Original description species: Hodnett, Elliott, Olson & Wittke, 2012
Genus: Kaibabvenator Hodnett, Elliott, Olson & Wittke, 2012
Family: incert. fam.
Order: Ctenacanthiformes
Superorder: Cladodontomorphi
Subclass: Elasmobranchii

Original description species: Engelbrecht, Mörs, Reguero & Kriwet, 2017
Genus: Kallodentis Engelbrecht, Mörs, Reguero & Kriwet, 2017
Family: Triakidae Gray, 1851
Order: Carcharhiniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Märss & Gagnier, 2001
Genus: Kannathalepis Märss & Gagnier, 2001
Family: Kannathalepididae Märss & Gagnier, 2001
Order: Elegestolepidida

Original description species: Lebedev, 2014
Genus: Kanodus Lebedev, 2014
Family: Psephodontidae Jaekel, 1898
Order: Cochliodontiformes
Superorder: Holocephalimorpha
Subclass: Holocephali

Original description species: Kozlov in Zhelezko & Kozlov, 1999
Genus: Karaisurus Kozlov In Zhelezko & Kozlov, 1999
Family: Lamnidae Bonaparte, 1835
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Genus: Karaisurus Kozlov In Zhelezko & Kozlov, 1999
Family: Lamnidae Bonaparte, 1835
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Märss, Kleesment & Niit, 2008
Genus: Karksilepis Märss, Kleesment & Niit, 2008
Family: incert. fam.
Order: incert. sedis

Original description species: Ivanov & Märss, 2011
Genus: Karksiodus Ivanov & Märss, 2011
Family: incert. fam.
Order: incert. sedis
Subclass: Elasmobranchii

Original description species: Gagnier & Wilson, 1996
Genus: Kathemacanthus Gagnier & Wilson, 1996
Family: incert. fam.
Order: Climatiformes

Original description species: Pradel, Tafforeau, Maisey & Janvier, 2011
Genus: Kawichthys Pradel, Tafforeau, Maisey & Janvier, 2011
Family: incert. fam.
Order: Symmoriiformes
Superorder: Cladodontomorphi
Subclass: Holocephali

Synonyms: Cetorhinus aff. parvus, Cetorhinus cf. parvus, Cetorhinus parvus, Praecetorhinus parvus, Selache parvus
Original description species: (Leriche, 1908)
Genus: Keasius Welton, 2013
Family: Cetorhinidae Gill, 1861
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Reinecke, Von Der Hocht & Dufraing, 2015
Genus: Keasius Welton, 2013
Family: Cetorhinidae Gill, 1861
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Reinecke, Von Der Hocht & Dufraing, 2015
Genus: Keasius Welton, 2013
Family: Cetorhinidae Gill, 1861
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Genus: Keasius Welton, 2013
Family: Cetorhinidae Gill, 1861
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Welton, 2013
Genus: Keasius Welton, 2013
Family: Cetorhinidae Gill, 1861
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Li, Sun, Cuny, Ji, Jiang & Zhou, 2021
Genus: Keichouodus Li, Sun, Cuny, Ji, Jiang & Zhou, 2021
Family: incert. fam.
Order: Synechodontiformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Synonyms: Cretolamna gunsoni
Original description species: (Siverson, 1996)
Genus: Kenolamna Siverson, Lindgren, Newbrey, Cederström & Cook, 2015
Family: Otodontidae Glickman, 1964
Order: Lamniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Synonyms: Phoebodus brodiei, Phoebodus keuperinus
Original description species: Woodward, 1893
Genus: Keuperodus Ivanov, Duffin & Richter, 2021
Family: Jalodontidae Ginter, Hairapetian & Klug, 2002
Order: Jalodontiformes
Subclass: Elasmobranchii

Original description species: Cuny, Suteethorn, Kamha & Buffetaut, 2008
Genus: Khoratodus Cuny, Suteethorn, Kamha & Buffetaut, 2008
Family: Thaiodontidae Cuny, Suteethorn, Kamha & Buffetaut, 2008
Superfamily: Hybodontoidea
Order: Hybodontiformes
Cohort: Euselachii
Subclass: Elasmobranchii

Synonyms: Galeorhinus aff. gomphorhiza, Galeorhinus gomphorhiza
Original description species: (Arambourg, 1952)
Genus: Khouribgaleus Noubhani & Cappetta, 1997
Family: Triakidae Gray, 1851
Order: Carcharhiniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Koot, Cuny, Tintori & Twitchett, 2013
Genus: Khuffia Koot, Cuny, Tintori & Twitchett, 2013
Family: Sphenacanthidae Maisey, 1982
Order: incert. sedis
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Koot, Cuny, Tintori & Twitchett, 2013
Genus: Khuffia Koot, Cuny, Tintori & Twitchett, 2013
Family: Sphenacanthidae Maisey, 1982
Order: incert. sedis
Cohort: Euselachii
Subclass: Elasmobranchii

Genus: Kiestus Cappetta & Case, 1999
Family: Sclerorhynchidae Cappetta, 1974
Suborder: Sclerorhynchoidei
Order: Rajiformes
Superorder: Batomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Synonyms: Ischyrhiza cf. texana, Ischyrhiza texana, Kiestus texanus, Ptychotrygon ritchiei
Original description species: (Cappetta & Case, 1975)
Genus: Kiestus Cappetta & Case, 1999
Family: Sclerorhynchidae Cappetta, 1974
Suborder: Sclerorhynchoidei
Order: Rajiformes
Superorder: Batomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Valid name: Kiestus texana
Original description species: (Cappetta & Case, 1975)
Genus: Kiestus Cappetta & Case, 1999
Family: Sclerorhynchidae Cappetta, 1974
Suborder: Sclerorhynchoidei
Order: Rajiformes
Superorder: Batomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Underwood & Claeson, 2017
Genus: Kimmerobatis Underwood & Claeson, 2017
Family: Spathobatidae Dames, 1888
Superorder: Batomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Gunnell, 1933
Genus: Kirkella Gunnell, 1933
Subclass: Elasmobranchii

Original description species: Gunnell, 1933
Genus: Kirkella Gunnell, 1933
Subclass: Elasmobranchii

Genus: Kirkella Gunnell, 1933
Subclass: Elasmobranchii

Original description species: Gunnell, 1933
Genus: Kirkella Gunnell, 1933
Subclass: Elasmobranchii

Valid name: Knerialepis mashkovae
Original description species: Karatajute-Talimaa, 1997
Genus: Kneria Karatajute-Talimaa, 1997
Family: incert. fam.
Order: incert. sedis
Subclass: Elasmobranchii

Valid name: Knerialepis mashkovae
Original description species: Karatajute-Talimaa, 1968
Genus: Knerialepis Hanke & Karatajute-Talimaa, 2002
Family: incert. fam.
Order: incert. sedis
Subclass: Elasmobranchii

Synonyms: Kneria mashkovae, Knerialepis cf. mashkovae
Original description species: (Karatajute-Talimaa, 1997)
Genus: Knerialepis Hanke & Karatajute-Talimaa, 2002
Family: incert. fam.
Order: incert. sedis
Subclass: Elasmobranchii

Original description species: Cappetta, Morrison & Adnet, 2019
Genus: Komoksodon Cappetta, Morrison & Adnet, 2019
Family: Komoksodontidae Cappetta, Morrison & Adnet, 2019
Order: Hexanchiformes
Superorder: Squalomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Original description species: Laurito Mora, 1999
Genus: Kruckowlamna Laurito Mora, 1999
Family: Carcharhinidae Jordan & Evermann, 1896
Order: Carcharhiniformes
Superorder: Galeomorphii
Subcohort: Neoselachii
Cohort: Euselachii
Subclass: Elasmobranchii

Synonyms: Cobelodus obliquus
Original description species: (Ivanov, 2005)
Genus: Kungurodus Ivanov, 2016
Family: incert. fam.
Order: Symmoriiformes
Superorder: Cladodontomorphi
Subclass: Holocephali

Genus: Kungurodus Ivanov, 2016
Family: incert. fam.
Order: Symmoriiformes
Superorder: Cladodontomorphi
Subclass: Holocephali