Michael A. Murphy

Time-rock model for Siluro-Devonian continental shelf, western United States

The carbonate shelf, shelf edge, and outer shelf basin were the sites of deposition of a facies complex that shifted in response to transgressive-regressive (T-R) cycles. In the Silurian-Lochkovian, three T-R cycles are identified, and seven are identified from mid–Lower Devonian (Pragian) to high Upper Devonian (middle Famennian). The last of these produced a thick, upward-deepening sequence truncated above by a Famennian-lower Kinderhookian hiatus, due to foreland effects of the Antler orogeny. The middle and upper members of the Pilot Shale compose an eighth cycle, which spans the Devonian-Mississippian boundary on the carbonate shelf. Most of the short-lived T-R cycles resulted from rapid deepening and progradation of the carbonate-shelf edge. Exceptions occurred during the late Early Devonian, when the carbonate-shelf edge was a ramp, and during the Taghanic and Frasnian onlaps, when transgressions are known to have been strong. The dolomite front tended to coincide approximately with the carbonate-shelf edge, but it was situated cratonward during extensive onlaps and basinward during the pre–Middle Devonian regression.

Early Devonian vertebrate microfossils from the Simpson Park Range, Eureka County, Nevada

Vertebrate microfossils as minor constituents of acid-etched limestone residues in the Lochkovian (Lower Devonian). This paper describes the fish taxa from the Simpson Park Range section at Coal Canyon, central Nevada. These include thelodont scales of the family Nikoliviidae; heterostracan scales; acanthodian scales, platelets, and spines of Nostolepis type, Gomphonchus type, Acanthodes type, Machaeracanthus type, and climatiid type; placoderm scales of buchanosteid and radotinid types; and the shark, Polymerolepis whitei.

Evidence for Late Devonian movement within the Roberts Mountains allochthon, Roberts Mountains, Nevada

New evidence allows better understanding of the sequence of formations and emplacement events during the Antler orogeny in the Roberts Mountains, Nevada. Lower to lower Upper Devonian strata were deformed and unconformably overlain by middle Upper Devonian siliceous shale and chert somewhere west of their present positions in the Roberts Mountains. During a younger episode of deformation, Vinini Group (Ordovician) rocks were thrust over the Devonian rocks that were still west of the present Roberts Mountains at the time of thrusting. Concurrent with this younger thrusting, the ?Webb formation accumulated at the toe of the moving allochthon in the Early Mississippian. As the basal Roberts Mountains thrust stepped eastward, it brought the whole allochthon to its present site above the ?Webb sometime in the Early Mississippian.

Morphometric study of the platform elements of Amydrotaxis praejohnsoni n. sp. (Lower Devonian, conodonts, Nevada)

The platform element of the conodont Amydrotaxis praejohnsoni n. sp. shows statistically significant morphological changes from the base to the top of the delta Zone (Lower Devonian). The changes occur particularly in mean denticle number, height and character of the anterior denticles, and shape of the basal cavity. The earliest forms have fewer denticles ( = 7.1), an enlarged, high anterior denticle, and a broadly flared posterior basal cavity, whereas late forms have more denticles ( = 9.4), equal-sized anterior denticles, and a narrow posterior basal cavity. There is no stasis phase in the species history, but rather a mosaic pattern in which the observed changes in the character states are seemingly independent of each other and proceed at variable rates.

Stratigraphy and Correlation of the Lower Nevada Group (Devonian) North and West of Eureka, Nevada

The McColley Canyon Formation, Lower Devonian of central Nevada, is divisible into three members, the Kobeh, Bartine, and Coils Creek in ascending order. The two lower members have been mapped in the Sulphur Springs Range, Roberts Mountains, Lone Mountain, and Table Mountain. The Coils Creek Member has been mapped in the latter three ranges, but its stratigraphic position is occupied by the lower Union Mountain Formation in the Sulphur Springs Range. This correlation indicates a late Early Devonian age for the lower part of the Union Mountain Formation. The Coils Creek Member bears the Elythyna fauna in its upper part, which, though small, is distinct trom the Eurekasfirifer pinvonensis Zone fauna below and the Leptathyris circula above.

A NEW WORLD OCCURRENCE OF NOTIDANODON LANCEOLATUS (CHONDRICHTHYES, HEXANCHIDAE) AND COMMENTS ON HEXANCHID SHARK EVOLUTION

Notidanodon lanceolatus Woodward is reported from Late Aptian strata of northern California. This specimen, the oldest fossil cow shark (Hexanchidae) in the New World, greatly extends the geographic distribution of this species and confirms the eurytopic distribution of this genus. We suggest that cow shark teeth evolve in an orderly sequence in which the mesial edge of the tooth is at first smooth (Notidanus muensteri), then serrate (Notidanus serratus, Notorynchus aptiensis), and finally dentate (Notidanodon lanceolatus).

Statistical study of Ozarkodina excavata (Branson and Mehl) and O. tuma Murphy and Matti (Lower Devonian, delta Zone, conodonts, Nevada)

Denticle number per unit of length in the (P) element of contemporaneously occurring Ozarkodina excavata (Branson and Mehl) and 0. tuma Murphy and Matti is a characteristic that shows that these taxa belong to two discrete species. Their morphological ranges with respect to this character do not overlap. Ozarkodina tuma has a short range within the delta Zone (Lower Devonian) of the central Great

Two occurrences of the genus Pictetia (Early Cretaceous, Albian, Ammonoidea) in California

r-TWO specimens of the Cretaceous genus Pictetia Uhlig, 1883, have been found in the Cottonwood District, northern California, the first record of this genus in North America. The larger specimen is a septate whorl fragment from the Brewericeras hulenense zone that is associated with Douvilleiceras mammillatum. It is identified as Pictetia sp. The smaller specimen is a septate fragment of one and a half whorls from the Oxytropidoceras packardi zone associated with Cleoniceras. It is identified with the type species, Pictetia astieriana Orbigny, 1842, previously recorded from Europe. A review of the genus Pictetia suggests that species assigned to the genus have an open coil with a rounded dorsum. The occurrences of these Tethyan elements in the Albian fauna of the Cottonwood District suggest easy communication for many Cretaceous taxa between northern California and the Tethyan realm of Europe, the Caucasus, and Madagascar.

Morphometric study of the genus Ancyrodelloides (Lower Devonian, conodonts), central Nevada

This paper presents a morphometric study of the conodont genus Ancyrodelloides. It is one of a series of such papers whose goal is to increase the precision of correlation within the Lower Devonian by refining the taxonomic basis of its biostratigraphic units. Ancyrodelloides species are confined to the delta Zone and may be used to divide it into three parts. Morphometrics verify the species rank of A. eleanorae, A. limbacarinatus, A. trigonicus, and A. transitans. Ancyrodelloides delta and A. omus are retained as species on qualitative grounds, but need larger samples for statistical evaluation. Ancyrodelloides asymmetricus and A. kutscheri are classified as varieties, but lack adequate samples.

THE PAPILIOPHYLLIDAE (LOWER DEVONIAN RUGOSA): THEIR SYSTEMATICS AND REINTERPRETED BIOSTRATIGRAPHIC VALUE IN NEVADA

Abstract Field work has greatly increased the number of well-dated papiliophyllid corals available from Nevada. The established range of the family is expanded from Pragian and lower Emsian to Pragian and almost the entire Emsian. Ranges of species are calibrated against Johnson faunal intervals and a revised Pragian and lowermost Emsian conodont zonation proposed by Murphy for Nevada. Study of all reposited material has led to some revision of every member of the family. Eurekaphyllum, previously imperfectly known from a single specimen of vague stratigraphic origin, is shown to be a useful upper Emsian index. Nine reported occurrences of the family in Europe and Asia are re-examined and, except for a possible occurrence on Novaya Zemlya, all are rejected. The three named genera of the family are apparently endemic to the southwestern North American craton. Papiliophyllum elegantulum asymmetricum new subspecies, P. murphyi new species and Eurekaphyllum vescum new species are described by Pedder.