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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

Strict consensus cladogram.Phylogenetic analysis of Isthminia and other inioid odontocetes, showing a strict consensus cladogram resulting from six most parsimonious trees, 95 steps long, with the ensemble consistency index equal to 0.283 and the ensemble retention index equal to 0.451. Numbers below nodes indicate decay index/bootstrap values; stem-based clades are indicated by arcs, while open circles denote node-based clades.
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fig-13: Strict consensus cladogram.Phylogenetic analysis of Isthminia and other inioid odontocetes, showing a strict consensus cladogram resulting from six most parsimonious trees, 95 steps long, with the ensemble consistency index equal to 0.283 and the ensemble retention index equal to 0.451. Numbers below nodes indicate decay index/bootstrap values; stem-based clades are indicated by arcs, while open circles denote node-based clades.

Mentions: We obtained six most parsimonious trees (length = 1,922; ensemble consistency index = 0.283, and ensemble retention index = 0.451), in our phylogenetic analysis, with the strict consensus cladogram shown in Fig. 13. The resulting topology is overall very similar to that obtained by Aguirre-Fernández & Fordyce (2014) (see their Fig. 8), with the notable difference that the relationship of Pontoporia, Brachydelphis and Pliopontos with other inioids which is unresolved in our analysis, yielding a polytomy for Pontoporiidae (sensuGeisler, Godfrey & Lambert, 2012). Our results also resolved a clade (Pan-Inia) of taxa more related to Inia than Pontoporia, which consists of: Meherrinia, Ischyrorhynchus and Isthminia, the latter which is sister to Inia. Although Bremer support values for most of these nodes is low (i.e., 1 step), there is stronger support (i.e., 2 steps) for the clade that includes Ischyrorhynchus + Isthminia + Inia. The new position of Ischyrorhynchus is likely a result of our rescoring of several characters based on observations of the type and additional specimens of Ischyrorhynchus. This position differs from all previous phylogenetic analyses (e.g., Geisler, Godfrey & Lambert, 2012; Aguirre-Fernández & Fordyce, 2014) but it is consistent with Cozzuol (2010)’s proposal for a subfamily grouping of Ischyrorhynchinae within Iniidae (Cozzuol, 1996). Our analysis did not include Saurocetes spp., a large Pan-Inia known from the late Miocene age Ituzaingó Formation of Argentina and Solimões Formation of Brazil, and represented mainly by fragmentary mandibular remains (Cozzuol, 1996; Cozzuol, 2010). We also did not include Goniodelphis hudsoni from the Mio-Pliocene age Bone Valley Formation of Florida (Allen, 1941), which is represented by a poorly preserved cranium with some similarities to Ischyrorhynchus. Both taxa require reexamination that remains outside the scope of this study.


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)

Strict consensus cladogram.Phylogenetic analysis of Isthminia and other inioid odontocetes, showing a strict consensus cladogram resulting from six most parsimonious trees, 95 steps long, with the ensemble consistency index equal to 0.283 and the ensemble retention index equal to 0.451. Numbers below nodes indicate decay index/bootstrap values; stem-based clades are indicated by arcs, while open circles denote node-based clades.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-13: Strict consensus cladogram.Phylogenetic analysis of Isthminia and other inioid odontocetes, showing a strict consensus cladogram resulting from six most parsimonious trees, 95 steps long, with the ensemble consistency index equal to 0.283 and the ensemble retention index equal to 0.451. Numbers below nodes indicate decay index/bootstrap values; stem-based clades are indicated by arcs, while open circles denote node-based clades.
Mentions: We obtained six most parsimonious trees (length = 1,922; ensemble consistency index = 0.283, and ensemble retention index = 0.451), in our phylogenetic analysis, with the strict consensus cladogram shown in Fig. 13. The resulting topology is overall very similar to that obtained by Aguirre-Fernández & Fordyce (2014) (see their Fig. 8), with the notable difference that the relationship of Pontoporia, Brachydelphis and Pliopontos with other inioids which is unresolved in our analysis, yielding a polytomy for Pontoporiidae (sensuGeisler, Godfrey & Lambert, 2012). Our results also resolved a clade (Pan-Inia) of taxa more related to Inia than Pontoporia, which consists of: Meherrinia, Ischyrorhynchus and Isthminia, the latter which is sister to Inia. Although Bremer support values for most of these nodes is low (i.e., 1 step), there is stronger support (i.e., 2 steps) for the clade that includes Ischyrorhynchus + Isthminia + Inia. The new position of Ischyrorhynchus is likely a result of our rescoring of several characters based on observations of the type and additional specimens of Ischyrorhynchus. This position differs from all previous phylogenetic analyses (e.g., Geisler, Godfrey & Lambert, 2012; Aguirre-Fernández & Fordyce, 2014) but it is consistent with Cozzuol (2010)’s proposal for a subfamily grouping of Ischyrorhynchinae within Iniidae (Cozzuol, 1996). Our analysis did not include Saurocetes spp., a large Pan-Inia known from the late Miocene age Ituzaingó Formation of Argentina and Solimões Formation of Brazil, and represented mainly by fragmentary mandibular remains (Cozzuol, 1996; Cozzuol, 2010). We also did not include Goniodelphis hudsoni from the Mio-Pliocene age Bone Valley Formation of Florida (Allen, 1941), which is represented by a poorly preserved cranium with some similarities to Ischyrorhynchus. Both taxa require reexamination that remains outside the scope of this study.

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