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Isthminia panamensis, a new fossil inioid (Mammalia, Cetacea) from the Chagres Formation of Panama and the evolution of 'river dolphins' in the Americas.

Pyenson ND, Vélez-Juarbe J, Gutstein CS, Little H, Vigil D, O'Dea A - PeerJ (2015)

Bottom Line: Phylogenetic analysis of fossil and living inioids, including new codings for Ischyrorhynchus, an enigmatic taxon from the late Miocene of Argentina, places Isthminia as the sister taxon to Inia, in a broader clade that includes Ischyrorhynchus and Meherrinia, a North American fossil inioid.This phylogenetic hypothesis complicates the possible scenarios for the freshwater invasion of the Amazon River system by stem relatives of Inia, but it remains consistent with a broader marine ancestry for Inioidea.Based on the fossil record of this group, along with Isthminia, we propose that a marine ancestor of Inia invaded Amazonia during late Miocene eustatic sea-level highs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution , Washington, DC , USA ; Departments of Mammalogy and Paleontology, Burke Museum of Natural History and Culture , Seattle, WA , USA.

ABSTRACT
In contrast to dominant mode of ecological transition in the evolution of marine mammals, different lineages of toothed whales (Odontoceti) have repeatedly invaded freshwater ecosystems during the Cenozoic era. The so-called 'river dolphins' are now recognized as independent lineages that converged on similar morphological specializations (e.g., longirostry). In South America, the two endemic 'river dolphin' lineages form a clade (Inioidea), with closely related fossil inioids from marine rock units in the South Pacific and North Atlantic oceans. Here we describe a new genus and species of fossil inioid, Isthminia panamensis, gen. et sp. nov. from the late Miocene of Panama. The type and only known specimen consists of a partial skull, mandibles, isolated teeth, a right scapula, and carpal elements recovered from the Piña Facies of the Chagres Formation, along the Caribbean coast of Panama. Sedimentological and associated fauna from the Piña Facies point to fully marine conditions with high planktonic productivity about 6.1-5.8 million years ago (Messinian), pre-dating the final closure of the Isthmus of Panama. Along with ecomorphological data, we propose that Isthminia was primarily a marine inhabitant, similar to modern oceanic delphinoids. Phylogenetic analysis of fossil and living inioids, including new codings for Ischyrorhynchus, an enigmatic taxon from the late Miocene of Argentina, places Isthminia as the sister taxon to Inia, in a broader clade that includes Ischyrorhynchus and Meherrinia, a North American fossil inioid. This phylogenetic hypothesis complicates the possible scenarios for the freshwater invasion of the Amazon River system by stem relatives of Inia, but it remains consistent with a broader marine ancestry for Inioidea. Based on the fossil record of this group, along with Isthminia, we propose that a marine ancestor of Inia invaded Amazonia during late Miocene eustatic sea-level highs.

No MeSH data available.


Related in: MedlinePlus

Stratigraphically calibrated phylogenetic tree of Inioidea.Time calibrated phylogenetic tree of select Delphinida, pruned from our consensus cladogram in Fig. 13, including Isthminia, with Delphinoidea collapsed. Stratigraphic range data derives from published accounts for each taxon, including global ranges. Geologic time scale based on Cohen et al. (2013). Calibration for major nodes depths follow mean divergence date estimates by McGowen, Spaulding & Gatesy (2009: table 3) for the following clades: a, Delphinida (24.75 Ma); b, Inioidea + Lipotes (22.15 Ma); c, Delphinoidea (18.66 Ma); and Inioidea (in open white circle, 16.68 Ma). All minor node depths are graphical heuristics, and not intended to reflect actual divergence dates. Arc indicates stem-based clade, Pan-Inia. Ecological habitat preference is based on depositional environment or extant habitat. Abbreviations: Aquitan., Aquitanian; H., Holocene; Langh., Langhian; Mess., Messinian; P., Piacenzian; Ple., Pleistocene; Plioc., Pliocene; Serra., Serravallian; Zan., Zanclean.
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fig-15: Stratigraphically calibrated phylogenetic tree of Inioidea.Time calibrated phylogenetic tree of select Delphinida, pruned from our consensus cladogram in Fig. 13, including Isthminia, with Delphinoidea collapsed. Stratigraphic range data derives from published accounts for each taxon, including global ranges. Geologic time scale based on Cohen et al. (2013). Calibration for major nodes depths follow mean divergence date estimates by McGowen, Spaulding & Gatesy (2009: table 3) for the following clades: a, Delphinida (24.75 Ma); b, Inioidea + Lipotes (22.15 Ma); c, Delphinoidea (18.66 Ma); and Inioidea (in open white circle, 16.68 Ma). All minor node depths are graphical heuristics, and not intended to reflect actual divergence dates. Arc indicates stem-based clade, Pan-Inia. Ecological habitat preference is based on depositional environment or extant habitat. Abbreviations: Aquitan., Aquitanian; H., Holocene; Langh., Langhian; Mess., Messinian; P., Piacenzian; Ple., Pleistocene; Plioc., Pliocene; Serra., Serravallian; Zan., Zanclean.

Mentions: Hamilton et al. (2001) suggested that the marine ancestors of Inia, subsequent to their divergence from Pontoporia, invaded freshwater ecosystems of Amazonia during eustatic sea-level highs of the middle Miocene, and evolved freshwater habits prior to the subsequent drop in eustatic sea-level late in the Neogene. This proposed evolutionary scenario is entirely consistent with the late Miocene (Messinian) antiquity of Isthminia, which establishes a minimum boundary on its divergence with Inia (Fig. 15). Fossil remains attributable directly to Inia spp. have been reported from Pleistocene age freshwater deposits of the Rio Madeira Formation in Brazil (Cozzuol, 2010). An isolated Pan-Inia humerus from the late Miocene Ituzaingó Formation implies that this clade had already invaded turbid, obstructed shallow rivers and flooded forests typical of today’s Amazonian freshwater ecosystems by this time, although this humerus may belong to extinct taxon more closely related to Ischyrorhynchus (Gutstein et al., 2014a).


Isthminia panamensis, a new fossil inioid (Mammalia, Cetacea) from the Chagres Formation of Panama and the evolution of 'river dolphins' in the Americas.

Pyenson ND, Vélez-Juarbe J, Gutstein CS, Little H, Vigil D, O'Dea A - PeerJ (2015)

Stratigraphically calibrated phylogenetic tree of Inioidea.Time calibrated phylogenetic tree of select Delphinida, pruned from our consensus cladogram in Fig. 13, including Isthminia, with Delphinoidea collapsed. Stratigraphic range data derives from published accounts for each taxon, including global ranges. Geologic time scale based on Cohen et al. (2013). Calibration for major nodes depths follow mean divergence date estimates by McGowen, Spaulding & Gatesy (2009: table 3) for the following clades: a, Delphinida (24.75 Ma); b, Inioidea + Lipotes (22.15 Ma); c, Delphinoidea (18.66 Ma); and Inioidea (in open white circle, 16.68 Ma). All minor node depths are graphical heuristics, and not intended to reflect actual divergence dates. Arc indicates stem-based clade, Pan-Inia. Ecological habitat preference is based on depositional environment or extant habitat. Abbreviations: Aquitan., Aquitanian; H., Holocene; Langh., Langhian; Mess., Messinian; P., Piacenzian; Ple., Pleistocene; Plioc., Pliocene; Serra., Serravallian; Zan., Zanclean.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4562255&req=5

fig-15: Stratigraphically calibrated phylogenetic tree of Inioidea.Time calibrated phylogenetic tree of select Delphinida, pruned from our consensus cladogram in Fig. 13, including Isthminia, with Delphinoidea collapsed. Stratigraphic range data derives from published accounts for each taxon, including global ranges. Geologic time scale based on Cohen et al. (2013). Calibration for major nodes depths follow mean divergence date estimates by McGowen, Spaulding & Gatesy (2009: table 3) for the following clades: a, Delphinida (24.75 Ma); b, Inioidea + Lipotes (22.15 Ma); c, Delphinoidea (18.66 Ma); and Inioidea (in open white circle, 16.68 Ma). All minor node depths are graphical heuristics, and not intended to reflect actual divergence dates. Arc indicates stem-based clade, Pan-Inia. Ecological habitat preference is based on depositional environment or extant habitat. Abbreviations: Aquitan., Aquitanian; H., Holocene; Langh., Langhian; Mess., Messinian; P., Piacenzian; Ple., Pleistocene; Plioc., Pliocene; Serra., Serravallian; Zan., Zanclean.
Mentions: Hamilton et al. (2001) suggested that the marine ancestors of Inia, subsequent to their divergence from Pontoporia, invaded freshwater ecosystems of Amazonia during eustatic sea-level highs of the middle Miocene, and evolved freshwater habits prior to the subsequent drop in eustatic sea-level late in the Neogene. This proposed evolutionary scenario is entirely consistent with the late Miocene (Messinian) antiquity of Isthminia, which establishes a minimum boundary on its divergence with Inia (Fig. 15). Fossil remains attributable directly to Inia spp. have been reported from Pleistocene age freshwater deposits of the Rio Madeira Formation in Brazil (Cozzuol, 2010). An isolated Pan-Inia humerus from the late Miocene Ituzaingó Formation implies that this clade had already invaded turbid, obstructed shallow rivers and flooded forests typical of today’s Amazonian freshwater ecosystems by this time, although this humerus may belong to extinct taxon more closely related to Ischyrorhynchus (Gutstein et al., 2014a).

Bottom Line: Phylogenetic analysis of fossil and living inioids, including new codings for Ischyrorhynchus, an enigmatic taxon from the late Miocene of Argentina, places Isthminia as the sister taxon to Inia, in a broader clade that includes Ischyrorhynchus and Meherrinia, a North American fossil inioid.This phylogenetic hypothesis complicates the possible scenarios for the freshwater invasion of the Amazon River system by stem relatives of Inia, but it remains consistent with a broader marine ancestry for Inioidea.Based on the fossil record of this group, along with Isthminia, we propose that a marine ancestor of Inia invaded Amazonia during late Miocene eustatic sea-level highs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution , Washington, DC , USA ; Departments of Mammalogy and Paleontology, Burke Museum of Natural History and Culture , Seattle, WA , USA.

ABSTRACT
In contrast to dominant mode of ecological transition in the evolution of marine mammals, different lineages of toothed whales (Odontoceti) have repeatedly invaded freshwater ecosystems during the Cenozoic era. The so-called 'river dolphins' are now recognized as independent lineages that converged on similar morphological specializations (e.g., longirostry). In South America, the two endemic 'river dolphin' lineages form a clade (Inioidea), with closely related fossil inioids from marine rock units in the South Pacific and North Atlantic oceans. Here we describe a new genus and species of fossil inioid, Isthminia panamensis, gen. et sp. nov. from the late Miocene of Panama. The type and only known specimen consists of a partial skull, mandibles, isolated teeth, a right scapula, and carpal elements recovered from the Piña Facies of the Chagres Formation, along the Caribbean coast of Panama. Sedimentological and associated fauna from the Piña Facies point to fully marine conditions with high planktonic productivity about 6.1-5.8 million years ago (Messinian), pre-dating the final closure of the Isthmus of Panama. Along with ecomorphological data, we propose that Isthminia was primarily a marine inhabitant, similar to modern oceanic delphinoids. Phylogenetic analysis of fossil and living inioids, including new codings for Ischyrorhynchus, an enigmatic taxon from the late Miocene of Argentina, places Isthminia as the sister taxon to Inia, in a broader clade that includes Ischyrorhynchus and Meherrinia, a North American fossil inioid. This phylogenetic hypothesis complicates the possible scenarios for the freshwater invasion of the Amazon River system by stem relatives of Inia, but it remains consistent with a broader marine ancestry for Inioidea. Based on the fossil record of this group, along with Isthminia, we propose that a marine ancestor of Inia invaded Amazonia during late Miocene eustatic sea-level highs.

No MeSH data available.


Related in: MedlinePlus