Sauceback

Saucebacks are bipedal fauna that descended from binucleid worms. Together with murkworms, they form a larger group called beastworms.

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 (see cephalic segment). 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 or five 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 merely 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. In living species, the limbs are biramous--that is, they branch, forming a cloven hoof instead of the single hoof ancestral to the group.

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 tusk-like jaws to grab their prey, but there used to be ones who had four jaws to bite. While saucebacks were ancestrally carnivorous hunters of large game, many modern species are omnivorous or even herbivorous.

Some saucebacks will consume large amounts of chitinous flora to help build their skeletons. However, this is not a requirement for all species.

As endotherms, exceptionally small saucebacks have fairly high metabolisms and must eat very often.

Evolution
The saucebacks all evolved from the first sauceback, the golden sauceback. They quickly split into two lineages, vicious saucebacks (descended from the vicious sauceback) and what would eventually become modern saucebacks (descended from the leaping sauceback). At the time, Sagan 4 had two continents; vicious saucebacks lived on Glicker, while the ancestors of modern saucebacks lived on Wright.

In general, vicious saucebacks showed little diversity early on, while the ancestors of modern saucebacks diverged into many forms. The tusked sauceback, which elongated a pair of teeth and internalized its first limb segment, evolved in the Flischian period, and it gave rise to a handful of dead-end branches such as the twin-tailed saucebacks and aquatic swimming saucebacks. It also gave rise to the feathered sauceback--an active, warm-blooded species which would go on to produce many descendants.

When the gamma-ray burst struck during the Martykian period, it wiped out all but two species, those being the falsequill sauceback and the long eared sauceback. The falsequill sauceback would produce a small number of descendants, mainly burrowing ambush predators, but diversity of its lineage continued to be fairly low. The long eared sauceback, on the other hand, continued its ancestral tend of diversification. One descendant, the cleaner sauceback, was the first sauceback with cloven hooves--and the last common ancestor of all modern saucebacks. The other immediate descendant, the dark sauceback, would give rise to the beach sauceback--the first sauceback to develop any form of photoreception.

When the ice comet struck in the Raptorian period, all remaining vicious saucebacks went extinct. However, the smaller feathered saucebacks continued to thrive. The beach sauceback would give rise to scorpion saucebacks and dagger saucebacks (descendants of scorpion sauceback and four dagger sauceback, respectively). Meanwhile, the cleaner sauceback and its descendants would go on to produce three major groups: polar saucebacks (descendants of snow sauceback), larvabacks (descendants of the false-larva sauceback), and waxfaces (descendants of the waxface. Larvabacks and waxfaces are more closely related to one another than to snow saucebacks, sharing a common ancestor--the foi-devourer sauceback. While snow saucebacks were simply basal cold-adapted saucebacks, the larvabacks are neotenous marine creatures while the waxfaces had internalized all their exposed carapace to protect them from chitinase.

When Sagan 4 entered its snowball event in the Bloodian period, only the snow saucebacks, waxfaces, scorpion saucebacks, and larvabacks would survive. Scorpion saucebacks notably went through a radiation of forms utilizing mimicry. However, scorpion saucebacks would go on to be wiped out by the solar flare that followed at the start of the Masonian period. Waxfaces saw a radiation on Jaydoh, where they were isolated, and they nearly became extinct due to rising sea levels; however, they were ultimately survived by the Pirate Waxface, which followed its prey out to sea. This leaves larvabacks, waxfaces, and snow saucebacks as the current living sauceback groups.

Modern Saucebacks
On the larvaback side of evolution, they diversified into a global genus of marine predators. The first finback, which has a dorsal fin-snorkel bearing its spiracles, appeared in the Darthian period.

Meanwhile, snow saucebacks, survived by the glacial sauceback, had managed to become global during the snowball event and diverged into a huge variety of new forms all over the planet once the ice receded. In fact, it holds the current record for most immediate descendants of any species of sauceback. Among its immediate descendants, the Masonian period saw the rise of megatusk saucebacks (descendants of the megatusk sauceback), which have enlarged tusks and later beaked trunks, and loafshells (descended from the loafshell), which have a segmented carapace, venom, and tridactylism. Later descendants into the Blargian period would produce more major groups, including harnessbacks (descendants of the harnessback), which have a more advanced respiratory system protected by enlarged back plates and even produced an eyed descendant, and Hagloxes (descendants of the haglox), which are very large muscular herbivores as well as the largest saucebacks to ever live.

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

Reproduction
Most 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. With no exception, sauceback larvae breathe air just like their parents, though a handful of species have aquatic larvae regardless. They grow in a gradual metamorphosis, changing from larval form to adult form over time. Some saucebacks are ovoviviparous.

The eggs of saucebacks are more similar to those of insects than to those of vertebrates. The earliest saucebacks had to lay their eggs somewhere moist, such as underground or in a carcass. However, somewhere along the way, the ancestors of modern saucebacks evolved a serosa, which secretes a chitinous desiccation-resistant cuticle, or shell, over the egg. While this was lost in the line leading up to larvabacks, it is present in most other saucebacks.

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 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 9 m Long all the way down to 3 cm Long.

Meta

 * For a time, Sauceback clones were very common in Spore-based worldbuilding projects.
 * Saucebacks have been subject to a great amount of misinterpretation compared to other lineages.
 * It is very common for the nostrils around the face to be misinterpreted as eyes. The "eyestrils" of the hearthead are a light-hearted reference to this phenomenon.
 * As a result of a woefully inaccurate skeletal diagram being added to this very page, for a time it became extremely common for saucebacks to be misinterpreted as having completely toothless mouths apart from immobile tusks. Some extant branches, such as hagloxes, are still afflicted by the lingering effects of this misinterpretation.