For the first Sci-Day post, I'd like to cover a very important topic that is relied upon heavily in our representations of prehistoric creatures in Dinosaur Battlegrounds.
Cladistics and phylogenetics are critical tools for portraying prehistoric creatures in the most accurate possible way. These two tools allow us to figure out what a prehistoric animal's closest relatives are, and using that information we can have a more informed idea as to what its soft tissue anatomy may have been like, despite the original tissue being lost to the processes of geologic time.
This is also very important if a species is based on very fragmentary or incomplete remains. If there is enough material to determine the species' relationship(s), it is possible to make an accurate skeletal restoration despite not having complete remains of that species.
Cladistics is a relatively new branch of a field known as "Systematics" - this field is dedicated to classifying and better understanding the evolutionary interrelationships and diversification of life on our planet. Cladistics, in particular, is a method of classification that places taxa based on their hypothesized ancestry. Various characteristics are quantifiably measured in each of the species - these may be as simple as the presence or absence of some specific feature (a "binary character"), or it may be something such as the number of vertebrae in the tail, where there may be a range of values. Using this information, a cladogram is then created, utilizing the "principle of parsimony" - the tree with the fewest character state changes is usually considered to be the best.
For example, let's say we have species A, B, C, and D. We have classified them on the basis of 4 binary characters (1, 2, 3, and 4). For these characters, a value of "0" means the character is absent, and a value of "1" indicates that character is present. Species A has a character state of 1/0/0/0, Species B has a character state of 1/1/0/0, species C has a character state of 1/1/1/0, and species D has a character state of 1/1/1/1. In this example, the best possible tree places C and D closest together, followed by B, with taxon A as the "outgroup". Alternatively, you could place B and D closest together, but this would add more character state changes to the tree that can be avoided and thus the first tree is preferable.
Keep in mind, however, that most cladograms are not nearly that simple, and there may not be a single clear tree that stands out, and certain characters may evolve or be lost multiple times in a lineage. For example, snakes lost the limbs that their lizard ancestors evolved, and human beings lost much of the fur that is observed in our closest relatives. This phenomenon is known as "secondary loss". There is also the phenomenon of "convergence", where two taxa evolve the same or very similar features independently - an example of this would be the evolution of venom, as it has evolved in multiple unrelated lineages.
A great example of the application of cladistics and phylogenetics in Dinosaur Battlegrounds is the skin covering of Tyrannosaurus rex. Due to the technique known as phylogenetic bracketing, where a well-supported cladogram is used to infer character states in some taxa in the tree based on the principle of parsimony and the known states of that character in other taxa in the tree. This method predicts that Tyrannosaurus rex did have at least some degree of feathery covering.
However, it is important to keep in mind that it is possible that Tyrannosaurus rex lost its ancestral feathers, in the same way that large mammals lost most of their fur; until direct evidence of preserved feathers is found associated with a T rex specimen, it is impossible to say with complete certainty that it did or did not have feathers. With the current evidence, though, it appears likely that Tyrannosaurus was at least partially feathered.
Well, I hope this post taught you something new about the science of Dinosaur Battlegrounds!
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