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A cathemeral organism is one that has sporadic and random intervals of activity during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are performed. It has been defined as follows: "The activity of an organism may be regarded as cathemeral when it is distributed approximately evenly throughout the 24 h of the daily cycle, or when significant amounts of activity, particularly feeding and/or traveling, occur within both, the light and dark portions of that cycle."12
Many animals do not fit the traditional definitions by being strictly nocturnal, diurnal, or crepuscular, often due to factors that include the availability of food, predation pressure, and variable ambient temperature. As a result, many species, particularly among primates, may be classified as cathemeral.3
Alternative patterns of cathemeral activity have been observed in specific lemurs.4 Seasonal cathemerality has been described for the mongoose lemur (Eulemur mongoz) as activity shifting from being predominantly diurnal to being predominantly nocturnal over a yearly cycle. Common brown lemurs (E. fulvus fulvus) have been observed seasonally shifting from diurnal activity to cathemerality.5
In the original manuscript for his paper, "Patterns of activity in the mayotte lemur, Lemur fulvus mayottensis," Ian Tattersall introduced the term "cathemerality" to describe a pattern of observed activity that was neither diurnal nor nocturnal.6 Though the term "cathemeral" was proposed, "a reviewer took exception to the introduction of what he regarded as unnecessary new jargon. The result was that the term 'diel' was substituted for 'cathemeral' in the published version." In 1987 Tattersall gave a formal definition of "cathemeral", turning to its Ancient Greek roots. The word is a compound of two Greek terms: κατα = kata, through, and ήμέρα = hemera, day. The combination yields "kathemeral" or, in conventional English transliteration, "cathemeral," meaning "through the day, 'day' in this case being used in its sense of the full 24 h from midnight to midnight." Tattersall credits his father, Mr. Arthur Tattersall, and Dr. Robert Ireland, two classicists, for considering this lexical problem and proposing its solution.2
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- Ankel-Simons, Friderun (2007). Primate Anatomy (3rd ed.). Academic Press. ISBN 0-12-372576-3.
- Tattersall, Ian (1987). "Cathemeral Activity in Primates: A Definition". Folia primatol 49: 200-202.
- Jacobs, G. H. (2008). "Primate color vision: A comparative perspective" (PDF). Visual Neuroscience 25 (5–6): 619–633. doi:10.1017/S0952523808080760. PMID 18983718.
- Kirk, E. C. (2006). "Eye morphology in cathemeral lemurids and other mammals". Folia Primatologica 77: 27–49. doi:10.1159/000089694.
- Colquhoun, Ian C. (2007). "7. Strategies of Cathemeral Primates, pp 148-149". In Gursky-Doyen, Sharon; Nekaris, K.A.I. Primate Anti-Predator Strategies. Springer. ISBN 978-0-387-34807-0.
- Tattersall, I. (1979). "Patterns of activity in the Mayotte lemur, Lemur fulvus mayottensis". Journal of Mammalogy 60 (2): 314–323. doi:10.2307/1379802.