Final answer:
Fossils found in Arkansas coal deposits likely belong to the extinct lycophyte group known as Protolepidodendrales or Lepidodendrales. These tree-like lycophytes were dominant in the Carboniferous period and significantly contributed to the formation of coal deposits, which are now utilized as vital fossil fuels.
Step-by-step explanation:
The extinct lycophyte that has fossils found in Arkansas coal deposits is likely one of the members of the Protolepidodendrales or Lepidodendrales (commonly known as scale trees), which thrived during the Carboniferous period. Although the specific genus or species present in Arkansas coal deposits is not mentioned, these lycophytes were once dominant in the swampy forests of that era and contributed significantly to the formation of coal deposits. It's important to recognize that these lycophytes, which could grow to tree-like sizes, are distinct from the smaller club mosses seen today. During the Carboniferous period, these lycophyte trees covered extensive areas and formed large swamp forests. The decayed remnants of these forests are now found in Arkansas coal deposits, giving us significant insight into the planet's ancient vegetation. Additionally, these coal deposits provide important fossil fuels that have been instrumental in the development of human society.