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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.


Map of fossil and living Inioidea.Global map of living and fossil inioids, projected onto an orthographic globe, centered on 15°N, 45°W. Extant distributions of Inia geoffrensis (teal and black waterways) and Pontoporia blainvillei (dark gray), follow data from the IUCN (International Union for Conservation of Nature) (2013) and Secchi, Ott & Danilewicz (2003), respectively. Occurrences for fossil data derive from location of type localities for each taxon, except for reports for the Northern Europe by Pyenson & Hoch (2007), Western South America by Gutstein et al. (2015), and Amazonia and Eastern South America by Cozzuol (2010). Major fossil localites for enumerated inioids identified at least to the generic level, are listed alphabetically by region, and represented by teal or blue dots, for freshwater and marine deposits, respectively. Base map generated by Indiemapper (http://indiemapper.com).
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fig-1: Map of fossil and living Inioidea.Global map of living and fossil inioids, projected onto an orthographic globe, centered on 15°N, 45°W. Extant distributions of Inia geoffrensis (teal and black waterways) and Pontoporia blainvillei (dark gray), follow data from the IUCN (International Union for Conservation of Nature) (2013) and Secchi, Ott & Danilewicz (2003), respectively. Occurrences for fossil data derive from location of type localities for each taxon, except for reports for the Northern Europe by Pyenson & Hoch (2007), Western South America by Gutstein et al. (2015), and Amazonia and Eastern South America by Cozzuol (2010). Major fossil localites for enumerated inioids identified at least to the generic level, are listed alphabetically by region, and represented by teal or blue dots, for freshwater and marine deposits, respectively. Base map generated by Indiemapper (http://indiemapper.com).

Mentions: Similarly, the fossil record of inioids extends well beyond South America (Fig. 1). Fossil pontoporiids have been described from shallow marine and estuarine strata of early late Miocene to Early Pliocene age from the Atlantic coast of North America, including Maryland, Virginia, North Carolina and Florida (Morgan, 1994; Whitmore, 1994; Godfrey & Barnes, 2008; Gibson & Geisler, 2009; Geisler, Godfrey & Lambert, 2012). Along the Atlantic coast of Europe, Protophocaena minimaAbel, 1905 from shallow marine Miocene of the Netherlands, is now recognized as a pontoporiid (Lambert & Post, 2005) based on additional cranial and periotic material from the Miocene of Belgium and the Netherlands. Pyenson & Hoch (2007) reported pontoporiids (cf. Pontistes sp. and indeterminate Pontoporiidae) from the marine Gram Formation in Denmark, which is early late Miocene age. To date, no fossil pontoporiids have been described from the North Pacific Ocean. The two species of ParapontoporiaBarnes, 1984, which are well known from abundant Mio-Pliocene localities in northern and southern California (Boessenecker & Poust, 2015), are not pontoporiids, but belong in a clade with Lipotes (Geisler, Godfrey & Lambert, 2012), although Parapontoporia is sometimes also grouped with Platanista, Lipotes and Ischyrorhynchus vanbenedeniAmeghino, 1891 (see Aguirre-Fernández & Fordyce, 2014). Historically, fossils referred to Iniidae include a variety of taxa (e.g., Goniodelphis hudsoniAllen, 1941; Ischyrorhynchus), supplementing the existing data showing a much broader geographic extent for inioids in the fossil record than today (Fig. 1). These fossil occurrences thus raise the question of how Inioidea evolved, and the evolutionary scenarios that led to their current distribution. Our description herein of a new genus and new species of Inioidea from the late Miocene of Panama, based on substantially more osteological material than most fossil inioids, provides new insight into the evolutionary scenarios under which this group evolved in South America, including the timing and mode of major ecological transitions.


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)

Map of fossil and living Inioidea.Global map of living and fossil inioids, projected onto an orthographic globe, centered on 15°N, 45°W. Extant distributions of Inia geoffrensis (teal and black waterways) and Pontoporia blainvillei (dark gray), follow data from the IUCN (International Union for Conservation of Nature) (2013) and Secchi, Ott & Danilewicz (2003), respectively. Occurrences for fossil data derive from location of type localities for each taxon, except for reports for the Northern Europe by Pyenson & Hoch (2007), Western South America by Gutstein et al. (2015), and Amazonia and Eastern South America by Cozzuol (2010). Major fossil localites for enumerated inioids identified at least to the generic level, are listed alphabetically by region, and represented by teal or blue dots, for freshwater and marine deposits, respectively. Base map generated by Indiemapper (http://indiemapper.com).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-1: Map of fossil and living Inioidea.Global map of living and fossil inioids, projected onto an orthographic globe, centered on 15°N, 45°W. Extant distributions of Inia geoffrensis (teal and black waterways) and Pontoporia blainvillei (dark gray), follow data from the IUCN (International Union for Conservation of Nature) (2013) and Secchi, Ott & Danilewicz (2003), respectively. Occurrences for fossil data derive from location of type localities for each taxon, except for reports for the Northern Europe by Pyenson & Hoch (2007), Western South America by Gutstein et al. (2015), and Amazonia and Eastern South America by Cozzuol (2010). Major fossil localites for enumerated inioids identified at least to the generic level, are listed alphabetically by region, and represented by teal or blue dots, for freshwater and marine deposits, respectively. Base map generated by Indiemapper (http://indiemapper.com).
Mentions: Similarly, the fossil record of inioids extends well beyond South America (Fig. 1). Fossil pontoporiids have been described from shallow marine and estuarine strata of early late Miocene to Early Pliocene age from the Atlantic coast of North America, including Maryland, Virginia, North Carolina and Florida (Morgan, 1994; Whitmore, 1994; Godfrey & Barnes, 2008; Gibson & Geisler, 2009; Geisler, Godfrey & Lambert, 2012). Along the Atlantic coast of Europe, Protophocaena minimaAbel, 1905 from shallow marine Miocene of the Netherlands, is now recognized as a pontoporiid (Lambert & Post, 2005) based on additional cranial and periotic material from the Miocene of Belgium and the Netherlands. Pyenson & Hoch (2007) reported pontoporiids (cf. Pontistes sp. and indeterminate Pontoporiidae) from the marine Gram Formation in Denmark, which is early late Miocene age. To date, no fossil pontoporiids have been described from the North Pacific Ocean. The two species of ParapontoporiaBarnes, 1984, which are well known from abundant Mio-Pliocene localities in northern and southern California (Boessenecker & Poust, 2015), are not pontoporiids, but belong in a clade with Lipotes (Geisler, Godfrey & Lambert, 2012), although Parapontoporia is sometimes also grouped with Platanista, Lipotes and Ischyrorhynchus vanbenedeniAmeghino, 1891 (see Aguirre-Fernández & Fordyce, 2014). Historically, fossils referred to Iniidae include a variety of taxa (e.g., Goniodelphis hudsoniAllen, 1941; Ischyrorhynchus), supplementing the existing data showing a much broader geographic extent for inioids in the fossil record than today (Fig. 1). These fossil occurrences thus raise the question of how Inioidea evolved, and the evolutionary scenarios that led to their current distribution. Our description herein of a new genus and new species of Inioidea from the late Miocene of Panama, based on substantially more osteological material than most fossil inioids, provides new insight into the evolutionary scenarios under which this group evolved in South America, including the timing and mode of major ecological transitions.

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.