Sauceback

Saucebacks are bipedal fauna that descended from binucleid worms.

Anatomy
Saucebacks are bipedal, and all extant saucebacks have feathers. Though many appear to have a neck, this is technically a proboscis--the carapace on the back, also known as the "sauce", is also the braincase and therefore part of the head. The inside of a sauceback's mouth is lined with teeth, the largest pair of which--the "tusks"--being mobile and serving as jaws. The oral ring, that is the teeth inside the mouth, are also mobile and are used in mastication. The number of teeth a sauceback has, including its tusks, directly corresponds to the number of nostrils it has, as the two are directly tied in development.

Saucebacks have lungs in their tails which serve for active respiration. They breathe out of four pairs of spiracles on their tail or back, which may be located close to the sauce or much further back. The nostrils are not used for breathing, instead being scent pits which are not connected to the lungs.

The legs of modern saucebacks are pillar-erect, meaning that rather than fitting into a socket that sticks inward from the femur like the legs of mammals or dinosaurs, the entire limb is anatomically like a pillar holding up the body. In all descendants of the Tusked Sauceback, part of the hip girdle is formed from an internalized limb segment.

Breathing & Blood
Saucebacks breathe using microlungs along the flank of the tail that are designed to take in oxygen. The ancestor of the saucebacks had pores all over the body. Saucebacks have an iron based blood which makes it red.

Diet & Energy
Saucebacks eat using a toothy radial mouth. Modern ones have tusks to stab or grab their prey with, but there used to be ones who had four jaws to bite with. Saucebacks commonly hunt large game, which they are adapted for.

Evolution
The saucebacks all came from the golden sauceback.

Locomotion
Saucebacks use two legs for locomotion. Modern saucebacks have cloven hooves, but there used to be ones in Glicker who had claws.

Reproduction
All saucebacks are sexual reproducers, they have two genders, and lay eggs. They have a larval form that resembles their ancestor the beach thornworm but several species have specialized their larvae for other lifestyles. They grow in a gradual metamorphosis, changing from larval form to adult form over time.

Senses
Saucebacks' primary sense is echolocation. They have bat-like ears. All saucebacks have a very strong sense of smell. They typically use this to seek out prey from long distances. To smell, they have moist olfactory patches or "nostrils" around the mouth.

Saucebacks almost universally lack eyes, though their ring of nostrils is commonly mistaken for them. Notably, the Hearthead actually converted its nostrils into pinhole eyes by adding dark light-sensing pigments to the inside, making it the first and so far only species where the "nostrils" really are eyes.

A group of extinct saucebacks descended from the Beach Sauceback have an infrared-receptor on the forehead.

Size
Saucebacks have ranged from 5 m Long all the way down to 20 cm Long.