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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.


Scapula in lateral, medial, and distal views.Right scapula from Isthminia panamensis (USNM 546125) in lateral (A–B), medial (C–D), and distal (E–F) views. Each respective paired view shows photographs alongside orthogonal digital three-dimensional polygon model prepared from CT data, with lighting and color modifications using the Smithsonian X 3D browser. See http://3d.si.edu/explorer?s=dmsTMl (lateral view), http://3d.si.edu/explorer?s=jPwTGO (medial view), and http://3d.si.edu/explorer?s=hwGm9I (distal view). Anatomical terminology for the scapula follows Tanaka & Fordyce (2015) and Uhen (2004).
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fig-11: Scapula in lateral, medial, and distal views.Right scapula from Isthminia panamensis (USNM 546125) in lateral (A–B), medial (C–D), and distal (E–F) views. Each respective paired view shows photographs alongside orthogonal digital three-dimensional polygon model prepared from CT data, with lighting and color modifications using the Smithsonian X 3D browser. See http://3d.si.edu/explorer?s=dmsTMl (lateral view), http://3d.si.edu/explorer?s=jPwTGO (medial view), and http://3d.si.edu/explorer?s=hwGm9I (distal view). Anatomical terminology for the scapula follows Tanaka & Fordyce (2015) and Uhen (2004).

Mentions: Only the right scapula is preserved in the type specimen of Isthminia (Fig. 11). In dorsoventral dimensions, the preserved element is 16.8 cm tall, and approximately 15 cm in anteroposterior length (Table 2). The scapula is incomplete, and the following parts are missing from the type specimen: most of the dorsal margin, and especially most of the anterior aspect; most of the acromion; and the anterior tip of the coracoid process. The posterior margin of the suprascapular border is intact, as well as the glenoid fossa and most of the region surrounding the ventral aspect of the scapula.


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)

Scapula in lateral, medial, and distal views.Right scapula from Isthminia panamensis (USNM 546125) in lateral (A–B), medial (C–D), and distal (E–F) views. Each respective paired view shows photographs alongside orthogonal digital three-dimensional polygon model prepared from CT data, with lighting and color modifications using the Smithsonian X 3D browser. See http://3d.si.edu/explorer?s=dmsTMl (lateral view), http://3d.si.edu/explorer?s=jPwTGO (medial view), and http://3d.si.edu/explorer?s=hwGm9I (distal view). Anatomical terminology for the scapula follows Tanaka & Fordyce (2015) and Uhen (2004).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-11: Scapula in lateral, medial, and distal views.Right scapula from Isthminia panamensis (USNM 546125) in lateral (A–B), medial (C–D), and distal (E–F) views. Each respective paired view shows photographs alongside orthogonal digital three-dimensional polygon model prepared from CT data, with lighting and color modifications using the Smithsonian X 3D browser. See http://3d.si.edu/explorer?s=dmsTMl (lateral view), http://3d.si.edu/explorer?s=jPwTGO (medial view), and http://3d.si.edu/explorer?s=hwGm9I (distal view). Anatomical terminology for the scapula follows Tanaka & Fordyce (2015) and Uhen (2004).
Mentions: Only the right scapula is preserved in the type specimen of Isthminia (Fig. 11). In dorsoventral dimensions, the preserved element is 16.8 cm tall, and approximately 15 cm in anteroposterior length (Table 2). The scapula is incomplete, and the following parts are missing from the type specimen: most of the dorsal margin, and especially most of the anterior aspect; most of the acromion; and the anterior tip of the coracoid process. The posterior margin of the suprascapular border is intact, as well as the glenoid fossa and most of the region surrounding the ventral aspect of the scapula.

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.