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415 words
Science & Nature

Mamifere Page 1
Mamifere Page 2
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CLASA : Mammalia
ORDINUL : Ceteaceea
SUBORDINUL : Odontoceti

Capabili sa despice apele marilor si oceanelor cu o viteza de doi metri pe secunda,ba chiar sa-si ofere uneori cate un mic sprint de 10m /s(adica sa inoate de cinci ori mai repede decat marii campioni olimpici),delfinii sunt cu adevarat cele mai gratioase si mai elegante vietuitoare din mediul marin.Placerea lor de a inota si de a face surf pe coama valurilor,in urma sau in fata marilor vapoare, uluitoarele lor salturi acrobatice fac din ei niste virtuosi fara seaman ai necuprinselor intinderi marine.
Delfinii sunt mamifere marine din familia cetaceelor.In functie de morfologia si modul lor de hraire differentiate,speciile de cetacee se grupeaza in doua subordine:

* Mysticeti
* Odontoceti

Desi seamana cu pestii,delfinii sunt inruditi cu ungulatele,mamiferele terestre cu copita.Stamosii balenelorsi ai delfinilor erau niste mamifere terestre cu labe scurte,de marimea unui lup sau vulpi,care nu prea aduceau cu vacile sau caii de azi.In urma cu 50 MA,unele dintre aceste mamifere,care traiau de-a lungul coastelor marii primareau inceput sa-si petreaca tot mai multa vreme in apa.Timp de 10 MA,aceste balene si delfini primitivi au dobandit un corp alungit si hidrodinamic, care le-a permis sa se deplaseze tot mai lesne in apele oceanice.
Membrele anterioare s-au transformat in inotatoarele ce le servesc la mentinerea directiei si la franare.In ceea ce priveste coada,atat pestii,cat si cetaceele o folosesc la inot,dar fiecare in felul sau.
Ca toate mamiferele,cetaceele sunt inzestrate cu plamani,prin intermediul carora respira aer.Cand animalul revine la suprafata pentru a respira,acesta se deschide rapid, mai intai pentru a elimina aerul viciat,apoi pentru a inspira aer proaspat.Dupa o plonjare de durata,aerul expulzat poate atinge o vitaza de 150km/h.Toate cetaceele cu dinti,printre care se numara si delfinii,dispun de un sistem complex de saci si conducte chiar sub event.Facand sa circule aerul pe aici,delfinii produc toate acele sunete de care se servesc pentru comunicare si ecolocatie.
Cele 45 de specii de delfinide recenzate pe intreg globul au nu doar habitate foarte diferite,ci si comportamente,legaturi sociale moduri de reproducere specifice,precum si morfologii adaptate la mediile in care traiesc.Delfinul de apa dulce de pe Amazon,de pilda,o adevarata ralicva de acum 18 milioane de ani,e un animal indesat,oarecum lent,...

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