Chilcatay Formation Research Articles

Chronology and Paleoenvironment of the Tunga Formation, a new lowermost Miocene sequence in the East Pisco Basin of southern Peru

The East Pisco Basin, occupying the coastal plain of Peru between 13°S and 16°S, is widely known for its extensive Eocene to Quaternary biosiliceous deposits and excellent preservation of fossil marine vertebrates. Biochronologic studies published over the past 35 years record a hiatus of about 13 million years (*32–19 Ma) separating the youngest Paleogene deposits (Otuma Formation) from the oldest Neogene deposits (Chilcatay Formation). We describe a newly identified Lower Miocene depositional sequence that lies below documented Chilcatay strata, rich in diatoms and benthic foraminifers, which we name the Tunga Formation. A low-latitude diatom assemblage from the Tunga Formation indicates an age of 21.6 to 20.5 Ma age, whereas an ash within basal Tunga strata yields an 206Pb/238U weighted mean age of 20.58 ± 0.13 Ma. Benthic foraminifer paleodepth analysis and the diatom assemblage of the Tunga Formation indicate deposition took place along the continental margin at upper bathyal depths under hypoxic conditions beneath highly productive waters, a scenario also supported by the presence of abundant clupeoid fish scales and dolomitized horizons. The Tunga Formation is characterized by a profound scarcity of cetacean fossils, unlike the cetacean-rich neritic sediments of the overlying Chilcatay Formation.

A puzzling occurrence of the bite mark ichnogenus Linichnus from the Lower Miocene Chilcatay Formation of Peru

A puzzling occurrence of the bite mark ichnogenus Linichnus from the Lower Miocene Chilcatay Formation of Peru

Dental Morphology, Palaeoecology and Palaeobiogeographic Significance of a New Species of Requiem Shark (Genus Carcharhinus) from the Lower Miocene of Peru (East Pisco Basin, Chilcatay Formation)

Nowadays, the requiem sharks comprise one of the most diverse and widespread families of selachians, i.e., Carcharhinidae. Among the carcharhinids, the genus Carcharhinus has the largest number of living species, namely, at least 35. Known from fossils as old as the Cretaceous, the requiem sharks did not significantly radiate before the Eocene (when Carcharhinus also appeared), and their diversification mainly occurred in Neogene times. Here, we describe a new species of requiem shark, Carcharhinus dicelmai sp. nov., based on fossil teeth from Lower Miocene (18.4–18.1 Ma) strata of the Chilcatay Formation of the East Pisco Basin (southern Peru). Upper teeth of C. dicelmai sp. nov. are typically provided with a slender, smooth-edged cusp; a marked coronal twist; and a distal heel that bears 1–5 coarse, angularly lobate serrae that become more prominent toward the base of the cusp. The dentition of C. dicelmai sp. nov. appears less akin to that of most other carcharhines to the cutting-clutching type, and seemingly testifies to the development of more predominantly clutching adaptations. A carcharhinid tooth from the Burdigalian to lower Langhian Cantaure Formation of Venezuela is reassigned to C. dicelmai sp. nov., suggesting a trans-Panamanian distribution for this extinct shark species.

Ultrastructure, composition, and 87Sr/86Sr dating of shark teeth from lower Miocene sediments of southwestern Peru

Bioapatite of fossil bone and teeth is susceptible to alteration and ion exchange during burial and diagenesis, varying its Sr content through the geological time. Nevertheless, fossil shark teeth are a powerful proxy for both chronostratigraphic and paleoecological reconstructions, thanks to the presence of the enameloid, a hard outer layer consisting of resistant fluorapatite crystallites. Here, we analyze fossil shark teeth from the Miocene sediments of the Chilcatay Formation of the Pisco Basin (southwestern Peru) with the aim of dating poorly constrained strata in this region. (Ultra)structural and compositional analyses of fossil lamniform and carcharhiniform teeth are performed through macroscopical observations, optical microscopy and SEM-EDS for evaluating the preservation state of the collected teeth. Shark teeth display a compact and well preserved outer enameloid layer formed by highly ordered bundles of crystallites that is distinctly separated by a more porous and heterogeneous inner core of dentine featuring diagenetic artefacts and microborings. Compositional mapping highlights differences in the distribution of Ca, P, F, and S in the enameloid and dentine, and chemical results show a Sr content that is consistent with the range reported for extant shark teeth. The best preserved teeth were selected for Strontium Isotope Stratigraphy (SIS), measuring the 87Sr/86Sr values in the enameloid and obtaining numerical (absolute) age estimates. In the Ica River Valley, SIS dates the Chilcatay strata to the Burdigalian (between 19.1 and 18.1 Ma), in agreement with previous radiometric, isotopic and biostratigraphic ages obtained in the same region. At Media Luna, the Chilcatay strata are dated herein for the first time, resulting in a slightly older age of 21.8–20.1 Ma (late Aquitanian–early Burdigalian). These results strengthen the notion that the Sr-ratio of shark teeth can be successfully applied for obtaining reliable age estimates via SIS.

(Bio)stratigraphic overview and paleoclimatic-paleoceanographic implications of the middle-upper Eocene deposits from the Ica River Valley (East Pisco Basin, Peru)

The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive.This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic-bioclastic sand-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8–41.2 Ma) through the Bartonian (41.2–37.7 Ma) to the early Priabonian (37.7–33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sandstone, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere.Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147–170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.

An investigation of vermetid reefs from the Miocene of Peru, with the description of a new species

Exquisitely preserved fossils of a new reef-building vermetid species from shallow-marine lower Miocene (Burdigalian) deposits of the Chilcatay Formation and upper Miocene (Tortonian) sediments of the Pisco Formation of Peru are here reported and described in detail for the first time. These finds are assigned to the living genus Thylacodes and recognized as representatives of a new species, Thylacodes devriesi sp. nov. This new taxon is known by long, almost straight tube-like shells that display peculiar ornamentations in form of striated lamellae and are arranged in an organ-pipe fashion. This discovery represents an important addition to the knowledge of the systematics and distribution of Thylacodes in South America in the geological past. Paleoenvironmental and taphonomic inferences drawn by the fossil remains of this reef-forming species are herein discussed for both the Chilcatay and Pisco Formations in the broader framework of the South American fossil record of Vermetidae.

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 longirostrine sperm whale (Cetacea, Physeteroidea) from the lower Miocene of the Pisco Basin (southern coast of Peru)

The modern sperm whales Kogia and Physeter (superfamily Physeteroidea) represent highly disparate, relict members of a group of odontocetes that peaked in diversity during the middle to late Miocene. Based on a highly informative specimen (including the cranium with ear bones, mandibles, teeth and some postcranial elements) from the lower Miocene (early Burdigalian, 19–18 Ma) of the Chilcatay Formation (Pisco Basin, Peru), we describe here a new genus and species of physeteroid, Rhaphicetus valenciae gen. et sp. nov. The latter is one of the geologically oldest physeteroids. This medium-sized species (estimated body length between 4.7 and 5.7 m) differs from all other physeteroids by the following, probably autapomorphic, features: a narrow, cylindrical rostrum comprising nearly 75% of the condylobasal length; the two main dorsal infraorbital foramina located posterior to the antorbital notch; an upper tooth count of at least 36 teeth per quadrant; and anterior-most upper alveoli filled by thick bony pads. Our phylogenetic analysis recovers R. valenciae as one of the earliest branching stem physeteroids. The highly unusual filling of the anterior upper alveoli by bony pads is interpreted as part of a mechanism leading to the loss of apical and subapical upper teeth. By comparison with other odontocetes displaying some degree of anterior reduction of the dentition, this condition may have corresponded to the rostrum being anteriorly longer than the mandible. The elongated rostrum with a circular cross-section, the long temporal fossa, and the high number of slender, pointed upper and lower teeth all suggest that R. valenciae used its dentition to grasp relatively small prey, possibly via rapid movements of the head. On the one hand, this new Peruvian record increases our knowledge of the morphological disparity of sperm whales during the Miocene. On the other hand, it may provide clues to the ancestral morphotype for all physeteroids. http://zoobank.org/urn:lsid:zoobank.org:pub:3E1CEFC8-0F23-416E-9C02-03750D7199BA

Tephrochronology and chronostratigraphy of the Miocene Chilcatay and Pisco formations (East Pisco Basin, Peru)

Strata of Chilcatay and Pisco formations exposed in the Ica Desert (East Pisco Basin, southern Peru) preserve one of the most complete and rich records of Miocene marine vertebrates of the world. Despite its exceptional importance, the chronostratigraphy of these fossil-bearing deposits has been only sporadically studied in the literature until recently. This work presents a detailed reconstruction of the chronostratigraphic framework, achieved by mapping and measuring of seven sections (totaling a height of almost 1000 m) of the Miocene Chilcatay and Pisco formations along the western side of the Ica River. The Chilcatay Formation consists of two allomembers, namely Ct1 and Ct2, bounded at the base by unconformities CE0.1 and CE0.2, respectively. Similarly, the immediately overlying Pisco Formation is divided into allomembers P0, P1, and P2, bounded at the base by unconformities PE0.0, PE0.1 and PE0.2, respectively. The new 39Ar–40Ar results presented here, combined with ages of previous work, provide precise constraints on the age of several stratigraphically referenced volcanic ash layers intercalated in the studied fossil-bearing succession, placing its vertebrate fossil fauna within a refined temporal framework and laying the solid ground for its detailed regional and global comparison. The ages of the allomembers, and thus their associated faunas, can be reliably estimated by the combination of 39Ar–40Ar dating on tephra layers with diatom biostratigraphy. In the study area, two methods are mutually consistent and constrain the deposition of the Chilcatay Formation between 19.2 and 18.0 Ma, that of P1 between 9.5 and 8.6 Ma, and that of P2 between 8.4 and 6.7 Ma. In the absence of direct dating of the P0 allomember, which lacks both preserved tephra suitable for 39Ar–40Ar dating and microfossils, its age can be constrained to the temporal gap between the youngest age available from the underlying Chilcatay strata (18.0 Ma) and the oldest age available from the overlying P1 strata (9.5 Ma).

Extensive Diversity and Disparity of the Early Miocene Platanistoids (Cetacea, Odontoceti) in the Southeastern Pacific (Chilcatay Formation, Peru).

Several aspects of the fascinating evolutionary history of toothed and baleen whales (Cetacea) are still to be clarified due to the fragmentation and discontinuity (in space and time) of the fossil record. Here we open a window on the past, describing a part of the extraordinary cetacean fossil assemblage deposited in a restricted interval of time (19–18 Ma) in the Chilcatay Formation (Peru). All the fossils here examined belong to the Platanistoidea clade as here redefined, a toothed whale group nowadays represented only by the Asian river dolphin Platanista gangetica. Two new genera and species, the hyper-longirostrine Ensidelphis riveroi and the squalodelphinid Furcacetus flexirostrum, are described together with new material referred to the squalodelphinid Notocetus vanbenedeni and fragmentary remains showing affinities with the platanistid Araeodelphis. Our cladistic analysis defines the new clade Platanidelphidi, sister-group to Allodelphinidae and including E. riveroi and the clade Squalodelphinidae + Platanistidae. The fossils here examined further confirm the high diversity and disparity of platanistoids during the early Miocene. Finally, morphofunctional considerations on the entire platanistoid assemblage of the Chilcatay Formation suggest a high trophic partitioning of this peculiar cetacean paleocommunity.

Perumegabalanus calziai gen. et sp. nov., a new intertidal megabalanine barnacle from the early Miocene of Peru

Living members of the tribe Austromegabalanini are large balanid barnacles (Crustacea: Cirripedia: Neobalanoformes) that live in temperate and cold waters of the Southern Hemisphere. During the Neogene, however, the austromegabalanines also inhabited the Northern Hemisphere, as well as some low- latitude tropical environments. This paper describes a new taxon of austromegab-alanines, Perumegabalanus calziai gen. et sp. nov., from the shallow-marine, nearshore, lower Miocene (19 to 17 Ma, Burdigalian) deposits of the Chilcatay Formation (East Pisco Basin, southern Peru). Among austromegabalanines, this new taxon is characterised by the presence of thick, ornamented, multitubiferous parietes, where the parietal tubes are irregularly partitioned by auxiliary sep - ta; in addition, the sheath is vesicular. Based on morphofunctional considerations, the peculiar shell architecture of P. calziai is here interpreted as well-suited for an existence in the intertidal zone. In the Chilcatay strata, two taxa of Austromegabalanini (i. e., Austromegabalanus carrioli and P. calziai) coexist, representing some of the geologically oldest records of austromegabalanines worldwide – an observation that strongly supports the hypothesis of a circum-equatorial origin and early diversification for this successful lineage of acorn barnacles.

Strontium Isotope Stratigraphy and the thermophilic fossil fauna from the middle Miocene of the East Pisco Basin (Peru)

New age estimates obtained via Strontium Isotope (87Sr/86Sr) Stratigraphy and new paleoclimatic data are here presented for the Miocene Chilcatay and Pisco formations exposed in the East Pisco Basin, an Andean forearc basin of southern Peru, which is renowned worldwide for its exceptional content of fossil marine vertebrates. Mollusk and barnacle shells, carbonate nodules, and shark teeth were collected along three stratigraphic sections for applying Strontium Isotope Stratigraphy on both carbonates and phosphates. To avoid diagenetic biases, mollusk and barnacle shells were analyzed in detail by means of optical and scanning electron microscopy, cathodoluminescence, and inductively coupled plasma-optical emission spectrometry, whereas only the enameloid from the best-preserved shark teeth was sampled. The obtained 87Sr/86Sr ages confirm a late early Miocene (Burdigalian) age for the Chilcatay strata, and reveal middle Miocene (Langhian to Serravallian) ages for the lower Pisco unit (i.e., the P0 sequence) – a result that matches the relatively archaic aspect of its cetacean fossil assemblage. New and literature data about the fossil assemblage of the lower Pisco beds highlight the presence of several thermophilic invertebrates and vertebrates, thus suggesting a warm-water, tropical paleoenvironment for this middle Miocene sequence. Such a paleoenvironmental scenario recalls the warm conditions associated with the Chilcatay Formation, rather than the cooler setting inferred for the remainder of the Pisco Formation (i.e., the P1 and P2 sequences). This pattern likely reflects the late Miocene trend of global cooling, as well as a middle to early late Miocene strengthening of the Humboldt Current.

A new barnacle (Cirripedia: Neobalanoformes) from the early Miocene of Peru: Palaeoecological and palaeobiogeographical implications

A new megabalanine barnacle, Austromegabalanus carrioli sp. nov., is described from lower Miocene strata of the Chilcatay Formation (East Pisco Basin, southern Peru). An assessment of the value of interlaminate figures in distinguishing species within the tribe Austromegabalanini from thin sections is provided-a useful identification tool with fossil taxa such as the austromegabalanines, which are commonly found only as fragmented shells. The paper concludes with a reassessment of the palaeobiogeography and distribution patterns of the austromegabalanines, proposing a circum-equatorial origin for this tribe.

Allostratigraphy and paleontology of the lower Miocene Chilcatay Formation in the Zamaca area, East Pisco basin, southern Peru

ABSTRACT Based on mapping of laterally traceable stratigraphic discontinuities, we propose a high-resolution allostratigraphic scheme for one of the world’s foremost fossil marine vertebrate Lagerstätten: the lower Miocene strata of the Chilcatay Formation exposed along the Ica River near Zamaca, southern Peru. Measured sections combined with 1:10,000 scale mapping of a 24 km2 area provide an overview of the stratal architecture, as well as a general facies framework and interpretation of the various depositional settings. As a whole, the Chilcatay alloformation is bounded by the CE0.1 unconformity at the base and the PE0.0 unconformity at the top. An internal Chilcatay surface, termed CE0.2, splits the alloformation into two distinct allomembers (Ct1 and Ct2). The Ct1 allomember comprises three facies associations recording deposition in shoreface, offshore, and subaqueous delta settings. The Ct2 allomember comprises two facies associations, recording deposition in shoreface and offshore settings. Using these data, we place the rich marine vertebrate assemblage in a precise spatial and stratigraphic framework. The well-diversified vertebrate assemblage is dominated by cetaceans (mostly odontocetes) and sharks (mostly lamniforms and carcharhiniforms); rays, bony fish, and turtles are also present. Taxonomic novelties include the first records of baleen whales, platanistids, and eurhinodelphinids from the Chilcatay Formation.

Taphonomy and palaeoecology of the lower Miocene marine vertebrate assemblage of Ullujaya (Chilcatay Formation, East Pisco Basin, southern Peru)

The taphonomy and palaeoecology of the early Miocene (Burdigalian) vertebrate assemblage of Ullujaya (East Pisco Basin, Peru) is here described. Vertebrate remains are concentrated in marine facies (Ct1a association) of the exposed Chilcatay Formation (dated 19–18 Ma) deposited within a 30–40 m deep, semi-enclosed, offshore environment. Coupled with ichnological observations, the size distribution of pyrite framboid relics reveals fluctuation of euxinic and oxic-dysoxic conditions at the seafloor. The assemblage is dominated by toothed cetaceans (kentriodontids, squalodelphinids, physeteroids, and the eurhinodelphinid-like Chilcacetus), together with a large dermochelyid turtle, some bony fish, and diverse elasmobranchs, mostly juveniles of Carcharhinus brachyurus and Cosmopolitodus hastalis. The vertebrate assemblage comprises a coastal community, dominated by mesopredators, representative of a warm-temperate, sheltered embayment connected with riverine and open-ocean environments. Vertebrate skeletons are typically disarticulated and incomplete, and some bone elements display shark bite marks. Microborings are observed at the bone surface. Bones exhibit a good degree of apatite mineralisation and bone cavities are locally filled by Ca-Mg carbonates. Our taphonomic observations suggest prolonged flotation of carcasses during which they were subject to biogenic and physical processes of partial destruction (including scavenging by sharks), before final deposition on a soft compact substrate. Preservation was favoured by the oxygen-deficient bottom conditions that inhibited the action of benthic macro-scavengers.

The early Miocene elasmobranch assemblage from Zamaca (Chilcatay Formation, Peru)

A newly discovered elasmobranch assemblage from the fossil-bearing area of Zamaca (Chilcatay Formation, southern Peru) is described herein, providing a first comprehensive view on the early Miocene shark and ray paleocommunities of the East Pisco Basin, whose sedimentary infill represents one of the most important Cenozoic Fossil-Lagerstätten worldwide. The studied assemblage includes at least twenty-two species attributed to twelve families and five orders. Thirteen taxa are recorded for the first time from the Chilcatay Formation, and four of them are recorded for the first time from the Pacific coast of South America. The reconstructed paleoenvironmental scenario is consistent with a shallow-marine coastal area, representative of a sheltered shelfal setting, influenced by both brackish and open-ocean waters. This paleoenvironment was inhabited by a community of small mesopredator elasmobranchs that exploited the Zamaca area as a nursery ground and recruitment area. The structure of the Zamaca assemblage is mainly explained by three key-features: 1) a taxonomic composition dominated by two shark lineages, Lamniformes and Carcharhiniformes, the former being predominant; 2) the leading role played by two species, Carcharhinus brachyurus and †Cosmopolitodus hastalis, accounting for about 60% of the analyzed specimens; 3) the distinctly juvenile imprint of the entire assemblage. Striking similarities emerge between the elasmobranch assemblage from Zamaca and the late Miocene one from Cerro Colorado (Pisco Formation, East Pisco Basin), thus suggesting the persistence of a peculiar “biological enclave” driven by the concurrence of the ecological, environmental, and oceanographic factors that characterized the coast of present-day Peru during the Neogene.

Facies analysis, stratigraphy and marine vertebrate assemblage of the lower Miocene Chilcatay Formation at Ullujaya (Pisco basin, Peru)

ABSTRACTThis paper is the first integrated account of the sedimentology, stratigraphy, and vertebrate paleontology for the marine strata of the Chilcatay Formation exposed at Ullujaya, Pisco basin (southern Peru). An allostratigraphic framework for the investigated strata was established using geological mapping (1:4000 scale) and conventional sedimentary facies analysis and resulted in recognition of two unconformity-bounded allomembers (designated Ct1 and Ct2 in ascending order). The chronostratigraphic framework is well constrained by integration of micropaleontological data and isotope geochronology and indicates deposition during the early Miocene. The marine vertebrate fossil assemblage is largely dominated by cetaceans (odontocetes), whereas isolated teeth and spines indicate a well-diversified elasmobranch assemblage. Our field surveys, conducted to evaluate the paleontological sensitivity of the investigated strata, indicate that vertebrate remains only came from a rather restricted stratigraphic interval of the Ct1 allomember and reveal the high potential for these sediments to yield abundant and scientifically significant fossil assemblages.

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 ± 0.08 Ma (Burdigalian, Early Miocene). 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 Early Miocene radiation of crown odontocetes.

A new odontocete (toothed cetacean) from the Early Miocene of Peru expands the morphological disparity of extinct heterodont dolphins

A key step in the evolutionary history of Odontoceti (echolocating toothed cetaceans) is the transition from the ancestral heterodont condition – characterized by the presence of double-rooted cheek teeth bearing accessory denticles – to the homodont dentition displayed by most extant odontocete species. During the last few decades, new finds and the reassessment of specimens in collections revealed an increased morphological disparity amongst the Oligo–Miocene heterodont odontocetes. Based on a partly articulated skeleton from late Early Miocene (Burdigalian, 18.8–18.0 Ma) beds of the Chilcatay Formation (Pisco Basin, Peru), we describe a new genus and species of heterodont odontocete, Inticetus vertizi, in the new family Inticetidae. This large dolphin is characterized by, amongst other things, a long and robust rostrum bearing at least 18 teeth per quadrant; the absence of procumbent anterior teeth; many large, broad-based accessory denticles in double-rooted posterior cheek teeth; a reduced ornament of dental crowns; the styliform process of the jugal being markedly robust; a large fovea epitubaria on the periotic, with a correspondingly voluminous accessory ossicle of the tympanic bulla; and a shortened tuberculum of the malleus. Phylogenetic analyses (with and without molecular constraint; with and without down-weighting of homoplastic characters) yielded contrasting results, with Inticetus falling either as a stem Odontoceti or as an early branching member of a large Platanistoidea clade. With its large size, robust rostrum and unusual dental morphology, and the absence of conspicuous tooth wear, Inticetus increases the morphological and ecological disparity of Late Oligocene–Early Miocene heterodont odontocetes. Finally, this new taxon calls for caution when attempting to identify isolated cetacean cheek teeth, even at the suborder level.http://zoobank.org/urn:lsid:zoobank.org:pub:5B306B49-EB1B-42F9-B755-B0B05B4F938F

A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’ clade

We describe a new large otodontid lamniform shark, Megalolamna paradoxodon gen. nov. et sp. nov., chronostratigraphically restricted to the early Miocene (Aquitanian–Burdigalian). This new species is based on isolated teeth found from five globally distributed localities: the Jewett Sand in southern California, USA; the Pungo River Formation of North Carolina, USA; the Chilcatay Formation of Peru; the Oi Formation in Mie Prefecture, Japan; and the O’oshimojo Formation in Nagano Prefecture, Japan. Extrapolations based on available published data on modern macrophagous lamniforms suggest that the largest specimen of M. paradoxodon gen. nov. et sp. nov. possibly came from an individual that measured at least 3.7 m in total length. All specimens came from deposits in the mid-latitudinal zones representing shallow-water, shelf-type, coastal environments. Its dentition likely exhibited monognathic heterodonty suited for capturing and cutting relatively large prey (e.g. medium-sized fishes). We recommend the genus Otodus to include sharks of the ‘megatoothed’ (e.g. megalodon) lineage in order to avoid Otodus paraphyly. We also propose the following phylogenetic hypothesis: [Kenolamna + [Cretalamna + [Megalolamna + Otodus]]].ZooBank LSID for the genus Megalolamna is: urn: lsid:zoobank.org:act:B4791DEF-4D96-4FEB-9B7B-0EF816B96079ZooBank LSID for the species Megalolamna paradoxodon is: urn:lsid:zoobank.org:act:7D3D7442-53C6-43A2-9E8D-6339729565B6