**Yüzgeçayaklılar** (Pinnipedia), etçiller (Carnivora) takımının köpeğimsiler alt takımına ait, üyelerinin ayakları yüzgeç şeklinde evrimleşerek suda yaşama adapte olmuş deniz memelileridir. Yaşayan tek üyesi mors olan Odobenidae, deniz aslanlarından oluşan Otariidae ve gerçek foklardan oluşan Phocidae familyalarını barındırır. Yüzgeçayaklıların yaşayan 33 türü bulunur ve fosillerden 50'den fazla türü tanımlanmıştır. Yüzgeçayaklıların iki ayrı atadan evrimleştiği düşünülmüş olsa da, moleküler kanıtlar yüzgeçayaklıların monofiletik olduğunu yani tek bir atadan evrimleştiğini gösterir. En yakın yaşayan akrabaları ayıgiller, sansargiller, rakungiller, kokarcagiller ve kızıl pandalardır. Soylarının, en yakın akrabaları ile yaklaşık 50 milyon yıl önce (alt Eosen) ayrıldığı düşünülür.

Yüzgeçayaklıların boyutları boyu 1 m ile ağırlığı 45 kg olan Baykal foku ile aynı zamanda etçiller takımının en iri üyesi olan 5 m boyunda ve 3200 kg ağırlığındaki Güney deniz fili arasında değişir. Bazı türlerinde eşeysel dimorfizm görülür. İnce, uzun ve yüzmeyi kolaylaştıran gövdeleri ile birlikte ayakları, yüzgeç veya kürek biçimini almıştır. Su içinde yunuslar kadar hızlı hareket edemeseler de daha esnek ve çeviktirler. Deniz aslanları ön yüzgeçlerini kullanarak kendilerini su içinde ileri iterek hareket ederken mors ve foklar arka yüzgeçlerini kullanırlar. Deniz aslanları ve morslar, arka yüzgeçlerini gövdelerinin altına çekerek karada yürümek için kullanırlar. Buna karşın fokların karada hareket etmesi daha zahmetlidir. Deniz aslanlarının kulakları dışarıdan görülebilirken fok ve morsların dış kulakları yoktur. Yüzgeçayaklıların duyuları oldukça gelişmiştir; görme ve işitme duyuları hem hava hem de su için uyum sağlamıştır. Yüzlerindeki kıllarda ileri derecede gelişmiş dokunsal duyu sistemi bulunur. Bazı türler oldukça derine dalabilmektedir (400 m). Derilerinin altında soğuk suda kendilerini sıcak tutacak bir yağ tabakası vardır ve mors dışında tüm türleri kürk ile kaplıdır.

Her ne kadar yüzgeçayaklılar dünya üzerine yayılmışsa da türlerin çoğu Kuzey ve Güney yarımkürenin soğuk sularını tercih eder. Yaşamlarının çoğunu su içinde geçirir; karaya yalnızca çiftleşmek, doğum yapmak ve köpekbalıkları ile katil balinalar gibi avcılardan kaçmak için çıkar. Çoğunluğu balık ve deniz omurgasızları ile beslenir; ancak pars foku gibi çok az türü, penguenler ve diğer foklar gibi büyük omurgalılarla da beslenir. Morslar, dipte yaşayan yumuşakçalarla beslenme konusunda uzmanlaşmıştır. Erkek yüzgeçayaklılar tipik olarak birden fazla dişi ile çiftleşir ancak bu durum türden türe farklılık gösterir. Karada çiftleşen türler genellikle buzda ya da suda çiftleşen türlere göre daha fazla sayıda eş ile çiftleşir. Erkek yüzgeçayaklıların üreme başarısı üzerine olan stratejileri dişileri savunma, dişilerin tercih ettiği bölgeyi savunma, ritüel kur davranışları ya da toplu hâlde kur davranışı gibi çeşitlilik gösterir. Yavrular genellikle ilkbahar ve yaz aylarında doğar ve yavruları büyütme sorumluluğu tamamen dişilere aittir. Bazı türlerin dişileri anne olduklarında görece kısa bir süre için yemek yemeden yavrularını büyütürlerken diğerleri yavrularına bakarken denizde besin aramak için yanlarından ayrılırlar. Morsların yavrularını denizde büyüttükleri bilinmektedir. Yüzgeçayaklılar iletişim için oldukça çeşitli sesler çıkarırlar, bunların arasında Kaliforniya deniz aslanının köpek havlamasına benzer sesi, morsların gong sesine benzer çağrıları ve Weddell foklarının karmaşık şarkıları sayılabilir.

Yüzgeçayaklıların eti, yağı ve kürkü geleneksel olarak Arktika'da yaşayan yerli halklar tarafından kullanılmıştır. Dünya üzerinde farklı kültürlerde fok tasvirlerine rastlanır. Yaygın olarak esâret altında tutulurlar ve hatta bazıları çeşitli oyunlar yapmaları için eğitilirler. Bir zamanlar ticari olarak ürünlerinden faydalanmak için acımasızca avlanan bu hayvanlar artık uluslararası yasalarla korunmaktadırlar. Japon deniz aslanı ile Karayip keşiş fokunun soyu geçen yüzyılda tükenmiş, Akdeniz foku ile Hawaii foku da Dünya Doğa ve Doğal Kaynakları Koruma Birliği tarafından kritik tehlikedeki türler listesine alınmıştır. Avlanmanın yanı sıra yüzgeçayaklıların karşılaştıkları tehditler arasında balıkçı ağlarına takılma, deniz kirliliği ve yerli halklarla yaşanan çatışmalar sayılabilir.

Sistematik
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|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Phocidae | 

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|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |
| --- | --- |
|   | halkalı fok |
|   |
|   | Baykal foku |
|   |

 |
|   |
|   | Hazar foku |
|   |

 |
|   |
|   | 

|  |  |
| --- | --- |
|   | *Phoca largha* |
|   |
|   | *Phoca vitulina* |
|   |

 |
|   |

 |
|   |
|   | Boz fok |
|   |

 |
|   |
|   | 

|  |  |
| --- | --- |
|   | *Histriophoca fasciata* |
|   |
|   | *Pagophilus groenlandicus* |
|   |

 |
|   |

 |
|   |
|   | *Cystophora cristata* |
|   |

 |
|   |
|   | sakallı fok |
|   |

 |
|   |
|   | 

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |
| --- | --- |
|   | *Leptonychotes weddellii* |
|   |
|   | pars foku |
|   |

 |
|   |
|   | *Lobodon carcinophagus* |
|   |

 |
|   |
|   | *Ommatophoca rossii* |
|   |

 |
|   |

 |
|   |
|   | 

|  |  |
| --- | --- |
|   | güney deniz fili |
|   |
|   | *Mirounga angustirostris* |
|   |

 |
|   |

 |
|   |
|   | 

|  |  |
| --- | --- |
|   | Akdeniz foku |
|   |
|   | *Neomonachus schauinslandi* |
|   |

 |
|   |

 |
|   |
|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Otariidae | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |
| --- | --- |
|   | *Arctocephalus gazella* |
|   |
|   | 

|  |  |
| --- | --- |
|   | *Arctocephalus townsendi* |
|   |
|   | *Arctocephalus philippii* |
|   |

 |
|   |

 |
|   |
|   | 

|  |  |
| --- | --- |
|   | *Arctocephalus galapagoensis* |
|   |
|   | *Arctocephalus forsteri* |
|   |

 |
|   |

 |
|   |
|   | 

|  |  |
| --- | --- |
|   | *Neophoca cinerea* |
|   |
|   | *Phocarctos hookeri* |
|   |

 |
|   |
|   | 

|  |  |
| --- | --- |
|   | Subantarktik deniz ayısı |
|   |
|   | Güney Afrika kürklü foku |
|   |
|   | yeleli denizaslanı |
|   |

 |
|   |

 |
|   |
|   | 

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|   | 

|  |  |
| --- | --- |
|   | *Zalophus californianus* |
|   |
|   | *Zalophus wollebaeki* |
|   |

 |
|   |
|   | *Zalophus japonicus* |
|   |

 |
|   |
|   | *Eumetopias jubatus* |
|   |

 |
|   |

 |
|   |
|   | *Callorhinus ursinus* |
|   |

 |
|   |
| Odobenidae |  mors |
|   |

 |
|   |

 |
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| Çeşitli filogenetik analizleri bir araya getiren ve yüzgeçayaklılar arasındaki bağları gösteren kladogram (Berta & Churchill, 2012). |

Alman doğa bilimci Johann Karl Wilhelm Illiger yüzgeçayaklıları ayrı bir taksonomik birim olarak tanımlayan ilk biliminsanıdır ve 1811 yılında Pinnipedia adını hem bir familyaya hem de bir takıma vermiştir. Amerikalı zoolog Joel Asaph Allen dünya üzerinde bilinen yüzgeçayaklıların sınıflandırmasını 1880 tarihli monografisinde gözden geçirmiştir. Bu eserinde isimlerin tarihçesini belirtmiş, familya ve cinslerin ayırtedilebilmesi için gereken özellikleri vermiş, Kuzey Amerika'da yaşayan türleri tanımlamış ve dünyanın diğer bölgelerinde yaşayan türler hakkında özet bilgiler sağlamıştır. 1989 yılında Annalisa Berta ve çalışma arkadaşları sınıflandırılmamış klâd Pinnipedimorpha'nın fosil cins *Enaliarctos* ile modern yüzgeçayaklıların kardeş grup olarak içermesini önermişlerdir. Yüzgeçayaklılar Etçiller takımında ve Köpeğimsiler alt takımında yer alırlar. Günümüzde yaşayan üç familyadan Otariidae ve Odobenidae, Otarioidea üst familyasında yer alırken Phocidae familyası ise Phocoidea üst familyasında sınıflandırılır.

Otariidae familyasının üyelerinin dış kulaklarının varlığı diğer yüzgeçayaklılardan ayırıcı bir özeliktir. Bu hayvanlar su içinde gelişmiş ön üyelerini kullanarak ilerlerler. Ayrıca arka üyelerini öne doğru kıvırarak karada görece daha rahat hareket edebilirler. Alın kemiklerinin ön ucu burun kemiklerinin arasından geçerek aşağı uzanır ve supraorbital foramen geniş ve düzdür. Fossa supraspinata ikincil bir tepecik ile ikiye ayrılmıştır ve bronşlar önden ayrılır. Otariidae familyasında yedi cins ve birinin soyu tükenmiş olan on altı türü sınıflandırılmaktadır.

Özellikleri
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Göz çukurları büyük, vücutları silindirik şekildedir. El ve ayak parmakları arasındaki yüzme derisi palet şeklini alır. Vücudun arka kısmının hareketi ile kıpırdarlar. Derinin altında kalın bir yağ tabakası vardır. Yüzde dokunma kılları vardır. Dış kulakları körelmiş ya da tümüyle yok olmuştur. Burun delikleri yüzerken kapanır. Bazı üyelerde köpekdişleri, fildişi gibi uzamıştır. Diğer deniz memelilerinden farklı olarak postlarını değiştirmek ve üremek için karaya çıkarlar. Fokların kürk değişimi için karaya çıkış dönemleri, kimi primitif kabilelerce mit konusu olmaktadır. Faroe Adalarında, fokların post değişimi yaptıkları süreçte metamorfoza uğrayıp, insanlar gibi içki içip, eğlendiklerine; değişimin ertesi günü yeniden kıyıya indiklerine inanılır.[*kaynak belirtilmeli*]

Kaynakça
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1. ↑  Berta, A.; Churchill, M. (2012). "Pinniped taxonomy: Review of currently recognized species and subspecies, and evidence used for their description". *Mammal Review*. **42** (3). ss. 207-34. doi:10.1111/j.1365-2907.2011.00193.x. KB1 bakım: Birden fazla ad: yazar listesi (link)
2. ↑  Scheffer, p. 52. 19 Nisan 2016 tarihinde Wayback Machine sitesinde arşivlendi.
3. ↑  Allen, J. A. (1880). *History of North American pinnipeds, a monograph of the walruses, sea-lions, sea-bears and seals of North America*. Miscellaneous publications (Geological and Geographical Survey of the Territories (U.S.)). Washington: Government Printing Office. 6 Aralık 2015 tarihinde kaynağından arşivlendi. Erişim tarihi: 4 Kasım 2015.
4. ↑  Berta, A.; Ray, C. E.; Wyss, A. R. (1989). "Skeleton of the oldest known pinniped, *Enaliarctos mealsi*". *Science*. **244** (4900). ss. 60-62. doi:10.1126/science.244.4900.60. JSTOR 1703439. PMID 17818847. KB1 bakım: Birden fazla ad: yazar listesi (link)
5. ↑  Arnason, U.; Gullberg, A.; Janke, A.; Kullberg, M. (2007). "Mitogenomic analyses of caniform relationships". *Molecular Phylogenetics and Evolution*. **45** (3). ss. 863-74. doi:10.1016/j.ympev.2007.06.019. PMID 17919938. KB1 bakım: Birden fazla ad: yazar listesi (link)
6. ↑  "Superfamily Otarioidea Lucas 1899". Paleobiology Database. Erişim tarihi: 1 Temmuz 2013.
7. ↑  "Superfamily Phocoidea Smirnov 1908". Paleobiology Database. 9 Mart 2016 tarihinde kaynağından arşivlendi. Erişim tarihi: 1 Temmuz 2013.
8. ↑  Riedman, s. 64.
9. ↑  Berta, A. "Pinniped evolution" in Perrin, Würsig & Thewissen 2009, ss. 861–866

Dış bağlantılar
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| Otorite kontrolü Bunu Vikiveri'de düzenleyin | 
* BNF: cb119329682 (data)
* GND: 4135831-4
* LCCN: sh85102257
* NDL: 00563246
* NKC: ph115747
* NLI: 987007548567305171

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