Information: - The Eocene Epoch, lasting from , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by a brief period in which the concentration of the carbon isotope C in the atmosphere was exceptionally low in comparison with the more common isotope C. The end is set at a major extinction event called the "Grande Coupure" (the "Great Break" in continuity) or the EoceneOligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay. As with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are slightly uncertain. - Holostei are bony fish that retain basal characteristics inherited from an early time in their evolution . There are eight species divided among two orders , the Amiiformes represented by a single living species , the Bowfin ( Amia calva ) , and the Lepisosteiformes , represented by seven living species in two genera , the gars . Further species are to be found in the fossil record and the group is often regarded as paraphyletic . Holosteians are closer to teleosts than are the chondrosteans , the other group intermediate between teleosts and cartilaginous fish . The spiracles are reduced to vestigial remnants and the bones are lightly ossified . The thick ganoid scales of the gars are more primitive than those of the bowfin . - The Amiiformes order of fish has only one extant species, the bowfin ("Amia calva"). - A fish is any member of a group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered obsolete or paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification. - Bowfin ("Amia calva") are basal bony fishes related to gars in the infraclass Holostei. Common names include mudfish, mud pike, dogfish, griddle, grinnel, cypress trout and choupique. They are regarded as taxonomic relicts, being the sole surviving species of the order Amiiformes which dates from the Jurassic to the Eocene, persisting to the present. Although bowfin are highly evolved, they are often referred to as "primitive fishes" because they have retained some morphological characteristics of their early ancestors. - Gars (or garpike) are members of the Lepisosteiformes (or Semionotiformes), an ancient order of ray-finned fish; fossils from this order are known from the late Cretaceous onwards. The family Lepisosteidae includes seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine, waters of eastern North America, Central America and the Caribbean islands. Gars have elongated bodies that are heavily armored with ganoid scales, and fronted by similarly elongated jaws filled with long, sharp teeth. All of the gars are relatively large fish, but the alligator gar ("Atractosteus spatula") is the largest, as specimens have been reported to be in length; however, they typically grow to and weigh over . Unusually, their vascularised swim bladders can function as lungs, and most gars surface periodically to take a gulp of air. Gar flesh is edible and the hard skin and scales of gars are used by humans. Given the information above, choose from the list below the object entity that exhibits the relation 'taxon rank' with the subject 'holostei'. Choices: - division - family - form - group - infraclass - order - species
A:
infraclass