Orangel A. Aguilera

Formation of the Isthmus of Panama

Independent evidence from rocks, fossils, and genes converge on a cohesive narrative of isthmus formation in the Pliocene. The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed many millions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways, with formation of the Isthmus of Panama sensu stricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.

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.

North American Glyptodontines (Xenarthra, Mammalia) in the Upper Pleistocene of northern South America

The Glyptodontidae is one of the most conspicuous groups in the Pleistocene megafauna of the Americas. The Glyptodontinae were involved in the Great American Biotic Interchange (GABI) and their earliest records in North America are about 3.9 Ma, suggesting an earlier formation of the Panamanian landbridge. Taxonomically it is possible to recognize two Pleistocene genera of Glyptodontinae:Glyptodon (ca. 1.8 – 0.008 Ma), restricted to South America, andGlyptotherium (ca. 2.6 – 0.009 Ma), including records in both North and Central America. Here we present the first report of the genusGlyptotherium in South America, from the Late Pleistocene of several fossil localities in Falcón State, northwestern Venezuela. A comparative analysis of the material, represented by cranial and postcranial parts, including the dorsal carapace and caudal rings, suggests a close affinity withGlyptotherium cylindricum (Late Pleistocene of Central Mexico). This occurrence in the latest Pleistocene of the northernmost region of South America Supports the bidirectional faunal migration during the GABI and the repeated re-immigration from North America of South American clades, as has been reported in other members of the Cingulata (e.g., Pampatheriidae).KurzfassungDie Glyptodontidae ist eine der auffälligsten Faunengruppen des Pleistozäns Südamerikas. Die Glyptodontinae waren in dem „Great American Biotic Interchange“ (GABI) involviert, und ihre frühesten Reste aus Nordamerika sind etwa 3,9 Ma alt, was für eine frühere Entstehung der Panamanischen Landbrücke spricht. Es ist taxonomisch möglich, zwei Genera von pleistozänen Glyptodontinae zu unterscheiden:Glyptodon (ca. 1,8–0,008 Ma) aus Südamerika undGlyptotherium (ca. 2,6 – 0,009 Ma) aus Nord- und Mittelamerika. Hier stellen wir den ersten Nachweis vonGlyptotherium in Südamerika, aus dem oberen Pleistozän von verschiedenen Lokalitäten des Bundesstaates Falcón, nordwestliches Venezuela, vor. Eine vergleichende Untersuchung von Schädel- und Postkranialelementen, einschließlich des dorsalen Panzers und kaudaler Ringe, unterstützt eine nahe Verwandtschaft mitGlyptotherium cylindricum (Spätes Pleistozän Mittel-Mexikos). Diese spät-pleistozäne Verbreitung im nördlichsten Teil Südamerikas ist ein Nachweis für eine bidirektionale Migration während des GABI und für das Zurückkehren von Taxa von Nordamerika nach Südamerika, wie schon für andere Vertreter der Cingulata (z. B. Pampatheriidae) berichtet wurde.

The Oligocene–Miocene Transition on coral reefs in the Falcón Basin (NW Venezuela)

Abstract The Oligocene–Miocene Transition (OMT) was an interval of regional environmental and biotic change on Caribbean reefs. During the late Oligocene, a diverse Tethyan biota contributed to extensive reef building across the region, but by the early Miocene, reef building had declined, and a regional extinction had removed up to 50% of the late Oligocene diversity. The general decline in reef building in the Caribbean has been attributed to changes in regional water quality. New collections of scleractinian reef corals from four different units in the northwestern Falcón Basin of Venezuela include distinct late Oligocene and early Miocene assemblages. The distribution of fossil coral species and reef limestones suggests that the thick carbonates of the San Luis Formation were deposited during the late Oligocene and that changing water quality during the OMT resulted in the demise of San Luis coral-reef ecosystems. Previous studies have noted an increase in surface-water productivity after the OMT in the region and have suggested oceanographic reorganization as the primary cause; this interval, however, also coincides with a switch in the outlet position of an ancestral Orinoco River. A change in the terrestrial geography of South America might have caused the regional decline in reef building by altering surface-water characteristics, just as modern Orinoco and Amazon outflows exert strong control on shallow-water habitats off the coast of northeastern South America.

The Tropics as Reservoir of Otherwise Extinct Mammals: The Case of Rodents from a New Pliocene Faunal Assemblage from Northern Venezuela

We report a new vertebrate assemblage from the Pliocene Vergel Member of the San Gregorio Formation in northwestern Venezuela, which includes Crocodylia and Testudines indet., toxodonts, at least four species of xenarthrans of the Dasypodidae, Pampatheriidae, Glyptodontidae and Megatheriidae, and rodents. The last are Cardiatherium, cf. Caviodon (Hydrochoeridae), Neoepiblema (Neoepiblemidae), and what is here described as a new genus of a low-crowned octodontoid. cf. Caviodon is the first cardiomyine for northern South America. The rodent assemblage resembles in its ecological composition those of the late Miocene (Huayquerian) from the “Mesopotamian” of Argentina and the Acre region in Brazil, with partially overlapping systematic composition. The stratigraphic position of the San Gregorio Formation and mammals other than caviomorphs suggest a late Pliocene age for these sediments, implying the endurance of rodent taxa beyond their biochron in southern 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.

The world’s largest gharialsGryposuchus: description ofG. croizati n. sp. (Crocodylia, Gavialidae) from the Upper Miocene Urumaco Formation, Venezuela

A new fossil gharialGryposuchus species is described from the Upper Miocene Urumaco Formation, Venezuela.Gryposuchus croizati new species can be distinguished from other gavialoids, includingGryposuchus colombianus andGryposuchus neogaeus by the following combination of diagnostic characters: 1) slenderness of the parietal interfenestral bar; 2) dental formula, mainly the lesser number of maxillary teeth, with four premaxillary, 19 maxillary and 22 mandibular teeth; 3) large width of palatines between the reduced palatine fenestrae; 4) medial hemicondyle of the quadrate smaller but detached and much more posteriorly elongated than the lateral one and projected ventromedially; 5) pterygoid morphology, with two posterior vacuities. The polymorphism in the contour of the external naris inGryposuchus was evaluated for taxonomic significance. The body size ofG. croizati n. sp. was estimated in 10.15 m (9.67–10.67 m) using the dorsal skull length and the estimation of the body mass was 1,745 kg (1,280–2,379 kg) based on the braincase length. These maximal values placeG. croizati n. sp. among the world’s largest gharials and even Crocodyliforms as a whole.KurzfassungEine neue Gavialart vonGryposuchus wird aus der obermiozän Urumaco-Formation von Venezuela beschrieben.Gryposuchus croizati n. sp. kann von anderen Gavialoiden, einschließlichGryposuchus colombianus undGryposuchus neogaeus, anhand der folgenden diagnostischen Merkmale unterschieden werden: 1) Schlankheit des Interfenestralstabs des Parietale; 2) Zahnformel, vor allem die reduzierte Anzahl von Maxillarzähnen, mit vier Prämaxillar-, 19 Maxillar- und 22 Mandibularzähnen; 3) große Breite der Palatinae zwischen reduzierten Gaumenfenstern; 4) medialer Hemicondylus des Quadratums kleiner aber getrennt und sehr viel stärker posterior verlängert und ventromedial ausgerichtet als der laterale Hemicondylus; 5) Morphologie des Pterygoids, mit zwei posterioren Einbuchtungen. Die Polymorphismen in den Umrissen der äußeren Nasenöffnung inGryposuchus werden taxonomisch evaluiert. Die Körperlänge vonG. croizati n. sp. wurde, basierend auf der dorsalen Schädellänge, auf 10.15 m (9.67–10.67 m) geschätzt. Weiterhin wurde die Körpergröße basierend auf der Gehirnkapsellänge auf 1745 kg (1280–2379 kg) geschätzt. Anhand dieser maximalen Werte dürfteG. croizati n. sp. zu den weltweit größten Gavialen und sogar der Crocodyliformes gehört haben, die je existierten.

Two new species of the side necked turtle genus,Bairdemys (Pleurodira, Podocnemididae), from the Miocene of Venezuela

The side-necked turtle genusBairdemys (Podocnemididae,Shweboemys Group) from the Miocene of Venezuela and Puerto Rico is revised, and four species are diagnosed on the basis of skull characters; two are de-scribed as new.B. hartsteiniGaffney & Wood, 2002, from the Cibao Formation of Puerto Rico, is characterized by a higher skull, with a straight labial ridge and a premaxillary notch;B. venezuelensis (Wood & Díaz de Gamero 1971), from the Urumaco Formation of Venezuela, is characterized by the absence of a premaxillary notch, a high anterior triturating surface convexity, a deep posterior triturating surface concavity, and a short pterygoid mid-line contact;B. sanchezi, new species, from the Urumaco Formation of Venezuela, is characterized by a very low anterior triturating surface convexity and shallow posterior triturating surface concavity, a premaxillary notch, small size, and extensive temporal and cheek emargination;B. winklerae, new species, from the Urumaco Formation of Venezuela, is characterized by an elongate, narrow snout, with a concave labial ridge, and no premaxillary notch. Based on osteological and bone histological results, an additional strongly crushed skull and associated cara-pace fragment of a previously undetermined podocnemidid from the Urumaco Formation of Venezuela can be further referred toPodocnemis or a closely related taxon — again underscoring the importance of this formation as one of the major fossil lagerstätten of turtles in South America.ZusammenfassungDie Halswenderschildkröten der GattungBairdemys (Podocnemididae,Shweboemys-Gruppe) aus dem Miozän von Venezuela und Puerto Rico werden revidiert. Aufgrund von diagnostischen Schädelmerkmalen werden vier Arten unterschieden, inklusive zwei hierin neu beschriebener Arten.B. hartsteiniGaffney & Wood, 2002, aus der Cibao Formation, Puerto Rico, ist durch einen hohen Schädel, eine gerade Labialkante des Prämaxillare und eine Prämaxillarkerbe gekennzeichnet,B. venezuelensis (Wood & Diaz de Gamero 1971) aus der Urumaco-Formation Venezuelas durch das Fehlen einer Prämaxillarkerbe, eine hohe anteriore Konvexität und eine tiefe posteriore Konkavität der Kauflächen und einen kurzen Mittellinienkontakt der Pterygoide. Die hier neu beschriebeneB. sanchezi n. sp. aus der Urumaco-Formation, Venezuela, ist charakterisiert durch eine sehr niedrige anteriore Konvexität und eine flache posteriore Konkavität der Kauflächen, eine geringe Größe und starke Temporal- und Wangeneinbuchtungen, wogegenB. winklerae n. sp. aus der Urumaco Formation, Venezuela, durch eine verlängerte schmale Schnauze mit einer konkaven Labialkante charakterisiert ist. Durch osteologische und knochenhistologische Befunde lassen sich ein weiterer stark verdrückter Schädel sowie ein assoziiertes Panzerfragment einer bisher unbestimmten Podocnemidide der GattungPodocnemis oder deren unmittelbarer Verwandtschaft zuordnen. Dies unterstreicht wiederum die Bedeutung der Urumaco-Formation als eine der wichtigsten Lagerstätten fossiler Schildkröten in Südamerika.

Giant-toothed white sharks and cetacean trophic interaction from the Pliocene Caribbean Paraguaná Formation

The role of the extinct giant-toothed white sharkCarcharodon megalodon (Agassiz) in the Caribbean Neogene is discussed based on new evidence of predation on cetaceans from the Lower Pliocene Paraguaná Formation in Venezuela. Large sharks have occupied the highest trophic level in the marine environment. However, based on the recovery of a giant white shark tooth piercing a cetacean lumbar vertebra, the predator-prey relationship is discussed under the hypothesis of initial shark attack, subsequent floating transport of the cetacean carcass, and scavenging prior to deposition on the bottom. The scarce Caribbean fossil records of both giant-toothed sharks and cetaceans suggest that these species were transients during the Pliocene on the Venezuelan coast.KurzfassungDie Rolle des ausgestorbenen RiesenweißhaiesCarcharodon megalodon (AGASSIZ) im Neogen der Karibik wird anhand eines neuen Predationsbefundes aus der unter-pliozänen Paraguaná-Formation in Venezuela diskutiert. Große Haie haben die höchste trophische Ebene im marinen Milieu besetzt. Hier wird ein Zahn eines Riesenweißhaies dokumentiert, der noch in einem Lumbarwirbel eines Wales steckt, was für ein Räuber-Beute-Verhältnis spricht. Die Befunde sprechen für einen Angriff des Räubers, gefolgt von Transport des Walkadavers, Aasfressen und schließlich Ablagerung am Boden des Meeres. Riesenweißhaie und Cetaceen waren im Pliozän in den Küstenregionen von Venezuela vorhanden.

Past Colonization of South America by Trionychid Turtles: Fossil Evidence from the Neogene of Margarita Island, Venezuela

Abstract An incomplete left hypoplastron of a trionychid turtle from the late Miocene-Early Pliocene Cubagua Formation of Margarita Island, Venezuela, represents the youngest occurrence of trionychids in South America. Large size and depositional environment of the Margarita Island specimen indicate marginal marine habits. The Neogene Venezuelan record is more extensive than previously considered and may represent an interval of successful colonization of the northern margin of South America by trionychids, as opposed to previous hypotheses of failed waif immigration.