disparity of sperm whales during the Early Miocene, but without displaying any of the cranial and dental changes occurring in later, macroraptorial and suction feeding sperm whales. The description of a new species of Diaphorocetus from southern Peru increases the similarities between the toothed whale faunas from the local Chilcatay Formation and the Gaiman and Monte Leon formations of Argentinian Patagonia, pointing not only to dispersal routes between the southeastern Pacific and southwestern Atlantic during the Burdigalian, but also to relatively similar ecological settings along the coasts of Peru and Patagonia at that time

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 B66Ma (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.Facultad de Ciencias Naturales y Muse

Palaeoproteomics resolves sloth relationships

The living tree sloths Choloepus and Bradypus are the only remaining members of Folivora, a major xenarthran radiation that occupied a wide range of habitats in many parts of the western hemisphere during the Cenozoic, including both continents and the West Indies. Ancient DNA evidence has played only a minor role in folivoran systematics, as most sloths lived in places not conducive to genomic preservation. Here we utilize collagen sequence information, both separately and in combination with published mitochondrial DNA evidence, to assess the relationships of tree sloths and their extinct relatives. Results from phylogenetic analysis of these datasets differ substantially from morphology-based concepts: Choloepus groups with Mylodontidae, not Megalonychidae; Bradypus and Megalonyx pair together as megatherioids, while monophyletic Antillean sloths may be sister to all other folivorans. Divergence estimates are consistent with fossil evidence for mid-Cenozoic presence of sloths in the West Indies and an early Miocene radiation in South America