What’s in a name?
How can an animals’ scientific classification help us determine their diet?
We’ll classify the domestic cat and domestic dog as an example.
Developed by Carl Linneaus in the 1700’s, (1) Taxonomy or the classifications of animals became a standard way to group related organisms into broad and then more specific characteristics that defined them. We can look at Taxonomy like a beautiful tree. At the bottom we have the trunk, the broadest classifications that encompass every living thing. As you go up the trunk, you soon form the branches and the limbs acting like more specific identifiers. We have twigs that are many but reside on the same brand and at the very top of this beautiful tree we have individual and very unique leaves that are like specific organisms. They represent the most specific classifications.
The true classifications (which have been expanded upon after Linneaus (2)) are not trunks, limbs, branches, twigs and leaves but rather:
Domain is the broadest classification and includes three divisions Archaea, Bacteria and Eukarya (3). Archaea are single celled microscopic organisms that do not contain a nucleus or central operating hub. They typically can withstand extreme living conditions like high temperatures or highly salty environments (4). Eukarya on the other hand are nucleus containing organisms. Bacteria are similar to Archaea but have a different function and structure and therefore are classified into another domain.(5)
This classification is the broadest of the classifications and mainly describes a) if the cell has a nucleus and b) basic cell structure such as if there are specific structures with thin, skin like walls separating itself from other structures.
A Kingdom, groups all organisms together that share foundational characteristics. There are six Kingdoms. They are named Animalia, Plantae, Fungi, Protista, Archaea/Bacteria, and Bacteria/Eubacteria (6). Each has their own characteristics for this discussion we will focus on Animalia as this begins our classifications of our carnivore companions. Cats and Dogs are placed in the Animalia kingdom. Animals in this kingdom are multicellular organisms. They have a nucleus and enclosed cells which have individualized functions in the cell that help it work. In addition to the Animalia Kingdom, Plantae (plants), Fungi and Protista are multicellular.
These cells differ from Archaea and Bacteria because Archaea and Bacteria are single celled organisms. They do not have a nucleus or specialized cells. The main difference here is how the cells are organized.
The Animalia Kingdom differs itself from Plantae and Fungi who have very ridge cell walls that are hard to breakdown (8).
The Phylum is a classification that groups together organisms with similar body types (9). This includes both structural and developmentally similar characteristics as well as common ancestry (10). There are six main phyla (2):
Each of these main phyla contain many subphyla. The animal phyla alone contain 34. While we could write paper upon paper of each of these and how they differ, we will again focus on what applies to our cats and dogs.
For cats and dogs their phylum is Chordata or Chordates which are classified by having a nerve cord. This develops into the brain and spinal cord that constitute the central nervous system. Chordates are also classified with pharyngeal slits which is a filter system similar to fish gills. They also have a tail These are all features present at some stage of development. For animals like cats and dogs these are during a very basic stage of develop that has potential for further growth. During this stage, Chordates develop the anus first than the mouth. Chordates also develop a circulatory system that circulates blood and lymph that is responsible for replenishing proteins and tissue fluids back into the blood (11).
The Class is yet another more specific classification for organisms who share similar attributes such as physical characteristics and systematic functions. Each class belongs to a phylum discussed above. Cats and dogs are categorized in the Mammalia Class.
The Mammalia class includes over 5000 species. They differ from reptiles by being warm blooded (12), have mammary glands to nurse their young, hair or fur and finally an inner ear with 3 bones derived from the ancestral mammalian jaws (13, 14).
Now we come to the most important classification for this discussion
Order. Order is a more specific specialized classification that groups organisms in terms of fixed personality traits, habits and nature. The Order that our cats and dogs belong to are the Carnviora Order. The word Carnivora is derived from Latin, carō (stem carn-) "flesh" and vorāre "to devour")
Of all the mammalian orders, it contains some of most diverse organisms ranging in size from the 0.88 oz. least weasel to 11,000 lbs. elephant seal!
There are many characteristics of the carnivore that group them in this order.
The mouth is a great defining characteristic. These organisms have very sharp pointy teeth such as the incisors that grip, tear and ripe flesh easily from carcasses and bone. Other teeth called carnassial teeth, are used to shear meat. The jaw in the carnivore moves like scissors, opening wide and closing in a vertical manner (15, 16). In herbivores, the teeth are flatter and are designed for grinding and breaking down plant matter. The jaw moves side to side, horizontally to achieve this (17). While there are some small adaptions in the mouth, this arrangement isn’t new, it has been present for over 60 million years (16). Evolution can tell us a lot, but it does not occur quickly.
The skull is characteristic of the carnivore as well. They are typically heavy and encase a large brain. There are several skull components that are specific to the carnivore but the most indicative are highly developed bones that form the cheek bones. This bone development allows for various muscle groups that are specific for biting and chewing (18, 25). There are still more specialized muscles that allow for the jaw to crush meat and bone forcefully that are also connected (19).
Sight, hearing and sense of smell is very specialized in the carnivore. Many have very long, lean bodies that are able to run fast. While some can run long distances, many are short distance sprinters. This is to better hunt prey as efficiently as possible (20).
When it comes to the digestive tract, it is simple and short unlike that of the herbivore and omnivore. Fat and protein provide quick nutrients that is easy to breakdown, digest, absorb and utilize within the body. Plant matter on the other hand require lots of processing by the body. While there are other digestive mechanisms and components that make a carnivore a carnivore, one very distinct feature is the cecum. The cecum is a pouch where the small and large intestine meet. In herbivores, this pouch mixes food stuff with beneficial bacteria that break down plant material and especially cellulose that make up the cell walls of plants. This pouch is greatly reduced in carnivores. (21, 22)
The Family is the next classification that “have evolved from the same ancestors and share relatively common characteristics”. The family name of animals always ends with "idae"(23) For example the cat family is labeled as Felidae and the dog family is labeled as Canidae.
In addition to the characteristics of the above classifications, the Felidae family can be characterized by an obligate diet of meat, organs and bones (24, 27, 28), retractable claws (18), generally patterned coats and walk on their toes versus flat footed (such as seen in the Canidae family) Their feet are well padded as well. Behaviorally they are more solitary (25) and more active at night. There are of course exceptions.
The Canidae family includes not only the characteristics of the carnivore order above but also are facultative carnivores meaning only in dire need will they consume plant material like berries. They also have non-retractable claws (26, 27, 28) unlike the Felidae family. They also lack patterned coats. Canidae species are also solitary and tend to hunt alone except a few species who hunt in packs and take down larger animals (25).
A Genus gets yet more specific again classifying according to common characteristics. Our domestic feline friends fall under the Felis Genus whereas dogs, under Canis.
Felis, the Latin term for “feline” are small to medium sized cat species (29). They hunt small prey such as rodents and birds. These cats differ from more-wild genus by the lack of a white dot on the back of their ears which are typically narrow and pointed. The pupils contract to slits (the stereotypical cat’s eye) (30).
Canis meaning “dog” in Latin and as one could guess, has given rise to the name canine tooth31 is a noticeable characteristic of these hunting creatures. This genus includes medium to large canines that have long legs, but short ears and tails (32, 33).
A Species includes organisms that are even more closely related to each other not only in behavior and characteristics but in their abilities that two individuals of the species can produce viable and fertile offspring (34) .
Here we begin putting Genus and Species together in a naming system. Cats are Felis silvestris or F. silvestris (35) and dogs are Canis lupus or C. lupus (36). While a tad larger than the domestic cat, F. silvestris shares many common characteristics of the tabby cat such as a slightly striped pattern on a grey ish colored coat with some red tones. The tail is thicker and round at the end (37).
This species was the one to begin the domestication process around 7500 BCE that has led to our modern day domestic cat. Farmers quickly realized these creatures could easily control rodents that would otherwise eat their grain stocks. (38) In addition to round eyes that also contract into slits like the Felis genus, they have amazing night vision that is 20-100% more specific than the average house cat which great aids their hunting ability. This classification also includes creatures with glands that aid in reproduction (39).
C. Lupus on the other hand comes from the words “dog wolf”. Many of these are wolf species that through hybridization and domestication have formulated the modern-day dog. C. Lupus is typically the size of a medium to large breed dog and sport various colors such as black, grey, cream etc. but are primarily solid versus patterned. Although it ranges by region males are typically 25-185 lbs. with females being 5-10 lbs smaller. They have large pointy ears and long tails. They have a heavy and large head with teeth and jaws that are extremely strong that can easily break bone K.
Finally, the most specific of classification is the Subspecies. For cats this is Felis silvestris catus or F.s. catus. The domestic house cat is a small, carnivorous mammal typically found in the modern family home. Like their ancestors they have long lean bodies, retractable claws and sharp teeth for hunting and eating smell prey. Domestication typically began in Egypt with today’s cats changing little (except color and pattern) compared to their ancestors (while related to lions, tigers and larger cats, their descendants where smaller wild cats (7)). This means their dental structure; anatomy, physiology and prey drive have not changed. Domestic cats could easily survive in the wild and can breed with F. catus without extensive measures such as artificial insemination.
For dogs, Canis lupus familiaris or C. l. familiaris is the Subspecies. Nowadays dogs come in various sizes, colors and are designed to perform various jobs like protection, transportation and companionship.
Dogs and their wolf ancestors are so genetically similar that they can interbreed with each other. Domestic dogs also retain many similar characteristics such as impeccable hearing, sight and smell for hunting, anatomy and physiology for a meat based diet.
There are some differences. Many domestic dogs are smaller in body size as well as skull and brain size. Their teeth are smaller as well. While most ancestors go through a reproductive cycle once a year, domestic dogs cycle twice a year.
Although Carl Linnaeus began the classification of organisms in the 1700’s and developments have evolved and changed throughout the years on the topic, one thing remains the same, the inarguable classifications of our modern-day carnivore companions. Not only are we able to see the connections among organisms via the great ancestral tree, but we can track and identify through classifications, defining characteristics that these groups have in common. We can see that even among thousands of years of evolution and change, similarities in structure, anatomy, physiology and behavior have changed on a very minor scale compared to the much bigger picture. We can see, despite marketing tactics that in addition to anatomical and physiological study, at the very root of similar taxonomic classification and comparison that our cats and dogs are in fact carnivores.
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