When studying the life sciences, there are a lot of in-depth concepts to take in. Depending on the the type of science you are studying, biology vs. evolution, for example, you may even have to learn a handful of mathematical formulas to fully appreciate the material. Here, we are just having a light-hearted overview of the life sciences, so a light serving of sativa will do just fine. In my experience, sativa helps me to not get lost in wordy texts (reading that is not broken up by graphics/tables or formulas) and keep my mind sharp and able to take in all relevant information. Grinding about 60mg (less than 1/4 of a 1g bud) of sativa and smoking just a small pinch of that for over a 3-5hr period is perfect for maintaining a healthy attention span for learning. Black Flower Science Co. does not claim to be a medical professional and does not offer recommendations as a substitute for medical advice. All advice and recommendations are based on personal experience of the benefits of medical marijuana. If you are experiencing severe or declining mental health symptoms, please seek the advice of a medical professional.
We’ve made it! We’ve arrived at Class Mammalia, our final destination in this series. So, what classifies a mammal? Mammals are distinguished by the presence of the traits listed below (and more!):
- Hair, fur, or wool
- A jaw formed by the dentary bone only
- Mammary and sweat glands
- External ears
- Enucleated red blood cells (RBCs without a nucleus)
- Endothermy (internal regulation of body temperature)
This modest list does little to show the vast range of characteristics that make mammals, in my opinion, one of the most incredible taxa (group of species) on the planet.
For example, there are mammals with scales (i.e., pangolins), mammals with a pouch that gestate their babies outside of their bodies (i.e., marsupials), and some species from this Class are the largest animals on Earth (i.e., the biggest mammal on Earth, the blue whale)!
Let’s dive into the details of this group and get to know them a little better.
Table of Contents
Biological Advances for Warmth and Breathing
As it was briefly noted, there are many things that set Class Mammalia apart from all other organisms. The presence of hair, fur or wool, is just one of the things that allow us as mammals to independently regulate our internal body temperatures.
This is in contrast to our reptilian and amphibian friends who, are not “cold-blooded,” but ectothermic, meaning they depend on the external environment for regulation of body temperature. A mammal’s hair provides insulation and reduces heat loss, allowing it to keep warm in colder temperatures. The accompanying sweat glands enable it to cool off when the hair keeps just a bit too much heat in.
The heightened metabolic rate (the number of calories needed to keep your body functioning) and activity levels of this class call for several biological advances that strengthen the respiratory system as well.
Even at rest, mammals’ metabolic rate is 5x that of other vertebrates, with the exception of birds. Crazy stuff!Tweet
These biological advances include a muscular diaphragm (a muscle that aids in the inhaling/exhaling process; maximizing amount of oxygen taken in and carbon dioxide pushed out) and enucleated RBCs.
RBCs without a nucleus have more room for hemoglobin. Thus, they have a higher carrying capacity for oxygen and greater ability to distribute oxygen throughout the body.
Our 4-chambered heart – which birds have as well – is another huge component in efficient oxygen distribution throughout the body. An additional feature which boosts breathing proficiency is the second palate, also known as a “false ceiling,” which gives mammals the ability to breathe while chewing.
Taking in Energy: How Do Mammals Do It?
Caloric intake, or the amount of energy taken in by a mammal’s diet, is an important factor in the metabolic rate. The number of calories the body takes in influences how well the body can use that energy (and how much energy there is to use).
A part of what classifies a mammal is the single dentary bone. This bone makes up the lower jaw, and increases chewing strength and efficiency when grinding and processing food material. This feature is especially important for omnivorous or herbivorous mammals. Why?
Plant material tends to be harder to break down than animals’ flesh, so the type of teeth in the mammal’s mouth is crucial to energy intake. Those with flat molars like humans and herbivores (called bunodont teeth) combined with secodont, or carnassial teeth (like the sharp teeth of a cat) tend to have the widest variety in their diet. The multiple types of teeth in the mouth enable them to eat all kinds of things with the utmost efficiency.
Reptiles’ lower jaw consists of not only the dentary bone, but bones called the “quadrate” and “articular” as well. A key part of what classifies a mammal, though, is that these bones are located inside the ear. There, they are known as the “incus” and “malleus,” respectively.
Different Groups of Mammalia: The Egg-Layers, Marsupials, and the “True” Mammals
Class Mammalia’s name is derived from the Latin word mamma or mammae, meaning “breast” or “milk producing.” As we know, this is a unique method of feeding that mammals use when rearing their young. Although all mothers in this group share this behavior, the three types of mammals all do this quite differently.
Mammals is the overarching name for three different groups: Monotremata, Metatheria and Eutheria (both belonging to Theria).
Monotremata is home to the egg-layers. This includes the platypus and echidnas. Now, I know what you’re thinking: If it lays eggs, how in the world is it a mammal?
Well, nearly everything about it, really. The platypus displays nearly all traits included in what classifies a mammal. However, in its particular clade, or branch of Mammalia, this single trait of egg-laying was not lost, but remained in a more “primitive” state, as some would say. Though it does not give live birth, it’s not any less of a mammal.
Metatherians are marsupials – kangaroos, koalas, opossums and more. These animals do have “intrauterine gestation” (gestation within the womb, a part of what classifies a “true” mammal), but this gestation is much shorter than that of the Eutherians’.
They give live birth, but extremely early, when the baby is still only an embryo. The embryo must follow its instincts and climb toward mother’s pouch to nutrition and safety. There it remains for several more months, drinking the ever-changing composition of mother’s milk, growing to be big and strong enough to enter the outside world, as a “joey,” for good.
Eutherians, known to some as “true mammals,” are placental mammals. These are the species that most likely to come to mind upon speaking the word “mammal.”
The offspring of the Eutherians are born in a more advanced, developed state than those of the Metatherians, as they undergo a longer intrauterine gestation period. Whether that makes them better or “true” as opposed to a “false” mammal (what does that even mean?!)… eh, it’s up to you to decide.
There are countless distinctions to list off in answer to the question, “What classifies mammals as separate from the rest of Kingdom Animalia?” So many branches to climb up the Tree of Life that eventually lead to this class. The next time you see a mammal in the wild, hopefully, you’ll have a newfound appreciation for just how incredible these creatures are!
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