Rumpless chickens are characterised by caudal dysplasia, the absence of the pygostyle or caudal appendage – the "parson's nose". This is the result of inheritance of an autosomal dominant trait. The mutation which causes it is unknown; two candidates have been proposed.[1]: 10
Rumplessness in chickens has been documented for centuries. An early description is that of the Bolognese ornithologist Ulisse Aldrovandi in his Ornithologiae Tomus Alter of 1600.[2]: 127 [3]: 318
Rumpless breeds of chicken include: the Araucana or Rumpless Araucana of South America, both large fowl and bantam;[4]: 45 the Belgian Barbu de Boitsfort, Barbu de Grubbe and Barbu d'Uccle bantams;[4]: 75 the Japanese Uzurao, a rumpless equivalent of the Tosa-Kojidori bantam,[5]: 95 and Ingie (large fowl) from Kagoshima Prefecture;[5]: 103 the Rumpless Game of the United Kingdom (both large fowl and bantam), sometimes called the Manx Rumpy or Persian Rumpless;[4]: 272 [6]: 65 and the German Ruhlaer Zwerg-Kaulhühner or Rumpless Booted Bantam.[4]: 92
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