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Ultimately, all river cetaceans are threatened by the transforma-tion of their habitat to serve human needs. In addition to impeding the natural movements of dolphins and other aquatic organisms, dams in southern Asia divert water to irrigate farm fi elds and sup-ply homes and businesses in an arid landscape, reducing directly the amount of habitat available to the dolphins. As water becomes an increasingly strategic resource in a warming world with expand-ing human populations, the prospects for freshwater cetaceans are certain to deteriorate even further.

See Also the Following Articles Amazon River Dolphin ■ Baiji ■ Endangered Species and Populations■ Finless Porpoise ■ Franciscana ■ Irrawaddy Dolphin ■ Susu and Bhulan ■ Tucuxi

References Banguera-Hinestroza , E. , Cárdenas , H. , Ruiz-García , M. , Marmontel , M. ,

Gaitán , E. , Vázquez , R. , and García-Vallejo , F. ( 2002 ). Molecular identifi cation of evolutionarily signifi cant units in the Amazon river dolphin Inia sp. (Cetacea: Iniidae) . J. Hered. 93 , 312 – 322 .

Best , R. C. ( 1984 ). The aquatic mammals and reptiles of the Amazon .In “ The Amazon: Limnology and Landscape Ecology of a Mighty Tropical River and its Basin ” ( H. Sioli , ed. ) , pp. 371 – 412 . Dr W. Junk, Dordrecht , Dordrecht, The Netherlands .

Best , R. C. , and da Silva , V. M. F. ( 1989 ). Amazon river dolphin, boto Inia geoffrensis (de Blainville, 1817) . In “ Handbook of Marine Mammals ” ( S. H. Ridgway , and R. Harrison , eds ) , Vol. 4 , pp. 1 – 23 . Academic Press , London .

Brownell , R. L. , Jr. ( 1989 ). Franciscana Pontporia blainvillei (Gervais and d’Orbigny, 1844) . In “ Handbook of Marine Mammals ” ( S. H. Ridgway , and R. Harrison , eds ) , Vol. 4 , pp. 45 – 67 . Academic Press , London .

Caldwell, M. C., Caldwell, D. K., and Brill, R. L. (1989). Inia geoffren-sis in captivity in the United States. In “ Biology and Conservation of the River Dolphins ” Occasional Papers of the IUCN Species Survival Commission No. 3 (W. F. Perrin, R. L. Brownell, Jr., K. Zhou, and J. Liu, eds), pp. 35–41. IUCN, Gland, Switzerland .

Chen , P. ( 1989 ). Baiji Lipotes vexillifer Miller, 1918 . In “ Handbook of Marine Mammals ” ( S. H. Ridgway , and R. Harrison , eds ) , Vol. 4 , pp. 25 – 43 . Academic Press , London .

Herald , E. S. , Brownell , R. L. , Jr. , Frye , F. L. , Morris , E. J. , Evans , W. E. , and Scott , A. B. ( 1969 ). Blind river dolphins: First side-swimming cetacean . Science 166 , 1408 – 1410 .

Jefferson, T. A., and Smith, B.D. (eds.) (2002). Facultative freshwater cetaceans of Asia: Their ecology and conservation. Raffl es Bull. Zool. Suppl. 10, 187 pp .

Kasuya , T. ( 1999 ). Finless porpoise Neophocaena phocaenoides (G. Cuvier, 1829) . In “ Handbook of Marine Mammals ” ( S. H. Ridgway , and R. Harrison , eds ) , Vol. 6 , pp. 411 – 442 . Academic Press , San Diego .

Martin , A. R. , and da Silva , V. M. F. ( 2004 a ). River dolphins and fl ooded for-est: Seasonal habitat use and sexual segregation of botos Inia geoffrensisin an extreme cetacean environment . J. Zool. (Lond). 263 , 295 – 305 .

Martin , A. R. , and da Silva , V. M. F. ( 2004 b ). Number, seasonal move-ments and residency characteristics of river dolphins using an Amazonian fl oodplain lake system . Can. J. Zool. 82 , 1307 – 1315 .

Martin , A. R. , and da Silva , V. M. F. ( 2006 ). Sexual dimorphism and body scarring in the boto (Amazon river dolphin) Inia geoffrensis . Mar. Mamm. Sci. 22 ( 1 ) , 25 – 33 .

May-Collado , L. J. , and Wartzok , D. ( 2007 ). The freshwater dolphin Iniageoffrensis geoffrensis produces high frequency whistles . J. Acoust. Soc. Am. 121 ( 2 ) , 1203 – 1212 .

Perrin, W. F., Brownell, R. L., Jr., Zhou, K., and Liu, J. (eds.) (1989). “ Biology and Conservation of the River Dolphins. ” Occasional Papers

of the IUCN Species Survival Commission No.3. IUCN–The World Conservation Union, Gland, Switzerland .

Reeves , R. R. , and Brownell , R. L. , Jr. ( 1989 ). Susu Platanista gangetica(Roxburgh, 1801); and Platanista minor Owen, 1853 . In “ Handbook of Marine Mammals ” ( S. H. Ridgway , and R. Harrison , eds ) , Vol. 4 , pp. 69 – 99 . Academic Press , London .

Reeves, R. R., Smith, B. D., and Kasuya, T. (eds.) (2000). “ Biology and Conservation of Freshwater Cetaceans in Asia. ” Occasional Papers of the IUCN Species Survival Commission No. 23. IUCN–The World Conservation Union, Gland, Switzerland.

Rice , D. W. ( 1998 ). “ Marine Mammals of the World: Systematics and Distribution . ” Society for Marine Mammalogy , Lawrence, KS , Special Publication No. 3 .

Smith , B. D. ( 1993 ). 1990 status and conservation of the Ganges river dolphin Platanista gangetica in the Karnali River, Nepal . Biol.Conserv. 66 , 159 – 169 .

Smith , B. D. , Thant , U. H. , Lwin , J. M. , and Shaw , C. D. ( 1997 ). Investigation of cetaceans in the Ayeyarwady River and northern coastal waters of Myanmar . Asian Mar. Biol. 14 , 173 – 194 .

Turvey, S. T., Pitman, R. L., Taylor, B. L., Barlow, J., Akamatsu, T., Barrett, L. A., Zhao, X., Reeves, R. R., Stewart, B. S., Wang, K., Wei, Z., Zhang, X., Pusser, L. T., Richlen, M., Brandon, J. R., and Wang, D. (2007). First human-caused extinction of a cetacean species? Biol. Letters 3, 537–540.

Vidal , O. , Barlow , J. , Hurtado , L. A. , Torre , J. , Cendón , P. , and Ojeda , Z. ( 1997 ). Distribution and abundance of the Amazon river dolphin (Inia geoffrensis ) and the tucuxi ( Sotalia fl uviatilis ) in the upper Amazon River . Mar. Mamm. Sci. 12 , 427 – 445 .

Wang , K. , and Wang , D. ( 2006 ). Estimated detection distance of a bai-ji’s (Chinese river dolphin, Lipotes vexillifer ) whistles using a passive acoustic survey method . J. Acoust. Soc. Am. 120 , 1361 – 1365 .

Zhou , K. , and Zhang , X. ( 1991 ). “ Baiji: The Yangtze River Dolphin and Other Endangered Animals of China . ” Stone Wall Press , Washington, DC .

River Dolphins, Evolutionary History and Affi nities

CHRISTIAN DE MUIZON

The term “ river dolphins ” or Platanistoids has been traditionally used to include the recent odontocetes that live in freshwater and are not members of the other clades of odontocetes: del-

phinoids, ziphioids, and physeteroids. Their affi nities to other groups of odontocetes were unresolved, mainly because they have many ple-siomorphic characters (e.g., Slijper, 1936 , Simpson, 1945 ). There are four genera of living “ river dolphins ” ( Platanista , Lipotes , Inia , and Pontoporia ). Other (partly) freshwater odontocetes include Orcaella(Irrawadi River) and Sotalia (Amazon River) are not included in the Platanistoidea because they are clearly related to the marine dol-phins, Delphinidae. Although it was previously assumed that platan-istoids were monophyletic, this is almost certainly not the case, and some of their included taxa have been regarded as closely related to several groups of fossil odontocetes: e.g., the Squalodontidae, the Eurhinodelphinidae, the “ Acrodelphinidae. ” There is now consen-sus that Platanistoidea is para- or polyphyletic ( Muizon, 1984, 1987, 1988, 1991, 1994 ; Heyning, 1989 ; Fordyce, 1994 ; Messenger and McGuire, 1998 ; Fig. 1 ).

The genus Platanista appears to be an early diverging group of odontocetes, Platanistoidea, and the three other genera ( Lipotes ,

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Pontoporia , and Inia ) are regarded as closely related to the Delphinoidea. Platanistoidea was a diversifi ed and widely distributed group during the Oligocene and the Miocene. This group includes the modern Platanistidae as well as the fossil families Prosqualodontidae, Squalodontidae, Waipatiidae, Squalodelphinidae, and possibly the Dalpiazinidae. The other “ river dolphins ” are included with the Delphinoidea within the monophyletic infraorder Delphinida. There is no consensus on their position within the Delphinida, although they are generally regarded as basal taxa.

I. Platanistoidea This monophyletic superfamily of odontocetes includes one recent

genus ( Platanista ) and approximately 15 fossil taxa ( Fordyce and Muizon, 2000 ). The monophyly of the Platanistoidea is supported by several synapomorphies such as the reduction or loss of the coracoid process of the scapula, the development of articular ridge or peg on the periotic, and the ventral defl ection of the anterior process of the periotic ( Fordyce, 1994 ; Muizon, 1994 ). This superfamily includes fi ve (possibly six) families: the Squalodontidae, the Prosqualodontidae, the Waipatiidae, the Squalodelphinidae, and the Platanistidae. In contrast to their recent representative, all the fossil platanistoids are marine, which indicates that adaptation to freshwater environment is probably a derived condition.

A. Squalodontidae Squalodonts (literally shark-toothed) are the most common fos-

sil platanistoids. They have a heterodont dentition, where the poste-rior teeth are triangular with serrated edges (similar to some sharks). Heterodonty is primitively present in all cetaceans, and not restricted to platanistoids. In the past, this condition was used to include clades in platanistoids, but this view has been abandoned. The squalodontid

genera based on partial or complete skulls are Squalodon , Kelloggia(a possible synonym of Squalodon ), Eosqualodon , and ? Phoberodon . Synapomorphies of Squalodontidae as defi ned by Fordyce (1994) are essentially based on the morphology of one of the earbones, the periotic, a bone which is unknown in Phoberodon , Eosqualodon , and Kelloggia . The monophyly and content of the Squalodontidae has still to be evaluated by careful anatomy and further fossil fi nds. Patriocetus was also included in Squalodontidae ( Rothausen, 1968 ),but this needs to be confi rmed.

The Squalodontidae are cosmopolitan basal platanistoids. All their remains were found in marine coastal environment. Squalodonis present in the Miocene of Europe, Asia, and North America; Eosqualodon is present in the Miocene of Europe; Kelloggia is present in the late Oligocene of Asia; Phoberodon is from the early Miocene of South America. Undescribed squalodontids have also been found in Australia and New Zealand ( Fordyce and Muizon, 2000 ). Squalodontids are relatively large odontocetes approaching the size of the living Mesoplodon . They had a long rostrum with strongly procum-bent anterior teeth ( Fig. 2 ). In fact, the medial incisors were almost horizontal. The teeth were strongly heterodont. The vertex was low and the skull was symmetrical. As all platanistoids, the Squalodontidae have enlarged and slightly concave premaxillary fossae anterolateral to the nares. These fossae received premaxillary sacs of the nasal tract. Premaxillary sacs are tightly related to the presence of nasal plugs and melon and their presence in the Squalodontidae is an indication of effi cient echolocation ability.

B. Prosqualodontidae The single genus Prosqualodon is included in this family. Initially

placed in the Squalodontidae (e.g., Simpson, 1945 ; Rothausen, 1968 ), Prosqualodon has been removed from this family by Muizon

Physeteroidea

Ziphioidea

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PlatanistidaeSqualodelphinidae

DalpiazinidaeSqualodontidaeProsqualodon

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EurhinodelphinoideaLipotoideaIniidaePontoporiidae

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KentriodontidaePontoporiidae

DelphinidaeSqualodontidae

WaipatiidaePlatanistidae

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Phocoenidae

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Lipotidae

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Muizon (1987, 1988,1991, 1994)

Fordyce (1994)

Heyning (1989)

Messenger andMcGuire (1998)

Figure 1 Cladograms of hypotheses on the affi nities of “ river dolphins. ”

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(1991) because it does not possess the synapomorphies of the audi-tory region observed in the other platanistoids; however, it was maintained in the superfamily because it bears the scapula synapo-morphies of the group. This suggests that Prosqualodon is the sis-ter group of the other platanistoids. However, Prosqualodon has sometimes been included in the infraorder Delphinida on the basis of the presence of a synapomorphy of the palatine (presence of a lateral lamina as defi ned by Muizon, 1988 ) but these may not be homologous.

Prosqualodon is a southern genus that has been found so far in the early Miocene of Argentina, Australia, and New Zealand. It is a medium-sized odontocete, and its size ranges from a small Globicephala to a large Tursiops . As squalodontids, it had hetero-dont teeth. The anterior teeth are elongated conical and project anteroventrally; the posterior teeth are triangular, low, transversely compressed with a rugose enamel and bear several denticles on their anterior and posterior crests. The rostrum is short, the vertex is symmetrical, and the braincase is lower than in the Squalodon . Premaxillary fossae are clearly present but they are less developed and shallower than in Squalodon ( Fig. 3 ).

C. Dalpiazinidae The single known genus of this family, Dalpiazina , is probably

related to the Platanistoidea given the presence of several similari-ties with Squalodon ( Muizon 1991, 1994 ), although critical synapo-morphies are not observable in the preserved fossils. Dalpiazina is a medium-sized odontocete (small Tursiops ). The rostrum is rela-tively long and bears homodont dentition. It is known from the early

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Figure 2 Skulls of Squalodontidae. (A) Eosqualodon langewi-eschei (late Oligocene, Germany), reconstruction of the skull in dorsal view (from Rothausen, 1968 , modifi ed). (B) Squalodonbellunensis (early Miocene, Italy), reconstruction of the skull in dorsal view (from Rothausen, 1968 , modifi ed). (C) S. bellunensis(early Miocene, Italy), skull and mandible (IGUP 26131, 26132, 26133) in lateral view. (D) Squalodon bariensis (early Miocene, France), skull (apex of the rostrum missing) in ventral view (MHNL Dr 15). (A) and (B) are reproduced with permission of Paläontologische Zeitschrift.

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Figure 3 Skull (MLP 5–9) of Prosqualodon australis (early Miocene, Argentina) in dorsal (A) and lateral (B) views.

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Miocene of Italy and some possible dalpiazinids have been discov-ered in New Zealand ( Fordyce et al ., 1994 ).

D. Waipatiidae Waipatia is well documented by a relatively complete skull with

ear bones and partial skeleton. This genus displays the synapomor-phies of the auditory region of the platanistoids and, although its scapula is unknown, is best placed in this superfamily than in any other group of odontocete ( Fordyce, 1994 ; Fordyce and Muizon, 2000 ). It is a medium-sized platanistoid similar in size to Tursiops . The rostrum is long and slender ( Fig 4 ). It bears heterodont teeth but the posterior triangular and double-rooted teeth are smaller than in the Squalodontidae. The incisors are conical and strongly procumbent. The skull roof is very low as in squalodontids. The skull of Waipatia shows clear directional asymmetry of the bones. The fossae for the premaxillary sacs are well developed and the pre-maxillae extend posterior to the nasals and contact the frontals on the vertex as in the other platanistoids. Waipatia maerewhenua , the only species unambiguously pertaining to this family is from the late Oligocene of New Zealand.

Sulakocetus is a primitive odontocete from the late Oligocene of the Caucasus (Asia) that has been referred to platanistoids. It bears heterodont dentition but its posterior double-rooted teeth are small as in Waipatia . One of its earbones, the tympanic, is squalodont-like, and the scapula bears a small coracoid process, indicating that it is not a platanistoid. However, it is probable that the small (reduced) size of the process represent an incipient development of the pla-tanistoid condition. This genus has been classifi ed by Fordyce and Muizon (2000) as a possible Waipatiidae.

E. Squalodelphinidae This family includes the genera Notocetus , Medocinia , Phocageneus ,

and Squalodelphis . The four taxa are based on reasonably well-pre-served skulls and/or ear bones. The Squalodelphinidae present the

platanistoid synapomorphies of the scapula (loss of the coracoid proc-ess, anterior position of the acromion) and of the ear region (e.g., sub-circular fossa, articular ridge of the periotic, morphology of the apex of the tympanic; see Muizon 1987, 1994 ). The Squalodelphinidae are cosmopolitan and marine. Notocetus is from the early Miocene of South America and New Zealand; Squalodelphis and Medocinia are from the early to middle Miocene of Europe; Phocageneus is from the early Miocene of North America. The Squalodelphinidae are medium-sized odontocetes similar in size to the living Tursiops . The rostrum is of moderate length and slender ( Fig. 5 ). The teeth are more or less homodont: the posterior teeth are single rooted but they are clearly lower and more triangular than the anterior. An interesting charac-teristic of the Squalodelphinidae is the thickening of the supraorbital region of the skull (maxilla and/or frontal; Fig 5B and D ), reminiscent of the specialized supraorbital morphology of Platanistidae (see later, Fig. 6 ).

F. Platanistidae Platanistids are represented in the fossil record by two gen-

era, Zarhachis and Pomatodelphis ( Fig. 6 ). They both present all the Platanistoid synapomorphies of the ear region, palatine, and scapula. The main characteristic of the Platanistidae is the develop-ment of large maxillary ( Platanista ) or maxillofrontal ( Zarhachis , Pomatodelphis ) crests, which are already incipiently developed in the Squalodelphinidae (see earlier discussion). A peculiarity of Platanistais that the palatine is entirely covered by the maxilla and the pterygoid. In Zarhachis and Pomatodelphis this condition is incipiently devel-oped since the palatine is partially covered ( Muizon 1987, 1994 ) and the visible portion of the bone is displaced laterally. Both genera have a very long and slender rostrum bearing homodont teeth. Zarhachisis slightly larger than Pomatodelphis and similar in size to a small Mesoplodon. Allodelphis has been regarded as a platanistid; however, this genus is still too poorly known to be referred unambiguously to this family. It is regarded here as a possible Platanistoidea, which has

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Figure 4 Skulls of squalodelphinids. (A) Squalodelphis fabianii (early Miocene, Italy), a, skull and mandible (IGUP 26134) in dorsal view. (B) The same in lateral view (note the thickness of the supraorbital region). (C) Reconstruction of the skull of Medociniatetragorhina (early Miocene of France), in dorsal view. (D) The same in lateral view (from Muizon, 1988 ). Reproduced with permi-sion of the Bulletin du Muséum national d’Histoire naturelle.

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A. Lipotoidea This superfamily includes a single family with two genera. Lipotes

(Recent, China) and Parapontoporia (Neogene, West coast of North America). Prolipotes from the Miocene of China is based on a non-diagnostic mandible fragment and is regarded as an incertae sedis ( Fordyce and Muizon, 2000 ). Parapontoporia ( Fig. 7 ) is regarded here as a lipotid, although classifi ed by its author ( Barnes 1985 )in the Pontoporiidae. The skull of Parapontoporia presents a dis-tinct narrowing at the base of the rostrum, which is always present in Lipotes and generally absent in pontoporiids (when present in Pontoporia it is weak); Parapontoporia does not bear the premaxil-lary eminences which are present in all pontoporiids and iniids; the nasals of Parapontoporia tend to be subvertical and not subhorizon-tal as in pontoporiids.

Parapontoporia is the only fossil lipotid for which well-preserved skull material is available. Although its braincase is only slightly larger than that of Lipotes , its rostrum is almost twice as long. The asym-metry is less pronounced than in Lipotes . The teeth are small, single-cusped, and numerous ( � 80 on each side). In Lipotes the number of teeth varies from approximately 30 to 36. Lipotids are known in the Northern Hemisphere only (China and California) and it is possible that the evolution of the family took place in the Northern Pacifi c.

B. Inioidea This superfamily includes the Iniidae and Pontoporiidae. The two

families share synapomorphies of the periotic (great reduction of the anterior and posterior processes), malleus (unique extreme develop-ment of the processus muscularis), premaxilla (presence of premax-illary eminences), maxilla (frontomaxillary crests: dorsal infl exion of the postorbital edges of the maxilla and frontal). The superfamily is documented by a few well-established fossil genera mostly from South America.

LacrimalAntorbital notch

Depression around notch

Maxilla

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Premaxilla

Mesorostral groove

Anteromedial sulcusPremaxillary foramenPosteromedial sulcus

Premaxillary sac fossaPosterolateral sulcus

Supraorbital process of maxilla Frontal Temporal crest

Post-tympanic processExternal auditory meatus

Subtemporal crestPostorbital ridge of frontal

FrontalInfraorbital foramen

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Figure 5 Reconstruction of the skull of Waipatia maerewhenua (late Oligocene, New Zealand). (A) Dorsal view; (B) ventral view; (C) lat-eral view (from Fordyce, 1994 , modifi ed). Reproduced with permission of the San Diego Society of Natural History.

to be confi rmed by a better knowledge of its anatomy. Zarhachis and Pomatodelphis were found in marine deposits. They are from the mid-dle Miocene of North America and Europe ( Pomatodelphis only). No fossil Platanistids have been found, so far, neither in the southern Hemisphere nor in Asia.

II. Non-platanistoid “River Dolphins ” Non-platanistoid river dolphins are represented by the recent

families Lipotidae ( Lipotes ), Iniidae ( Inia ), and Pontoporiidae (Pontoporia ). Most authors recognize separate families for the three modern genera, but others place all in one family (Iniidae, Heyning,1989 ), or two, Pontoporiidae ( Pontoporia and Lipotes ) and Iniidae (Inia ; Fordyce, 1994 ). Fordyce and Muizon (2000) include these three families in the infraorder Delphinida on the basis of several synapomorphies: the development of a lateral lamina of the palatine, the sigmoid morphology of the involucrum of the tympanic and its posterior excavation, the development of a ventral rim on the ventro-medial face of the anterior process of the periotic and the increase in size of the processus muscularis of the malleus. The Lipotidae are the earliest divergent Delphinida. The other Delphinida [Inioidea (Inidae � Pontoporiidae) and Delphinoidea] differ from the Lipotidae in the following synapomorphies: e.g., the reduction of the anterior process of the periotic, which loses the bullar facet; increase in size of the processus muscularis of the malleus, which is distinctly more developed than the manubrium, the presence of a pair of ventral processes on the anterior region of the sternal manubrium ( Muizon, 1988 ). The second diverging clade is the Inioidea. The third clade, the Delphinoidea have an apomorphic thickening of the apex of the anterior process of the periotic and a great reduction of the dorsal portion of the transverse process of the atlas. Therefore, the Delphinida include three superfamilies of odontocetes, the Lipotoidea, the Inoidea, and the Delphinoidea ( Muizon, 1988 ).

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The Iniidae are represented in the fossil record by a single genus known by relatively well-preserved cranial remains: Ischyrorhynchus . The genera Saurocetes , Plicodontinia , Hesperocetus , Hesperoinia , and Lonchodelphis that have been related to the Iniidae, are based on non-diagnostic rostra, mandible fragments or isolated teeth, and may or may not pertain to this family. Goniodelphis , is based on a partial skull, which probably belongs to an iniid. However, because of its incompleteness, this specimen has been questionably referred to the family by Fordyce and Muizon (2000) .

One of the major characteristic of the Iniidae ( Ischyrorhynchusand Inia ) is the development of a frontal hump on the vertex, which is expanded at its apex. Iniidae also present an extreme reduction of the posterior process of the periotic.

Ischyrorhynchus is approximately 30% larger than Inia and its rostrum is relatively longer. Besides these features, Ischyrorhynchusis very similar to the recent iniid. It is from the late Miocene of the Paraná Basin (Argentina) and, therefore, was living in a freshwater environment.

The Pontoporiidae are known by two fossil genera based on well-preserved cranial remains (with associated ear bones): Pliopontosand Brachydelphis ( Fig. 8 ). Pontistes is another pontoporiid and is based on a single partial skull with a well-preserved vertex. Pontivaga

has been referred to pontoporiids, however this genus, which is based on a partial mandible is regarded as an incertae sedis. The Pontoporiidae share synapomorphies such as a low vertex with fl at, more-or-less horizontal nasals and the posterior, blade-like extension of the posterior process of the periotic.

Pliopontos is 50% larger than Pontoporia . As in the recent taxon, the rostrum is long and slender with sharp small teeth. Except for its size, Pliopontos is very similar to Pontoporia . It is from the early Pliocene of Peru and was marine. Brachydelphis is a much less clas-sical pontoporiid. It has a very short rostrum, which is as long as the braincase. The latter is much larger than in Pontoporia and similar in size to that of Pliopontos . Because of these unique features for a pontoporiid, Brachydelphis has been placed in its own subfamily, the Brachydelphinae. It is from the Middle Miocene of Peru and was liv-ing in a marine environment.

III . Conclusions There is near consensus that the odontocetes traditionally placed in

the “ river dolphins ” (the “ Platanistoidea ” of Simpson 1945 ) belong to two different groups of dolphins and are polyphyletic: the Platanistoidea and the Delphinida (Lipotoidea and Inioidea). The Platanistoidea repre-sent the sister group of a clade, which includes the Delphinida and the

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Figure 6 Skulls of Platanistidae. (A) Pomatodelphis cf. inaequalis(middle Miocene, Maryland, USA), skull (USNM 187414) in dorsal view. (B) Zarhachis fl agellator (middle Miocene, Maryland, USA), skull (most of the rostrum missing) in dorsal view (USNM 10911).

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Figure 7 Reconstruction of the skull of Parapontoporia sternbergi(early Pliocene, California, USA). (A) Dorsal, (B) ventral, and (C) lateral views (from Barnes, 1985 modifi ed). Reproduced with per-mission of the Contribution in Science, Los Angeles County Museum of Natural History.

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fossil superfamily Eurhinodelphinoidea ( Fig. 1 ). The non-platanistoid “ river dolphins ” do not represent a monophyletic grouping. In contrast, an exhaustive analysis of cetaceans phylogeny by Geisler and Sanders (2003) did fi nd monophyly of river dolphins but polyphyly of the Delphinoidea. These results are contradicted by all other morphological and molecular analyses ( Cassens et al ., 2000 , Nikaido et al ., 2001 ).

Fossil platanistoids are diverse and distributed into several fami-lies. Fossil Lipotids and Inioids are still relatively scarce but can be easily related to one of the three non-Platanistoid families of “ river dolphins. ” Most fossil “ river dolphins ” are from marine environments and the adaptation to freshwater is a convergence at least in three modern groups: the Platanistidae, the Lipotidae, and the Iniidae. Adaptation to this environment also appeared independently in two delphinoids ( Orcaella and Sotalia ).

See Also the Following Articles Cetarean Evolution ■ Cetacean Fossil Record

References Barnes , L. G. ( 1985 ). Fossil pontoporiid dolphins (Mammalia: Cetacea)

from the Pacifi c coast of North America . Contributions to Science, Natural History Museum of Los Angeles County 363 , 1 – 34 .

Cassens, I., Vicario, S., Waddell, V. G., Balchowsky, H., Van Belle, D., Ding, W., Fan, C., Mohan, L., Simões-Lopez, P. C., Bastida, R., Meyer, A., Stanhope, M. J., and M.C. Milinkovitch. (2000). Proc.Natl. Acad. Sci. , 97: 11343–11347 .

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Figure 8 Skulls of Pontoporiidae: Pliopontos littoralis (early Pliocene, Peru), reconstruction of the skull in (A) dorsal, (B) ventral, (C) and lateral views (from Muizon, 1984 ); Brachydelphys mazeasi (middle Miocene, Peru), reconstruction of the skull in dorsal (D), ventral (E), and lateral (F) views (from Muizon, 1988 ). Reproduced with permission of the Institut Français d ’ Études Andines.

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Rookeries GEORGE ANTHONY ANTONELIS

Pinnipeds reproduce in a wide range of marine habitats, includ-ing various forms of ice, tidal fl ats, rock outcroppings, and coastal beaches ( Scheffer, 1958 ). Some species form annual

breeding aggregations at traditional locations known as rookeries. These reproductive sites are an integral component of the animals ’life history patterns, resulting from a complex suite of adaptive fac-tors involving physiology, morphology, ecology, and distribution. Rookery-breeding pinnipeds exhibit varying forms of polygyny ( Boness, 1991 ); this mode of social organization is believed to have evolved as a consequence of two key traits, parturition on solid sub-strate and offshore marine foraging ( Bartholomew, 1970 ). The infl u-ence of these traits in conjunction with phylogenetic and ecological constraints has likely infl uenced the development of the polygynous mating systems observed on rookeries today ( Emlen and Oring, 1977 ;Stirling, 1983 ; Boness, 1991 ; Boyd, 1991 ).

Rookery-breeding pinnipeds are subdivided into two families, Otariidae and Phocidae. Rookeries are formed by all otariids (15 species) and three phocids [2 species of elephant seal, Miroungaangustirostris and M. leonina , and gray seals, Halichoerus grypus( Reeves et al. , 1992 ; Rice, 1998 )]. This chapter describes the salient social–biological, physical–geographical, and environmental charac-teristics of pinniped rookeries and provides information on the eco-logical context in which they occur.

I . Social–Biological Characteristics Rookeries are formed at specifi c times and locations, which

optimize the reproductive success and survival of offspring ( Bartholomew, 1970 ; Stirling, 1983 ; Boyd, 1991 ). After foraging at sea during the nonbreeding season, adult males return to rookeries and begin establishing territories shortly before or about the same time as the arrival of parturient females. Overt aggression, frequent threat vocalizations, and ritualized boundary displays are common among males when establishing and defending territories ( Fig. 1 ).

Males also attempt to herd females in an effort to keep them within their areas of infl uence ( Fig. 2 ). Adult females come ashore to fi nd suitable parturition sites and tend to be highly gregarious. Parturient females frequently threaten one another either vocally or visually and are often aggressive toward offspring of other females. Otariid females suckle their pups for about 4–12 months, although longer periods have been documented for some species ( Oftedal et al. , 1987 ; Bowen, 1991 ). Lactation of rookery-breeding phocid females lasts about 0.5 (gray seals) to 1.0 (elephant seals) month. Estrus occurs early in lactation for otariids and late in lactation for phoc-ids ( Oftedal et al. , 1987 ). Most copulations occur on land at or near the parturition site, but a few species commonly breed aquatically in the intertidal zone where males maintain aquatic territories. Otariid females intermittently leave the rookery to forage between suckling periods, and phocid females fast on land during the entire lactation period. Thus, some pinniped rookeries may be occupied continu-ously, but most breeding is completed within a relatively short time period of about 2 months.

Sexual dimorphism is apparent on pinniped rookeries, as adult males usually have distinctly different characteristics and are larger than females. Each sex and species emits stereotypic vocalizations for long- and short-distance communication ( Stirling and Warneke, 1971 ; Miller, 1991 ). Males emit loud long-distance threat calls toward other males. Lactating otariid females also emit loud pup attraction calls on rookeries to locate their offspring among hun-dreds of pups. Short-distance threat vocalizations are common on all pinniped rookeries and have less amplitude than long-distance calls. Noise from rookeries initially may be perceived as a cacophony of sounds, but what seems to be chaos is really a well-organized social structure that has evolved over millions of years.

Figure 1 Adult male California sea lions ( Zalophus californianus ) compete for territories at San Miguel Island, California (NMFS, George Antonelis).