According to Wikipedia (generally a trustworthy source of information), the most common speculation among believers is that the creature represents a line of long-surviving plesiosaurs.
And is precisely that, a plesiosaur, what we're going to do.
First, I'll show you a diagram of a generic plesiosaur. You can see the hydrodynamic body, composed by a small head, long neck, and compact torso, and equipped with four fins.
See also how I divided the spine in three curves with different directions. While these curvatures certainly changed in different positions of the animal, this is the 'rest' pose.
Remember that there was a great diversity of plesiosaurs (for more info, visit www.plesiosauria.com), so it's okay if you modify a bit the proportions.
Let's start, then. Draw a circle for the head and a curve for the spine (remember to change the direction for the segments of neck, torso and tail).
Draw a big oval for the body, and smaller ones for the hips and the pectoral region.
Before drawing the limbs, here's a little tip:
The limbs of the plesiosaurs had the same bones that many other animals, but just arranged differently. In this case you can see an arm (the biggest bone is the humerus).
As an aid for drawing, I resumed the shape in a sticks diagram.
Draw the fins. Remember that the most probable way of locomotion was alternate movement between the front and rear limbs (when ones are up, the others are down).
Adding the flesh to the 'skeleton'...
Now adding the volume: Muscular yet stylized neck, powerful chest, short tail. The head is relatively east. Just remember that the big eyes were placed in th eupper part of the skull.
Deciding which parts are illuminated and which remain in the dark.
Blending! It depends of your medium, for example if you work with chalks, you may use a cotton.
The plesiosaur is finished!...but it is not complete without the lake, right?
You can paint the environment in a different paper, then cut and paste the plesiosaur in here.
First, I did a blue degrade, the darker blue at the bottom of the lake.
For the surface, I use to draw irregular ovals, that are getting smaller, and fading, as they are more distant(basic perspective).
Now place Nessie and it's done! You can add some air bubbles, too.
Hope you like it.
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