In the backcountry wilds of Nevada lie two truly classic Early Triassic ammonoid localities. Both sites yield innumerable, beautifully preserved ammonoids--an extinct order of cephalopods--in what geologists, stratigraphers and fossil cephalopod researchers alike refer to as the Lower Triassic Thaynes Formation, roughly 240 million years old. The Thaynes is exposed at several localities in the rugged mountain ranges of the Great Basin, yet it is nowhere as reliably fossiliferous as its stratigraphic development at two specific, classic exposures in Nevada. Each of the Thaynes localities is highly regarded among ammonoid specialists, of course--and both are visited rather frequently by paleontologists the world-over--but one of those two specific fossil sites, the place that happens to produce the most prolific numbers of and best-preserved cephalopods, is not only the finest Early Triassic ammonite-bearing site in North America, it is also one of the great Mesozoic Era cephalopod horizons in the United States, in general--and this, despite the fact that the overall aerial outcrop of fossiliferous sedimentary rock is confined to a meager few hundred feet of limestone and shale deposited approximately 240 million years ago in a vast tropical sea. The entire section lies within what ammonoid enthusiasts call the Meekoceras beds--a unit of cephalopod-bearing rocks in which the ammonoid Meekoceras gracilitatus is the most distinctive and characteristic specimen.

What makes that single, specific ammonoid locality so special in a paleontological sense is that nowhere in North America are the world-famous Meekoceras beds exposed through anywhere near the thickness that they are at the fossil-rich section. Through roughly 175 feet of exposed strata, abundant ammonoids representing the Meekoceras beds can be found. At the most fossiliferous and famous of the Early Triassic geologic sections, the extinct cephalopods occur in three of the seven limestone beds in the lowermost portions of Lower Triassic Thaynes Formation. Above that principally carbonate interval, the Thaynes consists of several hundred feet of thin-bedded grayish brown to tan shales in which organic remains of any kind are completely absent. Recent geologic studies, though, have demonstrated that the fossiliferous section consists of several faulted, fractured and vertically displaced blocks, and at least one of the blocks is overturned. The upshot here is that, contrary to the opinion expressed by early geological studies, there is only one ammonoid-bearing horizon at the locality, not several separate zones as previously determined--yet, that zone can still be correlated with several other notable Meekoceras occurrences worldwide, places such as the Olenek-Lena River Basin in Siberia; Okhostsk-Kolyma Land, Siberia; Japan; Kwangai, China; Timor; New Zealand; Himalayas, India; Salt Range, Pakistan; Barabanja, Madagascar; northern Caucasus Mountains; Arctic Canada and Yugoslavia.

At the most-special of ammonoid-bearing localities, the uppermost and youngest fossiliferous bed in the Thaynes, member "g", consists of 12 feet of gray limestone that tends to weather into shades of dark brown. It is a fine to medium-crystalline carbonate unit characterized by thick to irregular bedding, with fragmental and complete ammonoid conchs throughout. While the cephalopods are perhaps not as well preserved as in the oldest member at the measured section, at least eight species of ammonoids have been described from the rich interval, including Juvenites septentrionalis, Owenities koeneni, Owenoites stokesi, Parannanites mulleri, Pseudosageceras multilobatum, Meekoceras gracilitatus, Flemingites russeli, and Wyomingites arnoldi.

Unit "f", just below the fossiliferous "g" member, is a barren section of fine to medium ,crystalline light gray limestone some 48 feet thick; it is difficult to distinguish the two from a distance, but the uniformly unfossilferous nature of "f" suggests that if you come upon it in the field, you should walk up section a short distance, through the barren carbonates, to intersect the productive limestones of member "g" above it.

The next oldest unit in the Thaynes section, member "e" is a rusty-brown weathering, fine to medium crystalline limestone roughly 45 feet thick. Here can be found abundant remains of a genuine "living fossil"--the inarticulate brachiopod called Lingula, which is considered by most paleontologists to represent one of the great survivors of geologic time, a species that has persisted through the eons when many other, perhaps more glamorous creatures such as the dinosaur, the trilobite and the ammonite vanished from Earth many millions of years ago. Resembling a slender fingernail, Lingula first appears in the fossil record during the Early Cambrian Period, approximately 540 million years ago. It has survived, unchanged in physical appearance, for all that time.

Immediately below the productive Lingula zone lies the second ammonoid-rich layer, unit "d". It is a fine to medium-crystalline light-gray limestone, massively bedded with slabby partings, some 15 feet in thickness. It is everywhere crammed with plentiful cephalopodal remains, mostly fragmental, but the coquinoid nature of member "d" keeps many collectors busy for hours at a time, gently cracking the organic-rich carbonates to free the prized ammonoids within. Kummel and Steele identified eight species of ammonoids from the horizon: Juvenites septentrionalis, Aspenites acutis, Owenites koeni, Inyoites stokesi, Paranannites mulleri, Meekoceras gracilitatus, Wyomingites aplanatus, and Preflorianites toulai.

Units "c" and "b" are both poorly exposed--and unfossiliferous. They have a combined thickness of roughly 30 feet, consisting of pale gray limestone and occasional micaceous calcareous shales that tend to weather into platy slabs.

But the underlying unit "a", which reaches a maximum development of some 33 feet, is abundantly fossiliferous with both broken and complete cephalopods. As a matter of fact, approximately half or more of the light-gray, brown-weathering limestone, characterized by frequent limonitic flecks and partings, is composed of ammonoid remains. It is, indeed, a stunning deposit that has been visited by innumerable fossil collectors over the past decade. As a consequence, horizon "a" has suffered a noticeable decline in outstanding ammonoid specimens remaining to be collected; the perfect fossils have become increasingly difficult to find, especially the larger, showy shells, several inches in diameter, for which commercial dealers pay top dollar. There is obviously no way to prevent commercial fossil collectors from visiting the area, but one can only make the observation that if the trend continues, within three to five years there won't be much left to find there except unidentifiable fragments. Member "a" of the Thaynes Formation is justifiably a world-famous ammonoid deposit; some 23 species have been described from it, including Dieneroceras (three species), Xenocelities (two species), Juvenites (two species), Meekoceras gracilitatus, Hemiaspinites obtusus, Flemingites russeli, Anaflemingites silberlingi, Preflorianites toulai, Pseudospidites wheeleri, Owenites koeneni, Paranannites apenensis, Prophingites slossi, Parussuria compressa, Lanceolites compactus, Aspenites acuts, Wyomingites whiteanus, Arctoceras tuberculum, Arctoprionites sp. and Pseudosageceras multilobatum.

A second major Early Triassic ammonoid also occurs in Nevada. While not as world-famous as the primary locality just discussed, it does bear abundant, nicely preserved cephalopods of identical geologic age as those found elsewhere in the Thaynes Formation of Nevada--though curiously enough, the remote, yet accessible area apparently has been visited far less frequently by paleontology enthusiasts: at last visit the fossiliferous section was still in essentially pristine condition, even though the ammonoidiferous horizon--amateurs call it the Meekoceras beds, while professional ammonite specialists refer to the same series of fossil-bearing strata as the Tardus and Romunderi Zones--has been known to fossil hunters since at least the late 1800s. Famed ammonoid specialist James Perrin Smith visited the locality in the early 1900s and took away loads of identifiable cephalopods; of course, sporadic numbers of fossil enthusiasts have since found their way to the productve deposits, including a smattering of commercial collectors (who for the benefit of all conscientious collectors must keep their distance, or the Bureau of Land Management will surely close it all down, enacting severe restrictions on who can keep what they find there)--yet, even after decades of semi-regular visitation the area remains rich with well preserved Early Triassic ammonoids, roughly 240 million years old. The ammonoids occur, of course, in the Lower Triassic Thaynes Formation, which is sporadically exposed throughout a specific geographic area of Nevada. In California, noteworthy fossiliferous outcrops of ammonoid-bearing Early Triassic strata also occur at Union Wash (Inyo County, in the shadows of Mount Whitney; the ammonoids there can be found in the Union Wash Formation).

Both fossil localities in the Early Triassic Thaynes Formation described here provide collectors with numerous well-preserved invertebrate animal remains: ammonoids and braciopods from the Lower Triassic Thaynes Formation. They are remote localities, but a system of well-graded dirt roads provides surprisingly easy access to the fossil zones. Most conventional cars in perfect working order should have no difficulty reaching the productive sites.

At the Nevada ammonoid zones in the Early Triassic Thaynes Formation, it is intriguing to realize that as you hold in your hand an ammonoid specimen collected from the famous Meekoceras beds, an identical species of extinct cephalopod may be weathering out thousands of miles away, in China, in Madagascar or in Siberia--a species that swam through the same Mesozoic sea at an identical moment in geologic time, some 240 million years ago, is now preserved on distant continents.