Temporal range: Campanian to Present 
Squalus is a large genus of dogfish sharks, one of two genera in the family Squalidae. Commonly known as spurdogs, these sharks are characterized by smooth dorsal fin spines, teeth in upper and lower jaws similar in size, caudal peduncle with lateral keels; upper precaudal pit usually present, and caudal fin without subterminal notch.
In spurdogs, the hyomandibula (the bone connecting the braincase to the jaws) is oriented at a right angle to the neurocranium while in other sharks the hyomandibula runs more parallel to the body. This led some to think that the upper jaw of Squalus would not be as protractile as the jaws of other sharks. However, a study that compared different jaw suspension types in sharks showed that this is not the case and that Squalus is quite capable of protruding its upper jaw during feeding.
There are currently 26 recognized species in this genus:
- Squalus acanthias Linnaeus, 1758 (Spiny dogfish)
- Squalus acutipinnis Regan, 1908 (Bluntnose spiny dogfish) 
- Squalus albifrons Last, W. T. White & J. D. Stevens, 2007 (Eastern highfin spurdog)
- Squalus altipinnis Last, W. T. White & J. D. Stevens, 2007 (Western highfin spurdog)
- Squalus blainville A. Risso, 1827 (Longnose spurdog)
- Squalus brevirostris S. Tanaka (I), 1917 (Japanese shortnose spurdog)
- Squalus bucephalus Last, Séret & Pogonoski, 2007 (Bighead spurdog)
- Squalus chloroculus Last, W. T. White & Motomura, 2007 (Greeneye spurdog)
- Squalus crassispinus Last, Edmunds & Yearsley, 2007 (Fatspine spurdog)
- Squalus cubensis Howell-Rivero, 1936 (Cuban dogfish)
- Squalus edmundsi W. T. White, Last & J. D. Stevens, 2007 (Edmund's spurdog)
- Squalus formosus W. T. White & Iglésias, 2011 (Taiwan spurdog)
- Squalus grahami W. T. White, Last & J. D. Stevens, 2007 (Eastern longnose spurdog)
- Squalus griffini Phillipps, 1931 (Northern spiny dogfish)
- Squalus hemipinnis W. T. White, Last & Yearsley, 2007 (Indonesian shortsnout spurdog)
- Squalus japonicus Ishikawa, 1908 (Japanese spurdog)
- Squalus lalannei Baranes, 2003 (Seychelles spurdog)
- Squalus megalops W. J. Macleay, 1881 (Shortnose spurdog)
- Squalus melanurus Fourmanoir & Rivaton, 1979 (Blacktailed spurdog)
- Squalus mitsukurii D. S. Jordan & Snyder, 1903 (Shortspine spurdog)
- Squalus montalbani Whitley, 1931 (Indonesian greeneye spurdog)
- Squalus nasutus Last, L. J. Marshall & W. T. White, 2007 (Western longnose spurdog)
- Squalus notocaudatus Last, W. T. White & J. D. Stevens, 2007 (Bartail spurdog)
- Squalus rancureli Fourmanoir & Rivaton, 1979 (Cyrano spurdog)
- Squalus raoulensis C. A. J. Duffy & Last, 2007 (Kermadec spiny dogfish)
- Squalus suckleyi Girard, 1854 (Spotted spiny dogfish)
- Squalus sp. Not yet described (Lombok highfin spurdog)
- Sepkoski, J. (2002). "A compendium of fossil marine animal genera (Chondrichthyes entry)". Bulletins of American Paleontology, 364: p.560.
- Wilga, Cheryl D., Philip J. Motta, and Christopher P. Sanford. "Evolution and ecology of feeding in elasmobranchs." Integrative and Comparative Biology47.1 (2007): 55-69.
- Naylor, G.J.P., Caira, J.N., Jensen, K., Rosana, K.A.M., White, W.T. & Last, P.R. (2012): A DNA sequence–based approach to the identification of shark and ray species and its implications for global elasmobranch diversity and parasitology. Bulletin of the American Museum of Natural History, 367: 1–262.