The question of whether any kind of creatures, particularly complex life forms, lived on Mars 3.5 billion years ago is a subject of ongoing scientific investigation and speculation. To date, there is no definitive evidence or consensus about the existence of past life on Mars.
However, scientists have been studying Mars extensively through various missions, such as the Mars rovers and orbiters, to search for signs of ancient microbial life or conditions that might have supported it. The search has primarily focused on finding evidence of past water, as liquid water is a crucial ingredient for life as we know it.
Based on the geological features observed on Mars, such as ancient riverbeds, lake deposits, and the presence of minerals that form in the presence of water, scientists believe that Mars had liquid water on its surface in the past. This leads to speculation that if life did exist on Mars billions of years ago, it might have been microbial in nature, similar to early life forms on Earth.
In 2013, the Mars rover Curiosity discovered that Mars had habitable conditions in its ancient past, including a lakebed environment that could have supported microbial life. However, the rover has not detected any direct evidence of past life.
Further exploration and analysis, including upcoming missions like the Mars 2020 Perseverance rover, which aims to collect samples for future return to Earth, will continue to shed light on the potential for past life on Mars. But at present, any claims about specific creatures or forms of life that might have existed on Mars 3.5 billion years ago would be speculative and not based on concrete evidence.