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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.


Locality and geology.Geographic and stratigraphic context of Isthminia panamensis. (A) Map of Central America with a yellow star representing the type locality, STRI locality 650009. (B) Map of north-central Panama with the distribution of the Chagres Formation, with type locality of Isthminia in the vicinity of Piña, along with other fossil vertebrates. (C) Chronostratigraphic and lithostratigraphic relationships of the Chagres Formation (modified from Hendy et al., in press, and Velez-Juarbe et al., 2015).
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fig-2: Locality and geology.Geographic and stratigraphic context of Isthminia panamensis. (A) Map of Central America with a yellow star representing the type locality, STRI locality 650009. (B) Map of north-central Panama with the distribution of the Chagres Formation, with type locality of Isthminia in the vicinity of Piña, along with other fossil vertebrates. (C) Chronostratigraphic and lithostratigraphic relationships of the Chagres Formation (modified from Hendy et al., in press, and Velez-Juarbe et al., 2015).

Mentions: The type specimen of this new taxon was initially discovered in an intertidal zone outcrop of the Chagres Formation, near the town of Piña, along the Caribbean coastline of Panama, in early 2011 (Fig. 2 and Fig. S1). The infrequency of low tides at the type locality created a narrow time window for excavating the specimen, which several co-authors (NDP, JVJ, DV, and AO) undertook on 18 June 2011 with the assistance of staff from Smithsonian Tropical Research Institute (STRI). After exporting the specimen under permits from Panama’s Ministerio de Comercio e Industrias (MICI number DNRM-MC-074-11) to the Smithsonian’s National Museum of Natural History (NMNH) in Washington, D.C., USA, the specimen was prepared using mechanical tools and consolidated using standard fossil vertebrate preparation techniques by DV, S Jabo, and P Kroehler in the Vertebrate Paleontology Preparation Laboratory in the Department of Paleobiology at NMNH.


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)

Locality and geology.Geographic and stratigraphic context of Isthminia panamensis. (A) Map of Central America with a yellow star representing the type locality, STRI locality 650009. (B) Map of north-central Panama with the distribution of the Chagres Formation, with type locality of Isthminia in the vicinity of Piña, along with other fossil vertebrates. (C) Chronostratigraphic and lithostratigraphic relationships of the Chagres Formation (modified from Hendy et al., in press, and Velez-Juarbe et al., 2015).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-2: Locality and geology.Geographic and stratigraphic context of Isthminia panamensis. (A) Map of Central America with a yellow star representing the type locality, STRI locality 650009. (B) Map of north-central Panama with the distribution of the Chagres Formation, with type locality of Isthminia in the vicinity of Piña, along with other fossil vertebrates. (C) Chronostratigraphic and lithostratigraphic relationships of the Chagres Formation (modified from Hendy et al., in press, and Velez-Juarbe et al., 2015).
Mentions: The type specimen of this new taxon was initially discovered in an intertidal zone outcrop of the Chagres Formation, near the town of Piña, along the Caribbean coastline of Panama, in early 2011 (Fig. 2 and Fig. S1). The infrequency of low tides at the type locality created a narrow time window for excavating the specimen, which several co-authors (NDP, JVJ, DV, and AO) undertook on 18 June 2011 with the assistance of staff from Smithsonian Tropical Research Institute (STRI). After exporting the specimen under permits from Panama’s Ministerio de Comercio e Industrias (MICI number DNRM-MC-074-11) to the Smithsonian’s National Museum of Natural History (NMNH) in Washington, D.C., USA, the specimen was prepared using mechanical tools and consolidated using standard fossil vertebrate preparation techniques by DV, S Jabo, and P Kroehler in the Vertebrate Paleontology Preparation Laboratory in the Department of Paleobiology at NMNH.

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.