Skip to main content
    • Aa
    • Aa

Endocranial anatomy of a new fossil porpoise (Odontoceti, Phocoenidae) from the Pliocene San Diego Formation of California

  • Rachel A. Racicot (a1) and Timothy Rowe (a2)

The Pliocene fossil porpoise SDSNH 65276 has extremely elongate mandibular morphology, unlike that of any marine amniote, and is superficially most similar to the living bird species known as skimmers (Rynchops sp.). Endocasts of the pterygoid sinuses and endocranial cavity were digitally segmented from high-resolution X-ray CT scans of the specimen to explore internal anatomy of functionally and phylogenetically important anatomical features of this specimen and odontocetes in general. The sinuses are similar in volume and shape to extant porpoise species, but the dorsal extension of the preorbital lobes are particularly elongate as in the harbor porpoise (Phocoena phocoena). The cranial endocast also shows similarities with extant porpoises, but has much deeper interhemispheric fissures, which are filled by ossified meninges, particularly a deep falx cerebri and shallower tentorium cerebelli. Ossifications of these parts of the meninges may reflect faster angular accelerations of the head, deeper diving ability, or both. Penetrations of the endocranial cavity for cranial nerves and blood vessels are like those of extant porpoises. The internal skull morphology of this unique delphinoid sheds additional light both on its phylogenetic affinities and novel odontocete adaptations.

Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

A. M. Balanoff , G. S. Bever , and T. Ikejiri 2010. The braincase of Apatosaurus (Dinosauria: Sauropoda) based on computed tomography of a new specimen with comments on variation and evolution in sauropod neuroanatomy. American Museum Novitates, 3677:132.

L. G. Barnes 1985. Evolution, taxonomy and antitropical distribution of the porpoises (Phocoenidae, Mammalia). Marine Mammal Science, 1:149165.

G. S. Bever , S. L. Brusatte , A. M. Balanoff , and M. A. Norell 2011. Variation, variability, and the origin of the avian endocranium: insights from the anatomy of Alioramus altai (Therapoda: Tyrannosauroidea). PLoS One, 6:e23393.

A. M. Burrows and T. D. Smith 2005. Form and patterns of the external aspect of the brain and the superficial dural venous sinuses of the river dolphins (Cetacea: Odontoceti) from endocasts and their bearing on phylogenetic reconstruction. Annals of the Carnegie Museum, 74:201215.

M. W. Colbert , R. A. Racicot , and T. Rowe 2005. Anatomy of the cranial endocast of the bottlenose dolphin, Tursiops truncatus, based on HRXCT. Journal of Mammalian Evolution, 12:195207.

A. Costidis and S. A. Rommel 2012. Vascularization of air sinuses and fat bodies in the head of the Bottlenose dolphin (Tursiops truncatus): morphological implications on physiology. Frontiers in Physiology, 3:123.

T. W. Cranford , M. Amundin , and K. S. Norris 1996. Functional morphology and homology in the odontocete nasal complex: implications for sound generation. Journal of Morphology, 228:223285.

L. Fajardo-Mellor , A. Berta , R. L. Brownell Jr., C. Boy , and R. N. P. Goodall 2006. The phylogenetic relationships and biogeography of true porpoises (Mammalia: Phocoenidae) based on morphological data. Marine Mammal Science, 22:910932.

A. Galatius , A. Berta , M. S. Frandsen , and R. N. P. Goodall 2011. Interspecific variation of ontogeny and skull shape among porpoises (Phocoenidae). Journal of Morphology, 272:136148.

J. Gatesy , J. H. Geisler , J. Chang , C. Buell , A. Berta , R. W. Meredith , M. S. Springer , and M. R. McGowen 2013. A phylogenetic blueprint for a modern whale. Molecular and Phylogenetic Evolution, 66:479506.

J. H. Geisler and Z. Luo 1998. Relationships of Cetacea to terrestrial ungulates and the evolution of cranial vasculature in Cete, p. 163212. In J. G. M Thewissen (ed.), The Emergence of Whales. Plenum Press, New York.

W. E. Grus , P. Shi , and J. Zhang 2007. Largest vomeronasal Type 1 receptor gene repertoire in the semiaquatic platypus. Molecular Biology and Evolution, 24:2,1532,157.

D. S. Houser , J. Finneran , D. Carder , W. Van Bonn , C. Smith , C. Hoh , R. Mattrey , and S. Ridgway 2004. Structural and functional imaging of bottlenose dolphin (Tursiops truncatus) cranial anatomy. Journal of Experimental Biology, 207:3,6573,665.

D. S. Houser , P. W. Moore , S. Johnson , B. Lutmerding , B. Branstetter , and S. Ridgway 2010. Relationship of blood flow and metabolism to acoustic processing centers of the dolphin brain. Journal of the Acoustical Society of America, 128:1,4601,466.

H. Ichishima and M. Kimura 2005. Haborophocoena toyoshimai, a new early Pliocene porpoise (Cetacea; Phocoenidae) from Hokkaido, Japan. Journal of Vertebrate Paleontology, 25:655664.

H. Ichishima and M. Kimura 2013. New material of Haborophocoena toyoshimai (Odontoceti: Phocoenidae) from the lower Pliocene Embetsu Formation of Hokkaido, Japan. Paleontological Research, 17:127137.

M. Jacobs , A. Galaburda , W. McFarland , and P. Morgane 1984. The insular formation of the dolphin brain: quantitative cytoarchitectonic studies of the insular limbic lobe. Journal of Comparative Neurology, 225:396432.

M. Jacobs , W. McFarland , and P. Morgane 1979. The anatomy of the brain of the bottlenose dolphin (Tursiops truncatus). Rhinic lobe (Rhinencephalon): the archicortex. Brain Research Bulletin, 4:1108.

M. Jacobs , P. Morgane , and W. McFarland 1971. The anatomy of the brain of the bottlenose dolphin (Tursiops truncatus) Rhinic lobe (Rhinencephalon) I: the paleocortex. Journal of Comparative Neurology, 141:205272.

R. Kellogg 1926. The history of whales—their adaptation to life in the water (concluded). The Quarterly Review of Biology, 3:174208.

O. Lambert 2005. Phylogenetic affinities of the long-snouted dolphin Eurhinodelphis (Cetacea, Odontoceti) from the Miocene of Antwerp, Belgium. Palaeontology, 48:653679.

O. Lambert 2008. A new porpoise (Cetacea, Odontoceti, Phocoenidae) from the Pliocene of the North Sea. Journal of Vertebrate Paleontology, 28:863872.

O. Lambert , G. Bianucci , K. Post , C. de Muizon , R. Salas-Gismondi , M. U, and J. Reumer 2010. The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature, 466:105108.

O. Lambert , C. de Muizon , and G. Bianucci 2013. The most basal beaked whale Ninoziphius platyrostris Muizon, 1983: clues on the evolutionary history of the family Ziphiidae (Cetacea: Odontoceti). Zoological Journal of the Linnean Society, 167:569598.

T. E. Macrini 2009. Description of a digital cranial endocast of Bathygenys reevesi (Merycoidodontidae; Oreodontoidea) and implications for apomorphy-based diagnosis of isolated, natural endocasts. Journal of Vertebrate Paleontology, 29:1,1991,211.

L. Marino , R. C. Conner , R. E. Fordyce , L. M. Herman , P. R. Hof , L. Lefebvre , D. Lusseau , B. McCowan , E. A. Nimchinsky , A. A. Pack , L. Rendell , J. S. Reidenberg , D. Reiss , M. D. Uhen , E. Van Der Gucht , and H. Whitehead 2007. Cetaceans have complex brains for complex cognition. PLoS Biology, 5:966972.

L. May-Collado and I. Agnarsson 2006. Cytochrome b and Bayesian inference of whale phylogeny. Molecular Phylogenetics and Evolution, 38:344354.

M. R. McGowen , M. Spaulding , and J. Gatesy 2009. Divergence date estimation and a comprehensive molecular tree of extant cetaceans. Molecular Phylogenetics and Evolution, 53:891906.

L. Mellor , L. N. Cooper , J. Torre , and R. L. Brownell Jr. 2009. Paedomorphic ossification in porpoises with an emphasis on the vaquita (Phocoena sinus). Aquatic Mammals, 35:193202.

P. Morgane , M. Jacobs , and W. McFarland 1980. The anatomy of the brain of the bottlenose dolphin (Tursiops truncatus). Surface configurations of the telencephalon of the bottlenose dolphin with comparative anatomical observations in four other cetacean species. Brain Research Bulletin, 5:1107.

M. Murakami , C. Shimada , Y. Hikida , and H. Hirano 2012a. A new basal porpoise, Pterophocaena nishinoi (Cetacea, Odontoceti, Delphinoidea), from the upper Miocene of Japan and its phylogenetic relationships. Journal of Vertebrate Paleontology, 32:1,1571,171.

R. A. Racicot and A. Berta 2013. Comparative morphology of porpoise (Cetacea: Phocoenidae) pterygoid sinuses: phylogenetic and functional implications. Journal of Morphology, 274:4962.

R. A. Racicot and M. W. Colbert 2013. Morphology and variation in porpoise (Cetacea: Phocoenidae) cranial endocasts. Anatomical Record, 296:979992.

R. A. Racicot , Deméré T. A , Beatty B. L , and R. W. Boessenecker 2014. Unique feeding morphology in a new prognathous extinct porpoise from the Pliocene of California. Current Biology, 24:774779.

T. Rowe 1996b. Coevolution of the mammalian middle ear and neocortex. Science, 273:651654.

T. Rowe , T. P. Eiting , T. E. Macrini , and R. A. Ketcham 2005. Organization of the olfactory and respiratory skeleton in the nose of the gray short-tailed oppossum Monodelphis domestica. Journal of Mammalian Evolution, 12:303336.

T. Rowe , T. Macrini , and Z. Luo 2011. Fossil evidence on the origin of the mammalian brain. Science, 332:955957.

M. E. Steeman , M. B. Hebsgaard , R. E. Fordyce , S. Y. W. Ho , D. L. Rabosky , R. Nielsen , C. Rahbek , H. Glenner , M. V. S⊘rensen , and E. Willerslev 2009. Radiation of extant cetaceans driven by restructuring of the oceans. Systematic Biology, 58:573585.

J. G. M. Thewissen , L. N. Cooper , M. T. Clementz , S. Bajpai , and B. N. Tiwari 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature, 450:1,1901,195.

M. D. Uhen 2010. The origin(s) of whales. Annual Reviews of Earth and Planetary Science, 38:189219.

J. J. Weins 2006. Missing data and the design of phylogenetic analyses. Journal of Biomedical Informatics, 39:3442.

L. Yu , W. Jin , J. Wang , X. Zhang , M. Chen , Z. Zhou , H. Lee , and Y. Zhang 2010. Characterization of TRPC2, an essential genetic component of VNS chemoreception, provides insights into the evolution of pheromonal olfaction in secondary-adapted marine mammals. Molecular Biology and Evolution, 27:1,4671,477.

D. J. Zwickl and D. M. Hillis 2002. Increased taxon sampling greatly reduces phylogenetic error. Systematic Biology, 51:588598.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Journal of Paleontology
  • ISSN: 0022-3360
  • EISSN: 1937-2337
  • URL: /core/journals/journal-of-paleontology
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 12 *
Loading metrics...

Abstract views

Total abstract views: 66 *
Loading metrics...

* Views captured on Cambridge Core between September 2016 - 23rd September 2017. This data will be updated every 24 hours.