Wednesday, February 25, 2015

[Paleontology • 2015] A Miocene Hyperdiverse Crocodylian Community reveals Peculiar Trophic Dynamics in proto-Amazonian Mega-Wetlands

The massive wetlands once covered the Amazon River basin about 13 million years ago during the late middle Miocene. Three newly discovered species of crocodylians, including Kuttanacaiman iquitosensis (left), Caiman wannlangstoni (right) and Gnatusuchus pebasensis (bottom), look for clams, which they could likely scoop up with their mouths and crunch with their peglike teeth.
Illustration: Javier Herbozo  


Amazonia contains one of the world's richest biotas, but origins of this diversity remain obscure. Onset of the Amazon River drainage at approximately 10.5 Ma represented a major shift in Neotropical ecosystems, and proto-Amazonian biotas just prior to this pivotal episode are integral to understanding origins of Amazonian biodiversity, yet vertebrate fossil evidence is extraordinarily rare. Two new species-rich bonebeds from late Middle Miocene proto-Amazonian deposits of northeastern Peru document the same hyperdiverse assemblage of seven co-occurring crocodylian species. Besides the large-bodied Purussaurus and Mourasuchus, all other crocodylians are new taxa, including a stem caiman — Gnatusuchus pebasensis — bearing a massive shovel-shaped mandible, procumbent anterior and globular posterior teeth, and a mammal-like diastema. This unusual species is an extreme exemplar of a radiation of small caimans with crushing dentitions recording peculiar feeding strategies correlated with a peak in proto-Amazonian molluscan diversity and abundance. These faunas evolved within dysoxic marshes and swamps of the long-lived Pebas Mega-Wetland System and declined with inception of the transcontinental Amazon drainage, favouring diversification of longirostrine crocodylians and more modern generalist-feeding caimans. The rise and demise of distinctive, highly productive aquatic ecosystems substantially influenced evolution of Amazonian biodiversity hotspots of crocodylians and other organisms throughout the Neogene.

KEYWORDS: Miocene, caimanine crocodylians, proto-Amazonia, Pebas System, molluscs, durophagy

the newly discovered species Gnatusuchus pebasensis, a crocodylian [13 million years ago] with a short face and rounded teeth that may have shoveled through the mud at the bottom of lakes and swamps to find prey, such as clams and other mollusks. A crocodylian is an order that includes crocodiles, alligators, caimans and gharials 
Model: Kevin Montalbán-Rivera
Figure 4. Phylogenetic position of the Pebasian caimanines within the Alligatoroidea. Time-calibrated, strict consensus cladogram of 70 most parsimonious trees (see electronic supplementary material, figure S6 and test S1). Gnatusuchus pebasensis is the most basal caimanine and Globidentosuchus brachyrostris is the next outgroup to all remaining caimanines; these two taxa reveal unknown character states ancestrally present within the caimans (i.e. long splenial symphysis, posterior globular teeth) and their inclusion influenced the topology of relationships within the caimanine clade. Character support provides a novel sister-grouped relationship between the South American caimans and the North American Cretaceous globidontan alligatoroids (i.e. Brachychampsa, Albertochampsa and Stangerochampsa), whereas prior analyses showed either the monophyly of Alligatoridae (Caimaninae + Alligatorinae) exclusive of Cretaceous globidontans or, more recently, a polytomy within the globidontan alligatoroids (Caimaninae + [alligatorines and Cretaceous globidontans]). Here, this polytomy (dotted lines) is obtained when the alligatorine Allognathosuchus wartheni is excluded from the analysis. Results also suggest an early diversification of major groups within the Caimaninae dating back to the end of the Cretaceous or Palaeocene interval. (a) The Acre Phase (ca 9 Ma) after intense Andean uplift and onset of the transcontinental Amazon River System. (b) The Pebas Mega-Wetland System in northwestern South America during MZ8 (ca 13 Ma). Stratigraphic distribution of taxa (yellow bars for crushing-dentition caimanines, black lines for other taxa) relative to major Neogene stages and events in Amazonia. Palaeogeographical reconstructions, Andean uplift peaks (black triangles) and marine incursions (m) are from Hoorn et al. Molluscan Zones and diversity for the Pebas System (MZ1–12) are from Wesselingh et al. When suitable, internal nodes were time-calibrated with molecular data from Oaks. Darker grey marks MZ8. Alligatoroids are from South America, Asia (AS), Central America (CA), Europe (EU) or North America (NA).

Excavated fossils from Peru show that seven species of crocodylian lived together in the same place at relatively the same time. The skulls and jaws, shown above, are extremely diverse, the researchers said. They include (1) Gnatusuchus pebasensis, (2) Kuttanacaiman iquitosensis, (3) Caiman wannlangstoni, (4) Purussaurus neivensis, (5) Mourasuchus atopus, (6) Pebas Paleosuchus, and (7) Pebas gavialoid.
Reconstructions: Javier Herbozo & Rodolfo Salas-Gismondi

Rodolfo Salas-Gismondi, John J. Flynn, Patrice Baby, Julia V. Tejada-Lara, Frank P. Wesselingh and Pierre-Olivier Antoine. 2015. A Miocene Hyperdiverse Crocodylian Community reveals Peculiar Trophic Dynamics in proto-Amazonian Mega-Wetlands. Proceedings of the Royal Society B.

Crocs rocked pre-Amazonian Peru: New research uncovers 7 crocodile species in single 13-million-year-old bone bed via @physorg_com
Ancient Croc with 'Shovel Mouth', Likely Enjoyed Clam Dinners, Roamed the Amazon Photos: via @LiveScience