Classification

Figure 1. Morphological phylogeny of the American Black Bear

The beautiful truth about science is that the extent of our knowledge is constantly evolving. Technology allows us to divide each organism into a category by either morphological characteristics or molecular traits, which were previously unavailable. These leaps and bounds have been enlightening as well as confounding, as organisms are now being switched from old categories into new ones.

As of 2013 our understanding of evolution and how extant (existing) organisms came to be has expanded into three Domains: Archaea, Prokaryotes, and Eukaryotes. Eukaryotes include all organisms that have a

Black bear fur, credit to Christina Burkhart

Bear skull, credit to Christina Burkhart

Bottom molars, credit Christina Burkhart

Bear eye, credit to Chirstina Burkhart

Non-retractable claws, credit to Christina Burkhart

true nucleus.

     Inside of the Eukaryotic domain there are seven Major Clades (Figure 2). Animals, Fungi, and Choanoflagellates all fall within the Clade Opisthokonta, which contains organisms that have a single flagella during the reproductive stage and flat cristae within their mitochondria. The bear is categorized within the Kingdom Animalia because it is multi-cellular, lacks cell walls, and is mobile at some point in its life. After Kingdom are the nine Phyla, of which, the bear is a Chordate, meaning that it has a notochord, post-anal tail, and pharyngeal slits at some stage (usually embryonic) (Phylum Chordata, 1997). Classes are next, and both categorization and terminology become more well-known since it is often taught at a young age in the United States (Figure 1)(Campbell et al., 2007).

     Classes contain the organisms that can be differentiated between on sight, i.e. bird, toad, rabbit, snake, etc. Bears are Mammalian due to their synapomorphic features of hair/fur, mammary glands, being warm-blooded (endothermic), and

Canine tooth, credit to Christina Burkhart

having a diaphragm. From there, bears are sorted into the Order Carnivora because they eat meat, have pointed canine teeth, and molars. They are separated from other carnivores into the Family Ursidae by characteristics such as being omnivorous (eating plants and flesh), having large bodies, non-retractable claws, heavy limbs, plantigrade feet (walking on their whole foot rather than their toes), and elongated molars for chewing (Ursidae. 1997). The Genus Ursus sorts through the various types of bears, of which the Black Bear is known for its large nose, magnificent sense of smell, small round eyes, round ears, and short tails. The American Black Bear is known as the Species U. americanus largely due to its geographic habitat, which is coast to coast and a broad range from North to South, predominantly in North America (Figure 1). There are subspecies under U. americanus that are differentiated between via geographic location and molecular classification (not shown in Figure 2)(Genus Ursus. 2009).

As science continues to expand and new information is found and processed there may become a way to narrow down classifications even more. It embeds the hope that we may, someday, be able to track entire individual families, within any particular species, by their DNA, which has been started but is in its infancy. Having the ability to track the entire family tree of one individual and its entire life history, such as diet, home range and habits, would further our understanding of the past and the possible future of them, us, and every other organism out there.

Figure 2. Extended hierarchical phylogenetic tree, American Black Bear classifications in bold.

Interested in the Genus Ursus ? Check out the Polar Bear!