Conventional Definition - life is a characteristic of organisms that exhibit all or most of the following:

• Homeostasis: regulation of the internal environment to maintain a constant state
• Organization: structurally composed of one or more cells
• Metabolism: consumption of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism)
• Growth: a growing organism increases in size in all of its parts rather than simply accumulating matter
• Adaptation: the ability to change over a period of time in response to the environment
• Response to Stimuli: a response external and internal stimulus
• Reproduction: the ability to produce new organisms.

Contemporary Definition - based on minimizing specific characteristics applied to an organism in order to define it as “life”:

• Response to Change: living things are systems that tend to respond to changes in their environment and inside themselves in such a way as to promote their own continuation
• Feedback: “negative” stimulus to regulatory mechanisms is responded to by “positive” feedbacks (e.g., potential of expansion, reproduction
• Replication: a characteristic of self-organizing, self-recycling systems consisting of populations of replicators that are capable of mutation which facilitates a systems ability to evolve
• Organization: the type of organization of matter which produces various interacting forms whose main property is to replicate almost perfectly (i.e., adaptive mutations) by using matter and energy available in their environment to which they may adapt
• Self-perpetuation : life is a potentially self-perpetuating open system of linked organic reactions, catalyzed simultaneously by complex chemicals (e.g., enzymes) that are themselves produced by the open system
• Systemics: living things are self-organizing and autopoietic (i.e., self-producing).

So What's a Cladogram?
This section of The Dinosaur Fan presents life forms using a menu-driven pictorial cladogram* of the various classifications (a.k.a., families) of Earth life. The detail information is focused on extinct vertebrate animals (primarily prehistoric) however cursory information about invertebrates and non-animal life forms (e.g., plants, fungus, viruses, minerals) is also included. The simplified cladogram presented in this website was designed to serve as a reference as to where the various life forms (especially animals) fit within the Earth's biological macrocosm. This cladogram is by no means comprehensive and represents my interpretation of exhaustive works by many paleontologists, biologists, and scholars.

The overall cladogram structure utilized throughout this section of The Dinosaur Fan is based on those presented in the Tree of Life Project and Mikko's Phylogeny Archive along with additional input from The Phylogeny of Life (UC Berkeley), The Dinosauricon, The Kingdoms Project, and Palaeos. Some sections have been expanded and/or augmented with information from additional sources while other sections were contracted to best display life forms and related collectibles based on presumed family groupings. Each page includes references in case the reader would like to quickly obtain additional information pertaining to these life forms. While I am not qualified to support or refute the content of these sources, I have compared the data with other authoritative sources in an effort to maximize accuracy.

It is important to acknowledge two factors involved in this section of The Dinosaur Fan. First, there are numerous "authoritative" cladograms available and more often than not they differ from each other to one degree or another, sometimes significantly. Second, I built this section of the website during the first half of 2009. Over time, theories of evolution and family group associations change as new evidence and/or lines of thought emerge. While I will do my best to modify my material as appropriate to keep pace with modern theory, this section of the website was extremely labor intensive and major modifications may be slow in coming.

* A cladogram is a branching diagram representing the minimum (i.e., core) derived characteristics within supposedly related groups of life forms (e.g., animals). The cladogram provides a visual aid for the development of a hypothesis of the evolutionary closeness (kinship) of the various groups of life forms. In other words, a cladogram can be used to visualize hypotheses (educated guesses) as to which groups of life forms are more closely related to each other than to other groups of life forms. A cladogram is not a representation of the path that evolution took in producing various life forms. The branching pattern of a cladogram is intended to show the relative relationships among various life forms but in most cases it does not show a true "evolutionary tree" for those life forms.

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