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2. To add to the nomenclature, these are sometimes termed natural groups. using vs .net tocreate qr code jis x 0510 for asp.net web,windows application iPhone Phylogenetic systematics 41 Carnivora Mapping the course of evolution with the cladogram Because cladogram s are hierarchical, they are an excellent way to map the hierarchical distributions of characters in nature. Derived characters are evidence of monophyletic groups because, as newly evolved features, they are potentially transferable from the rst organism that acquired them to all its descendants: in short, they characterize the bifurcations at each node on the cladogram. Primitive characters those with a much more ancient history provide no such evidence of monophyly.

To illustrate this, we resort for the last time(!) to mammals and their fur. Mammalian fur, we said, is among the shared, derived characters that unite mammals as a monophyletic group. MAMMALIA On a cladogram, therefore, we look for characwarm-bloodedness ters that mark a node in the diagram.

All organfur- or hair-bearing isms characterized by shared, derived characters are linked by the cladogram into monophyletic groups. Re ecting the hierarchy of character dis- Figure 3.8.

A cladogram showing humans within the larger group Mammalia. Mammalia tributions in nature, the cladogram documents is diagnosed by warm-bloodedness and possession of fur (or hair); many other monophyletic groups within larger monophyletic characters unite the group as well. Carnivora, a group of mammals that includes bears groups.

In Figure 3.8, a small part of the hierar- and dogs (among others) is shown to complete the cladogram. Carnivores all uniquely chy is shown: humans (a monophyletic group, share a special tooth (the carnassial) and humans all uniquely share, among many other features of the skull and skeleton, a large cranium.

Note that all mammals (including possessing shared, derived characters) are nested humans and carnivores) are warm-blooded and have fur (or hair), but only humans have within mammals (another monophyletic group the gracile skeletal features, and only members of Carnivora have the carnassial tooth. possessing other shared, derived characters). Notice that the character of warm-bloodedness is primitive for Homo sapiens, but derived for Mammalia.

As we have seen, features can be derived or primitive, all depending upon what part of the hierarchy one is investigating. The cladogram need not depict every organism within a monophyletic group. If we are talking about humans and carnivores, we can put them on a cladogram and show the derived characters that diagnose them, but we might (or might not) include other mammals (for example, a gorilla).

So we said with regard to Figures 3.6 and 3.7, if the hierarchical relationships that we have established are valid, the addition of other organisms into the cladogram should not alter the basic hierarchical arrangements established by the cladogram.

Figure 3.9 shows the addition of one other group into the cladogram from Figure 3.8.

The basic relationships established in Figure 3.8 still hold, even with the new organism added. The cladogram is likely correct.

. How to read evolution in the cladogram We identi ed mono phyletic groups using derived characters, and that the hierarchies of characters designate hierarchies of groups. So, looking at Figure 3.9, the distribution of shared, derived characters suggests that humans and gorillas are more closely related to each other than either is to a bear.

It also suggests that all three are more closely related to each other than they are to something that does not possess the derived character of bearing fur or hair. And how does that apply to evolution The evolution of the derived character of fur is associated with the evolution of the group Mammalia. As we currently understand their.

Human 42 Who s related to whom and how do we know 3.1 Wristwatches: when is a watch a watch We ve used cladis tic techniques to infer the history of the biota. Here we ll try something different: we ll use cladistic techniques to infer the evolutionary history of watches. Analog and digital timepieces are comonly called watches.

Implicit in the term watches is some kind of evolutionary relationship: that these instruments have a common heritage beyond merely post-dating a sundial. But is this really so Consider three types of watch: a wind-up watch, a digital watch, and a watch with a quartz movement. Six cladograms are possible for these instruments (Figure B3.

1.1), but it can be seen that, by the de nition of a cladogram, a and b for each type are identical. This is because the groups at a node share the characters listed at that node, regardless of order.

For this reason, we really have only three cladograms to consider (Figure B3.1.2).

One might at rst wish to place the digital watch in the smallest subset, in the most derived position (as in types I and II), since it is the most modern, technologically advanced, and sophisticated of the three. Remember, however, how the cladogram is established: on the basis of shared, derived characters. Cladograms types I and II say that the digital watch shares the most characters in common with either a wind-up watch (type I) or a quartz watch (type II).

A look at the characters themselves suggests that this is not correct: wind-up and quartz watches are both analog watches (have a dial with moving, mechanical hands) and their internal mechanisms consist of complex gears and cogs to drive the hands at an appropriate speed. The digital watch, on the other hand, consists of microcircuitry and a microchip, with essentially no moving parts. It is apparently something very different and, from its characters, bears little relationship to the other watches.

What is the digital watch In an evolutionary sense, it is really a computer masquerading (or functioning) as a timepiece. The computer has been put in a case, and a watchband has been added, but fundamentally this watch is really a computer. In our hypothesis of relationship, the watchbands and cases of watches have evolved independently two times (once in computers and once in watches), rather than the guts of the instrument, itself, having evolved twice.

That the watchbands and cases evolved independently two times is a more parsimonious hypothesis than arguing that the distinctive and complex internal mechanisms (themselves consisting of many hundreds of characters) of the watches evolved independently twice. What, then, is a watch If the term watch includes digital watches as well as the other two more conventional.
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