When a fossil enthusiast reflects on the numerous universally acknowledged classic invertebrate animal localities of Paleozoic Era geologic age (roughly 542 to 251 million years ago) exposed throughout the US, several special specific places naturally materialize in the mind's eye. For example, for early Cambrian paleontologic assemblages (trilobites, archaeocyathids, annelids, algae, salterella, brachiopods, hyoliths, and early echinoderms), the Great Basin and Mojave Deserts of western Nevada and eastern California hold a practically preeminent interest; for middle Cambrian trilobites, one is invariably drawn to the spectacular extinct arthropod occurrences in western Utah; for late Ordovician brachiopods, bryozoans, corals, and echinoderms probably no other district rivals southern Ohio; for Silurian Period paleontology, a visit to the upper Midwestern states of Minnesota, Wisconsin, Michigan, Indiana, and Ohio is a definite necessity; for Devonian-age invertebrate material, the world-famous New York state outcrops remain the standard by which all geologically correlative fossiliferous strata in North America are compared; for Mississippian fossil abundance, Missouri, Illinois and Arkansas provide ample opportunities for satisfying fossil experiences; and for fantastically productive Permian paleontology, the west Texas outback remains perennially popular. But for late Pennsylvanian invertebrate fossil associations--roughly 307 to 299 million years old--probably no other area of comparable geologic age rivals Kansas. True, that same vast- shallow upper Pennsylvanian sea that deposited its fossil wealth in Kansas also left sedimentary evidence over a considerable distance within Paleozoic territory presently assigned to the North American mid-continent, mainly from eastern New Mexico and north Texas, north to Indiana and Illinois (just in case folks are wondering, the world-famous Illinois Mazon Creek concretion localities are middle Pennsylvanian in geologic age, around 309 million years ancient)--not to mention significant Late Pennsylvanian deposits also available for inspection in a number of Northern Appalachian Basin and western US states (notably--Arizona, California, Colorado, Idaho, Kentucky, Montana, Nevada, Ohio, Pennsylvania, West Virginia, Wyoming, and Utah), where dedicated students of invertebrate animal life can certainly explore not a few surprisingly reliable producers of late Paleozoic fossil material--yet, nowhere is latest Pennsylvanian Period paleontology better exhibited than in Kansas. Here is a fossil-finding paradise of rare perfection. Bountiful, beautifully preserved specimens from all major categories of invertebrate animals can be secured from late Pennsylvanian strata identified in Kansas. The list is definitively inclusive, and exciting to consider collecting: algae; annelids (represented by abundant minute scolecodonts, the jaws of polychaete worms); arthropods (famously--insects, horseshoe crabs, and sea spiders); brachiopods (myriads of species distributed among every major and most minor Pennsylvanian brachiopod genera); bryozoans (every conceivable kind present and accounted for--wildly branching digitate varieties, lattice-fenestrate types, and innumerable encrusting species); conodonts (minute tooth-like dentical structures, unrelated to modern jaws, that helped process food in an extinct lamprey eel-like organism); corals (solitary, so-called horn corals and colonial kinds very well-represented); echinoderms (crinoids--practically every individual skeletal constituent exquisitely preserved: stems, columnals, crown plates, spines, and dorsal cups among the numbered; starfish; and loads of superior echinoid spines and plates, too, revealing great morphological detail); fusulinids (an extinct single-celled animal that secreted a small wheat grain to American football-shaped shell; indeed, prolific associations of fusulinids occur in Kansas calcium carbonate accumulations); ichnofossils (trace fossils of tracks and trails made by invertebrate animals); mollusks (all major types wonderfully kept intact for approximately 300 million years: gastropods--showy coiled species, curious bellerophon snails, and many finely detailed high-spired types; pelecypods--clams of every possible example, from stunning large Myalina, Septimyalina and Orthomyalina genera to more diminutive varieties with intricately sculpted exterior valves; cephalopods--including orthoconic forms, nautiloids, and numerous ammonoids; and scaphopods--commonly called a "tusk shell"); ostracods (tiny crustaceans that frequently contribute prolific monotypic quantities of their spendidly preserved bivalved shells to limestone and shale layers); sponges (remarkable, well-preserved examples of the Phylum Porifera, with the enigmatic Chaetetes sponge abundantly represented, indeed); and trilobites (on their way out, geologically speaking; along with fully 90 percent of all life on Earth, trilobites would go extinct at the conclusion of the Permian Period, some 48 million years after providing their remains in the Kansas late Pennsylvanian sedimentary rocks). The stratified sequence from which such an astounding abundance and diversity of late Pennsylvanian fossil forms derives is considered within earth science communities the world-over a genuinely classic association of cyclothemic (repetitive alternating between marine and non-marine coal-bearing facies) limestones, shales, and sandstones whose formalized stratigraphic nomenclature has been committed to fond memory by many a student of Kansas Paleozoic Era paleontology. Within North America, the late Pennsylvanian is officially divided into two great subdivisions: the Missourian Stage (early late Pennsylvanian--307 to 305 million years ago) --which in Kansas is on average roughly 650 feet thick--and the Virgilian Stage (latest late Pennsylvanian--305 to 299 million years ago), approximately 1,200 feet thick throughout its Kansas stratigraphic development. A more precise resolution of relative geologic ages of Kansas late Pennsylvanian rocks is established by further dividing each stage into three major groups. That is to say, in ascending order of geologic time (oldest to youngest) the Missourian Stage gets additionally separated into three more categories: the Pleasanton Group (307-306.5 million years); the Kansas City Group (306.5 to 305.5 million years); and the youngest Lansing Group (305.5 to 305 million years). And the succeeding Virgilian Stage receives the following partitioning: the Douglas Group (305 to 303 million years); the Shawnee Group (303 to 301 million years); and the Wabaunsee Group (301 to 299 million years). Above the Wabaunsee occur rocks of Permian age, the final formally established geologic Period of the Paleozoic Era, which ended 251 million years ago. From the instant that strata assigned to the Wabaunsee Group stopped accumulating, 299 million years ago, 90 percent of life on Earth had 48 million years to continue to exist, before it ceased to exist. The six late Pennsylvanian Groups that constitute the Missourian and Virgilian Stages contain numerous geologic rock formations, many separated once again by stratigraphers into distinct mappable subunits called "members," whose remarkably persistent carbonate and clastic lithologies can be traced for hundreds of miles across Kansas and contiguous Midwestern US states; indeed, not a few limestone intervals but a foot thick, or less, remain geologically obvious mappable intervals no matter where they outcrop in Kansas, Oklahoma, Nebraska, and Iowa--for example, from extreme northernmost state localities, to their southern boundaries. Within Kansas, those Missourian and Virgilian-age sedimentary accumulations of 307 to 299 million years ago reach their ultimate paleontologic deveolopment, providing an unprecedented supply of reliably abundant and diverse latest Pennsylvanian fossil resources: Paleontological prizes awaiting discovery in many of the interbedded marine limestone and shale units include: extraordinarily well-preserved invertebrate animals from every major zoological division; fascinating algal developments (peculiar "biscuit" and nodular kinds, plus intricate stromatolitic varieties); beaucoup bony fish skeletal elements; and sensational shark teeth. In the non-marine detrital deposits observed in stratigraphic relationships with marine-originated phases of the late Pennsylvanian cyclothems, many additional spectacular fossil occurrences await discovery--among them: paleobotanical constituents (leaves, seeds, and woody structures of plants); commerical coal deposits, within which fern and horsetail "trees" have been preserved upright, in their original standing positions); paleoentomological preservations (the insects); and terrestrial vertebrate material (amphibians, reptile-like amphibians, reptiles and mammal-like reptiles). Here is the complete list of traditionally recognized Stages, Groups, Formations, and Members used for rocks of late Pennsyvanian geologic age in Kansas: Traditional Kansas Late Pennsylvanian Stratigraphy : The Missourian Stage (307 to 305 million years ago) consists of the following Groups and subunits: Pleasanton Group (307-306.5 million years), which includes the following subunits: Seminole Formation (Hepler Sandstone Member, South Mound Shale Member); Checkerboard Limestone; and the Tacket Formation. Kansas City Group (306.5-305.5 million years), which includes the following subunits: Heartha Limestone (Critzer Limestone Member, Mound City Shale Member, Sniabar Limestone Member); Ladore Shale; Swope Limestone (Middle Creek Limestone Member, Hushpuckney Shale Member, Bethany Falls Limestone Member); Galesburg Shale (Dodds Sandstone Member); Dennis Limestone (Canville Limestone Member, Stark Shale Member, Winterset Limestone Member); Cherryvale Shale (Fontana Shale Member, Block Limestone Member, Wea Shale Member, Westerville Limestone Member, Quivira Shale Member); Drum Limestone (Dewey Limestone Member, Corbin City Limestone Member); Chanute Shale (Noxie Sandstone Member, Cottage Grove Sandstone Member); Iola Limestone (Paola Limestone Member, Muncie Creek Shale Member, Raytown Limestone Member); Liberty Memorial Shale; Wyandotte Limestone (Frisbie Limestone Member, Quindaro Shale Member, Argentine Limestone Member, Island Creek Shale Member, Farley Limestone Member); and the Bonner Springs Shale. Lansing Group (305.5-305 million years), which includes the following subunits: Plattsburg Limestone (Merriam Limestone Member, Hickory Creek Shale Member, Spring Hill Limestone Member); Villas Shale; and the Stanton Limestone (Captain Creek Limestone Member, Eudora Shale Member, Stoner Limestone, Cheyenne Creek Sandstone Bed (locally), Hafer Run Shale Bed (locally), Onion Creek Sandstone Lentil (locally), Rock Lake Shale Member, South Bend Limestone Member). The Virgilian Stage (305 to 299 million years ago) consists of the following Groups and subunits: Douglas Group (305-303 million years), which includes the following subunits: Stranger Formation (Weston Shale Member, Iatan Limestone Member, Tonganoxie Sandstone Member, Westphalia Limestone Member, Vinland Shale Member); and the Lawrence Formation (Haskell Limestone Member, Bobbins Shale Member, Ireland Sandstone Member, Amazonia Limestone Member). Note: A recent revision places the beginning of the Virgilian Stage at the base of the Haskell Limestone in the Douglas Group--based on first appearance of a specific conodont species; that revision is here rejected in favor of the traditional placement of the Virgilian (beginning at the base of the Weston Shale Member of the Stranger Formation). Shawnee Group (303-301 million years), which includes the following subunits: Oread Limestone (Toronto Limestone Member, Synderville Shale Member, Leavenworth Limestone Member, Heebner Shale Member, Plattsmouth Limestone Member, Huemader Shale Member, Kereford Limestone Member); Kanwaka Shale (Jackson Park Shale Member, Clay Creek Limestone Member, Stull Shale Member); Lecompton Limestone (Spring Branch Limestone Member, Doniphan Shale Member, Big Springs Limestone Member, Queen Hill Shale Member, Beil Limestone Member, King Hill Shale Member, Avoca Limestone Member); Tecumseh Shale; Deer Creek Limestone (Ozawkie Limestone Member, Oskaloosa Shale Member, Rock Bluff Limestone Member, Larsh and Burroak Shale Member, Ervine Creek Limestone Member); Calhoun Shale; and the Topeka Limestone (Hartford Limestone Member, Iowa Point Shale Member, Curzon Limestone Member, Jones Point Limestone Member, Sheldon Limestone Member, Turner Creek Shale Member, Du Bois Limestone Member, Holt Shale Member, Coal Creek Limestone Member). Wabaunsee Group (301-299 million years), which includes the following subunits: Severy Shale; Howard Limestone (Bachelor Creek Limestone Member, Aarde Shale Member, Wauneta Limestone Member, Shangai Creek Shale Member, Church Limestone Member, Winzeler Shale Member, Utopia Limestone Member); Scranton Shale (White Cloud Shale Member, Happy Hollow Limestone Member, Cedar Vale Shale Member, Rulo Limestone Member, Silver Lake Shale Member); Bern Limestone (Burlingame Limestone Member, Soldier Creek Shale Member, Wakarusa Limestone Member); Auburn Shale; Emporia Limestone (Reading Limestone Member, Harveyville Shale Member, Elmont Limestone Member); Willard Shale; Zeandale Limestone (Tarkio Limestone Member, Wamego Shale Member, Maple Hill Limestone Member); Pillsbury Shale; Stotler Limestone (Dover Limestone Member, Dry Shale Member, Grandhaven Limestone Member); Root Shale (Friedrich Shale Member, Jim Creek Limestone Member, French Creek Shale Member); and the Wood Siding Formation (Nebraska City Limestone Member, Plumb Shale Member, Grayhorse Limestone Member, Pony Creek Shale Member, Brownville Limestone Member). Brief Editorial Comment Note: A year 2013 study that proposes placement of the Pennsylvanian-Permian border in rocks situated above the Brownville Limestone Member (latest Pennsylvnanian) and overlying Towle Shale Member of the Onaga Shale (lowermost Permian), based on conodont stratigraphy, is in my opinion completely unaccepatable and is here rejected. Similarly, the rather recent idea that the Admire Group and part of the Council Grove Group should now be placed in the late Pennsylvanian is also here rejected. Still and all, I recognize the need to present both sides here. The year 2013 revision of Kansas late Pennsylvanian stratigraphy: