new beginnings pt. 3: phylum chordata, bad to the backbone

new beginnings pt. 3: phylum chordata, bad to the backbone

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.
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​Phylum Chordata. Beginning of the backbone.

Part of what sets mammals (and fish, amphibians, reptiles and birds) apart from the rest of Kingdom Animalia is the presence of vertebrae in the body. Other biological advances of this group include…

  • Endoskeleton
  • Perforated pharynx (i.e. gill slits; openings connecting pharyngeal cavity to outside environment)
  • Highly differentiated brain and paired sense organs
  • Paired appendages
  • Notocord (stiff, but flexible, rod-like structure that runs along length of body; muscles can attach to this; aids in complex movement)
  • Post anal tail

As we’ve previously covered, animals such as jellyfish, octopi, and starfish, or insects like spiders and beetles do not have such characteristics, and so are not included in Phylum Chordata. They’re all multicellular, they’ve got 3 germ layers, and are either bilaterally or radially symmetrical, which are just a few of the things that allow them to be categorized in Kingdom Animalia – but that’s about as far as they’re going to get. ​

​In order to get any further, they would have had to have a couple more anatomical/physiological tricks up their sleeves, which lo and behold, we chordates had.

Subphylum Craniata: A-Head of the Game

Diving deeper into the details of what makes us, humans and wildlife, all unique and distinct within our respective taxa, we journey to the next taxonomic group, Subphylum Craniata.

It’s exactly what it sounds like: cranium! This group is characterized by having a distinct head region, with the anterior end of the notochord being incorporated into the skeleton.

The craniates are also distinguished by having one or more semicircular canals (structures of the inner ear), a brain consisting of at least three regions, the neural crest (which develops into nerve cells, skull and brain tissue), and more. These characteristics go hand-in-hand with the biological advance of cephalization – the physiological development that came along with bilateral symmetry.

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Vertebrates: A Myriad of Evolutionary Distinctions

Now, the craniates include animals that have both cartilaginous and bony endoskeletons. The next group, Vertebrata, however, only contains those animals which have a bony skeleton.

Vertebrates have two or three semicircular canals, more now than the craniates, movement of the eyes, heart palpitations controlled by the nervous system and much more.

Vertebrates are also distinguished by highly complex sensory capabilities. For instance, all vertebrates’ eyes are equipped with specialized cells to detect varying levels of light in the night or day time – rods and cones.

What’s interesting about this is that the ratio of rods (100x more sensitive than cones, useful for picking up light at night) to cones (less sensitive, more useful in daytime) in the animal’s eye is related to its activity pattern. Is the animal active in the night (nocturnal), day (diurnal) or at dawn/dusk (crepuscular)? Depending on the time of day the animal is most active, this will determine just how many rods versus cones they need.

The shape of the pupil can also be determined by the animal’s activity patterns, yet less directly so. Humans are naturally diurnal, so our eyes are circular – but so are nocturnal animals’ like owls. 

Horizontally elongated pupils provide wide peripheral vision – this can be coupled with the positioning of the eyes more toward the sides of the head, as seen in prey animals like deer. Vertically elongated pupils, however, typically belong to predatory species, who tend to be nocturnal (this shape can belong to animals active in day or night, though).

The semicircular canals are responsible for balance and orientation. Within this structure is a fluid called endolymph, which, when the individual moves around, flows throughout the structure and stimulates more nerves, alerting the brain of a change in orientation.

Vibrations in either water or air within the frequency range of 100Hz to 20kHz, produce sound, a sensation that this structure is partially responsible for. The exact structure and functionality of the semicircular canals differ based on what kind of vertebrate it is (fish or human?), as does the frequency it is capable of detecting.

A further distinction of mammals is that we are referred to as “gnathostomes.” The gnathostomes belong to the group Gnathostomata, which are the jawed vertebrates. Some of the main things that this group apart is that the standard is now 3 semicircular canals, the jaw is formed from the mandibular arch, and the members’ teeth contain dentine. So here we leave behind the lampreys and hagfishes.

Legs and Arms – Where Things Get Good

Skipping over a couple of groups, Gnathostomata hosts the familiar Tetrapoda, or tetrapods. These are the animals with four limbs, the paired pectoral and pelvic limbs that also have fingers, and hips attached to the spine. Whether all of those limbs are legs, like our beloved canine companions, or only two are legs and the others are arms, like monkeys, the presence of four limbs brings us a few steps closer to Class Mammalia

To begin the final stretch toward our favorite Class here Black Flower Science Co., we’ll take a quick look at Amniota.

The amniotes! Characterized by the presence of the extraembryonic membranes, the amnion, chorion and allantois, which encase the embryo either externally in a shelled egg or internally, within the uterus. This method of reproduction allows for greater protection of the offspring in the initial stages of development.

You might be asking, don’t sharks display something similar to this in the fact that they are capable of producing eggs or performing live birth? Well, yes. In this case, because they are not included in Amniota, this would be known as “convergent evolution,” where two or more groups of animals share the same characteristic, or “homoplasy” (character that evolved independently in two or more clades, or branches).

The animals that (almost) exclusively bear their young within their bodies, however, are known as “mammals.”

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