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Late Griesbachian (early Triassic) ammonoids and nautiloids from the Dinwoody Formation at Crittenden Springs, Elko County, Nevada.


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Abstract—We document a relatively small but very important late Griesbachian ammonoid and nautiloid assemblage from the Dinwoody Formation at Crittenden Springs, Elko County, Nevada. This discovery represents the first significant report of late Griesbachian ammonoids in the low-paleolatitudes of eastern Panthalassa, and it also signifies the first report of Wordieoceras wordiei and two co-occurring taxa outside of the Boreal Realm. This similarity in ammonoid faunas, irrespective of paleolatitude, provides support for the concept of weak latitudinal diversity gradients following the end-Permian extinction. The finding is even more noteworthy given the Dinwoody Formation’s reputation for poor fossil preservation and a near complete absence of documented and identifiable ammonoid and nautiloid occurrences. Consisting of four taxa of which two are newly described, the ammonoid fauna includes Wordieoceras wordiei (Spath), Kyoktites cf. K. hebeiseni Ware and Bucher, Wordieoceras mullenae n. sp. and a new taxon belonging to the Mullericeratidae family, Ophimullericeras paullae n. gen., n. sp. The nautiloids are attributed to a newly described species, i.e., Xiaohenautilus mulleni n. sp., a genus heretofore unknown in eastern Panthalassa but commonly reported from the late Griesbachian of South Primorye and the late Griesbachian/early Dienerian of South China.
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Bulletin 86
New Mexico Museum of Natural History & Science
A Division of the
Albuquerque, 2021
Bulletin 86
New Mexico Museum of Natural History & Science
A Division of the
New Mexico Museum of Natural History & Science
Albuquerque, 2021
Department of Cultural Aairs
Debra Garcia y Griego, Secretary
Margaret Marino, Executive Director
Michelle Lujan Grisham, Governor, State of New Mexico, ex ocio
Margaret Marino, Executive Director, ex ocio
Gary Friedman, President
Leonard Duda
Peter F. Gerity, Ph.D.
Laurence Lattman, Ph.D.
Viola Martinez
John Montgomery, Ph.D.
Kristina Nguyen
Laura Smigielski-Garcia
Matt Tracy
Steve West
Cover illustration: Crittenden Springs Early Triassic (Late Griesbachian) ammonoids and nautiloids:
1-Wordieoceras wordiei (Spath), 2-Wordieoceras wordiei (Spath), 3-Ophimullericeras paullae n. gen.,
n. sp., 4-Xiaohenautilus mulleni n. sp., 5- Xiaohenautilus mulleni n. sp., apertural view, 6-Kyoktites cf.
K. hebeiseni Ware and Bucher, 7- Ophimullericeras paullae n. gen., n. sp., 8-Wordieoceras mullenae
n. sp., 9- Xiaohenautilus mulleni n. sp., 10- Xiaohenautilus mulleni n. sp., apertural view
Associate editor for this bulletin: Spencer G Lucas
Original Printing
ISSN: 1524-4156
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Spencer G. Lucas New Mexico Museum of Natural History and Science,
Albuquerque, NM, USA (NMMNHS)
Adrian P. Hunt Flying Heritage Colection, Everett, WA, USA
Jason L. Malaney NMMNHS
Lawrence H. Tanner Le Moyne College, Syracuse, NY, USA
Asher J. Lichtig NMMNHS
Guillermo Alvarado Asociación Costarricense de Geotecnica, San José, Costa Rica
Marco Avanzini Museo Tridentino di Scienze Naturali, Trento, Italy
David Berman Carnegie Museum of Natural History, Pittsburgh, PA, USA
Brent Breithaupt Laramie, WY, USA
William DiMichele National Museum of Natural History, Washington, D.C., USA
John R. Foster Utah Field House of Natural History State Park Museum , Vernal,
Gerard Gierlinski Polish Geological Institute, Warsaw, Poland
Jean Guex University of Lausanne, Lausanne, Switzerland
Steven E. Jasinski State Museum of Pennsylvania, Harrisburg, PA, USA
Hendrik Klein Saurierwelt Paläontologisches Museum, Neumarkt, Germany
Karl Krainer University of Innsbruck, Innsbruck, Austria
Martin G. Lockley University of Colorado at Denver, Denver, CO, USA
Gary S. Morgan NMMNHS
Donald R. Prothero Occidental College, Los Angeles, CA, USA
Silvio Renesto Università degli Studi dell’Insubria, Varese, Italy
Joerg W. Schneider Technical University BergAkademie of Freiberg, Freiberg, Germany
Jingeng Sha Nanjing Institute of Geology and Palaeontology, Nanjing, China
Dana Ulmer-Scholle NM Bureau of Geology & Mineral Resources, Socorro, NM, USA
Sebastian Voigt Urweltmuseum GEOSKOP/Burg Lichtenburg, Thallichtenberg,
Bruce J. Welton NMMNHS
Ralf Werneburg Naturhistorisches Museum Schloss Bertholdsburg, Schleusingen,
Richard S. White, Jr. International Wildlife Museum, Tucson, AZ, USA
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Abstract ..............................................................................................................................................................................
Introduction .......................................................................................................................................................................
Locality and geological context ........................................................................................................................................
Location ..............................................................................................................................................................
Dinwoody Formation: History and Depositional Basin Setting .........................................................................
Lithostratigraphic Divisions .........................................................................................................................................
Depositional Environment ............................................................................................................................................
Depositional Basin Outcrops ........................................................................................................................................
Study Area Outcrops ....................................................................................................................................................
Location of Study Section and Measured Sections of Other Workers .........................................................................
Description of Ammonoid and Nautiloid-Bearing Beds: Attitude and Topography ....................................................
Ammonoid and nautiloid preservation ..............................................................................................................................
Induan ammonoid biostratigraphy .....................................................................................................................................
Western USA Basin .......................................................................................................................................................
Mid-Paleolatitude Eastern Panthalassa ........................................................................................................................
Boreal Realm ................................................................................................................................................................
Northern Indian Margin ................................................................................................................................................
South China ..................................................................................................................................................................
South Primorye .............................................................................................................................................................
Early Triassic nautiloid biostratigraphy ............................................................................................................................
Griesbachian conodont biostratigraphy at Crittenden Springs ..........................................................................................
Systematic Paleontology ...................................................................................................................................................
Class Cephalopoda Cuvier, 1797 ..........................................................................................................
Order Ceratitida Hyatt, 1884 ..................................................................................................
Superfamily Meekoceratoidea Waagen, 1895 ........................................................................
Family Ophiceratidae Arthaber, 1911 ....................................................................................
Genus Wordieoceras Tozer, 1971 ............................................................................
Wordieoceras wordiei (Spath, 1930) ...........................................
Wordieoceras mullenae n. sp. .....................................................
Genus Kyoktites Ware and Bucher, 2018 .................................................................
Kyoktites cf. K. hebeiseni Ware and Bucher 2018 ......................
Family Mullericeratidae Ware et al., 2011 .............................................................................
Genus Ophimullericeras n. gen. ..............................................................................
Ophimullericeras paullae n. sp. ..................................................
Order Nautilida Agassiz, 1847 ...............................................................................................
Superfamily Trigonoceratoidea Hyatt, 1884 ..........................................................................
Family Grypoceratidae Hyatt, 1900 .......................................................................................
Genus Xiaohenautilus Xu, 1988 ..............................................................................
Xiaohenautilus mulleri n. sp. ......................................................
Conclusions .......................................................................................................................................................................
Acknowledgements ...........................................................................................................................................................
References .........................................................................................................................................................................
Jenks et al., 2021, Late Griesbachian, Dinwoody Formation, Ammonoids and Nautiloids. New Mexico Museum of Natural History and Science Bulletin 86.
Jenks et al., 2021, Late Griesbachian, Dinwoody Formation, Ammonoids and Nautiloids. New Mexico Museum of Natural History and Science Bulletin 86.
11134 Johnson Ridge Lane, West Jordan, UT 84084, e-mail:; 2Osaka Museum of Natural History, 1-23 Nagai Park,
Higashi-sumiyoshi-ku, Osaka 546-0034, Japan, e-mail:; 3Museum für Naturkunde, Magdeburg, Otto-von-Guericke-Str.
68-73, 39104 Magdeburg, Germany, e-mail:; 4Department of Geology and Paleontology, National Museum
of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan, e-mail:; 5Biogéosciences, UMR 6282 CNRS,
Université Bourgogne Franche-Comté, 21000 Dijon, France, e-mail:;
6140 South 700 East, Spanish Fork, UT 84660
Abstract—We document a relatively small but very important late Griesbachian ammonoid and
nautiloid assemblage from the Dinwoody Formation at Crittenden Springs, Elko County, Nevada. This
discovery represents the rst signicant report of late Griesbachian ammonoids in the low-paleolatitudes
of eastern Panthalassa, and it also signies the rst report of Wordieoceras wordiei and two co-occurring
taxa outside of the Boreal Realm. This similarity in ammonoid faunas, irrespective of paleolatitude,
provides support for the concept of weak latitudinal diversity gradients following the end-Permian
extinction. The nding is even more noteworthy given the Dinwoody Formation’s reputation for poor
fossil preservation and a near complete absence of documented and identiable ammonoid and nautiloid
occurrences. Consisting of four taxa of which two are newly described, the ammonoid fauna includes
Wordieoceras wordiei (Spath), Kyoktites cf. K. hebeiseni Ware and Bucher, Wordieoceras mullenae
n. sp. and a new taxon belonging to the Mullericeratidae family, Ophimullericeras paullae n. gen.,
n. sp. The nautiloids are attributed to a newly described species, i.e., Xiaohenautilus mulleni n. sp., a
genus heretofore unknown in eastern Panthalassa but commonly reported from the late Griesbachian
of South Primorye and the late Griesbachian/early Dienerian of South China.
The Permian-Triassic mass extinction some 252 million
years ago, the most severe eradication of life in the Phanerozoic,
resulted in the disappearance of nearly 90% of all marine
species (Raup, 1979; Stanley, 2016). Although the ammonoids
and nautiloids survived, their diversity was severely diminished
from pre-extinction levels, with the ammonoids reduced to only
three surviving lineages (Brayard et al., 2007; Brayard and
Bucher, 2015; Dai et al., 2019). Quite remarkably, however,
and contrary to the suggestions of a delayed recovery by some
workers (Hallam, 1991; Tong et al., 2007; Chen and Benton,
2012), the ammonoids, together with a few other groups, i.e.,
conodonts and foraminifers, recovered their diversity following
this event much faster than other organisms (Brayard et al.,
2009; Song et al., 2011, 2013). Evidence of this recovery in the
ammonoid record, at least for the earliest part, i.e., the Induan,
and, in particular, the Griesbachian substage, is not all that
abundant, with occurrences limited to a few localities (Fig. 1C)
in the Boreal Realm (Arctic Canada [Tozer, 1967, 1971, 1994a],
East Greenland [Spath, 1930, 1935; Bjerager et al., 2006] and
NE Siberia [Dagys and Ermakova, 1996]), the Tethys (North
Indian Margin [NIM] [Zhang et al., 2017; Ware et al., 2018],
South China [Mu et al, 2007; Brühwiler et al., 2008; Dai et
al., 2019]) and South Primorye (Shigeta and Zakharov, 2009).
Until now, the ammonoid record for the Griesbachian in low-
paleolatitude eastern Panthalassa was virtually non-existent.
Recently, a relatively small, in situ late Griesbachian
ammonoid assemblage and several oat nautiloids in close
stratigraphic proximity were inadvertently discovered in the
Dinwoody Formation, while sampling for conodonts on the
north side of Long Canyon, a short distance east-northeast of
the well-known Crittenden Springs Smithian ammonoid site,
e.g., recently monographed by Jenks and Brayard (2018) (Fig.
2). While preservation is highly variable (Fig. 3), about half of
the ammonoid specimens retain fairly well-preserved diagnostic
features, i.e., whorl shape and suture lines, thus facilitating
reasonably accurate identication.
The newly reported ammonoid assemblage consists of
four taxa, of which two are newly described. Three of the taxa
have exclusive Boreal anities, i.e., Wordieoceras wordiei, W.
mullenae n. sp. and Ophimullericeras paullae n. gen., n. sp., the
latter rather loosely based on a somewhat dubious taxon from
East Greenland that Spath (1930, 1935) assigned to Ophiceras
(Lytophiceras) dubium. The fourth taxon, i.e., Kyoktites cf. K.
hebeiseni, is based on a poorly known taxon erected by Ware and
Bucher (2018a) from the latest Griesbachian/earliest Dienerian
of Spiti (India) and the Salt Range of Pakistan. Until now,
conrmed occurrences of Wordieoceras have been documented
only from the late Griesbachian of the Boreal Realm (Tozer,
1994a; Dagys and Ermakova, 1996; Bjerager et al., 2006).
The nautiloids, which comprise a newly described taxon,
Xiaohenautilus mulleni n. sp., consist of ve oat specimens
from a narrow stratigraphic interval (Figs. 4, 5) relatively close
to the ammonoid bed. Xiaohenautilus, erected by Xu (1988) for
late Griesbachian/early Dienerian taxa from South China (Mu
et al., 2007), also includes an additional taxon similar to the
present specimens, i.e., X. abrekensis Shigeta and Zakharov
2009, from Abrek Bay, South Primorye. Interestingly, the
apparent western Panthalassa anity of the nautiloids contrasts
with the Boreal anity of the ammonoid fauna. Conodont
diversity in the ammonoid-bearing section is rather low, and
not unexpectedly, none of the samples from the stratigraphic
proximity of the fossiliferous siltstone beds yielded conodonts.
However, samples from a bivalve coquina limestone bed ~50
m stratigraphically higher (201507a, b; Fig. 5) contained a few
typical Griesbachian-aged conodonts, i.e., Clarkina spp. and
Hindeodus spp.
The Griesbachian ammonoid site is located ~75 m
stratigraphically below the top of the Dinwoody Formation,
on a west-facing hillside (Fig. 2A-B) on the north side of Long
Canyon, ~ 230 meters east-northeast of the original classic
Crittenden Springs Smithian ammonoid site (Kummel and
Steele, 1962; Jenks, 2007; Jenks et al., 2010; Jenks and Brayard,
2018; Maekawa and Jenks, in press). This general area is located
~32 km north of Montello, Elko County, Nevada, and ~ 2.3 km
northeast of the abandoned ranch house at the north end of
Crittenden Reservoir (Fig. 1A).
Dinwoody Formation: History and Depositional Basin
The Dinwoody Formation, the oldest Triassic unit in the
Cordilleran western USA basin, was named and dened by
Blackwelder (1918), based on outcrops in Dinwoody Canyon
on the northeastern side of the Wind River Mountains near
Du Bois, Wyoming (Kummel, 1954; Paull, 1980). Deposited
unconformably on Permian strata during a rapid Early Triassic
FIGURE 1. A, Generalized map showing location of the Griesbachian ammonoid and nautiloid sites in the Dinwoody Formation
(indicated by black dot in Long Canyon) at Crittenden Springs. B, Location of Crittenden Springs area in relation to other western
USA Dienerian and Griesbachian localities mentioned in text: 1) Crittenden Springs, 2) Montpelier Canyon, 3) Sleight Canyon, 4)
Melrose, 5) Frying Pan Gulch, 6) Candelaria, 7) Willow Spring. Other Triassic exposures mentioned in text: 8) Immigrant Canyon,
9) Windemere Hills, 10) O’Neil Pass, 11) southern end of Pequop Range, 12) Dolly Varden Valley. C. Early Triassic paleoposition
of the western USA basin in relation to other world-wide localities discussed in text. (A to C modied from Jenks and Brayard,
FIGURE 2. A, Google Earth image showing location of Griesbachian ammonoid and nautiloid site (right arrow) in relation to
classic Smithian ammonoid site (left arrow) at Crittenden Springs. B, West-facing hillside with exposures of fossiliferous siltstone
bed (NMMNH L-12682) in erosional channel and about 4 m to the south on same hillside. Slope of hillside more or less matches
the dip angle of the beds.
FIGURE 3. West-facing hillside with exposures of fossiliferous siltstone beds, in A and C. Ammonoid phragmocone in B (NMMNH
P-81680, Wordieoceras mullenae n. sp.), arrow points to location in A. D (NMMNH P-81677, Wordieoceras wordiei), and E (poorly
preserved specimen, not collected) illustrate type of preservation, i.e., heavily corroded upper surfaces.
FIGURE 4. A, Gently sloping, east-facing hillside immediately west of ammonoid site with sampled beds demarcated. Nautiloids
(ve specimens) were found as oat within the 2.5 m- thick interval indicated by double-ended arrow (locality NMMNH L-12683)
between beds 5 (-1) and 5 (+1), e,g., in B, NMMNH P-81691, Xiaohenautilus mulleni n. sp. and C, NMMNH P-81692, Xiaohenautilus
mulleni n. sp. Of these sampled beds, only 5 (+2), a silty limestone bivalve coquina, yielded conodonts.
Dinwoody ammonoid section (this study)
Thaynes Group
Dinwoody Formation
Gerster Formation
Nautiloid ConodontsAmmonoids
Dark gray marl
Ammonoid bearing
limestone blocks
Bedded limestone
Limestone blocks
Thaynes Group
Dinwoody Formation
Lenticular limestone
Gerster Formation
Bivalve coquina/bed
Linguloid brachiopod coquina/bed
Permian Lower Triassic
Overturned Smithian ammonoid-bearing limestone blocks intermixed with 8-10 m
thick interval of unconsolidated marl and other sediments of uncertain age
[see Jenks and Brayard (2018) and Maekawa and Jenks (in press)].
Clarkina krystini
Clarkina griesbachiensis
Clarkina spp.
Clarkina taylorae
Clarkina carinata
Clarkina tulongensis
Hindeodus spp.
Merrillina spp.
Ramiform elements
Bellerophontoid gastropods
Kyokites cf. K. hebeiseni
Ophimullericeras paullae
n. gen., n. sp.
Wordieoceras wordiei
Wordieoceras mullenae
n. sp.
Xiaohenautilus mulleni
n. sp.
LC-6, 7
Clarkina carinata
Furnishius triserratus
Guangxidella bransoni
Discretella discreta
Conservatella conservativa
Novispathodus waageni
Ellisonia spp.
Merrillina sp.
[= Neospathodus peculiaris of Paull (1980)]
Segment B (Paull, 1980)
FIGURE 5. Columnar section showing stratigraphic occurrences of ammonoids, nautiloids, conodonts and bivalve/linguloid
coquina beds in the Dinwoody Formation study section. Also shown is the Segment B columnar section, the upper part of Paull’s
(1980) composite section, which is located only ~140 m north of the present study section.
marine transgression (Newell and Kummel, 1942; Paull and
Paull, 1994; Hofmann et al., 2013), the Dinwoody Formation is
overlain conformably either by basal rocks of the Thaynes Group
or by red beds of the Woodside Formation in the more easterly
areas (Paull, 1980). Sediments of the Dinwoody Formation
were deposited in the northern part of the Cordilleran western
USA basin, an elongate epicontinental marine basin, whose
axis extended in a northeasterly direction through east-central
Nevada, northwestern Utah and southeastern Idaho (Silberling,
1973; Collinson and Hasenmueller, 1978; Paull, 1980). The
Dinwoody sea, bounded on the south by an east-trending
structural high that bisected the western USA basin, extended
to the northeast through northeastern Nevada, south-central and
southeastern Idaho, and then northward in a wide band along the
Wyoming-Idaho border into southwestern Montana (Collinson
and Hasenmuller, 1978; Wardlaw et al., 1979: Paull, 1980; Carr
and Paull, 1983; Mullen, 1985; Caravaca et al., 2017). Initially,
the eastern shore of the Dinwoody sea bordered on the edge
of the craton, but it moved eastward during the Griesbachian
transgression as far as the Big Horn Mountains in north-central
Wyoming (Kummel, 1957; Collinson and Hasenmueller,
1978; Paull, 1980), before prograding back to the edge of
the western USA basin during late Dienerian time (Collinson
and Hasenmueller, 1978). According to Silberling (1973), the
western boundary of the Dinwoody sea in northeastern Nevada
probably shoaled against the Sonoma orogenic belt with an
opening to the Panthalassa Ocean at some point along the
margin, but very little is known about these orogenic sediments
in the region due to the lack of outcrops (Hofmann et al., 2013).
Lithostratigraphic Divisions
Newell and Kummel (1942) informally divided the
Dinwoody Formation in Wyoming into three lithostratigraphic
units, i.e., the basal siltstone, the Lingula zone and the Claraia
zone, but avoided extending this classication into other areas
until its usefulness could be tested (Hofmann et al., 2013).
Indeed, later work by Kummel (1954) in southeastern Idaho
indicated that these subdivisions were not widely recognizable.
Furthermore, Hofmann et al. (2013) in their survey of nine
Dinwoody Formation sections in southwestern Montana,
southeastern Idaho, western Wyoming and northern Utah, found
that the three units were dicult to recognize and of little value
other than in Wyoming. Lithologically, the Dinwoody Formation
generally consists of an interbedded complex of olive-gray to
tan, calcareous silty shale, brown to gray limestone and olive-
drab, calcareous siltstone (Paull, 1980). The deeper water, shale
facies component of these sediments accumulated in the Sonoma
Foreland Basin during early Dinwoody deposition, whereas
the siltstone and limestone facies buildup occurred during the
later stages (Collinson and Hasenmueller, 1978; Mullen, 1985).
Consequently, the Dinwoody Formation in the central part of
the basin, which encompasses the Crittenden Springs area,
is distinguished by a lower shaly unit and an upper siltstone
and limestone unit (Mullen, 1985). Accordingly, Paull (1980)
and Mullen (1985), both of whom extensively sampled the
Dinwoody Formation in the Long Canyon area for conodonts,
roughly divided the formation into two lithological units. The
lower unit, consisting mainly of poorly exposed, olive-gray
shales with a few thin, lenticular inter-beds of olive-grey, silty
limestone, contains abundant compressed bivalves (Claraia sp.)
in the lowermost portion of the shales (Mullen, 1985). Their
upper unit, while generally more resistant, is comprised of thin
to medium-bedded, gray calcareous siltstone and inter-bedded
thin to massive-bedded gray limestone, most of which contain
abundant bivalves and linguloid brachiopods (Mullen, 1985).
Weathered surfaces in the upper unit vary widely in color from
tan, gray, and brown to dark brown (Mullen, 1985).
Depositional Environment
In general, Paull (1980) based her interpretation of the
depositional environment of these rocks (wackestone-type
limestones as well as calcareous siltstones and shales) on the
facies belts of Wilson’s (1975) idealized carbonate model. That
is, the rocks likely represent a neritic shelf facies with good
current circulation and normal salinity, where water depth over
the shelf was quite shallow, i.e., probably only tens of meters,
but was below normal wave base, and sedimentation was fairly
uniform (Wilson, 1975; Paull, 1980). A few bivalve coquina
beds in the upper part of the formation hint at the existence
of tidal bars or shoals rising above the general level of the sea
oor (Wilson, 1975; Paull, 1980). Also indicative of a shelf
environment is the thin to thick bedding style combined with
the fairly wide range of rock colors resulting from variable
oxidizing and reducing conditions; the presence of sedimentary
structures, i.e., ripple marks and horizontal grazing traces, also
supports this interpretation (Wilson, 1975; Paull, 1980). Kummel
(1957), in his extensive faunal and lithofacies analysis of Lower
Triassic formations in the middle Rocky Mountain region, also
concluded that the Dinwoody Formation represents a shallow
shelf facies (Paull, 1980).
Depositional Basin Outcrops
Outcrops of the Dinwoody Formation, which occur in all
states originally covered by the Dinwoody sea (Fig. 1B), range
in thickness from ~30 m at the type locality (as redened by
Newell and Kummel, 1942) to ~740 m near the depo-center in
southeastern Idaho (Paull, 1980). In most outcrop areas, where the
formation is overlain by the Thaynes Group (sensu Lucas et al.,
2007), its uppermost limit is arbitrarily placed at the base of the
Meekoceras-bearing lower limestone member (or equivalents)
of the Thaynes Group (Paull, 1980). In the study area, however,
the typical lower limestone member of the Thaynes Group
is absent, and instead, the Dinwoody Formation is overlain
by an 8-10 m thick interval of unconsolidated sediments of
uncertain age (marls, thin-bedded, fractured siltstone debris
and unfossiliferous limestone boulders), which encompasses
the discontinuous and overturned Smithian ammonoid-bearing
blocks for which the Crittenden Springs locality is well known
(Jenks, 2007, Jenks et al., 2010; Jenks and Brayard, 2018;
Maekawa and Jenks, in press). The Dinwoody Formation is not
present in Triassic exposures to the west in the Windemere Hills
(Wilkins Ranch section of Clark, 1957) or the O’Neil Pass area
in the Snake Mountains (Clark, 1957; Paull and Paull, 1998)
and is absent to the south in several measured sections, e.g.,
southern end of Pequop Range and Dolly Varden Valley (Scott,
1954; Hose and Repenning, 1959; Collinson et al., 1976; Carr,
1981; Mullen, 1985). Exposures in Immigrant Canyon in the
Leach Range west of Montello represent the westernmost and
southernmost outcrops of the Dinwoody Formation in Nevada.
Study Area Outcrops
Lower Triassic marine strata, consisting of the Dinwoody
Formation (Griesbachian and Dienerian) and overlying Thaynes
Group (Smithian and Spathian) crop out just north of the
Long Canyon road and extend to the northeast for about 8 km,
covering an area of about 33 km2 (Clark, 1957; Mullen, 1985;
Jenks and Brayard, 2018). Mullen (1985) mapped the entire
area, dierentiating the following units, in ascending order:
Permian – undierentiated, Dinwoody Formation, and Thaynes
Group (Meekoceras limestone, black limestone, calcareous
siltstone and limestone, and Pentacrinus limestone). By far, the
calcareous siltstone and limestone unit of the Thaynes Group
covers the majority of the mapped area, especially the central
and northeastern portion. The area is heavily faulted, and,
according to Mullen (1985), the Dinwoody Formation is in
normal stratigraphic sequence with underlying Permian rocks at
only one location, which was chosen as the base of her measured
section. Elsewhere in the area, Permian rocks are either in
fault contact with the Dinwoody Formation, or the contact is
covered (Mullen, 1985). Nearly all the important outcrops of
the Dinwoody Formation are present within the southwestern
portion of the area, over a span stretching from the Long
Canyon road to a point ~4 km northeast of Long Canyon. A few
additional outcrops are present farther north and northeast, but
most are isolated, incomplete sections.
Location of Study Section and Measured Sections of Other
Mullen’s (1985) measured section (~395 m thick) is located
~3 km north of Long Canyon, whereas Paull’s (1980) composite
section (~305 m thick) consists of a 120 m thick lower part
(segment A) located ~1.25 km north of Long Canyon and a 185 m
thick upper part (segment B) located only ~0.28 km north of the
Long Canyon road. In contrast, the thickness of the Dinwoody
Formation in the immediate vicinity of the ammonoid discovery
site at the extreme southern end of the outcrop area, only a short
distance (~140 m) south of Paull’s upper section, is merely
~135 m. Thus, a sizeable portion (40 to 50 m) of the Dinwoody
Formation has been removed, most likely by concealed faulting,
near the southern end of the outcrop area. The lithology, color
and thickness of the various component beds of the formation
can vary greatly within a relatively short distance along strike,
plus the stratigraphic portion of the section that is covered varies
widely in the area of the Permian/Dinwoody contact. These
variances, combined with extensive faulting, much of which is
concealed, make it extremely dicult to nd and trace marker
beds or correlate beds within the above described units, other
than in a very general sense. Indeed, Paull (1985) commented
regarding these diculties and estimated that the lower and
upper parts of her composite section could possibly overlap by
as much as 20 meters.
Description of Ammonoid- and Nautiloid-Bearing Beds:
Attitude and Topography
The newly discovered ammonoids are preserved in a
westerly dipping, ~10 cm thick succession of calcareous shaly
siltstone beds (each 2-3 cm thick) exposed on a west-facing
hillside (Fig. 2B), where the dip of the beds more or less
matches the slope of the hill. Over time, meteoric water has
eroded the softer overlying siltstone beds and shales, exposing
the fossiliferous beds in stair-step fashion in a narrow erosional
channel; ammonoids appear to be more abundant and better
preserved in the lowermost or primary bed of the succession,
which is exposed near the bottom of the hill. This particular
bed is also exposed in a relatively large patch (~4 m2) on the
same hillside about 4 m south of the channel (Fig. 2B), and it
is from this exposure that the majority of the specimens have
been collected. Compared to the abundance of very poorly
preserved bivalves on these surfaces, ammonoids are quite rare,
but they usually are readily visible (Fig. 3B, D, E) because their
spiral form, deeply corroded phragmocones and reddish-brown
color tend to make them conspicuous in contrast to the irregular
surface formed by the bivalves.
Indeed, given the rarity of ammonoids in the Dinwoody
Formation, this discovery never would have occurred had it
not been for the concordance between the topographic slope
and the attitude of these fossiliferous beds on this relatively
small hillside (~250 m2). Eorts to expose more of the primary
fossiliferous bed by manually removing the overlying shales and
siltstone beds have resulted in the discovery of a few additional
specimens, but the excessive amount of generated dust tends to
obscure newly exposed specimens, whose discovery must await
dust-cleansing rain storms. In contrast, the coiled nautiloids
were found as oat about 15 m west of the ammonoid site, on
a gentle, east-facing slope, just across the small gulley at the
foot of the ammonoid-containing hillside. These oat specimens
occur within a ~2.5 m interval (fossil locality JJ6-19, Fig. 5)
located ~7 m stratigraphically above the ammonoid level; to
date, ve specimens have been found between siltstone beds
designated as 5(-1) and 5(+1) (Figs. 4, 5).
Ammonoids from the primary productive bed (NMMNH
L-12682; Fig. 5) mainly consist of complete phragmocones,
mostly without distortion or compaction, together with very
short portions (less than ¼ whorl) of body chambers, most of
which are badly distorted or crushed. The upper surfaces of
all phragmocones are corroded to varying degrees, some quite
deeply (Fig. 3B, D), whereas the bottom surfaces of about half of
the specimens are generally free of corrosion, except for the test,
which is usually corroded so that shell features, e.g., growth lines,
are not preserved. On many specimens, the nature of the ventral
surface (rounded, tabulate, etc.) has also been adversely aected
by corrosion for much of the circumference. In some cases, the
shell material on the bottom surfaces together with adhering
siltstone can be removed with an air pneumatic tool, revealing
well-preserved suture lines. As with the ammonoids, nautiloids
usually consist of either complete or partial phragmocones, but
the preservation of our ve oat specimens ranges from very
poor with some lateral distortion and severe corrosion, to fairly
good with well-preserved suture lines.
Western USA Basin
Until now, virtually nothing was known regarding
Griesbachian ammonoids in this region, other than for a
brief report by Newell and Kummel (1942, pl. 2, gs. 6 and
7) in which, after an extensive survey of some 20 measured
sections in Wyoming, Idaho and Montana, they were able
to document the occurrence of only two poorly preserved,
fragmental Griesbachian ammonoids, tentatively identied as
Discophiceras subkyokticum and Metophiceras subdemissum,
from the Dinwoody Formation at Montpelier Canyon, Idaho and
Melrose, Montana, respectively. Beyond this report, there are
no other documented occurrences of Griesbachian ammonoids
from the Dinwoody Formation.
Ware et al. (2011) documented a long known but never
illustrated, well preserved late middle and early late Dienerian
ammonoid fauna that includes the Ambites lilangensis
assemblage as well as two additional but informal ammonoid
horizons from the Candelaria Formation near the old “ghost
town” of Candelaria in southwestern Nevada. The late middle
Dienerian A. lilangensis assemblage, informally termed the
Proptychites beds”, includes P. haydeni, P. pagei, “Koninckites
a. krati and Mullericeras spitiense as well as the eponymous
taxon (Ware et al., 2011). Poole and Wardlaw (1978) mentioned
an additional Candelaria Formation locality containing a very
poorly preserved Dienerian ammonoid fauna near Willow
Spring in Nye County, Nevada, about 80 km northeast of the
Candelaria locality. This fauna has not been studied due to its
poor preservation, but it is assumed to be more or less equivalent
to that of the Candelaria locality. And, nally, Kummel
(1954) mentioned the occurrence of two poorly preserved
“Gyronitan” (=Dienerian) ammonoid faunas in succession in
the Dinwoody Formation at Frying Pan Gulch in southwestern
Montana, containing specimens identied as Prionolobus and
Koninckites in the lower horizon and Kymatites, Koninckites and
Xenodiscoides in the upper horizon, but he neither illustrated
these specimens nor provided precise collection locations. These
three localities essentially represent all that is known regarding
Dienerian ammonoids within the western USA basin.
Mid-Paleolatitude Eastern Panthalassa
Documented mid-paleolatitude Griesbachian ammonoid
occurrences in eastern Panthalassa are essentially nonexistent
except for an obscure report by Warren (1945) of attened
ammonoids in the Sulphur Mountain Member of the Spray
River Formation in Alberta, Canada. More specically, these
ammonoids occur in close stratigraphic proximity to beds
containing the bivalve Claraia stachei, which is generally
considered to straddle the Griesbachian-Dienerian boundary
(Kummel, 1954; Ware et al., 2011). According to Kummel
(1954), Warren (1945) thought the ammonoids represented the
genera Ophiceras, Proptychites and Otoceras, but the specimens
were never illustrated and, given their attened preservation,
even their identication at the generic level is questionable.
Boreal Realm
In contrast, Griesbachian ammonoid biostratigraphy
in the Boreal Realm is fairly well documented from more or
less correlative sections (Fig. 6) in eastern Panthalassa, i.e.,
Arctic Canada (Tozer, 1994a), Eastern Greenland (Spath, 1930,
1935; Bjerager et al., 2006), Svalbard (Weitschat and Dagys,
1989) and northeastern Siberia (Dagys and Weitschat, 1993;
Dagys and Ermakova, 1996). The Griesbachian in these areas
generally consists of the Otoceras concavum, Otoceras boreale,
Ophiceras commune and Bukkenites strigatus or B. rosenkrantzi
Zones or equivalents thereof, in ascending order (Bjerager et
al., 2006, g. 6). Zonal correlation schemes in East Greenland
and northeastern Siberia include Wordieoceras decipiens (=W.
wordiei) in the late or latest Griesbachian, respectively (Bjerager
et al., 2006). Although the East Greenland zonal correlation
scheme of Bjerager et al., (2006) is shown in the correlation chart
(Fig. 6), it is anticipated that extensive studies by Ware (ongoing
work) will eventually result in signicant modication to this
succession. Additionally, the ve-fold, Siberian Griesbachian
zonal scheme of Dagys and Ermakova (1996) has been reduced to
a four-fold succession with the elimination of the Tompophiceras
pascoei Zone by Zakharov et al. (2020). Also, it should be noted
that both Ware et al. (2018a) and Dai et al. (2019) have slightly
modied the zonation of Arctic Canada by placing the Bukkenites
strigatus Zone in the lowermost Dienerian. Furthermore, when
the IUGS formally dened the base of the Induan based on the
lowest occurrence of the conodont Hindeodus parvus at the
Meishan section, South China (Yin et al., 2001), the traditional
base of the Griesbachian, i.e., the FAD of Otoceras, eectively
became part of the Permian (Jenks et al., 2015). This change
has not been widely accepted by Triassic workers (e.g., Tozer,
2003; Shevyrev, 2006), especially given that the scarcity and
poor preservation of ammonoids in the Meishan section (Jenks
et al., 2015) essentially precludes their use for authenticating
the conodont-based boundary placement. Consequently,
considerable debate still exists regarding the placement of the
PTB in Arctic ammonoid zonations. However, we choose to
follow Tozer’s (1967) denition of the Griesbachian, with the
Otoceras concavum or Hypophiceras trivale Zone marking the
Northern Indian Margin
According to Ware et al. (2018a), the Griesbachian is not
well represented in the Salt Range, with ammonoids being rare
and generally poorly preserved. Consequently, it is dicult to
correlate their three regional biostratigraphical subdivisions,
i.e., Hypophiceras cf. H. gracile, Ophiceras connectens and
?Ophiceras sakuntala, with other NIM areas (Ware et al., 2018a).
Nevertheless, Ware et al. (2018a) described two new latest
Griesbachian/earliest Dienerian taxa from the Nammal Nala
section, upon which one of the present studied taxa is based, i.e.,
Kyoktites cf. K. hebeiseni. Krystyn et al. (2004, 2007) proposed
a somewhat more denitive zonal scheme for the Spiti Valley
area, i.e., the Otoceras woodwardi, Ophiceras tibeticum and
Discophiceras Zones, but because they did not provide sucient
explanations and taxonomic denitions as well as illustrations,
its usefulness for correlational purposes is uncertain (Ware et
al., 2018a). Zhang et al. (2017) documented Griesbachian and
Dienerian ammonoid occurrences from Qubu in the Mt. Everest
area, southern Tibet; zonation for the Griesbachian in this area
includes the basal Otoceras woodwardi Zone and overlying
Ophiceras tibeticum Zone.
South China
For the most part, Griesbachian faunas from the low-
paleolatitude South China Block are not well known, primarily
because of poor ammonoid preservation at most localities.
Furthermore, conrmed reports of earliest Griesbachian Otoceras
or equivalent faunas are as yet unknown (Brühwiler et al., 2008;
Dai et al., 2019). A supposed early Griesbachian “Hypophiceras
fauna” together with ?Otoceras sp. was reported from the
Meishan section by Wang (1984), but the poor preservation of
these specimens has cast serious doubt on the accuracy of these
attributions, and there is some question as to whether they are
even of Triassic age (Tozer, 1994b; Shevyrev, 2006; Brühwiler
et al., 2008). In contrast to the poor preservation in most areas,
Brühwiler et al. (2008) and Dai et al. (2019) have documented
fairly well-preserved Griesbachian and Dienerian ammonoid
faunas from northwestern Guangxi/southern Guizhou, South
China, respectively. Brühwiler et al. (2008) collected small, late
Griesbachian ophiceratid specimens from the Luolou Formation
at Shanggan, Guangxi that they suspected were juveniles of O.
sinense, but because they found no adult shells, they illustrated
their specimens in open nomenclature as Ophiceras sp. indet.
Dai et al. (2019) collected numerous Griesbachian (and
Dienerian) ammonoids from the Gujiao section, a well-exposed
outcrop of the Daye Formation created by new highway
construction about 20 km southeast of Guiyang, the capital of
Guizhou Province. Late Griesbachian ammonoids are placed
into two informal subdivisions, i.e., the Ophiceras medium
beds and the overlying Jieshaniceras guizhouense beds,
whose age is problematic (Dai et al., 2019). Taxa from the J.
guizhouense beds include Vishnuites pralambha, Mullericeras
gujiaoense and Proptychites sp. indet. While Ophiceras medium
is denitely of late Griesbachian age, taxa from the overlying J.
guizhouense beds are also considered to be of Dienerian age at
other localities, e.g., V. pralambha from Guangxi, J. guizhouense
from Guizhou, and Mullericeras from Nevada (Brühwiler et al.,
2008; Dai et al., 2019). According to Dai et al. (2019) and Ware
(ongoing work), the age of the J. guizhouense beds and, for that
matter, the Griesbachian/Dienerian boundary itself is poorly
constrained if based solely on ammonoids. On the other hand,
conodonts are known to have undergone a signicant change
at this boundary (Orchard, 2007; Brosse et al., 2017; Dai et al.,
2019), and taxa contained in the beds from which Brühwiler et
al. (2008) collected J. guizhouense clearly demonstrate that the
beds are of late Griesbachian age.
South Primorye
Shigeta and Zakharov (2009) documented a succession of
abundant and well-preserved Griesbachian, Dienerian and early
to middle Smithian ammonoid faunas from the Lazurnaya Bay
and Zhitkov formations at Abrek Bay, South Primorye. The
Griesbachian portion of these bedrock-controlled collections
includes ammonoids belonging to the late Griesbachian
Lytophiceras Zone and part of the overlying Gyronites
subdharmus Zone, as well as several nautiloid taxa (Shigeta
and Zakharov, 2009). Some controversy surrounds the possible
designation of the lower portion of the G. subdharmus Zone
as latest Griesbachian (see Dai et al., 2019, g. 18), but these
beds contain ammonoid co-occurrences not seen before in other
localities that lend credence to this designation. Ongoing work
by Shigeta et al. is expected to further resolve this issue.
In summary, world-wide Griesbachian ammonoid
distribution (Fig. 6) generally includes the Otoceras and
overlying Ophiceras faunas or equivalents thereof, even though
the Otoceras faunal record in the Tethyan Realm is not as
complete as in the Boreal Realm (e.g., Brühwiler et al., 2008).
Ophiceras and its various species are generally considered to be
cosmopolitan taxa that range throughout the upper Griesbachian
(Shevyrev, 2001; Brühwiler et al., 2008). Some areas, e.g.,
NIM, East Greenland, Arctic Canada, are characterized by
expanded sections that exhibit much higher faunal resolution.
Nevertheless, this general similarity in ammonoid faunas and
succession, irrespective of paleolatitude, tends to reinforce the
concept of weak latitudinal diversity gradients following the
end-Permian extinction (Brayard et al., 2006, 2009; Brühwiler et
al., 2008). And, the newly reported late Griesbachian ammonoid
assemblage from the Dinwoody Formation at Crittenden
Springs, which represents the rst documented occurrence of
Wordieoceras wordiei and two additional Boreal taxa in the low
paleolatitudes, provides convincing evidence of this concept.
Until now, reports of coiled nautiloids from the Dinwoody
Formation are even rarer than ammonoids, consisting of only
two specimens. Kummel (1953, p. 53, pl. 6, gs. 5, 6) described
a new taxon (Grypoceras milleri) based on one poorly preserved,
incomplete specimen found in the western part of Sleight
Canyon, west of Paris, Idaho. He also mentioned, but did not
illustrate a very large fragment of a nautiloid body chamber from
Montpelier Canyon, Idaho, whose original shell he estimated to
be ~30 cm in diameter (Kummel, 1953). Muller and Ferguson
(1939) listed Grypoceras cf. G. brahmanicum (Griesbach) from
the Candelaria Formation in southwestern Nevada. Beyond
these three reports, no other Griesbachian or Dienerian coiled
nautiloids have been reported from eastern Panthalassa until
now. It is somewhat surprising that nautiloids have not been
reported from British Columbia and/or Arctic Canada, given the
relatively large Induan ammonoid collections amassed over the
years by F. McClearn and E.T. Tozer, respectively.
In contrast, the record of Induan coiled nautiloids in the
Tethys and Boreal northeastern Siberia is considerably richer.
Griesbach (1880) and Diener (1895, 1897) reported nautiloids,
e.g., Grypoceras brahmanicum (Griesbach) and Pleuronautilus
sp. indet, from several areas in the Himalayas, but one of the more
prolic sites, Shalshal Cli, which is badly in need of restudy,
cannot be accessed because of its location in a geopolitically
sensitive area. Although Induan nautiloids are not well known
in South China, Xu (1988) erected a new genus, Xiaohenautilus,
from the late Griesbachian/early Dienerian in the Guizhou-
Hubei area to which he attributed two species, i.e., X. sinensis
and X. huananensis. Shigeta and Zakharov (2009) reviewed the
recovery of nautiloids in the Early Triassic and documented the
occurrence of well-preserved specimens attributed to ve species
(belonging to three genera) in succession throughout ~45 m of
Griesbachian and Dienerian sediments in the Abrek Bay section
of South Primorye, Russia. These authors suggest that these ve
taxa may belong to the same evolutionary lineage within the
Grypoceratidae (Shigeta and Zakharov, 2009). Indeed, given the
relative scarcity of nautiloid occurrences, the Abrek Bay section
likely represents the best documented late Griesbachian/early
Dienerian nautiloid succession in the world. One of these taxa,
Xiaohenautilus abrekensis, is similar to the present specimens.
Arctic Canada
Tozer 1994
East Greenland
latelate middleearlyearly
South Primorye
Zakharov, 1999
Shigeta & Zakharov, 2009
Shigeta, ongoing work
Pr. candidus Zone
Ot. boreale Zone
Ot. concavum Zone
Ot. boreale Zone
T. morpheos Zone
Ot. concavum Zone
South China
Brayard & Bucher 2008
Brühwiler et al., 2008
Dai et al., 2018
Ambe. radiatus beds
Op. medium beds
J. guizhouense beds
Ci. sp. indet. beds
“Ambo. fuliginatus” Zone
Co.spitiense Zone
Ot. woodwardi Zone
Gy. subdharmus Zone
Lytophiceras Zone
Indian Margin
Krystyn et al., 2004, 2007
Ware et al., 2015, 2018
USA Basin
Newell & Kummel, 1942
Kummel, 1954
Ware et al., 2011
this work
Discophiceras Zone
Op. tibeticum Zone
Gy. plicosus UAZ
Gy. frequens UAZ
Ambe. atavus UAZ
Ambe. bojeseni UAZ
Ambe. discus UAZ
Gy. dubius UAZ
Ambe. superior UAZ
Ambe. lilangensis UAZ Ambe. bjerageri bedsAmbe. lilangensis beds
V. meridialis beds
Ambe. subradiatus beds
V. meridialis UAZ
Ki. davidsonianus UAZ
Ko. vetustus UAZ
Aw. awani UAZ
M. subdemissum Zone
M. subdemissum beds*
Op. commune Zone
Op. commune Zone
W. decipiens Zone
B. rosenkrantzi Zone
M. triviale Zone
M. martini Zone
Bjerager et al., 2006
Verkhoyansk Basin
Dagys & Weitschat, 1993
Dagys & Ermakova, 1996
Zakharov et al., 2020
W. wordiei beds W. decipiens beds
V. sverdrupi Zone
V. turgidus Zone
Ki.? korostelevi Zone
B. strigatus Zone
V. sverdrupi Zone
Abbreviations of genera
FIGURE 6. Induan ammonoid zonation of the western USA basin and correlation with other global occurrences. Bold vertical black
bars represent uncertain correlation. Dashed line boxes encompassing Vavilovites meridialis beds and Metophiceras subdemissum
beds of western USA basin represent uncertain stratigraphic occurrences within late Dienerian and early Griesbachian, respectively.
Similarly, asterisk marking M. subdemissum beds denotes uncertain ammonoid identication. Note: Ongoing work by Ware is
expected to signicantly modify the zonation of Bjerager et al., (2006) for East Greenland. UAZ = Unitary Association Zone.
Sobolev’s (1989, 1994) work in Boreal northeastern
Siberia aptly demonstrates that this region contains by far the
most complete record of Triassic nautiloids known worldwide.
According to Sobolev (1994), nautiloid occurrences are not all
that common, but they occur throughout nearly the entire Triassic.
This statement is well supported by the ~ 50 sites shown on the
nautiloid locality map of northeastern Asia (Sobolev, 1994,
g. 1). Nautiloid diversity and abundance in the Boreal Realm
remained relatively low throughout the Griesbachian, consisting
only of two local P/T extinction event survivors, i.e., the
liroceratid genus Tomponautilus, which is a probable descendant
of the late Permian genus Permonautilus, and the late Permian
genus Tainionautilus (Sobolev, 1994). Nautiloids completely
disappeared from the Boreal fossil record during the Dienerian
and early Smithian, but orthoconic nautiloids migrated from the
Tethys and dominated the middle and late Smithian (Sobolev,
1994) of northeastern Asia. The Spathian witnessed an explosive
radiation of tainoceratids in the Tethyan Realm, some of which
also migrated to northeastern Asia and gave rise to the genus
Phaedrysmocheilus, on whose evolution Sobolev (1994) based
a biostratigraphic scheme with extremely high resolution for
northeastern Siberia. Nautiloids continued to diversify almost
without interruption throughout the Middle and Late Triassic,
and this resultant diversity enabled Sobolev (1994) to develop a
nautiloid-based biostratigraphic scheme for northeastern Siberia
consisting of 19 zones with nearly as much resolution and
correlation usefulness as the ammonoid-based scheme. Indeed,
a portion of Sobolev’s (1994) Spathian biostratigraphic scheme
can be correlated with the early Spathian Columbites beds of
southeastern Idaho from which Brayard et al. (2019) recently
illustrated two nautiloid taxa, i.e., Trematoceras sp. indet. and
Phaedrysmocheilus idahoensis.
Conodont biostratigraphy of the Dinwoody Formation in the
Crittenden Springs area has been studied by numerous workers,
beginning with Clark (1957) and culminating with Paull (1980),
Carr and Paull (1983) and Mullen (1985). According to the latter
three studies, conodonts within the Dinwoody Formation can
be divided into ve zones, in ascending order: the Hindeodus
typicalis Zone, Isarcicella isarcica Zone, Neogondolella
carinata Zone, Neospathodus kummeli Zone, and Neospathodus
dieneri Zone. The interval from the H. typicalis Zone to the Ng.
carinata Zone, and the Ns. kummeli and Ns. dieneri zones are
generally considered to be indicative of the Griesbachian and
Dienerian, respectively (Sweet et al., 1971; Mullen, 1985). In
particular, the Isarcicella isarcica Zone generally indicates an
early to middle Griesbachian age (Orchard, 2007).
According to Paull (1980), both the Hindeodus typicalis
and Isarcicella isarcica Zones are recognized in segment A,
(~1.25 km north of the Long Canyon road), which represents
the lowest part of the Dinwoody Formation. In contrast, only a
few index conodonts, e.g., Neogondolella carinata (= Clarkina
carinata) were reported from segment B (Fig. 5), ~280 m north
of the Long Canyon road. Paull (1980) stated that the upper 33
m interval of segment B was assignable to the upper Dienerian,
because of the presence of a few lenticular limestone beds
containing numerous linguloid brachiopods. However, it should
be noted that no age-diagnostic conodonts were reported from
this particular interval of segment B.
The ammonoid/nautiloid study section is located ~140 m
north of the Long Canyon road, which is only ~140 m south
of segment B. Sampling eorts in the study section yielded
eight conodont species belonging to three genera, i.e., Clarkina,
Hindeodus, and Merrillina, from six limestone beds (Fig. 5;
Fig. 14). These three genera are Permian conodont relics that
rapidly diversied in the Early Triassic (e.g., Orchard, 2007).
Most importantly, the various species of Hindeodus are limited
to the Griesbachian. More specically, the study section yielded
Hindeodus sp., Merrillina sp., and several species of Clarkina,
i.e., C. carinata, C. taylorae, C. tulongensis, C. griesbachiensis,
and C. krystini. Clarkina krystini, a late Griesbachian conodont,
was collected from Loc. 7, a linguloid brachiopod limestone bed
(Fig. 5). Furthermore, the basal Dienerian index conodont, i.e.,
Sweetospathodus kummeli, was not found in the studied section,
and it was not reported from segment B. Based on the above
conodont evidence, it is concluded therefore, that nearly all of
the Dinwoody Formation of the studied section is middle to late
Griesbachian in age. The following taxa are illustrated in Fig.
14: Clarkina carinata (Clark), C. griesbachiensis (Orchard), C.
tulongensis (Tian), Merrillina sp., and Hindeodus sp. (Table 2).
Systematic descriptions are mainly based on the classication
scheme of Tozer (1981, 1994a), but modications by Ware et
al. (2018a, b) are incorporated. Morphological measurements
are expressed using the four classic geometrical parameters of
the shell: diameter (D), whorl height (H), whorl width (W) and
umbilical diameter (U). Absolute values of H and U are plotted
versus diameter, as are the ratios H/D and U/D. Whorl width (W)
measurements are not included in ammonoid scatter diagrams
because of varying degrees of corrosion on upper surfaces.
Terminology used to express shell size, umbilical width and type
of coiling (whorl involution) is taken from Haggart (1989, table
8.1). All specimens are reposited in the New Mexico Museum of
Natural History and Science (NMMNH) in Albuquerque.
Class CEPHALOPODA Cuvier, 1797
Order CERATITIDA Hyatt, 1884
Superfamily MEEKOCERATOIDEA Waagen, 1895
Family OPHICERATIDAE Arthaber, 1911
Genus Wordieoceras Tozer, 1971
Type species: Vishnuites wordiei Spath
Wordieoceras wordiei (Spath)
Figure 7A-B’
1930 Vishnuites wordiei Spath, p. 31, pl. 2, gs. 11a, b
1930 Vishnuites decipiens Spath, p. 31, pl. 3, gs. 2a-g; pl. 4,
gs. 2a, b.
1935 Vishnuites wordiei Spath, p. 41, pl. 4, gs. 5a, b; pl. 12,
gs. 2a, b.
1935 Vishnuites decipiens Spath, p. 41, pl. 4, gs. 4a, b; pl. 9,
gs. 3a, b; pl. 10, gs. 2-5; pl. 12, gs. 1a, b; pl. 13, gs.
4, 7.
1967 Ophiceras decipiens (Spath), Tozer, p. 16, 17, 51, 52 and
1971 Wordieoceras wordiei (Spath), Tozer, p. 1031.
1987 Vishnuites domokhotovi Zakharov and Rybalka, p. 36, pl.
II, g. 5.
1994 Wordieoceras wordiei (Spath), Tozer, p. 58, pl. 5, gs.
1-3; pl. 6, gs. 1-3; pl. 7, gs. 1-4.
1996 Wordieoceras decipiens (Spath), Dagys and Ermakova, p.
416, pl. 11, gs. 1,2,4,5.
2006 Wordieoceras wordiei (Spath), Bjerager et al., p. 640, g.
2006 Wordieoceras decipiens (Spath), Bjerager et al., p. 640,
g. 5; g. 8, j-k; p. 644, 646.
non 2007 Wordieoceras a. wordiei (Spath), Mu et al., p. 862,
gs. 6.7, 6.9, 6.11, 7.1, 7.2, 8.
non 2009 Wordieoceras cf. wordiei (Spath), Shigeta and
Zakharov, p. 68, pl. 50, gs. 12-15.
2015 Wordieoceras wordiei (Spath), Jenks et al., p. 343, g.
13.3, i-j, GSC28060.
Material: Eight measured specimens consisting of complete
phragmocones with very short body chamber fragments, ranging
FIGURE 7. Wordieoceras wordiei (Spath). A-D, NMMNH P-81677, in A, lateral, B, ventral, C, apertural views, and D, unwhitened
lateral view showing suture lines. E-H, NMMNH P-81672, in E, lateral, F, ventral, G, apertural and H, unwhitened lateral view
showing suture lines. I-J, suture lines, in I, NMMNH P-81677, H = 32 mm, J, NMMNH P-81672, H = 23 mm. K-M, NMMNH
P-81673, in K, lateral, L, ventral and M, apertural views. N-P, NMMNH P-81675, in N, lateral, O, ventral and P, apertural views.
Q-S, NMMNH P-81674, in Q, lateral, R, ventral and S, apertural views. T-V, NMMNH P-81679, in T, lateral, U, ventral and V,
apertural views. W-Y, NMMNH P-81676, in W, lateral, X, ventral and Y, apertural views. Z-B’, NMMNH P-81678, in Z, lateral,
A’, ventral and B’, apertural views. All scale bars = 1 cm.
in diameter from ~29 to ~86 mm, NMMNH P-81672 (Fig. 7E-
H, J), NMMNH P-81673 (Fig. 7K-M), NMMNH P-81675 (Fig.
7N-P), NMMNH P-81674 (Fig. 7Q-S), NMMNH P-81676
(Fig. 7W-Y), NMMNH P-81677 (Fig. 7A-D, I), NMMNH
P-81678 (Fig. 7Z-B’) and NMMNH P-81679 (Fig. 7T-V). All
are illustrated.
Description: Small to medium sized, fairly evolute,
compressed shell with convex anks converging gently to highly
variable venter with/without distinct shoulders, that varies from
narrowly rounded on some specimens to fastigate with distinct
bordering shoulders to nearly acute on others. Maximum whorl
width occurs at ~ 40% of whorl height. Flank contour broadly
convex from top of umbilical shoulder to point of maximum
whorl width, then converging more rapidly to venter, forming
a sub-trigonal to ovoid whorl section. Venter tends to become
slightly more fastigate in an apertural direction on present
specimens. Umbilicus moderately wide (U/D avg, 0.31) and
fairly shallow with low, moderately inclined (~45°) wall and
barely perceptible, broadly rounded shoulders. Ornamentation
cannot be accurately assessed because test on most specimens is
corroded, and body chambers are not preserved. One specimen
(NMMNH P-81672) exhibits barely perceptible, distant, broad
fold-type ribs on the last quarter whorl of the phragmocone, and
it is assumed this feature would become more prominent on
the body chamber, if preserved. Suture line somewhat typical
of ophiceratids, with deep rst lateral lobe and relatively high
median saddle. Lobes well denticulated.
Measurements: See Table 1.
Discussion: As pointed out by Tozer (1994a), this taxon
exhibits an extremely wide range of intraspecic variation in
terms of both whorl morphology and ornamentation, and it is
obvious that much of this expanded variation results from his
inclusion of Vishnuites decipiens Spath, 1930, in synonymy with
W. wordiei Spath, 1930. The present specimens t well within this
variation, as is evident in the box plot comparison of the Nevada
specimens with those from Arctic Canada, East Greenland and
Siberia (Fig. 10). According to Tozer (1994a) many Canadian
specimens exhibit blunt ribbing, mainly on the phragmocone,
but also occasionally on the body chamber. In contrast, ribbing
is not reported on any of the specimens from East Greenland
and Siberia (Spath, 1930, 1935; Dagys and Ermakova, 1996),
and only one of the present specimens exhibits very weak, blunt
ribbing near the end of its phragmocone. Nearly all specimens
exhibit a fastigate venter, but this feature is also highly variable,
in that the degree to which the gabled venter is obvious varies
widely. Unlike specimens from Nevada and East Greenland,
most Canadian specimens retain nearly complete, well preserved
body chambers, and Tozer (1994a) commented that, while most
specimens maintain an obvious fastigate venter throughout
ontogeny, a few specimens transition to a nearly rounded or
fastigate venter with barely perceptible angularity.
Not only does the present study represent the rst report
of late Griesbachian ammonoids from low-paleolatitude eastern
Panthalassa, but it is also the rst documented low-paleolatitude
occurrence of clearly identied Wordieoceras, until now known
only from the late Griesbachian of the Boreal Realm. This
discovery thus suggests a more cosmopolitan occurrence for
this taxon. Zakharov and Mu in Mu et al. (2007) described two
late Griesbachian taxa, i.e., Wordieoceras a. W. wordiei and
Wordieoceras guizhouensis, from the lower part of the Daye
Formation at Guiding, South China, but Brühwiler et al. (2008)
disputed this assignment and erected a new proptychitid genus,
i.e., Jieshaniceras, with “W”. guizhouensis as the type species
and also synonymized “W”. a. W. wordiei with the new taxon.
Shigeta and Zakharov (2009) assigned a single specimen from
Abrek Bay, South Primorye, to Wordieoceras cf. W. wordiei, but
its whorl parameters clearly do not match Wordieoceras, and
Shigeta (ongoing work) indicates the specimen likely represents
a new genus and species.
Dagys and Ermakova (1996) established a new species,
i.e., Wordieoceras tompoense, from the Decipiens Zone of the
eastern Verkhoyansk area, Siberia. While the inner whorls of
this taxon bear some resemblance to the present specimens (see
Dagys and Ermakova, text-g. 11, p. 418), it diers signicantly
upon reaching large mature size with its much inated whorl
section (W/D, 0.32 vs. 0.23) and much more involute coiling
(U/D, 0.21 vs. 0.31). It should be noted, however, that the
W/D measurements provided by Dagys and Ermakova (1996)
represent only specimens in excess of 64 mm in diameter, which
is considerably larger than most of our specimens. Zakharov and
Rybalka (1987) erected a new species Vishnuites domokhotovi
from Eastern Verkhoyansk that was later synonymized with
W. decipiens by Dagys and Ermakova (1996). This new taxon,
based on a single, small fragmental specimen (D = 21 mm), is
poorly illustrated, but the features of its whorl, e.g.., fastigate
venter, appear similar to the smaller present specimens.
The type specimen of Vishnuites pralambha Diener, 1897,
from Shalshal Cli, Kashmir, exhibits a supercial resemblance
to at least one of the present specimens, i.e., NMMNH P-81677,
but this taxon is much more compressed, and considerable
confusion exists as to its taxonomy and stratigraphic distribution
at Shalshal Cli, as well as its relationship to specimens from
South China (Brühwiler et al., 2008; Dai et al., 2019). Dai et
al. (2019) emphasized the need for both a reinvestigation of
the Shalshal Cli site, located in a geopolitically sensitive area
between India and China, and a thorough revision of the various
Vishnuites taxa from central Himalaya and South China.
Occurrence: Found in a 2-3 cm thick siltstone bed
represented by locality number NMMNH L-12682, ~75 m
below the top of the Dinwoody Formation.
Wordieoceras mullenae n. sp.
Figure 8A-M
1935 Vishnuites decipiens var. discoidea, Spath, p. 44, pl. XII,
g. 1; pl. XIII, g. 4. Not pl. X, g. 5.
Type series: Four specimens: Holotype, specimen NMMNH
P-81680 (Fig. 8A-C, M), paratypes, three specimens: NMMNH
P-81681 (Fig. 8G-I), NMMNH P-81682 (Fig. 8D-F), NMMNH
P-81683 (Fig. 8J-L). Type series reposited in the NMMNH.
Etymology: Named in honor of Donna M. Mullen of
Denver, Colorado.
Diagnosis: Fairly small, very involute compressed shell
with sub-trigonal whorl section characterized by convex anks
converging to narrowly rounded to fastigate venter with barely
perceptible angularity. Fairly narrow umbilicus with inclined
wall and well-rounded shoulder. Maximum whorl width at
~30% of whorl height or top of umbilical shoulder. No visible
ornamentation except for a barely perceptible, broad fold-type
rib on the holotype, near the end of the phragmocone.
Description: Fairly small, fairly involute compressed shell
with gently convex anks converging to narrowly rounded venter
without distinct ventral shoulders. Maximum whorl width occurs
at 40 to 45% of whorl height. Flank contour broadly convex from
top of umbilical shoulder to point of maximum whorl width, then
converging more rapidly to venter, forming a high-whorled, sub-
trigonal whorl section. Fairly narrow umbilicus (U/D avg, 0.20)
with low, moderately steep wall and barely perceptible, broadly
rounded shoulders. No obvious ornamentation on paratypes, but
holotype bears one barely perceptible, broad fold-type rib near
end of phragmocone. Suture line with relatively low, broadly
rounded saddles, fairly wide, well denticulated rst lateral lobe,
nely denticulated 2nd lateral lobe and short auxiliary series with
weak indentations.
Measurements: See Table 1.
Discussion: At rst glance, Wordieoceras mullenae n.
sp. appears similar in whorl morphology to the W. wordiei
FIGURE 8. (facing page) A-M, Wordieoceras mullenae n. sp. A-C, NMMNH P-81680, holotype, in A, lateral, B, ventral and
C, apertural views. D-F, NMMNH P-81682, paratype, in D, lateral, E, ventral and F, apertural views. G-I, NMMNH P-81681,
paratype, in G, lateral, H, ventral and I, apertural views. J-L, NMMNH P-81683, paratype, in J, lateral, K, ventral and L, apertural
views. M, suture line, NMMNH P-81680, H = 24 mm. N-Z, Kyoktites cf. K. hebeiseni Ware and Bucher. N-Q, NMMNH P-81688,
in N, lateral, O, ventral, P, apertural views, and Q, unwhitened lateral view showing suture lines. R-U, NMMNH P-81690, in R,
lateral, S, ventral, T, apertural views, U, unwhitened lateral view showing suture lines. V-X, NMMNH P-81689, in V, lateral, W,
ventral and X, apertural views. Y-Z, suture lines, in Y, NMMNH P-81690, H = 17 mm, Z, NMMNH P-81688, H=23 mm. A’-G’,
Ophimullericeras paullae n. gen., n. sp. A’-D’, NMMNH P-81684, paratype, in A’, lateral, B’, ventral, C’, apertural views and D’,
unwhitened lateral view showing suture lines. E’-G’, NMMNH P-81687, holotype, in E’, lateral, F’, ventral (sub-tabulate venter
preserved near end of phragmocone) and G’, apertural views. All scale bars = 1 cm.
specimens from Crittenden Springs, but as is evident from the
plot of U/D and H/D for the two taxa (Fig. 9), W. mullenae n. sp.
is clearly more involute and well dierentiated from W. wordiei.
Spath (1935) attributed three specimens from East
Greenland to Vishnuites decipiens var. discoidea, two of which
exhibit very similar coiling geometry and whorl parameters to
W. mullenae n. sp. It is clear from Spath’s illustrations (pl. XII,
g. 1; pl. XIII, g. 4) and measurements that these specimens are
much more involute than V. decipiens and are very close to the
present specimens. Thus, they are herein placed in synonymy
with W. mullenae n. sp.
Wordieoceras mullenae n. sp. is much closer to W. tompoense
Dagys and Ermakova in terms of coiling geometry (U/D avg,
0.20 vs. 0.21) than W. wordiei, and its whorl width is closer to
the inner whorls of W. tompoense. But, again, the specimens for
which these authors provided measurements are much larger
than the present specimens, and their mature whorls are much
more inated (W/D avg. 0.32 vs. 0.23). It is unlikely that the
body chambers of W. mullenae n. sp., if preserved, would exhibit
such ination, even at larger diameters.
The suture line of Wordieoceras mullenae n. sp. (Fig. 8M),
with its shallower lobes and longer saddles, contrasts somewhat
with that of W. wordiei, but according to Ware (ongoing work),
this slight deviation is not all that uncommon and simply
represents intraspecic variation. Spath (1930, 1935) and Tozer
(1994a) both show similar divergences in ophiceratids, and some
specimens from East Greenland also exhibit the same variation.
Occurrence: Found in a 2-3 cm thick siltstone bed
represented by locality number NMMNH L-12682, ~75 m
below the top of the Dinwoody Formation.
Genus Kyoktites Ware and Bucher 2018
Kyoktites cf. K. hebeiseni Ware and Bucher 2018
Figure 8N-Z
2018a Kyoktites cf. H. hebeiseni Ware et al., p. 37, pl. 2, gs.
Material: Three measured specimens, NMMNH P-81688
(Fig. 8N-Q, Z), NMMNH P-81689 (Fig. 8V-X), NMMNH
P-81690 (Fig. 8R-U, Y), consisting of complete phragmocones
ranging in diameter from ~32 to 55 mm, two of which include
very short body chamber fragments. One specimen (NMMNH
P-81688) includes ~1/4 whorl of badly distorted/crushed body
chamber. Two specimens (NMMNH P-81688 and NMMNH
P-81690) are fairly well preserved with exposed suture lines.
NMMNH P-81689 is poorly preserved with corrosion aecting
both sides. All are illustrated.
Description: Fairly small, very involute, compressed,
platyconic shell with very slightly convex, sub-parallel anks
that converge very slightly to well-rounded venter without
distinctive shoulders. Maximum whorl width occurs at 40-
45% of whorl height. Flank contour broadly convex from top
of umbilical shoulder to point of maximum whorl width, then
converging very gently in a sub-parallel manner to a rounded
venter. Whorl section is sub-quadrate. Fairly narrow, shallow
umbilicus (U/D avg. 0.19) with steep, nearly vertical wall and
narrowly rounded shoulders. No visible ornamentation. Suture
line with shallow, well-developed ventral lobe, deep rst lateral
lobe and shallow second lateral lobe, both well denticulated.
Elongated rst and second lateral saddles and broad but low
third lateral saddle. Short auxiliary series with several small
Measurements: See Table 1.
Discussion: Kyoktites hebeiseni and K. cf. K. hebeiseni
were erected by Ware and Bucher (2018a) based on three fairly
well preserved specimens (one from the Nammal Nala section
and two from the Amb section) from condensed horizons of
latest Griesbachian/earliest Dienerian age in the Salt Range,
Pakistan. In terms of whorl geometry, the present specimens t
well within K. hebeiseni, but the type specimen exhibits weak
sigmoidal ribbing on the lower half of the ank. The present
specimens bear no such ornamentation, and since the taxon is
based on only one specimen, nothing is known regarding its
range of intraspecic variation. Hence, we prefer to place our
specimens in open nomenclature. The suture line of specimen
NMMNH P-81690 is very similar to K. hebeiseni, and there
is little doubt this specimen is correctly attributed. However,
the suture line of the largest specimen, NMMNH P-81688, is
problematic in that it does not exhibit the low, wide third lateral
saddle typical of the taxon. The height of this particular saddle
on NMMNH P-81688, which is about the same as the second
lateral, is considerably higher than that of the holotype, and it is
missing most of the lower part of the dorsal side of the saddle wall.
Essentially, it merges without a clear boundary with the weakly
indented auxiliary series. Taken as a whole, this suture line more
closely matches that of the early Dienerian taxon Ghazalaites
roohii Ware and Bucher (2018a) with its asymmetrical third
lateral saddle, but this taxon’s whorl geometry is signicantly
dierent. Basically, the inner whorls of G. roohii are much more
involute, with a nearly closed umbilicus, and these are then
followed by very distinctive egressive coiling. In addition, its
anks are not sub-parallel, but instead are convex, converging
toward the venter.
We choose to attribute specimen NMMNH P-81688 to
Kyoktites cf. K. hebeiseni with some reservation. It is possible that
this divergence in the suture line is due to extreme intraspecic
variability, but additional specimens would be needed to quantify
this speculation. According to Ware (ongoing work), this part of
the suture line in some ophiceratids/gyronitids can often exhibit
signicant variability. In addition, a pathological cause for this
discrepancy cannot be ruled out, even though there is no obvious
evidence of sub-lethal shell damage in the immediate area where
the suture line was drawn. However, there is a slight but sudden
increase in whorl width near the umbilical margin at about 10
adapical septa removed, but it is impossible to determine if this
change is pathological or caused by post-burial compaction.
The present specimens are also similar to the Kyoktites cf.
K. hebeiseni specimen from the Amb section (Ware et al., 2018a,
pl. 2, gs. 5-7), but they dier primarily by their slightly more
involute coiling (U/D-0.19 vs. 0.24, respectively).
Occurrence: Found in a 2-3 cm thick siltstone bed
represented by locality number NMMNH L-12682, ~75 m
below the top of the Dinwoody Formation.
TABLE 1. Measurements. Note: Width measurements for all ammonoids slightly aected by corrosion.
Location Taxon Specimen No. D (mm) W H U W/D H/D U/D
Crittenden Spr. Wordieoceras
wordiei P-81672 54.4 11.9 22.3 17.7 0.22 0.41 0.33
P-81673 49.8 11.5 18.7 17.0 0.23 0.38 0.34
P-81674 34.8 8.3 14.4 10.0 0.24 0.41 0.29
P-81675 44.1 9.6 18.3 13.2 0.22 0.41 0.30
P-81676 28.7 6.5 11.4 8.2 0.23 0.40 0.29
P-81677 86.2 16.3 32.7 29.6 0.19 0.38 0.34
P-81678 36.6 9.4 14.8 11.5 0.26 0.40 0.31
P-81679 33.6 8.4 13.2 10.5 0.25 0.39 0.31
Arctic Canada
(Tozer, 1994) 28060 121 25.4 44.8 43.6 0.21 0.37 0.36
28059 73 18.3 32.1 21.2 0.25 0.44 0.29
28062 96 26.9 44.2 27.8 0.28 0.46 0.29
28067 27 7.8 11.3 7.8 0.29 0.42 0.29
28065 59 14.8 23.0 20.1 0.25 0.39 0.34
28066 65 13.7 26.0 20.8 0.21 0.40 0.32
East Greenland
Holotype 57 15.4 22.8 18.8 0.27 0.40 0.33
W. decipiens Holotype 44 12.8 19.8 11.9 0.29 0.45 0.27
Pl. 10, 3 54 13.0 21.6 17.8 0.24 0.40 0.33
Pl. 9, 3 62 14.9 26.7 21.1 0.24 0.43 0.34
Pl. 13, 7 55 11.6 23.1 16.0 0.21 0.42 0.29
No. 357d 60 13.2 27.6 16.8 0.22 0.46 0.28
Siberia (Dagys &
Ermakova, 1996) W. decipiens 921/99 64 16.7 26.7 19.0 0.26 0.42 0.30
921/102 67 17.0 25.5 23.0 0.26 0.45 0.34
Crittenden Spr. W. mullenae n. sp. P-81680, holotype 47.9 9.2 22.6 9.7 0.19 0.47 0.20
P-81681, paratype 40.9 9.0 19.4 8.6 0.22 0.47 0.21
P-81682, paratype 39.2 10.1 18.6 9.0 0.26 0.47 0.23
P-81683, paratype 34.3 7.9 17.1 5.5 0.23 0.50 0.16
O. n. gen., paullae
n. sp. P-81684, paratype 49.1 11.1 23.5 9.3 0.23 0.48 0.19
P-81685, paratype 46.7 9.1 22.2 10.7 0.19 0.48 0.23
P-81686, paratype 55.7 11.9 27.7 10.7 0.21 0.50 0.19
P-81687, holotype 65.5 12.8 31.7 12.5 0.20 0.48 0.19
K. cf. K. hebeiseni P-81688 54.6 12.5 24.8 11.3 0.23 0.45 0.21
P-81689 32.3 6.5 15.8 6.2 0.20 0.49 0.19
P-81690 38.4 8.1 17.7 7.0 0.21 0.46 0.18
X. mulleni n. sp. P-81691, paratype 40.8 19.0 20.5 10.1 0.47 0.50 0.25
P-81692, paratype 25.8 13.2 13.6 7.4 0.51 0.53 0.29
P-81693, holotype 49.4 19.0 21.5 14.9 0.38 0.44 0.30
P-81694, paratype 59.7 29.3 31.2 13.0 0.49 0.52 0.22
P-81695, paratype 47.1 28.8 22.5 11.5 0.61 0.48 0.24
Gray highlight – excessive corrosion, measurement estimated.
Family MULLERICERATIDAE Ware et al., 2011
Genus Ophimullericeras n. gen.
Type species: Ophimullericeras paullae n. gen., n. sp.
Composition of the genus: Type species only.
Etymology: A combination of the genus names Ophiceras
and Mullericeras, to emphasize that it represents a transitional
form between Ophiceratidae and Mullericeratidae.
Diagnosis: Small to medium sized, fairly involute,
compressed Mullericeratidae with slightly convex anks
converging to tabulate venter with angular shoulders on inner
whorls, which transitions to a broadly rounded venter without
distinct shoulders at end of phragmocone. Umbilicus fairly
narrow and moderately deep with steeply (~75°) inclined wall
and gently rounded but distinct shoulders.
Discussion: Erected by Ware et al. (2011), the family
Mullericeratidae, whose original diagnosis included
Hedenstroemidae-like shells without adventitious lobes and
saddles, consisted of one middle Dienerian genus, Mullericeras,
which included two species, i.e., M. spitiense and M. fergusoni,
from the Candelaria Formation of Nevada. Both taxa exhibit
relatively compressed, very involute shells with tabulate
venters. Ware et al. (2018a) then emended the diagnosis to
include involute, tabulate, platyconic shells with a suture line
composed of a long auxiliary series and no adventitious element
in the ventral lobe, and expanded the composition of the family
to include Ussuridiscus Shigeta and Zakharov, 2009. Some of
the taxa included in these two genera by Ware et al. (2018a), i.e.,
U. ventriosus and M. indusense, exhibit close similarity with the
present specimens, but these two forms are characterized by a
tabulate venter on the body chamber and a vertical to slightly
overhanging umbilical wall that contrasts with the steep wall
of the present specimens. Dai et al. (2019) erected one new
late Griesbachian species of Mullericeras, i.e., M. gujiaoense
from Guizhou, South China, but its umbilicus is nearly closed,
its venter remains tabulate on the body chamber, and the
indentations of it lobes and auxiliary series are irregular.
These three taxa dier from other forms of the genus in that
they are more openly coiled, with coiling geometry and umbilical
width of some specimens, e.g., M. indusense (see Ware et al.,
2018a, pl. 28, gs. 1-9), nearly identical to that of the present
specimens. However, there is one signicant characteristic that
is typical of not only these three species but of all Mullericeras
taxa (and Ussuridiscus as well), regardless of coiling geometry
– they all maintain a tabulate venter throughout ontogeny. This
feature is in contrast with Ophimullericeras paullae n. gen., n.
sp., whose inner whorls exhibit a tabulate venter with angular
shoulders that transition to a broadly rounded venter at the end
of the phragmocone. It is not unreasonable to postulate that this
transition would continue to a well-rounded venter had the body
chamber been preserved. Furthermore, the present specimens’
oblique umbilical wall diers from other genera of the family.
Thus, we consider these dierences to be sucient justication
to erect the new genus Ophimullericeras.
Apart from Mullericeratidae, the present specimens are
very close to some involute Ophiceratidae of similar age, e.g.,
Discophiceras, Kyoktites, from which they dier mostly by
their ventral features, tabulate on inner whorls (Ophiceratidae
typically have a rounded or occasionally acute venter) and
their steeper umbilical wall. We therefore consider the present
specimens to be a transitional form between the Ophiceratidae
and Mullericeratidae, and furthermore, because of their tabulate
early whorls, we opt to place them within the Mullericeratidae.
It is recognized that the architecture of the present specimens’
relatively simple suture line may be closer to some forms of
Ophiceratidae, e.g., Kyoktites hebeiseni Ware and Bucher (2018,
p. 37, pl. 2, g. 4), with its wide, elongated rst and second lateral
saddles, deep rst lateral lobe, shallow second lateral lobe, and
relatively short auxiliary series. Both taxa lack an adventive
series, but the third lateral saddle of O. paullae n. gen., n. sp.
appears to be signicantly higher. In short, this similarity in
suture lines between O. paullae n. gen., n. sp. and Ophiceratidae
is considered to be less signicant than the dierence in whorl
geometry, i.e., the distinctively tabulate inner whorls.
Ophimullericeras paullae n. sp.
Figures 8A’-G’, 11A-H
?1935 Ophiceras (Lytophiceras) dubium Spath, p. 26, pl. 2,
gs. 4a-d; pl. 11, gs. 8a, b; pl. 12, gs. 7a-c; pl. 13,
gs. 11-12; pl. 14, gs. 4, 5.
Type series: Four specimens consisting of complete
phragmocones without body chambers: Holotype, specimen
NMMNH P-81687 (Fig. 8E’-G’, 11H); paratypes, three
specimens: NMMNH P-81686 (Fig. 11A-C), NMMNH P-81684
(Fig. 8A’-D’, 11G), NMMNH P-81685 (Fig. 11D-F).
Etymology: Named in honor of Dr. Rachel Paull of Denver,
Diagnosis: As for the genus.
Description: Medium sized (diameter complete
phragmocone = 65 mm, estimated diameter complete shell
~100 mm) fairly involute, compressed (W/D = 20%, W/H =
40%) shell with slightly convex anks gently converging to
venter that transitions from tabulate with angular shoulders
on inner whorls to sub-tabulate or broadly rounded, without
distinct shoulders at end of phragmocone. Because of corrosion
in ventral region, this transitional feature is preserved on only
two specimens (Figs. 8E’-G’,11A-C), and it is assumed that the
venter would transition from sub-tabulate or broadly rounded
to well-rounded or circular on body chambers if preserved.
Maximum whorl width occurs at ~ 35 to 40% of whorl height.
Flank contour broadly convex from top of umbilical wall to point
of maximum width, then gradually converges to ventral area,
forming compressed sub-trapezoidal whorl section. Umbilicus
fairly narrow and moderately deep with steeply (~75°) inclined
wall and gently rounded but distinct shoulders. One specimen
(NMMNH P-81687, holotype) preserves the umbilical seam of
its body chamber, which exhibits a slight egression. No apparent
ornamentation. Suture line simple with rather broad lobes and
saddles, moderately wide ventral lobe without adventitious
series, broadly rounded lateral saddles of approximately equal
size, lateral lobes and auxiliary series with small regular
indentations, and no auxiliary lobe.
Measurements: See Table 1.
Discussion: Ophimullericeras paullae n. gen., n. sp.
resembles the nine variable, relatively small ophiceratid
specimens that Spath (1935) described and illustrated as
Ophiceras (Lytophiceras) dubium from the Upper Vishnuites and
Lower Proptychites beds (late Griesbachian–early Dienerian)
of East Greenland. These specimens dier in that, according to
Spath (1935), they exhibit various degrees of egressive coiling,
some are slightly more inated than others, and their umbilical
wall is more oblique and less dierentiated. Spath’s specimens
are poorly illustrated, and it is dicult to assess the amount of
egression and ination present in each specimen. Spath (1935)
stated that some of the specimens exhibit a “truncated” venter
on the inner whorls that transitions to more rounded on the
adult body chamber, but this transition is not apparent on all
specimens, in particular the holotype (Spath, 1935, pl. XIV, gs.
5a, b).
Because of these variations, we strongly suspect that these
specimens comprise an inadvertently mixed collection from
dierent horizons, with some being true ophiceratids, while
others may belong to Mullericeratidae. All Spath’s (1930, 1935)
East Greenland material was collected by others, and much of it
was collected as oat, some of which came from sections greatly
aected by soliuction (D. Ware, ongoing work). We therefore
prefer to erect a new species for the present specimens, and we
FIGURE 9. Scatter diagram comparison of H and U, and H/D and U/D for Wordieoceras wordiei (Spath) (gray-shaded circles and
triangles) and Wordieoceras mullenae n. sp. (white circles and triangles).
FIGURE 10. Box plot comparison of H/D and U/D for Wordieoceras wordiei (Spath) vs. specimens from Arctic Canada, East
Greenland and Siberia. Asterisks indicate values for holotypes of W. wordiei (blue) and W. decipiens (red).
FIGURE 11. A-H, Ophimullericeras paullae n. gen., n. sp. A-C, NMMNH P-81686, paratype, in A, lateral, B, ventral (sub-tabulate
venter preserved near end of phragmocone) and C, apertural views. D-F, NMMNH P-81685, paratype, in D, lateral, E, ventral and
F, apertural views. G-H, suture lines, in G, NMMNH P-81684, H = 26 mm, H, NMMNH P-81687, H = 29 mm. I-D’, Xiaohenautilus
mulleni n. sp. I-N, NMMNH P-81692, paratype, in I, lateral (right), J, apertural, K, lateral (left), L, ventral, M, unwhitened left
lateral, and N, unwhitened ventral views. O-S, NMMNH P-81691, paratype, in O, lateral (right), P, apertural, Q, lateral (left), and
R, ventral views. S, close-up view of venter (Fig. 11P) showing V-shaped hyponomic sinus. T-W , NMMNH P-81693, holotype, in
T, lateral (right), U, apertural, V, lateral (left), and W, ventral views. X-Y, D’, NMMNH P-81694, paratype, in X, lateral (right), Y,
ventral and D’, lateral (left). Z-C’, NMMNH P-81695, paratype, in Z, lateral (right), A’, apertural, B’ lateral (left), and C’ ventral
views. All scale bars = 1 cm.
FIGURE 12. Scatter diagrams of H and U, and H/D and U/D for
Ophimullericeras paullae n. gen., n. sp.
FIGURE 13. Scatter diagrams of H, W and U, and H/D, W/D
and U/D for Xiaohenautilus mulleni n. sp.
FIGURE 14. A-C, Clarkina carinata (Clark), NMMNH P-81697, from Loc. , in A, lateral, B, upper and C, lower views. D-F,
Clarkina griesbachiensis (Orchard), NMMNH P-81698, from Loc. +2, in D, lateral, E, upper and F, lower views. G, Clarkina
tulongensis (Tian), NMMNH P-81699, from Loc. , upper view. H-J, Merrillina sp., NMMNH P-81700, from Loc. +2, in H,
lateral, I, upper and J, lower views. K-M, Hindeodus sp., NMMNH P-81701, from Loc. 201507b, in K, lower, L, upper and M,
lateral views. See Fig. 5 for conodont sample points.
consider Ophiceras (Lytophiceras) dubium as a nomen dubium
until a proper revision of this species becomes available.
Occurrence: Found in a 2-3 cm thick siltstone bed
represented by locality number NMMNH L-12682, ~75 m
below the top of the Dinwoody Formation.
Order NAUTILIDA Agassiz, 1847
Superfamily TRIGONOCERATOIDEA Hyatt, 1884
Family GRYPOCERATIDAE Hyatt, 1900
Genus Xiaohenautilus Xu, 1988
Type species: Xiaohenautilus sinensis Xu, 1988
Xiaohenautilus mulleni n. sp.
Figure 11I-D’
Type series: Five specimens: Holotype, specimen
NMMNH P-81693 (Fig. 11T-W); paratypes, four specimens:
NMMNH P-81691 (Fig. 11O-S), NMMNH P-81692 (Fig. 11I-
N), NMMNH P-81694 (Fig. 11X-Y, D’), NMMNH P-81695
(Fig. 11Z-C’).
Etymology: Named in honor of Chris E. Mullen of Denver,
Diagnosis: Moderately evolute Xiaohenautilus with
subquadratic (early growth stages) to quadratic (later growth
stages) whorl section.
Description: Moderately evolute, fairly compressed shell
with subquadratic whorl section, broadly rounded venter,
rounded ventral shoulder and slightly convex anks with
maximum whorl width just above umbilical shoulder on early
growth stages. As shell increases in size, whorl section becomes
quadratic with broadly tabulate venter, abruptly rounded ventral
shoulders and nearly parallel anks. Umbilicus fairly narrow
with moderately high, vertical wall and rounded shoulders.
Umbilical perforation fairly small (2-4 mm). Embryonic shell
and body chamber lengths unknown. Ornamentation consists of
ne, sinuous growth lines with deep, V-shaped hyponomic sinus
on venter. Siphuncle located near venter at one fth of whorl
height. Suture simple with shallow, wide ventral lobe (Fig. 11M,
Measurements: See Table 1.
Discussion: Xiaohenautilus mulleni n. sp. is easily
distinguished from X. sinensis Xu (1988, p. 439) by its more
evolute coiling, and X. huananensis Xu (1988, p. 439) and X.
abrekensis Shigeta and Zakharov (2009, p. 53) by its quadratic
whorl section at later growth stages. However, the shells of X.
mulleni n. sp. and X. abrekensis are very similar at early growth
stages, which suggests they may be closely related.
Occurrence: Five specimens found as oat, within a
~2.5 m interval (locality NMMNH L-12683) located ~11 m
stratigraphically above the ammonoid bed, about 15 m west of
the ammonoid site, on a gentle, east-facing slope, just across
the small gulley at the foot of the ammonoid-containing hillside
(Fig. 4).
1. Newly discovered cephalopod assemblage from the
Dinwoody Formation at Crittenden Springs represents the rst
signicant report of late Griesbachian ammonoids and nautiloids
in the low-paleolatitudes of eastern Panthalassa.
2. This discovery greatly expands our knowledge of
the earliest part of the ammonoid recovery record in eastern
Panthalassa following the P-T extinction event.
3. This discovery also signies the rst report of
Wordieoceras wordiei and two co-occurring taxa, i.e., W.
mullenae n.sp. and Ophimullericeras paullae n. gen., n. sp.,
outside of the Boreal Realm.
4. The similarity in low-paleolatitude and Boreal ammonoid
faunas corroborates the concept of weak latitudinal diversity
gradients following the end-Permian extinction.
5. The Boreal anity of the late Griesbachian ammonoid
fauna contrasts with the western Panthalassa anity of the
nautiloids, i.e., Xiaohenautilus mulleni n. sp., a genus reported
only from South China and South Primorye.
The Griesbachian ammonoid and nautiloid locality lies on
land owned by the Winecup Gamble Ranch. We are grateful
for their cooperation, but we caution future paleontological
researchers that access to WGR land is restricted unless a prior
agreement is in place that may include access/exploration
fees and insurance requirements. We are especially grateful to
Rachel Paull, and Chris and Donna Mullen for sharing their past
research. We thank reviewers Romain Jattiot, Claude Monnet
and Spencer G. Lucas for their many helpful suggestions that
have greatly improved the manuscript. This research was
nancially supported by the 2015 annual research grant of the
Tokyo Geographical Society and the 2019 annual research
grant of the Fukada Geological Institute (Fukada Grant-in-Aid)
to T. Maekawa. This work is also a contribution to the ANR
project AFTER (ANR-13-JS06-0001-01) and to the French
“Investissements d’Avenir” program, project ISITE-BFC
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... This means to come back to the Griesbachian Stage as primarily defined by Tozer (1965Tozer ( , 1967Tozer ( , 1994 in the Arctic Canada. The primarily defined Griesbachian is used as such by Dagys & Weitschat (1993), Dagys & Ermakova (1996), Zakharov et al. (2020), Bjerager et al. (2006) and Jenks et al. (2021) in the Induan chronostratigraphy from Verkhoyansk Basin (Siberia), East Greenland and western USA Basin. Another example of how the conodonts are preferentially used in redrawing the Triassic time scale, to the detriment of ammonoid biostratigraphy, particularly with regard to the Norian-Rhaetian stage boundary, is the case of the Sevatian Substage, traditionally the last substage of the Norian Stage (e.g., Zapfe, 1974;Krystyn, 1980Krystyn, , 1988Krystyn, , 1990Krystyn, , 1991Golebiowski, 1990). ...
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The conodont Chiosella timorensis (Nogami, 1968) has for a long time been considered to be a suitable biotic proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. The recently acquired ammonoid record around that boundary clearly shows that the FAD of this conodont is located well below the boundary, i.e., in the late Spathian. In the present paper, it is underlined that the conodont Chiosella timorensis was promoted as a proxy for the nominated boundary in the early 1980s when the ammonoid record around the boundary was not yet well established. On the other side, until the mid 1990s the taxonomic definition and the lineage of the conodont Chiosella timorensis were not well stated, and even now there are still controversial interpretations of the taxonomic content of this conodont species. The new data achieved from the ammonoid/conodont record around the nominated boundary, especially in the western USA, and also in the Deşli Caira section in Romania, firmly demonstrate that the conodont Chiosella timorensis is a defunct proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. As a consequence, the present data on the ammonoid-documented Olenekian-Anisian/Early-Middle Triassic boundary requires the recalibration of all physical events that have been tied to the FAD of the conodont Chiosella timorensis. The case of the Albanian Kçira-section, for which the chronostratigraphic interpretation of the ammonoid record is proved incorrect, definitely makes the conodont Chiosella timorensis a defunct proxy for the nominated boundary. Also, the case of the two Chinese sections recently proposed as being "exceptional" GSSP candidates for the Early-Middle Triassic boundary, which is based on an inconsistent ammonoid/conodont biochronology, fully strengthens this conclusion. The history of the controversial usage of the conodont species Chiosella timorensis in defining the Olenekian-Anisian boundary justifies a discussion about the usefulness of conodonts in the chronostratigraphic calibration of the standard Triassic timescale. One may conclude that the conodonts are not qualified, and have not a reasonable potential, to be used to define or to redefine the boundaries of chronostratigraphic units in the standard Triassic timescale, which have been basically defined on ammonoid biochronology.
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We propose an updated ammonoid zonation for the Permian–Triassic boundary succession (the lower Nekuchan Formation) in the Verkhoyansk region of Siberia: (1) Otoceras concavum zone (uppermost Changhsingian); (2) Otoceras boreale zone (lowermost Induan); (3) Tompophiceras morpheous zone (lower Induan); and (4) Wordieoceras decipiens zone (lower Induan). The Tompophiceras pascoei zone, previously defined between the Otoceras boreale and Tompophiceras morpheous zones, is removed in our scheme. Instead of this the Tompophiceras pascoei epibole zone is proposed for the lower part of the Tompophiceras morpheous zone. New and previously published nitrogen isotope records are interpreted as responses to climatic fluctuations in the middle to higher palaeolatitudes of Northeastern Asia and these suggest a relatively cool climatic regime for the Boreal Superrealm; however the trend towards warming across the Permian–Triassic boundary transition is also seen. The evolutionary development and geographical differentiation of otoceratid ammonoids and associated groups are considered. It is likely that the Boreal Superrealm was their main refugium, where otocerid, dzhulfitid and some other ammonoids survived the major biotic crisis at the end of the Permian. The similarity of ontogenetic development of suture lines of Otoceras woodwardi Griesbach and O. boreale Spath gives some grounds for suggesting a monophyletic origin of the genus Otoceras, having bipolar distribution.
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Sediments deposited from the Permian–Triassic boundary (~252 Ma) until the end-Smithian (Early Triassic; c. 250.7 Ma) in the Sonoma Foreland Basin show marked thickness variations between its southern (up to c. 250 m thick) and northern (up to c. 550 m thick) parts. This basin formed as a flexural response to the emplacement of the Golconda Allochthon during the Sonoma orogeny. Using a high-resolution backstripping approach, a numerical model and sediment thickness to obtain a quantitative subsidence analysis, we discuss the controlling factor(s) responsible for spatial variations in thickness. We show that sedimentary overload is not sufficient to explain the significant discrepancy observed in the sedimentary record of the basin. We argue that the inherited rheological properties of the basement terranes and spatial heterogeneity of the allochthon are of paramount importance in controlling the subsidence and thickness spatial distribution across the Sonoma Foreland Basin.
Intensive sampling of three earliest Spathian sites represented by the Lower Shale unit and coeval beds within the Bear Lake vicinity and neighboring areas, southeastern Idaho, yielded several new ammonoid and nautiloid assemblages. These new occurrences overall indicate that the lower boundary of the Tirolites beds, classically used as a regional marker for the base of the early Spathian, and therefore the regional Smithian/Spathian boundary, must be shifted downward into the Lower Shale unit and coeval beds. Regarding ammonoids, one new genus (Caribouceras)and two new species (Caribouceras slugense and Albanites americanus)are described. In addition, the regional temporal distribution of Bajarunia, Tirolites, Columbites, and Coscaites is refined, based on a fourth sampled site containing a newly reported occurrence of the early Spathian Columbites fauna in coeval beds of the Middle Shale unit. As a complement to ammonoids, changes observed in nautiloid dominance are also shown to facilitate correlation with high-latitude basins such as Siberia during this short time interval, and they also highlight the major successive environmental fluctuations that took place during the late Smithian–early Spathian transition.
The Guryul Ravine section (Kashmir, India) exposes one the world's most continuous carbonate rock successions throughout the Permian-Triassic boundary and beyond. Due to political instability in this region, the biostratigraphy of this section has not been updated for nearly three decades. Following new high-resolution sampling, we reassess here the conodont biochronology and isotopic records of the fifteen lowermost stratigraphical metres (Member E) of the Khunamuh Formation at Guryul Ravine section. This interval includes both the Permian-Triassic and the Griesbachian-Dienerian (lower-upper Induan) boundaries. The First Occurrence of Hindeodus parvus, the index for the base of the Triassic, is confirmed in the middle of sub-member E2 (Unit 56 in Matsuda, 1981 [Journal of Geosciences, Osaka City University 24, 75-108]; our bed GUR09). We characterize 11 Unitary Association Zones based on the conodont record from China and from Guryul Ravine. UAZ1-2 are Late Permian and identified only in South China, UAZ3-11 are identified both in China and Guryul Ravine. The Griesbachian-Dienerian boundary is included within the interval of separation between UAZ8 and UAZ9. At Guryul Ravine, this boundary is precisely constrained between beds GUR310 and GUR311, and corresponds to the replacement of segminiplanate (here Clarkina and Neoclarkina) by segminate (Sweetospathodus and Neospathodus) conodonts. This faunal turnover was possibly linked to a climate change at the Griesbachian-Dienerian transition, from a cool and dry to a hot and humid climate. This transition could be the trigger of the migration of neogondolellids towards high latitudes and of the radiation of neospathodids during the Dienerian.
At the boundary between the Paleozoic and Mesozoic eras (~ 252 myr), the end-Permian mass extinction was the most devastating global-scale event ever recorded, resulting in the loss of more than 90 % of marine species (Raup 1979) and the disappearance or severe reduction in diversity of typical Paleozoic organisms (e.g., trilobites, tabulate and rugose corals, brachiopods). The ecological recovery of the benthos is traditionally assumed to have spanned the entire Early Triassic (i.e. ~ 5 myr), thus strikingly contrasting with that of pelagic environments and their dwellers. Whether or not this difference is the result of a selective preservation bias against the benthos cannot be excluded. However, extreme diversity fluctuations of nekto-pelagic organisms (e.g., ammonoids and conodonts) during the entire Early Triassic indicate major environmental upheavals in the ocean in the wake of the end-Permian extinction(s). In support of markedly unstable Early Triassic times, several major events are known from the sedimentary, geochemical and palynological records (e.g., Payne et al. 2004, 2010; Galfetti et al. 2007a, b, c; Hermann et al. 2011, 2012; Sun et al. 2012; Grasby et al. 2013; Romano et al. 2013; Fig. 17.1a), suggesting profound global changes in climate, sea-level and oceanic geochemistry (e.g. anoxia, euxinia, acidification). The initial low resolution time frames of These recurrent environmental deterioration events after the Permian-Triassic boundary (PTB) crisis were therefore first lumped into a “delayed recovery” model which is still the standard in effect in some recent reviews (e.g., Chen and Benton 2012).
The ammonite species Hypophylloceras (Neophylloceras) marshalli (Shimizu), Saghalinites maclurei (White), Gaudryceras striatum (Jimbo), G. aff. venustum Matsumoto, Desmophyllites sp. cf. larteti (Seunes), Damesites sugata (Forbes), Anagaudryceras politissimum (Kossmat), Eubostrychoceras cf. japonicum (Yabe), and Anapachydiscus sp. nov. aff. subtililobatus (Santonian - Maastrichtian) succession of southwestern British Columbia and Washington State. Pseudoschloenbachia (Pseudoschloenbachia) umbulazi (Baily) and Ryugasella ryugasensis Wright and Matsumoto, previously reported from the Nanaimo Group but never described, are figured for the first time. The stratigraphic distributions of Gaudryceras denmanense Whiteaves and Desmophyllites diphylloides (Forbes) in the Nanaimo Group are revised and restricted, based on re-examination of all available specimens of the two species. -Author