Rodolfo Sánchez

Crocodylian diversity peak and extinction in the late Cenozoic of the northern Neotropics

Northern South America and South East Asia are todays hotspots of crocodylian diversity with up to six (mainly alligatorid) and four (mainly crocodylid) living species respectively, of which usually no more than two or three occur sympatrically. In contrast, during the late Miocene, 14 species existed in South America. Here we show a diversity peak in sympatric occurrence of at least seven species, based on detailed stratigraphic sequence sampling and correlation, involving four geological formations from the middle Miocene to the Pliocene, and on the discovery of two new species and a new occurrence. This degree of crocodylian sympatry is unique in the world and shows that at least several members of Alligatoroidea and Gavialoidea coexisted. By the Pliocene, all these species became extinct, and their extinction was probably related to hydrographic changes linked to the Andean uplift. The extant fauna is first recorded with the oldest Crocodylus species from South America.

New Glyptodont from the Codore Formation (Pliocene), Falcón State, Venezuela, its relationship with theAsterostemma problem, and the paleobiogeography of the Glyptodontinae

One of the basal Glyptodontidae groups is represented by the Propalaehoplophorinae (late Oligocene — middle Miocene), whose genera (Propalaehoplophorus, Eucinepeltus, Metopotoxus, Cochlops, andAsterostemma) were initially recognized in Argentinian Patagonia. Among these,Asterostemma was characterized by its wide latitudinal distribution, ranging from southernmost (Patagonia) to northernmost (Colombia, Venezuela) South America. However, the generic assignation of the Miocene species from Colombia and Venezuela (A.? acostae, A. gigantea, andA. venezolensis) was contested by some authors, who explicitly accepted the possibility that these species could correspond to a new genus, different from those recognized in southern areas. A new comparative study of taxa from Argentinian Patagonia, Colombia and Venezuela (together with the recognition of a new genus and species for the Pliocene of the latter country) indicates that the species in northern South America are not Propalaehoplophorinae, but represent the first stages in the cladogenesis of the Glyptodontinae glyptodontids, the history of which was heretofore restricted to the late Miocene — early Holocene of southernmost South America. Accordingly, we propose the recognition of the new genusBoreostemma for the species from northern South America and the restriction ofAsterostemma to the Miocene of Patagonia. Thus, the available data indicate that the Glyptodontinae would in fact have arisen in the northernmost regions of this continent. Their arrival to more southerly areas coincides with the acme of the “Age of Southern Plains”. The Propalaehoplophorinae are geographically restricted to Patagonia.KurzfassungEine der basalen Gruppen der Glyptodontidae stellen die Propalaehoplophorinae (spätes Oligozän — mittleres Miozän) dar, deren Gattungen (Propalaehoplophorus, Eucinepeltus, Metopotoxus, Cochlops undAsterostemma) man zuerst aus dem argentinischen Patagonien kannte. Darunter istAsterostemma durch eine weite latitudinale Verbreitung gekennzeichnet, welche sich vom südlichsten (Patagonien) zum nördlichsten (Kolumbien, Venezuela) Südamerika erstreckt. Allerdings wurde die Gattungszugehörigkeit der miozänen Arten Kolumbiens und Venezuelas (A.? acostae, A. gigantea undA. venezolensis) von einigen Autoren angezweifelt, die explizit die Möglichkeit in Betracht zogen, dass diese Taxa einer anderen Gattung angehören, die sich von der Gattung der südlichen Breiten unterscheidet. Ein neuer Vergleich der Taxa aus Patagonien, Kolumbien und Venezuela (zusammen mit einer neuen Gattung und Art aus dem Pliozän Venezuelas) zeigt, dass die Arten aus dem nördlichen Südamerika nicht zu den Propalaehoplophorinae gehören, sondern die ersten Stufen in der Kladogenese der glyptodontinen Glyptodontidae darstellen. Deren Geschichte war bislang auf das späte Miozän — frühe Holozän des südlichsten Südamerikas beschränkt. Dementsprechend stellen wir hier die neue GattungBoreostemma für die Arten des nördlichen Südamerikas auf;Asterostemma wird auf das Miozän Patagoniens beschränkt. Die Datenlage deutet somit darauf hin, dass Glyptodontinae sich tatsächlich im nördlichsten Teil Südamerikas entwickelten. Ihr Auftreten in den südlichen Gebieten fällt mit dem Höhepunkt des „Zeitalters der südlichen Ebenen“ zusammen. Die Verbreitung der Propalaehoplophorinae wird geographisch auf Patagonien beschränkt.

First Megatheriines (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco (Late Miocene) and Codore (Pliocene) Formations, Estado Falcón, Venezuela

Synopsis Two new genera and species of Megatheriinae are described from the Neogene of Venezuela: Urumaquia robusta gen. et sp. nov. from the Urumaco Formation (Late Miocene) and Proeremotherium eljebe gen. et sp. nov. from the Codore Formation (Pliocene). These represent only the second Tertiary record of the subfamily at low latitudes in South America. The anatomical features of Urumaquia robusta suggest that the levels of the Urumaco Formation bearing the fauna here studied may not be correlated with the Laventan SALMA, but with Chasicoan‐Huayquerian SALMAs.

New Mylodontoidea (Xenarthra, Phyllophaga) from the Middle Miocene‐Pliocene of Venezuela

Synopsis Two new genera of Mylodontoidea, Mirandabradys and Bolivartherium, and five new species, M. socorrensis (Socorro Formation, Middle Miocene), M. urumaquensis and B. urumaquensis (Urumaco Formation, Upper Miocene), M. zabasi and B. codorensis (Codore Formation, Pliocene) are described. There is a high diversity of tardigrades from Middle Miocene to Pleistocene sites of Northern Venezuela. Almost all the recorded species are large and close to the size of the late Pleistocene Glossotherium robustum or Lestodon armatus. This implies that either the ‘faunas’ were composed only of large‐sized tardigrades, or that the smaller taxa are missing because of taphonomic bias and that the faunal diversity was actually higher than currently indicated.

Carnivorans at the Great American Biotic Interchange: new discoveries from the northern neotropics

We report two fossil procyonids, Cyonasua sp. and Chapalmalania sp., from the late Pliocene of Venezuela (Vergel Member, San Gregorio Formation) and Colombia (Ware Formation), respectively. The occurrence of these pre-Holocene procyonids outside Argentina and in the north of South America provides further information about the Great American Biotic Interchange (GABI). The new specimens are recognized in the same monophyletic group as procyonids found in the southern part of the continent, the “Cyonasua group,” formed by species of Cyonasua and Chapalmalania. The phylogenetic analysis that includes the two new findings support the view that procyonids dispersed from North America in two separate events (initially, previous to the first major migration wave—GABI 1—and then within the last major migration wave—GABI 4—). This involved reciprocal lineage migrations from North to South America, and included the evolution of South American endemic forms.

Sawfishes and Other Elasmobranch Assemblages from the Mio-Pliocene of the South Caribbean (Urumaco Sequence, Northwestern Venezuela)

The Urumaco stratigraphic sequence, western Venezuela, preserves a variety of paleoenvironments that include terrestrial, riverine, lacustrine and marine facies. A wide range of fossil vertebrates associated with these facies supports the hypothesis of an estuary in that geographic area connected with a hydrographic system that flowed from western Amazonia up to the Proto-Caribbean Sea during the Miocene. Here the elasmobranch assemblages of the middle Miocene to middle Pliocene section of the Urumaco sequence (Socorro, Urumaco and Codore formations) are described. Based on new findings, we document at least 21 taxa of the Lamniformes, Carcharhiniformes, Myliobatiformes and Rajiformes, and describe a new carcharhiniform species (†Carcharhinus caquetius sp. nov.). Moreover, the Urumaco Formation has a high number of well-preserved fossil Pristis rostra, for which we provide a detailed taxonomic revision, and referral in the context of the global Miocene record of Pristis as well as extant species. Using the habitat preference of the living representatives, we hypothesize that the fossil chondrichthyan assemblages from the Urumaco sequence are evidence for marine shallow waters and estuarine habitats.

Additions to the knowledge ofUrumaquia robusta (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco Formation (Late Miocene), Estado Falcön, Venezuela

We describe new remains ofUrumaquia robustaCarlini, Brandoni & Sänchez, 2006, which significantly improve the knowledge of the species and allow a more precise discussion about the relationships with the rest of the South American Megatheriinae. The new remains (ulna, phalanx, femora, patella, tibia, astragalus, navicular, metatarsals IV–V) described here suggest close affinities of this taxon with the species ofPyramiodontherium and withMegatheriops rectidens, based on morphological similarities of the ulna (length, gracility), femur (general morphology, shape of the medial margin), and astragalus (angle between the discoidal and odontoid facets). In fact, the shape of femoral medial margin is a shared derived character amongUrumaquia, Pyramiodontherium andMegatheriops. However, and despite the increasing information concerning Tertiary species, their phylogenetic relationships are only partially understood.KurzfassungNeue Funde vonUrumaquia robusta Carlini, Brandoni & Sánchez, 2006 werden vorgestellt, die erheblich zum Verständnis der Art beitragen und eine präzisere Diskussion der Verwandtschaftsverhältnisse zu anderen Vertretern der südamerikanischen Megatheriinae erlauben. Das hierin beschriebene neue Material (Ulna, Phalange, Femura, Patella, Tibia, Astragalus, Navikulare, Metatarsalia IV–V) deutet auf nähere Verwandtschaft zu den TaxaPyramiodontherium undMegatheriops rectidens hin. Dies wird unterstützt durch morphologische Ähnlichkeit der Ulna (Länge, Grazilität), des Femurs (generelle Morphologie, Form des medialen Randes) und des Astragalus (Winkel zwischen der Diskoidal- und Odontoidfacette). Tatsächlich handelt es sich bei der Ausprägung des medialen Femurrandes um eine Synapomorphie vonUrumaquia, Pyramiodontherium undMegatheriops. Allerdings sind die phylogenetischen Verwandtschaftsverhältnisse, trotz Zunahme von Informationen über tertiäre Taxa, bisher nur teilweise verstanden.

Diversity and body size in giant caviomorphs (Rodentia) from the northern Neotropics—a study of femoral variation

ABSTRACT New discoveries of numerous fossil femora from giant caviomorph rodents from the Miocene of Venezuela and a specimen of aMiocene giant rodent from Trinidad in the collections of the Naturhistorisches Museum in Basel made possible the first examination of taxonomic, ontogenetic, and functional variation in these animals. We provide comparisons of femoral shape, metrics, and growth (epiphyseal closure), finding that four morphotypes are distinguishable based largely on degrees of robustness or gracility. This indicates that the diversity of giant caviomorphs was larger than previously known; Phoberomys pattersoni was not the only giant caviomorph that inhabited the Miocene of the northern Neotropics. The study of cortical cross-sectional area of fossils serves to estimate the body mass for two giant caviomorphs at 420–580 kg. The first description of patterns of bone microstructure in three fossil giant caviomorph femora reveals similarities to extant rodents: absence of Haversian tissue and presence of layers of lamellar followed by reticular-like bone.

Fossil Cetaceans (Mammalia, Cetacea) from the Neogene of Colombia and Venezuela

There are significant geographic gaps in our knowledge of marine mammal evolution because most fossils have been found and described from Northern Hemisphere localities and a few other high-latitude areas in the Southern Hemisphere. Here, we describe fossil cetacean remains from five geological units in the South American tropics (Urumaco, Codore, Castilletes, Cantaure, and Querales formations) generally representing marginal marine depositional environments (estuaries, deltas, and tidal flats). While fossil cetaceans from Venezuelan Neogene localities have been previously studied, this paper includes the first descriptions of fossil cetaceans from Colombia, including a diverse assemblage of mysticetes and odontocetes. We identified and provisionally referred fragmentary remains to the iniid Ischyrorhynchus vanbenedeni and to the platanistid Zarhachis flagellator. The latter suggests the presence of Platanistidae in the eastern coast of South America during the early-middle Miocene, representing the second record of Platanistidae in South America and the first record of Platanistidae in eastern South America. Other less-diagnostic specimens are characterized by features commonly seen in longirostrine odontocetes such as Iniidae, Platanistidae, Pontoporiidae, Lipotidae, Eoplatanistidae, and Squalodelphinidae.

A dolphin fossil ear bone from the northern Neotropics–insights into habitat transitions in iniid evolution

ABSTRACT An iniid fossil (Cetacea, Odontoceti) is reported based on a periotic found in the Codore Formation (late Miocene to middle Pliocene) of northwestern Venezuela. The marine sediments where the Codore dolphin was collected have yielded another cetacean and a diverse elasmobranch fauna. Cladistic analysis indicates a close relationship between the Codore dolphin and the extant Amazon River dolphin (Inia geoffrensis); key characteristics include a large cochlear portion that is dorsoventrally compressed and the extremely small size of the posterior process. High-resolution micro-computed tomography scans were used for the description and analysis of the bony labyrinth endocast. Geometric morphometric analysis of the bony labyrinth endocast places the Codore dolphin as intermediate between the La Plata dolphin (Pontoporia blainvillei) and Inia geoffrensis (principal component 1), but distinctive from both extant species (principal component 2). Comparisons of the depositional environment with cladistically informed reconstructions and inferences based on cochlear and vestibular anatomy suggest that the Codore dolphin had the flexibility to enter marine, brackish, and fluvial environments as some extant cetaceans do today (e.g., Pontoporia blainvillei).