Urumaco and Venezuelan Paleontology: The Fossil Record of the Northern Neotropics

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15 Urumaco INSERT.indd 1 4/20/10 3:33 PM Plate 2. Time of divergence of the >1400 neotropical species dated so far using molecular phylogenetics. Bars represent the time interval between the origin of the older (left) and the younger (right) species within each clade, and are sorted chronologically according to the emergence of the older species. Each clade is the “crown group” that contains extant representatives. Bar colors indicate the type of organisms. For more details and bibliography see Rull (2008). Time in million years before present (Oli = Oligocene, Plio = Pliocene, Ple = Pleistocene). Plate 1. previous page Top: Physiographic map of Venezuela, with the biogeographic and climatic zones of northern South America, identifying the main physiographic regions and many features mentioned in the text (base map courtesy of NASA/JPL-Caltech). Map shows the floristic regions of northern South America present in Venezuela. Redrawn after Berry et al. (1995). Seasonal oscillation of the Intertropical Convergence Zone (ITCZ) and general precipitation patterns of northern South America are summarized. Modified after McGregor and Nieuwolt (1998), with additional data from Lutgens and Tarbuck (2001) and Poveda et al. (2006). Bottom: Simplified vegetation map of Venezuela. Modified after Huber and Alarcón (1988). Base map downloaded from http://ecosig.ivic.ve/ with permission. Plate 3. following page Map of Venezuela indicating (top) fossil decapod and (bottom) fossil fish localities. 15 Urumaco INSERT.indd 2 4/20/10 3:33 PM 15 Urumaco INSERT.indd 3 4/20/10 3:33 PM 15 Urumaco INSERT.indd 4 4/20/10 3:34 PM Plate 4. Summary of the Neogene Formations and their main depositional environments in the western Falcon state, Urumaco region. Plate 5. following pages Shell bone histology of cf. Bairdemys sp. (?costal; UNEFM uncat.) in normal transmitted light (A, C) and polarized light (B, D). (A, B) Close-up of the external cortex of the shell fragment, which is strongly encrusted and eroded. (C, D) Close-up of the irregularly arranged bone trabeculae of the cancellous bone of the specimen. The bone trabeculae mainly consist of secondary lamellar bone. CB: cancellous bone; ECO: external cortex; LB: lamellar bone; PC: primary vascular canals. 15 Urumaco INSERT.indd 5 4/20/10 3:34 PM 15 Urumaco INSERT.indd 6 4/20/10 3:34 PM 15 Urumaco INSERT.indd 7 4/20/10 3:34 PM Plate 6. Bone histology of (A–F) Purussaurus (UNEFM-1367) and (G, H) Gryposuchus (AMU-CURS 58) osteoderms. The osteoderms were both sectioned transversely (in the posterior region of the osteoderm). Images (A), (C), (E), (G), and (H) in normal light; images (B), (D), and (F) in polarized light. (A, B) Close-up of the interior bone tissue of osteoderm just internal to the dorsal keel. The bone tissue consists of metaplastic interwoven structural fiber bundles. Vascularization is restricted to small scattered primary osteons and primary canals and a few larger secondary osteons. White arrows indicate growth marks in the bone tissue. (C, D) Close-up of the bone interior lateral to the keel of the osteoderm. The tissue is only weakly vascularized with scattered primary osteons (white arrow) and primary vascular canals. (E) Complete section of lateral part of the osteoderm showing external and internal cortices that frame interior bone tissue. Vascularization in the bone interior is only slightly higher compared to the cortical bone layers, which consist of parallel-fibered bone. (F) Zone of remodeling (white arrows) within metaplastic structural fiber bundles that make up the bone interior. (G) Close-up of the osteoderm interior that consists of structural fiber bundles vascularized by scattered primary canals and osteons. (H) Lamellar-zonal bone tissue of the internal cortex of the osteoderm. White arrows indicate two representative growth marks within the tissue. 15 Urumaco INSERT.indd 8 4/20/10 3:34 PM 15 Urumaco INSERT.indd 9 4/20/10 3:34 PM Plate 7. Restoration of diverse vertebrates from the Urumaco sequence. From left to right, on land: gavialid crocodile Gryposuchus croizati, nettosuchiid crocodile Mourasuchus arendsi, mylodontoid ground sloth Bolivartherium urumaquensis, megatheriine ground sloth Urumaquia robusta,, glyptodontoid Boreostemma pliocena , snake Boidae indet., neoepiblemid rodent Phoberomys pattersoni, soft-shelled turtle Trionychidae indet., megadolodine litoptern Bounodus enigmaticus...