Sedes Draconis:Life Cycle Key
From Sedes Draconis
Definitions of the life cycle characteristics given in species descriptions. Not all characteristics apply to all species.
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Gestation Period:
The amount of time the young is carried within the womb of the mother. Though given as a single number, there is of course individual variation. Note that Gestation period applies to all animals with internal fertilization (including all reptiles, birds, mammals) even those that lay eggs, because the egg develops for a time, however short, between fertilization and laying.
Incubation Period:
(1) In Oviparous (egg-laying) animals, the time between when the egg is laid and when the young emerge from the egg.
Viviparous (live-bearing, like most mammals) and ovoviviparous (retaining eggs inside the body until hatching) animals do not have an incubation period, except:
(2) In marsupials, the time spent attached to the mother's nipple after birth. In marsupials that have a pouch (which is many, but not all) this time is spent entirely inside the pouch. At the end of the incubation period, the young begin to emerge from the pouch, but still return to it often. Suckling continues well past the incubation period.
Base Infant Mortality:
Infant Mortality is the fraction of infants that die before one year of age. Given as the number that die before one year, out number of live births (live births being infants that are not still-born or die during birthing).
This is given as a baseline for the species, representing the degree of infant mortality which is based on the physiology of the species, rather than on environmental factors which may vary. In sentient species environmental influences on infant mortality may include a number of cultural factors, in addition to the environmental factors which effect other animals.
Actually infant mortality rates almost always exceed the baselines given, sometimes greatly. The baselines are more intended to give a comparison between species than to offer any real demographic information.
Skull Fusion:
Applies only to vertebrates (other animals do not have skulls), primarily to large-brained vertebrates.
This does not refer to complete skull fusion, which usually happens much later in life. Instead it represents the age at which the gaps between the different parts of the skull become unnoticeable. In large-brained vertebrates the skull is loose and flexible at birth to allow continued brain growth. The age at which skull fusion occurs is significant becuase it indicates most of brain growth has occured and also that the young animal is no longer as vulnerable to head injuries. Approximately defines the end of infancy.
Weaning:
Given as "minimum-maximum, standard".
(1) In mammmals, the age at which the young stop being suckled by the mother. Among sentient mammals, nomadic cultures will generally suckle for close to the standard, but in sedentary cultures weaning may happen closer to the minimum.
(2) In some non-mammals (particularily some dinosaurs, including some birds) young may be fed pre-digested food by the parents, and this characteristic may refer to weaning from this.
Fledging Age:
Physical Maturity:
The age at which the body is fully developed. This trait is always given as range, not only since individuals may vary, but also because different traits usually reach full development at different ages even within an individual.
Some animals may have two (or possibly more) distinct phases of physical maturity, for example a bird may reach adult form in the sense that it grows in flight feathers, well before it is sexually mature. Also dryopods reach (miniature) adult form and become land-dwelling, but continue to grow for some time after this. In such cases Physical Maturity is given as two (or more) seperate numbers.
Life Span:
The general age the animal can live if healthy throughout its life. In other words, Life Span represents the approximate age at which normal, age-based degredation of the body (i.e. senescence) critically endangers the otherwise healthy individual.
This is not to be confused with Life Expectancy, the average age an individual lives to, which is invariably much lower.
