View source for Pakicetidae

{{Short description|Family of mammals}}
{{Automatic taxobox
| fossil_range = [[Eocene|Early Eocene]], {{Fossil range|50|48}}
| image = Pakicetus BW.jpg
| image_caption = ''Pakicetus''
| taxon = Pakicetidae
| authority = {{Harvnb|Thewissen|Madar|Hussain|1996}}
| subdivision_ranks = Genera
| subdivision = *''[[Pakicetus]]'' <br />
*''[[Nalacetus]]''
*''[[Ichthyolestes]]''
}}

'''Pakicetidae''' ("Pakistani whales") is an [[Extinction|extinct]] [[Family (biology)|family]] of early whales that lived during the [[Early Eocene]] in northern [[South Asia]].<ref>{{Cite journal |last=Kumar |first=Kishor |last2=Sahni |first2=Ashok |date=June 1985 |title=Eocene mammals from the Upper Subathu Group, Kashmir Himalaya, India |url=http://www.tandfonline.com/doi/abs/10.1080/02724634.1985.10011853 |journal=Journal of Vertebrate Paleontology |language=en |volume=5 |issue=2 |pages=153–168 |doi=10.1080/02724634.1985.10011853 |issn=0272-4634|url-access=subscription }}</ref><ref name="Uhen-2010">{{Harvnb|Uhen|2010| pp=199–201}}</ref> Unlike modern cetaceans, they had well-developed limbs and were capable of walking. The species included were fox to wolf-sized.<ref name=":0" />

==Description==
{{Harvnb|Dehm|Oettingen-Spielberg|1958}} described the first pakicetid, ''[[Ichthyolestes]]'', but at the time they did not recognize it as a cetacean, identifying it, instead, it as a [[fish]]-eating [[Mesonychidae|mesonychid]]. Robert West was the first to identify pakicetids as cetaceans in 1980 and, after discovering a braincase, Phillip Gingerich and Donald Russell described the genus ''[[Pakicetus]]'' in 1981. During the following two decades, more research resulted in additional pakicetid cranial material and by 2001 postcranial material for the family had been described. Though all parts of pakicetid postcrania are known, no complete [[skeleton]] from a single individual has been recovered.<ref name="thewetal-2001">{{Harvnb|Thewissen|Williams|2002| pp=75–8}}</ref>
The pakicetid goldmine is the "H-GSP Locality 62" site in the [[Kala Chitta Range|Kala Chitta Hills]] where fossils from all three genera have been found.  However, this site is so littered with bones that identifying bones from a single individual is impossible, and pakicetid skeletons are consequently composites of bones from several individuals.<ref name=":0">{{Harvnb|Thewissen|Cooper|George|Bajpai|2009|p=277}}</ref>

Pakicetids have been found in or near [[river]] deposits in northern Pakistan and northwestern [[India]], a region which was probably [[arid]] with only temporary streams when these animals lived there. No pakicetids have been found in marine deposits, and they were apparently [[Terrestrial animal|terrestrial]] or freshwater animals. Their long limbs and small hands and feet also indicate they were poor swimmers. Their bones are heavy and compact and were probably used as [[ballast]]; they clearly indicate pakicetids were not fast runners in spite of their otherwise [[cursorial]] morphology. Most likely, pakicetids lived in or near bodies of freshwater and their diet could have included both land animals and aquatic organisms. During the [[Eocene]], [[Pakistan]] was part of the Indian island-continent off the coastal region of the [[Eurasia]]n land mass and therefore an ideal habitat for the evolution and diversification of the Pakicetids.<ref name="thewetal-2001" />

{| class="wikitable"
 | Pakicetids have many [[apomorphic]] traits (derived traits shared by several taxa) found in [[Even-toed ungulate|artiodactyls]], including:<ref name="Uhen-2010" />
 | Traits linking pakicetids to cetaceans include:<ref name="Uhen-2010" />
|-
|
* small [[mandibular foramina]] and [[Mandibular canal|canals]]
* elongated [[cervical vertebrae]]
* long and gracile limbs featuring "double-pulleyed" [[Talus bone|astragalus]] in the ankle
* long [[metapodial]]s and
* four fused [[sacrum|sacral]] vertebrae
|
* a pachyosteosclerotic (thick, heavy bone) [[auditory bulla]] with an [[involucrum]] and [[sigmoid process]]
* cheek teeth adapted for shearing with reentrant grooves on the anterior surfaces
* lower [[Molar (tooth)|molars]] lacking [[trigonid]] and [[talonid]] basins and upper molars with very small [[Molar (tooth)#Tribosphenic|trigon]] basins
* incisors and canines aligned to the cheek teeth
* narrow elongated postorbital (behind eyes) cranium
|}

==Hearing==
Pakicetid ears had an [[external auditory meatus]] and ear ossicles (i.e. [[incus]], [[malleus]], [[tympanic ring]], etcetera) similar to those in living land mammals and most likely used normal land mammal hearing in air. In the pakicetid mandible, the [[mandibular foramen]] is small and comparable in size to those of extant land mammals and the acoustic mandibular fat pad characteristic of later whales was obviously not present. The lateral wall of the mandible is also relatively thick in pakicetids, further preventing sound transmission through the jaw. The [[tympanic bulla]] in pakicetid ears is similar to those in all cetaceans, with a relatively thin lateral wall and thickened medial part known as the [[involucrum]]. However, in contrast to later cetaceans, the [[tympanic bone]] makes contact with the [[periotic bone]] which is firmly attached to the skull leaving no space for isolating air sinuses, effectively preventing directional hearing in water. Pakicetids most likely used bone conduction for hearing in water.<ref>{{Harvnb|Nummela|Thewissen|Bajpai|Hussain|2007|loc=Pakicetids, pp. 722–3}}</ref>

==Locomotion==
[[File:Pakicetus attocki.jpg|thumb|''Pakicetus attocki'']]
Interpretations of pakicetid habitat and [[Locomotion in animals|locomotory]] behaviour varies considerably. In 2001, it was concluded by Thiwissen et al. that "pakicetids were terrestrial mammals, no more amphibious than a [[tapir]]." According to them, none of the [[aquatic adaptation]]s found in the oldest obligate aquatic cetaceans, [[Basilosauridae|basilosaurids]] and [[Dorudontidae|dorudontids]], are present in pakicetids. Pakicetid cervical vertebrae are longer than in late Eocene whales, the thoracic vertebrae increase in size from the neck backwards, and the lumbar and caudal vertebrae are longer than in modern cetaceans (but still shorter than in some extinct cetaceans with undulating spines.) Motion in the spine of pakicetids was further reduced by the [[Revolute joint|revolute]] [[zygapophyses]] (processes between the vertebrae) like in stiff-backed runners such as [[mesonychia]]ns. The sacral vertebrae are fused and the sacroiliac joints present like in land mammals and amphibious cetaceans.<ref name="Thewetal-2001">{{Harvnb|Thewissen|Williams|Roe|Hussain|2001| pp=277–8}}</ref>

Furthermore, according to [[Hans Thewissen|Thewissen]] et al. (2001), the pakicetid [[scapula]]e have large [[supraspinous fossa]]e with small acromions, in contrast to other cetaceans. The [[deltopectoral crest]]s are absent in the long and slender humeri like in cursorial animals but unlike other Eocene cetaceans.  Pakicetid elbows are rigid hinge joints like in running mammals and the forearms are not flattened like in truly aquatic cetaceans. In the pakicetid pelvis, the innominates are large and the ischia are longer than the ilia.  The pakicetid tibiae are long with a short tibial crest. Hindlimb features that all more reminiscent of running and jumping animals than swimming animals.<ref name="Thewetal-2001" />

{{Harvnb|Gingerich|2003}} [[disagreed]] and got support from {{Harvnb|Madar|2007}}: [[postcrania]]l morphology and microstructural features suggest that pakicetids were adapted to an aquatic lifestyle which included bottom wading, paddling, and undulatory swimming, but probably not sustained running.  Isotopic evidence indicate Pakicetids spent a considerable part of their life in freshwater and probably ate freshwater prey.<ref name="Uhen-2010" /> This view was further reiterated by Gingerich in a 2017 paper.<ref>{{Cite journal |last=Gingerich |first=Philip D. |last2=Heissig |first2=Kurt |last3=Bebej |first3=Ryan M. |last4=von Koenigswald |first4=Wighart |date=28 June 2017 |title=Astragali of Pakicetidae and other early-to-middle Eocene archaeocetes (Mammalia, Cetacea) of Pakistan: locomotion and habitat in the initial stages of whale evolution |url=https://link.springer.com/article/10.1007/s12542-017-0362-8 |journal=[[PalZ]] |language=en |volume=91 |issue=4 |pages=601–627 |doi=10.1007/s12542-017-0362-8 |issn=0031-0220 |access-date=12 November 2024 |via=Springer Link|url-access=subscription }}</ref>

==Subtaxa==
* Family '''Pakicetidae'''<ref>{{Paleodb|63147|Pakicetidae}}. Retrieved February 24, 2013.</ref>
** ''[[Ichthyolestes]]'' ({{Harvnb|Dehm|Oettingen-Spielberg|1958}})
*** ''Ichtyolestes pinfoldi'' ({{Harvnb|Dehm|Oettingen-Spielberg|1958}})
** ''[[Nalacetus]]'' ({{Harvnb|Thewissen|Hussain|1998}})
*** ''Nalacetus ratimitus'' ({{Harvnb|Thewissen|Hussain|1998}})
** ''[[Pakicetus]]'' ({{Harvnb|Gingerich|Russell|1981}})
*** ''Pakicetus inachus'' ({{Harvnb|Gingerich|Russell|1981}})
*** ''Pakicetus attocki'' ({{Harvnb|West|1980}})
*** ''Pakicetus calcis'' ({{Harvnb|Cooper|Thewissen|Hussain|2009}})
*** ''Pakicetus chittas'' ({{Harvnb|Cooper|Thewissen|Hussain|2009}})

==See also==
{{Wikispecies|Pakicetidae}}
* [[Archaeoceti]]
* [[Evolution of cetaceans]]

==Notes==
{{Reflist}}

==References==
{{Refbegin|30em}}
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 | last3 = Hussain | first3 =  S. T.
 | title = New middle Eocene archaeocetes (Cetacea: Mammalia) from the Kuldana Formation of northern Pakistan
 | year = 2009 | journal = Journal of Vertebrate Paleontology | volume = 94 | issue = 4 | pages = 1289–99
 | doi = 10.1671/039.029.0423 | bibcode = 2009JVPal..29.1289C
 | s2cid = 84127292
 | oclc = 506008976 }}<!-- {{Harvnb|Cooper|Thewissen|Hussain|2009}} -->
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 | last2 = Oettingen-Spielberg | first2 = Therese zu
 | title = Paläontologische und geologische Untersuchungen im Tertiär von Pakistan. 2. Die mitteleocänen Säugetiere von Ganda Kas bei Basal in Nordwest-Pakistan
 | year = 1958 | location = Munich | publisher = Beck | series = Abhandlungen / Neue Folge, 91
 | oclc = 163296508 }}<!-- {{Harvnb|Dehm|Oettingen-Spielberg|1958}} -->
* {{Cite journal
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 | oclc = 716582744 | doi=10.1666/0094-8373(2003)029<0429:ltiewe>2.0.co;2| s2cid = 86600469
 }}<!-- {{Harvnb|Gingerich|2003}} -->
* {{Cite journal
 | last1 = Gingerich | first1 = Philip D.
 | last2 = Russell | first2 = Donald E.
 | title = ''Pakicetus inachus'', A New Archaeocete (Mammalia, Cetacea) from the Early-Middle Eocene Kuldana Formation of Kohat (Pakistan)
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 | oclc = 742729300 }}<!-- {{Harvnb|Gingerich|Russell|1981}} -->
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 | title = Systematic review of the Pakicetidae, Early and middle Eocene Cetacea (Mammalia) from Pakistan and India
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 | series = Courier Forschungsinstitut Senckenberg | volume = 191 | pages = 1–86 | year = 1996
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{{Refend}}

{{Archaeoceti}}
{{Taxonbar|from=Q1190158}}

[[Category:Pakicetidae| ]]
[[Category:Eocene first appearances]]
[[Category:Eocene extinctions]]
[[Category:Prehistoric mammal families]]