From Halopedia, the Halo wiki
Several highly varied species derived entirely from prehistoric Forerunner genetics, including one sapient species, were found on a world called Sedaaro. They began to diverge from the species' common ancestor around 10,000,000 BCE.
During the last stages of the Forerunner-Precursor war, after the Forerunners had already eradicated the Precursor presence in the Milky Way and followed them to the Path Kethona satellite galaxy, the ancestors of these Forerunners invoked the Mantle and disobeyed their commanders' orders to complete their genocide of the Precursors. Some were summarily executed aboard their ships, while others were marooned on Sedaaro. A functioning biosphere was created for the originally barren world—either by the exiled Forerunners themselves or those who abandoned them—using Forerunner genetics to bring forth a range of plant and animal species. Those who were abandoned were the only Forerunners to survive: their compatriots within the fleet refused to return to the ecumene, as they did not wish to spread the shame, fear, and knowledge of their actions.
They were rediscovered by the crew of the Audacity, led by the Librarian, circa 98,395 BCE. The initial exploration party consisted of the Librarian and Chant-to-Green, with Clearance-of-Old-Forests staying behind with the seekers. As the Librarian was the only one without armor to enter the Forerunner village, she got bitten by a local elder known as Glow-of-Old-Suns, after which Clearance immediately retrieved them. Thanks to the microbes transmitted by Glow-of-Old-Suns' bite, the Librarian began to learn the locals' language and gain a more intimate understanding of their way of thinking.
The Librarian, Chant and Clearance continued the following day with another exploration to the town. Due to the Librarian being able to understand the locals' speech she, together with Glow, traveled to a canyon where the ancient memories of the Forerunners that first arrived were stored. Here the Librarian spent several days interpreting the carvings created by mosses and the spores she inhaled. After this last exploration, Glow was taken back to the town and the crew of the Audacity departed Sedaaro and Path Kethona. This was likely the last interaction the Milky Way Forerunners had with them.
During the final stages of the Battle of the greater Ark, Omega Halo was fired in an attempt to stop the advance of the Precursor star roads. While decimating a small portion of the star roads, the blast also purged the satellite galaxy of all sentient life, while the star roads ended up destroying Omega Halo and the greater Ark anyway. Thus it is highly probable that the Sedaaro Forerunners were annihilated by the Halo blast and since it is not known if any of them were indexed or taken back with the Librarian, the subspecies has been rendered effectively extinct.
Following is a list of different Forerunner species, and possibly genera, that evolved on the unknown world in the Path Kethona galaxy. These Forerunners were killed when Master Builder Faber fired Omega Halo at the Path Kethona galaxy during the Battle of the greater Ark.
This species were most like the original Forerunners they separated from ten million years prior to being found by the Librarian. Their physiological changes were most likely caused by natural evolution, adapting to more simple forms to suit a simpler way of life. The obvious differences with the types of Forerunners in the Milky Way is that they had five digits on their hands and toes, whereas modern Forerunners had varying numbers of digits based on their rate and form. They had gray, human-like teeth, apparently in contrast to Milky Way Forerunners. The nose was still classically Forerunner, but their fur patterns were more expressed. On average, they were two-thirds the height and mass of a Manipular, being slightly less than 1.5 meters tall. Their build was broad-shouldered, as well as a broad midriff, thick legs, and short arms with long, curly fingers. They also ate meat, in contrast to the mainstream Forerunners. Their reproductive system was different from that of modern Forerunners, and due to their complete absence of artificially-induced rates and forms, their sexual dimorphism was less conspicuous.
The divergent Forerunners had a simple language entirely different from any other Forerunner language, even ancient Digon.
These creatures were large (roughly 500 kilograms) animals that preferred squatting. Their faces still largely resembled Forerunners, with eyes closely spaced. Their digits and phalanges were still recognizably Forerunner. These animals were used as livestock by the sapient species. Other animalistic types were also present on the planet.
These creatures were genetically altered on a large scale to become plants and mosses. The plants would serve as a food source for the herbivorous creatures, which in turn supplied the sentient Forerunners with meat. Thus, the species were able to maintain a stable biosphere. They were scrubby and set low to resist the wind. Some were in the form of gray-green bushes and others had stalks topped by spiky leaves with wrinkly looking fruits or pods beneath.
The moss and lichens were orange and fibrous. They could move on their own and scratch markings in rocks with their roots from memory.
They only had limited technology, consisting of fire, ceramics, and some metalworking. Their villages consisted of simple mud and stone houses and buildings no taller than one or two stories, or wider than five to ten meters. These were surrounded by mud and stone chest-high walls. They exercised some degree of population control.
Some of their advanced technology had been supplanted by purely biological means, the most notable being a form of deep genetic memory and information transfer accomplished via microbiological 'agents' in both their blood and mouth, which would transfer memory and understanding from Forerunner to Forerunner through biting. After this initial biting, touching was sufficient to spread information from one individual to another. They did not enjoy it, but occasionally did it to the most ignorant - such as outsiders, in the Librarian's case. They formed Quorums of 100 Forerunners linking hands to gain information from ancient times.
They had also created a biological analog to the Domain through the use of memory spores, which when inhaled revealed the entire past of their species and why they were brought there. They saved this memory in the spores mosses because they found some of these memories too hard to bear; they also wished to leave the past behind them and live their own lives. They still went to the location of the spores whenever they wished to know about tradition or settle a dispute.
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