Time-calibrated phylogeny of Sirenia.

<p>Consensus tree (length = 127; ri = 0.758; ci = 0.527). Taxa included in this study are highlighted in color, as follows: green, early Pliocene of Mexico; red, early Miocene of India; blue, late Oligocene of Florida. Open circles identify node-based clades; arcs indicate stem-based taxa. The poorly integrated group “Halitheriinae” is paraphyletic in this study.</p

List of sirenian taxa and categorization of corresponding ecomorphological features used in this study.

a<p><b>Small</b>, length less than half the length of the premaxillary symphysis; <b>medium</b>, length about half the length of the premaxillary symphysis; <b>large</b>, length greater than half the length of the premaxillary symphysis.</p>b<p>Estimate based on condylobasal length of skull of 41.5 cm.</p>c<p>Based on <i>Nanosiren garciae</i> with which it shares similar dimensions of the mandible.</p

Sirenian taxa and ecomorphological features used in this study.

<p>A) Fossil dugongids from the late Oligocene Parachucla Formation of Florida showing categories of upper incisor 1 alveolar size and depth (outlined in gray), compared to premaxillary symphysis length (dashed line denotes mid-length). <i>Metaxytherium</i> sp. based on UF 49051, <i>Crenatosiren olseni</i> and <i>Dioplotherium manigaulti</i> modified from Domning <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Reinhart1" target="_blank">[9]</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Morgan1" target="_blank">[8]</a>, respectively. B) Comparison of body sizes among dugongids used in this study. C) Fossil dugongids from the early Miocene Khari Nadi Formation of India showing differences in rostral deflection. Illustrations modified from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Edwards1" target="_blank">[10]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Thewissen1" target="_blank">[12]</a>. D) Cross-sectional outline of incisors of fossil dugongids from the early Pliocene Carrillo Puerto Formation of Mexico. Skull of <i>Corystosiren varguezi</i> (modified from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031294#pone.0031294-Bajpai1" target="_blank">[11]</a>) shown to demonstrate tusk cross-section.</p

Ventral views of kogiid skulls.

<p><i>Aprixokogia kelloggi</i> (USNM 187015), 12A, <i>Scaphokogia cochlearis</i> (MNHN PPI 229), 12B, <i>Praekogia cedrosensis</i> (UCMP 315229), 12C, <i>Nanokogia isthmia</i> gen. et sp. nov. (UF 273554), 12D, and (UF 280000), 12E, <i>Kogia sima</i> (LACM 47142), 12F, and <i>K</i>. <i>breviceps</i> (LACM 95745), 12G. Each bone is color-coded for ease of comparison. Areas in white are reconstructed, light gray areas are covered with sediment; diagonal lines denote broken surfaces. Illustrations based on direct observations of the specimens listed.</p

Evolutionary Patterns among Living and Fossil Kogiid Sperm Whales: Evidence from the Neogene of Central America

<div><p>Kogiids are known by two living species, the pygmy and dwarf sperm whale (<i>Kogia breviceps</i> and <i>K</i>. <i>sima</i>). Both are relatively rare, and as their names suggest, they are closely related to the sperm whale, all being characterized by the presence of a spermaceti organ. However, this organ is much reduced in kogiids and may have become functionally different. Here we describe a fossil kogiid from the late Miocene of Panama and we explore the evolutionary history of the group with special attention to this evolutionary reduction. The fossil consists of cranial material from the late Tortonian (~7.5 Ma) Piña facies of the Chagres Formation in Panama. Detailed comparison with other fossil and extant kogiids and the results of a phylogenetic analysis place the Panamanian kogiid, herein named <i>Nanokogia isthmia</i> gen. et sp. nov., as a taxon most closely related to <i>Praekogia cedrosensis</i> from the Messinian (~6 Ma) of Baja California and to <i>Kogia</i> spp. Furthermore our results show that reduction of the spermaceti organ has occurred iteratively in kogiids, once in <i>Thalassocetus antwerpiensis</i> in the early-middle Miocene, and more recently in <i>Kogia</i> spp. Additionally, we estimate the divergence between extant species of <i>Kogia</i> at around the late Pliocene, later than previously predicted by molecular estimates. Finally, comparison of <i>Nanokogia</i> with the coeval <i>Scaphokogia cochlearis</i> from Peru shows that these two species display a greater morphological disparity between them than that observed between the extant members of the group. We hypothesize that this reflects differences in feeding ecologies of the two species, with <i>Nanokogia</i> being more similar to extant <i>Kogia</i>. <i>Nanokogia</i> shows that kogiids have been part of the Neotropical marine mammal communities at least since the late Miocene, and gives us insight into the evolutionary history and origins of one of the rarest groups of living whales.</p></div

Dorsal, 4A-B, and ventral, 4C-D, views of referred specimen of <i>Nanokogia isthmia</i> gen. et sp. nov. (UF 273554).

<p>Abbreviations: amc, anterior meatal crest; as, alisphenoid; bo, basioccipital; boc, basioccipital crest; dif, dorsal infraorbital foramen; eam, external auditory meatus; en, external nares; fg, frontal groove; fo, foramen ovale; fp, falciform process of squamosal; fr, frontal; jf, jugular foramen; jn, jugular notch; la+j, lacrimal + jugal; lmc, lateral maxillary crest; mx, maxilla; oc, occipital condyles; pmx, premaxilla; pop, postorbital process; prp, preorbital process; prs, presphenoid; ptdl, dorsal lamina of pterygoid; ptml, medial lamina of pterygoid; ptsf, pterygoid sinus fossa; scb, supracranial basin; so, supraoccipital; sq, squamosal; tsr, tympanosquamosal recess; vif, ventral infraorbital foramen; vo, vomer. Gray shaded areas indicate sediment; diagonal lines denote broken surfaces.</p

Right lateral view of holotype skull of <i>Nanokogia isthmia</i> gen. et sp. nov. (UF 280000).

<p>Abbreviations: eo, exoccipital; fg, frontal groove; fr, frontal; la+j, lacrimal + jugal; ma, mandible; mx, maxilla; lmc, lateral maxillary crest; npp, notch for posterior process of tympanic; of, optic foramen; pa, parietal; pgp, postglenoid process; pmx, premaxilla; ptdl, dorsal lamina of pterygoid; ptha, pterygoid hamulus; ptml, medial lamina of pterygoid; ptn, pterygoid notch; ptsf, pterygoid sinus fossa; scb, supracranial basin; sfc, sagittal facial crest; sq, squamosal; tc, temporal crest; zp, zygomatic process. Gray shaded areas indicate sediment; diagonal lines denote broken surfaces.</p

Ventral view of holotype skull of <i>Nanokogia isthmia</i> gen. et sp. nov. (UF 280000).

<p>Abbreviations: an, antorbital notch; bo/bs, basioccipital/basisphenoid; boc, basioccipital crest; cb.e, cerebral endocast; eam, external auditory meatus; fg, frontal groove; in, internal nares; jn, jugular notch; la+j, lacrimal + jugal; ma, mandible; mx, maxilla; npp, notch for posterior process of tympanic; oc, occipital condyles; pl, palatine; prs, presphenoid; ptdl, dorsal lamina of pterygoid; ptha, pterygoid hamulus; ptml, medial lamina of pterygoid; ptsf, pterygoid sinus fossa; tsr, tympanosquamosal recess; vif, ventral infraorbital foramen; vo, vomer. Gray shaded areas indicate sediment; diagonal lines denote broken surfaces.</p

Right lateral views of kogiid skulls.

<p><i>Aprixokogia kelloggi</i> (left side, reversed, USNM 187015), 13A, <i>Scaphokogia cochlearis</i> (MNHN PPI 229), 13B, <i>Praekogia cedrosensis</i> (UCMP 315229), 13C, <i>Nanokogia isthmia</i> gen. et sp. nov. (based on UF 280000 and 273554), 13D, <i>Kogia sima</i> (LACM 47142), 13E, and <i>K</i>. <i>breviceps</i> (LACM 95745), 13F. Each bone is color-coded for ease of comparison. Areas in white are reconstructed; diagonal lines denote broken surfaces. Illustrations based on direct observations of the specimens listed.</p

Posterior views of holotype (UF 280000), 7A-B, and referred specimen (UF 273554), 7CD, skulls of <i>Nanokogia isthmia</i> gen. et sp. nov.

<p>Abbreviations: boc, basioccipital crest; eo, exoccipital; fm, foramen magnum; jn, jugular notch; oc, occipital condyles; so, supraoccipital; sop, supraorbital process of frontal; tc, temporal crest. Gray shaded areas indicate sediment; diagonal lines denote broken surfaces.</p