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The current Triassic chronostratigraphic scale is a hierarchy of three series divided into seven stages, divided further into 15 substages. Ammonoid and conodont biostratigraphies provide the primary basis for chronostratigraphic definition based on global stratotype sections and points (GSSP). I propose that Triassic chronostratigraphic definition should rely entirely on ammonoid biochronological events and thereby reject con-odont biostratigraphy and the GSSP methodology. Here I propose a new Triassic chronostratigraphy that divides the Triassic into four series (Scythian, Dinarian, Carnian and Norian), recognizes a four-stage Scythian (Griesbachian, Dienerian, Smithian and Spathian), elevates the Carnian and Norian substages (Julian, Tuvalian, Lacian, Alaunian and Sevatian) to stage rank, and includes the Rhaetian as a stage in the Norian Series. A sparse but growing database of precise radioisotopic ages supports the following calibrations: base of Triassic ~ 252 Ma, base Smithian ~ 251 Ma, base Anisian ~ 247 Ma, base Ladinian ~ 242 Ma, base Carnian ~ 237 Ma, base Norian ~ 221 Ma, base Rhaetian ~ 205 Ma, base Jurassic ~ 201 Ma. Triassic magnetostratigraphy is a series of multichrons at best, and needs vast improvement to make a substantial contribution to the Triassic timescale.
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Tanner, L.H., Spielmann, J.A. and Lucas, S.G., eds., 2013, The Triassic System. New Mexico Museum of Natural History and Science, Bulletin 61.
New Mexico Museum of Natural History and Science, 1801 Mountain Road N. W., Albuquerque, New Mexico 87104, email:
Abstract—The current Triassic chronostratigraphic scale is a hierarchy of three series divided into seven stages,
divided further into 15 substages. Ammonoid and conodont biostratigraphies provide the primary basis for
chronostratigraphic definition based on global stratotype sections and points (GSSP). I propose that Triassic
chronostratigraphic definition should rely entirely on ammonoid biochronological events and thereby reject con-
odont biostratigraphy and the GSSP methodology. Here I propose a new Triassic chronostratigraphy that divides
the Triassic into four series (Scythian, Dinarian, Carnian and Norian), recognizes a four-stage Scythian (Griesbachian,
Dienerian, Smithian and Spathian), elevates the Carnian and Norian substages (Julian, Tuvalian, Lacian, Alaunian
and Sevatian) to stage rank, and includes the Rhaetian as a stage in the Norian Series. A sparse but growing database
of precise radioisotopic ages supports the following calibrations: base of Triassic ~ 252 Ma, base Smithian ~ 251
Ma, base Anisian ~ 247 Ma, base Ladinian ~ 242 Ma, base Carnian ~ 237 Ma, base Norian ~ 221 Ma, base Rhaetian
~ 205 Ma, base Jurassic ~ 201 Ma. Triassic magnetostratigraphy is a series of multichrons at best, and needs vast
improvement to make a substantial contribution to the Triassic timescale.
….a GSSP is intended to be permanent, and thus immune to further changes in the status of its perceived
naturalness. —Walsh, Gradstein and Ogg (2004, p. 208)
The game of science is, in principle, without end. He who decides one day that scientific statements do not call for
any further test, and that they can be regarded as finally verified, retires from the game.
—Karl Popper (1959, p. 53)
Development of a Triassic timescale has a nearly 200-year-long
history that began when Alberti (1834) proposed the Triassic as a “for-
mation” between the Zechstein and Jura. During the last 40 years, devel-
opment of the Triassic timescale has been dominated by the work of the
Subcommission on Triassic Stratigraphy (STS), part of the I.U.G.S.
International Commission on Stratigraphy. This work has been under-
taken in the “Hedbergian” tradition of defining global stratotype sections
and points (GSSPs) for the bases of the Triassic stages. Thus, recently
proposed Triassic timescales (Lucas, 2010a; Ogg, 2012) are essentially
the STS timescale.
Here, I discuss the status of the Triassic timescale and reject both
conodont biostratigraphy and the GSSP methodology for timescale defi-
nition. Instead, I advocate a return to using ammonoid biochronological
events to define Triassic chronostratigraphic boundaries. I also provide a
critical evaluation of the state of Triassic radioisotopic ages,
magnetostratigraphy and an astronomically-calibrated Triassic timescale.
I thus present a new Triassic timescale that incorporates a modified
chronostratigraphy based on ammonoid biochronological events with
what I regard as reliable radioisotopic ages of most Triassic stage bound-
aries and a multichron-based step toward a Triassic geomagnetic polarity
What has been referred to by some as the “Hedbergian stratigra-
phy” is the method by which the geological timescale has been defined
(actually redefined) since the 1970s. The method focuses on agreeing on
GSSPs---global stratotype sections and points---to define stage bound-
aries and was driven largely by the efforts of Hollis Hedberg (1903-
1988), who was chairman of the International Commission on Stratigra-
phy. Walsh et al. (2004) provide a clear and brief review of the history of
the GSSP concept and methodology.
Hedberg argued for the definition of the limits of time strati-
graphic units in specific rock successions. This evolved into the current
method of defining the beginning of a time interval by fixing a base to a
chronostratigraphic unit (stage) at a single point in a single section---the
GSSP. Prior to the GSSP method, time boundaries were either defined by
equating them to major physical events (typically expressed as
unconformities) or to significant biological (evolutionary) events, which
I will refer to as biochronological events.
All three methods have strengths and weaknesses. The method of
equating time boundaries to unconformities came first and produced
readily correlateable boundaries. But, these boundaries often embodied a
hiatus of variable duration, and the method was justifiably rejected be-
cause it produced diachronous and discontinuous boundaries.
The biochronological method also has a long history, for, as
Schindewolf (1970, p. 18) well observed, “competent stratigraphy
is…only possible with the help of fossils, i.e., on the basis of irreversible
organic evolution.” Almost all Phanerozoic chronostratigraphic bound-
aries have long been defined by biochronological events. However, as is
well known, biochronological events are subject to diachroneity (nothing
happens instantly and globally) and also subject to debate (what is the
most significant event?) and can be destabilized by discovery (range
The GSSP method, which is also largely based on biochronological
events, has been claimed to be superior to both methods. GSSP defini-
tions of stage bases now focus on one biotic event, marked by the FAD
(first appearance datum) of a single taxon, in order to unambiguously
identify a single point in time at a single location. Unfortunately, the
focus on fixing a boundary in one place at one point has brought much
politics into the discussion, as many stratigraphers have a favorite place
to fix the boundary, usually the place they have worked at and too often
in their own country. Furthermore, the criterion to locate the boundary
also can be mired in the politics of specialties: ammonoid biostratigraphers
want ammonoid-based boundaries, conodont specialists want conodont-
based boundaries, etc. And, amazingly, many now believe that GSSPs are
fixed points that will not move even in the face of new data and analyses
(see, for example, the quote at the beginning of this article from an article
co-authored by former ICS Chairman Gradstein). In so believing, they
have relegated GSSPs to the status of non-scientific results (see the
quote by Popper at the beginning of this article).
The GSSP method fails primarily because of its quixotic goals,
beyond realization, and its reliance on a process confounded by politics.
Its claims to provide greater precision and stability to timescale defini-
tion than other methods are false. The fact is that many GSSPs still have
not been agreed on after nearly a half century of debate, and many of
those that received early acceptance, such as the stage boundaries of the
Silurian System, are now being redefined.
The failings of the Hedbergian stratigraphy are many, and deserve
a much longer essay than provided here. Suffice it to say that I reject the
GSSP method and advocate a return to agreed on biochronological events
as the bases of chronostratigraphic definition (see Teichert, 1958 for a
good explanation of the conceptual basis of this approach). This is not to
say I am averse to fixing boundary stratotypes, but that process as an
end in itself appears to have failed. Therefore, I return to identifying
ammonoid biochronological events as the criteria to define Triassic stage
boundaries. If we can agree on these events (and I acknowledge that this
will not always be easy), then we will have a workable timescale that we
can then improve further by studying the synchrony/diachroneity and
the correlateability of those events.
The Triassic chronostratigraphic scale was built on ammonoid
biostratigraphy. However, in the 1990s, a movement to define Triassic
stage boundaries with conodonts began, and at present the FADs of
conodont taxa will probably define as many as five stage boundaries
(bases of the Induan, Olenekian, Anisian, Norian and Rhaetian). I view
this as problematic because it broke with more than a century of practice
(see especially Mojsisovics et al., 1895) that relied on a Triassic
chronostratigraphic scale based on ammonoid-defined boundaries (which
are not always the same as the conodont-defined boundaries). By thus
abandoning priority, conodont-based definitions have not served the
stability of the Triassic timescale.
Furthermore, I see various problems with conodont-based Trias-
sic biostratigraphy, including: (1) the relative youth of Triassic conodont
taxonomy, which remains unstable for many taxa; (2) reworking of con-
odonts, which is not easily recognized and rarely addressed (Macke and
Nichols, 2007); (3) problems of facies restrictions, diachroneity and
provinciality, which do affect Triassic conodont distributions (Clark,
1984); and (4) the invisibility of conodonts on outcrop, so that they
cannot be used in the field to determine the ages of strata.
As an example of the drawbacks of using conodonts to define
Triassic stage boundaries, consider the article by Orchard (2013) in this
volume on the conodonts across the Carnian-Norian boundary at the
Black Bear Ridge section in British Columbia, Canada. Study of con-
odonts from this GSSP candidate section began in the 1980s, and
Orchard’s article well reveals the differing and frequently changing taxo-
nomic concepts and stratigraphic ranges of these conodonts (also see
Mazza et al., 2011). I believe it is premature to use these conodonts to
define a Norian base, as I doubt that this will produce a stable and long
agreed on boundary.
The ammonoid-based Triassic timescale is underpinned by nearly
two centuries of collecting and taxonomic work (e.g., Balini et al., 2010).
It provides macrofossil-based age assignments that can be used in the
field where ammonoids occur and suffers from very few reworking is-
sues. Moreover, the species-level evolution through time of ammonoids
is commonly obvious from the morphology of their shells, which record
their entire life history, whereas conodont evolution is necessarily inter-
preted from morphological change in a particular element among the
tooth-like elements that constitute their only commonly fossilized record.
To a large extent, Triassic conodont-based GSSPs were an answer
to longstanding disagreements over taxonomy and correlation among
ammonoid specialists. They were also an important part of developing
an integrated chronostratigraphic scale. As a relatively newly studied
taxonomic group, Triassic conodonts did not have the perceived “excess
baggage” of ammonoids—a long history of taxonomic changes and dis-
agreements, known provinciality (Tozer 1981; Dagys 1988) and the
demonstrably diachronous distributions of some taxa. Furthermore, the
ubiquity and perceived cosmopolitanism of conodonts as well as the
retirement in the 1990s and subsequent demise of the main Triassic
ammonoid workers, coupled with the rising ranks of younger conodont
workers, fueled the rise of Triassic conodont biostratigraphy. Neverthe-
less, future studies of Triassic conodonts will reveal that they, too, have
all of the “excess baggage” of the ammonoids and are not inherently
superior biostratigraphic tools with which to refine Triassic
chronostratigraphy. I thus reject conodont biostratigraphy as a basis for
defining Triassic chronostratigraphic units and advocate using ammonoid
biochronological events to define all Triassic stage boundaries (Fig. 2).
Current Triassic Chronostratigraphic Scale
I recently reviewed the nearly two-century-long development of
the Triassic chronostratigraphic scale (Lucas, 2010b), which is now a
hierarchy of three series, seven stages and 15 substages (Fig. 1). The first
geological studies of Triassic rocks began in Germany in the late 1700s
and culminated when Alberti (1834) coined the term Trias for the Bunten
Sandstein, Muschelkalk and Keuper of southwestern Germany, an ~1
km thick succession of strata between the Zechstein (Permian) and the
Lias (Jurassic).
Recognition of the Trias outside of Germany soon followed, and
by the 1860s Austrian geologist Edmund von Mojsisovics began con-
structing a detailed Triassic chronostratigraphy based on ammonoid bio-
stratigraphy. In 1895, Mojsisovics and his principal collaborators,
Wilhelm Waagen and Carl Diener, published a Triassic timescale that
contains most of the stage and substage names still used today
(Mojsisovics et al., 1895). Tozer (e.g., 1965, 1967, 1984, 1994; also see
Silberling and Tozer , 1968) proposed a Triassic ammonoid-based timescale
based on North American standards, particularly in the Canadian Arctic
islands and the Cordillera of British Columbia and Nevada. Distinctive
features of Tozer’s timescale included proposal of four Lower Triassic
stages (Griesbachian, Dienerian, Smithian and Spathian) and abandon-
ment of the Rhaetian as the youngest Triassic stage.
The STS began its work in the 1970s and now recognizes seven
Triassic stages in three series (Fig. 1). The 1990s saw the rise of Triassic
conodont biostratigraphy so that five agreed on (or nearly agreed on)
Triassic GSSPs use conodont events as defining features. However, after
more than 40 years of work, the STS has only achieved ratification of the
bases of three Triassic stages defined by GSSPs:
1. The base of the Induan Stage (= base of Triassic, = base of
Lower Triassic) is defined by the FAD of the conodont Hindeodus
parvus at the Meishan section in Guangxi, southern China (Yin et al.,
2. The base of the Olenekian Stage may be defined by the FAD of
a conodont at the Mud section in Spiti, India (Krystyn et al., 2007a), but
this is still under discussion. Ironically, the Mud section has an outstand-
ing ammonoid record, first monographed by Diener (1897) and Krafft
and Diener (1907), so why is a conodont-, instead of an ammonoid-based
datum to be chosen here for definition?
3. The base of the Anisian Stage (= base of the Middle Triassic)
may be defined by the FAD of a conodont at the Desli Caira section in
Romania (Orchard et al., 2007; Gradinaru et al., 2007). But, like the Mud
section, the Desli Caira section also has an excellent ammonoid record
that is not being used for GSSP definition.
4. The base of the Ladinian Stage is defined by the FAD of the
ammonoid Eoprotrachyceras curionii at the Bagolino section in Italy
(Brack et al., 2005).
5. The base of the Carnian Stage (= base of the Upper Triassic) is
defined by the FAD of the ammonoid Daxatina canadensis at the Stuores
Wiesen section in Italy (Mietto et al., 2012).
6. The base of the Norian Stage will apparently be defined by a
GSSP located either at Black Bear Ridge in British Columbia, Canada or
at Pizzo Mondello in Sicily, and it probably will be based on a conodont
event close to the base of the Stikinoceras kerri ammonoid zone, which
has been the traditional Norian base in North American usage (Orchard,
2010, 2013).
7. The base of the Rhaetian Stage is proposed to be defined by
the FAD of the conodont Misikella posthernsteini at the Steinbergkogel
section in Austria (Krystyn et al. 2007b), yet this level is essentially the
same as the FAD of the ammonoid Paracochloceras suessi, so why not
use the ammonoid FAD to define the base of the Rhaetian?
8. The base of the Hettangian Stage (= base of the Jurassic, = base
of the Lower Jurassic) is defined by the FAD of the ammonoid Psiloceras
spelae at the Kuhjoch section in Austria (Von Hillebrandt et al. 2007;
Morton, 2012).
These GSSPs define boundaries of the seven Triassic stages rec-
ognized by the STS and also define the boundaries of the three Triassic
Series and of the Triassic System (Fig.1). However, progress on such
definitions has been painfully slow--only three in more than 40 years--
so apparently the STS averages about 10-15 years per GSSP. Thus, we
can expect to wait for at least another half century before the process is
Triassic Series
I think the most significant thing we have learned from numerical
chronology about the Triassic timescale is how uneven in duration the
three traditional Triassic series are (see below). The traditional Early
Triassic is about 5 million years long, the traditional Middle Triassic is
about 10 million years long and the rest of the Triassic (the traditional
Late Triassic) is an amazingly 36 million years long! It makes no sense to
continue to divide the Triassic into three such unequal series. Indeed, by
numerical chronology, the so-called Early and Middle Triassic together
make up only about the first third of the period.
Therefore, I advocate recognizing four Triassic Series (Epochs)
(Fig. 2). Note that Mojsisovics et al. (1895) also divided the Triassic into
four series similar to (but not exactly congruent with) those I recognize
here. The four Triassic Series already have names: Scythian, Dinarian,
Carnian and Norian. The first two names are from Mojsisovics et al.
(1895), and the last two are elevation of the very long Carnian and Norian
stages to series rank. Some may argue that “Dinarian” is almost a homo-
phone of “Dienerian,” so the alternative series name Muschelkalk (or
Muschelkalkian) could be used.
The Carnian Series includes two stages (Julian and Tuvalian),
though recognition of the Cordevolian as a third, lowermost Carnian
Stage merits new discussion. The Norian Series encompasses four stages:
Lacian, Alaunian, Sevatian and Rhaetian.
It could also be argued that the four series can be justified as
bounded by major ammonoid biochronological events. Thus, the Scythian
begins with the mass extinction of ammonoids at the beginning of the
Triassic and the survival of the otoceratids. The Dinarian begins with a
major evolutionary turnover in ammonoid eviolution with extinctions
and the appearance of many new taxa. The Carnian begins with the rise
to dominance of the trachyceratines and sirenitines, and the Norian be-
gins with the extinction of the tropitids and the appearance of new
juvavitines and thisbitids. Arguably, the ammonoid events that mark the
beginnings of the Carnian and Norian are not as significant as those that
mark the beginnings of the Scythian and the Dinarian. Thus, the argu-
ment for a Triassic divided into four series is rooted more in numerical
chronology than in biochronology.
Scythian Series
Short stages are superior to long stages because they discriminate
shorter time intervals, one of the primary features of a good timescale.
The Scythian can be divided into four stages proposed by Tozer, so why
settle for two time intervals, Induan and Olenekian, especially given the
lengthy (and seemingly endless) disagreements about where and how to
define the base Olenekian GSSP? Arguments for a fourfold division of
the Lower Triassic have long been rooted in recognizing key ammonoid
biotic events that have demonstrable global correlateability (e. g., Tozer,
The beginnings of the four ages of the Scythian can be defined by
biochronological events based on ammonoid evolution. Thus, the
Griesbachian begins with the FAD of Otoceras; Otoceras is one of two
ammonoid genera that survived the end-Permian mass extinction. The
base of the Dienerian is marked by the appearance of abundant
meekoceratids, a globally recognizable event, here defined by the FAD of
Proptychites candidus.
The base of the Smithian is marked by the appearance of many
new ammonoid taxa, such as Flemingites, Kashmirites and
Hedenstroemia. This was accompanied by formation of a pronounced
latitudinal diversity of ammonoids (Brayard et al., 2006, 2007). The
Smithian base can be defined by the FAD of Hedenstroemia hedenstroemi.
FIGURE 1. The Triassic chronostratigraphic scale (from Lucas, 2010b).
The base of the Spathian is also marked by the appearance of
many new ammonoid taxa, notably the dinaritines, tirolitines and
columbitids. The disappearance of typical Smithian genera (Anasibirites,
Wasatchites, etc.) also marks the base of the Spathian. In other words, a
major ammonoid extinction occurred at the end of the Smithian/beginning
of the Spathian and was followed by a rather rapid major evolutionary
radiation (Tozer, 1982; Galfetti et al., 2007). This event corresponds to
a major perturbation of the carbon cycle that has been interpreted as a
change from warm and equable global climate (Smithian) to a latitudi-
nally-differentiated global climate (Spathian) (Galfetti et al., 2007). I
provisionally define the Spathian base by the FAD of Subolenekites
pilaticus, though work underway promises to redefine the Spathian base
with an older ammonoid event (e.g., Guex et al., 2010). For the most part
I am simply advocating a return to Tozer’s original definitions of these
stages pending further study.
Note that the beginning of the Griesbachian predates the con-
odont-based GSSP for the beginning of Triassic time. This will require
moving the base of the Triassic downward, back to its pre-conodont-
defined base.
Dinarian Series
The Dinarian Series seems to be the most stable part of the Trias-
sic chronostratigraphic scale. Anisian and Ladinian are relatively short
stages readily divided into six substages. Longstanding effort by the STS
to define the Anisian base by a GSSP in Romania based on the FAD of
the conodont Chiosella timorensis has been confounded by discovery of
Spathian records of this species. The base of the Anisian is marked by a
major ammonoid turnover. Most Spathian genera disappear at the begin-
ning of the Anisian, and a variety of taxa (Paracrochordiceras, Japonites,
Gymnites as well as danubitids, longobarditids and cladiscitids, among
others) first appear during the latest Spathian or at the Anisian base
(Tozer 1981, 1984; Brayard et al., 2006). The FAD of the ammonoid
Japonites welteri has long been available as a way to define the beginning
of the Anisian.
The Ladinian begins with the diversification of trachyceratid am-
monoids and its base has been defined by the FAD of the oldest
trachyceratid, Eoprotrachyceras curionii (Brack et al., 2005) In this
case, the GSSP method chose a significant ammonoid biochronological
event for chronostratigraphic definition.
Carnian and Norian Series
Mietto et al. (2012) recently published a ratified GSSP for the
base of the Carnian (base of the Julian)—the FAD of the ammonoid
Daxatina canadensis at the Stuores Wiesen section in northeastern Italy.
The Carnian base was long the FAD of Trachyceras aon, and I see no
reason why the FAD of Trachyceras aon could have been used to define
the beginning of the Carnian. I find it interesting that Mietto et al. (2012,
p. 414-415) state that the co-occurrence of Trachyceras and Daxatina
allows the D. canadensis zone to be considered Carnian and that they
somehow know that D. canadensis has a globally synchronous first
appearance. However, defining the base of the Carnian using the FAD of
Daxatina canadensis is at a point only a little below the FAD of
Trachyceras aon, and this is a second point in the Triassic
chronostratigraphic scale where the GSSP method has arrived at what I
considered a useful boundary definition.
In general, the Julian is dominated by Trachyceratinae, in particu-
lar Trachyceras and Austrotrachyceras, and by Sirenitinae. The base of
the Tuvalian is marked by one of the major changes in the evolution of
Triassic ammonoids, namely the near extinction of the Trachyceratinae,
as well as the radiation of Tropitidae (e.g., Tropites and closely allied
forms) and to a lesser extent Arpaditinae. For this reason, Tozer (1984)
argued that it might be better to define the Carnian base at the base of the
Definition of the Norian base by the GSSP method remains plagued
by problems of conodont taxonomy and biostratigraphy and mired in
STS politics. Two sections are the leading candidates---Black Bear Ridge
in western Canada and Pizzo Mondello in Italy. Both sections have
relatively poor ammonoid records but good conodont records, which
underscores that their candidacy has been heavily colored by the advo-
cacy of conodont-based definitions. The choice of a conodont-based
GSSP for the Norian base has been delayed for years by changing strati-
graphic ranges and the fluid taxonomy of the relevant conodonts (QED:
Orchard, 2013). The traditional boundary definition was by the FAD of
an ammonoid, Stikinoceras kerri, which is used here (Fig. 2). Indeed, the
base of the Norian and of the Lacian is characterized by major ammonoid
biochronological events: the nearly complete disappearance of Tropitidae
and the appearance of new members of Juvavitinae, such as Guembelites
and Dimorphites, and of the Thisbitidae such as Stikinoceras.
The base of the Alaunian is marked by the appearance of new
genera of Cyrtopleuritidae (Drepanites and Cyrtopleurites). Members of
this family (including Himavatites, Mesohimavatites, Neohimavatites)
FIGURE 2. The new Triassic timescale advocated here (see text for
together with some Haloritinae, such as Halorites and Thisbitidae, such
as Phormedites, characterize the Alaunian. The base of the Sevatian is
characterized by a decrease in ammonoid diversity and the first hetero-
morphic ammonoid, Rhabdoceras. Common Sevatian ammonoids are
Haloritinae (Gnomohalorites and Catenohalorites) and Sagenitidae
(Sagenites ex gr. S. quinquepunctatus). Here, I define the bases of the
Alaunian and Sevatian by traditional ammonoid FADs (Fig. 2).
The proposed definition of a GSSP for the base of the Rhaetian is
at the classic Steinbergkogel section in Austria based on the FAD of the
conodont Misikella posthernsteini (Krystyn et al., 2007b). As already
stated, the FAD of the ammonoid Paracochloceras suessi is essentially
the same level and very correlatable, so it can readily replace the con-
odont-based boundary criterion (Fig. 2).
The base of the Jurassic is defined by the FAD of the ammonoid
Psiloceras spelae at Kuhjoch, Austria. As a direct participant in the
process of selecting this GSSP, I can attest that politics (of the Subcom-
mission on Jurassic Stratigraphy: SJS) trumped agreed on procedures
and good scientific judgment. Thus, after years of study and political
wrangling, the SJS Working Group tasked to recommend a GSSP agreed
on four candidates for the GSSP location—New York Canyon in Ne-
vada, USA; Kunga Island in British Columbia, Canada; the Utcubamba
Valley in Peru; and St. Audrie’s Bay in the United Kingdom (see Lucas et
al., 2007 for a review of these). However, in 2006, when it became clear
that the European GSSP candidate (St. Audrie’s Bay) was much inferior
to the New World candidates, new European GSSP candidates, including
Kuhjoch, were added to the slate by the European-dominated working
group, long after the choice of four had been made.
Dominated by ammonoid specialists, the vote for the GSSP crite-
rion swept aside other criteria, which were a radiolarian biostratigraphic
datum or a carbon-isotope excursion. However, the voting group, which
was dominated by Europeans, chose a section in Europe, at Kuhjoch in
Austria, about which nothing had been published prior to its proposal as
a GSSP. Furthermore, the Kuhjoch GSSP is a man-made trench through
a saddle in a strike valley in the Austrian Alps (see Morton, 2012 for a
photograph), chosen over the much better exposed, more extensive and
much more fossiliferous outcrops of the New World candidates.
I realize that some will view these criticisms as little more than the
complaints of one who voted for a GSSP location not chosen. However,
the first important point here is that the choice to use the FAD of the
oldest psiloceratid ammonoid to define the Triassic-Jurassic boundary
was a good decision; it respected longstanding tradition and identified a
significant biochronological event to define the system boundary. The
second point is that the choice of the location of the GSSP was a political
one that adds little to correlateability of the boundary. Clearly, timescale
research needs to depart from the politics of choosing GSSPs.
Numerical calibration of the Triassic timescale still remains woe-
fully incomplete and imprecise, especially for the Late Triassic. The
most recent compilation (Mundil et al., 2010), some new dates (see Ogg,
2012) and a critical re-evaluation and rejection of the “long Norian”
(Lucas et al., 2012) provide the basis for the numerical calibration pre-
sented here (Fig. 3).
Some of the problems posed for numerical calibration of the Tri-
assic timescale are the same as those that face Triassic
magnetostratigraphy (see below). These include the “black box” nature
of laboratory analysis, so that the lab result is not readily evaluated and
rarely replicated; disagreements about laboratory standards (including
decay constants); changing technology; and differing standards (or thresh-
olds) for how many and what kinds of data support a reliable numerical
age determination. All of these factors should make it difficult to accept
any newly published numerical age on face value. Indeed, it is important
to see numerical ages for exactly what they are—approximations that
will change with new data and new technology. However, because they
are simple to understand as just numbers, many readily embrace newly
published numerical ages as reliable and often live to rue their decisions.
If we compare the Mundil et al. (2010) compilation to an earlier,
authoritative compilation by Forster and Warrington (1985), the most
important result of Triassic numerical chronology has been to show the
uneven duration of the three traditional Triassic series, with the Late
Triassic representing about two-thirds of Triassic time (see comments
above). Logically, it is worth using that knowledge to argue for eliminat-
ing the division of the Triassic into three very unequal series, as I have
done here (Fig. 2).
The few Triassic numbers that do calibrate the Triassic timescale
are of varied reliability:
1. To calibrate the beginning and end of the Triassic, enough num-
bers are known and have been discussed, debated and evaluated for long
enough (at least a decade) that concluding that the Triassic began about
250 Ma (more precisely 252.3 Ma) and ended about 200 Ma (more
precisely 201.5 Ma) seem highly reliable statements. These numbers are
unlikely to change by 1% or more.
2. There are a few ages that suggest a Dienerian-Smithian bound-
ary of ~ 251 Ma. A Smithian-Spathian boundary at ~ 249 Ma is an
3. Numerous Dinarian ages well-tied to marine biostratigraphy
have been known since the 1990s, especially for the Anisian. Calibration
of the beginning of the Anisian at ~247 Ma and the beginning of the
Ladinian at ~ 242 Ma seems almost as reliable as the ages of the Triassic
system boundaries.
4. Radioisotopic ages for the Carnian-Norian are scarce, and the
only “reliable” and biostratigraphically controlled age is from a Carnian
(lower Tuvalian) tuff dated at 230.9 Ma (Furin et al., 2006). A wealth of
detrital zircon ages from nonmarine strata of the Chinle Group in the
western USA are less precise because they are maximum ages of the
sediments (based on reworked zircons) and because of debate and impre-
cision relating them to marine biochronology. Lucas et al. (2012) argued
that these detrital zircon ages constrain the beginning of the Norian to ~
221 Ma.
5. The age of the Pedazzo granite and its inferred relationship to
marine biostratigraphy supports a Carnian base at ~ 237 Ma (Ogg, 2012),
but I consider this an estimate of relatively low reliability.
6. Ages of the bases of the former Carnian and Norian substages
cannot be reliably estimated. The Furin et al. (2006) age puts the Tuvalian
base close to 231 Ma. The other bases (of the Lacian, Alaunian and
Sevatian) cannot be estimated with any precision, and I simply use the
estimates of Ogg (2012) here.
7. Evidence that the Rhaetian is a relatively short stage (~ 4 million
years long) is complex to evaluate, involving an assessment of Newark
cyclostratigraphy, diverse biostratigraphy and detrital zircon ages in
nonmarine strata (Lucas et al., 2011, 2012). I estimate the Rhaetian base
as ~ 205 Ma based on such assessment, but this is one of the least reliable
estimates in the Triassic numerical timescale advocated here (Fig. 2).
The global polarity timescale for rocks of Late Jurassic, Creta-
ceous and Cenozoic age provides a valuable tool for evaluating and refin-
ing correlations that are based primarily on radioisotopic ages or bios-
tratigraphy. However, there is no agreed on geomagnetic polarity timescale
(GPTS) for the Triassic, and my assessment is that current Triassic
magnetostratigraphy has been more of a hindrance than a help to timescale
definition and correlation. The reasons are several and include inconsis-
tent results from different laboratories, poor age control of many Trias-
sic magnetostratigraphic sections and simple miscorrelation (or unsup-
portable correlation) of Triassic magnetostratigraphy, such as that which
created the “long Norian.”
Hounslow and Muttoni (2010) provided a comprehensive review
of Triassic magnetic polarity history. I rely on this review and some
FIGURE 3. Magnetostratigraphic correlations of the Pizzo Mondello and Newark sections. On the left, the correlation matches the marine and nonmarine,
biostratigraphically-determined Carnian-Norian boundary. On the right is the “pattern matched” correlation of Muttoni et al. (2004), which became the
basis of the “long Norian” (from Lucas et al., 2012).
more recent data and reappraisals (e.g., Lucas et al., 2011, 2012) and also
emphasize the multichron concept of Lucas (2011), which recognizes
intervals of dominant polarity rather than individual polarity chrons.
The reason for this is that I believe we are a long way from a well-
established succession of Triassic polarity chrons that can receive num-
bers (or names), like those of the Late Cretaceous-Cenozoic GPTS. We
do, however, at least seem to know the polarity of each of the Triassic
stage boundaries with some confidence (Hounslow and Muttoni, 2010).
One of the largest hindrances to developing a Triassic GPTS is the
polarity record of the Newark Supergroup in eastern North America,
which has confounded all attempts to correlate it to other Late Triassic
magnetostratigraphic records (Fig. 3). Given the great thickness of the
Newark section (~ 4 km of section is equivalent to much of the Late
Triassic), it arguably captures a more complete polarity history than do
the much thinner marine sections in Europe for which a magnetic polar-
ity record is available. That, however, is the only thing to recommend the
Newark magnetic polarity record, because age control of this record is
highly problematic. Thus, for example, the Triassic-Jurassic boundary
was located incorrectly in the Newark, below the CAMP basalt sheets,
for decades; this has only recently been corrected (Kozur and Weems,
2005, 2007, 2010; Lucas and Tanner, 2007; Lucas et al., 2011).
Biostratigraphic placement of the Carnian-Norian boundary in
the Newark (near the base of the Passaic Formation) is based on reinforc-
ing correlations to the Germanic Basin section from palynomorphs,
conchostracans and vertebrate biostratigraphy (Lucas et al., 2012). Aban-
donment of this boundary was based on a demonstrably incorrect corre-
lation of magnetostratigraphy in a marine section at Pizzo Mondelo in
Italy with the Newark and, coupled with a supposed astronomically-
calibrated timescale based on Newark cyclostratigaphy, created the no-
tion that the Carnian-Norian boundary is at about 228 Ma, the so-called
“long Norian” (Muttoni et al., 2004). Correct placement of the Carnian-
Norian boundary in the Newark section means it and the beginning of the
Jurassic are the only reliable biostratigraphic tiepoints for the Newark
magnetic polarity stratigraphy.
Placement of any divisions of the Carnian and Norian, including
identification of the base of the Rhaetian, are difficult to impossible in
the Newark section. Recent magnetostratigraphic correlations to a
“Rhaetian base” in the Newark (Muttoni et al., 2010; Hüsing et al., 2011)
are based on the same kinds of unsupportable magnetostratigraphic cor-
relations that produced the “long Norian,” and produce a “long Rhaetian”
of as much as 11 million years duration.
From its initial publication, no convincing correlation of the New-
ark magnetostratigraphy to broadly correlative magnetostratigraphies
could be made, simply because it contains approximately 10 times the
number of reversals found in correlative marine sections (Fig. 3). Given
what I call the rubber ruler effect---sedimentation rate stretches or con-
tracts magnetic polarity chron thicknesses so that matching patterns is
highly problematic---and the lack of biostratigraphic tiepoints, how could
any unambiguous correlation of the Newark magnetostratigraphy be
made to other polarity stratigraphies? And, why use the Newark polar-
ity history as the standard column for the Late Triassic if nothing else
can be correlated to it? Indeed, attempts to correlate the Newark polarity
record to broadly co-eval records have produced a fractious literature
with little agreement on what correlations are reliable. Both Hounslow
and Muttoni (2010) and Ogg (2012) have presented the “Solomonesque”
solution of advocating at least two correlations (notably “long Carnian”
and “long Norian”), neither of which is defensible (Lucas et al., 2012).
The Triassic magnetic polarity timescale I advocate is a set of
multichrons (Fig. 2). It is far less detailed that the provisional Triassic
GPTS of Hounslow and Muttoni (2010). But, I believe this is a realistic
abstraction of what we now reliably know about the Triassic GPTS.
Much more needs to be understood before Triassic magnetic polarity
history becomes an important part of Triassic correlation and timescale
Because the Earth’s astronomical parameters have a predictable
periodicity, they can be used, in theory, for geochronometric calibration
of the geological timescale. However, to do so, we must identify a
cyclostratigraphy in which the sedimentary cycles are forced by astro-
nomical parameters with known periods, and demonstrate that these
astronomical cycles are recorded faithfully and completely (Hinnov and
Hilgren, 2012). Such a cyclostratigraphy-based numerical timescale, called
the astronomical timescale (ATS), has been reasonably well-established
for much of Cenozoic time, from the beginning of the Oligocene (~ 34
Ma) to the present. Older parts of the timescale have less complete,
disconnected cyclostratigraphies that have been referred to as “floating
astrochronologies” (e.g., Hinnov and Ogg, 2007). The Newark
cyclostratigraphy has been identified as one such floating astrochronology
capable of providing a high resolution geochronometry for most of the
Late Triassic and the older part of the Early Jurassic (e.g., Kent and
Olsen, 1999; Ogg, 2012). However, it and other Triassic
cyclostratigraphies are fraught with problems.
Tanner (2010) reviewed the use of cycles in Triassic stratigraphy,
and he noted that high frequency (fourth and fifth-order) cyclicity is a
common feature of sedimentary sequences in Triassic depositional set-
tings. Tectonism and autocyclicity clearly drove some of this cyclicity,
but many Triassic cycles have been attributed to orbitally-forced varia-
tions in solar insolation at the Milankovitch frequencies--the precession,
as well as the short and long eccentricity cycles--at scales of tens of
thousands to hundreds of thousands of years. This orbital forcing is
thought to have controlled sedimentation through periodic changes in
climate or sea level. Examples of interpreted Milankovitch-frequency
cyclicity throughout the Triassic record include much of the Germanic
Triassic section, the Newark Supergroup of eastern North America, and
parts of the Alpine Triassic. The cyclostratigraphy of these sections has
been used as a tool for intrabasinal correlation and for chronostratigraphy.
However, conceptual arguments and radioisotopic age data call all
of these interpretations into question. Indeed, Triassic cyclostratigraphic
studies remain far from the goal of developing a reliable, astronomically-
calibrated Triassic timescale. In particular, the reliability of the
cyclostratigraphy of the Upper Triassic of the Newark basin is contra-
dicted by biostratigraphy that indicates a lack of completeness of the
Newark stratigraphic record (e.g., Kozur and Weems, 2010; Lucas et al.,
2011, 2012). Therefore, this so-called “floating astrochronology” should
sink from consideration.
The Triassic timescale proposed here (Fig. 2) is a way forward
that I see as the next logical step toward a timescale that best resolves
Triassic time with available data. It embodies the following:
1. Recognition that the three traditional Triassic series very un-
evenly divide the system. Therefore, the Triassic is divided into four
series (epochs).
2. Ammonoid biochronological events are used to define Triassic
chronostratigraphic divisions. Conodonts are not used for timescale defi-
3. The Scythian Series is divided into four stages—Griesbachian,
Dienerian, Smithian and Spathian. Induan and Olenekian are abandoned.
4. Carnian and Norian are elevated to series rank. Their subdivi-
sions (substages) are elevated to stage rank, and the Rhaetian is regarded
as the highest Triassic stage within the Norian Series.
5. The numerical age estimates of the stage boundaries are of
variable precision and reliability as discussed earlier.
6. The Triassic GPTS used here is a set of multichrons.
My expectation is that those wedded to the current GSSP method
of Triassic timescale definition will object to some or all of what has been
advocated here. Nevertheless, I challenge all interested in real progress
towards an improved Triassic timescale to consider the ideas presented
here as a way to move towards that goal.
I owe a heavy debt to many scientists who I met and (in some
cases) collaborated with during the last 20 plus years of my participation
in the STS. They taught me much about the Triassic. Adrian Hunt, Jim
Jenks, Kathy Nichols and Lawrence Tanner provided helpful reviews of
the manuscript. I dedicate this article to the memory of Tim Tozer and
Norm Silberling, who, in many ways, “got it right” decades ago.
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... The primary character supporting Theriodontia, a free-standing coronoid process of the dentary, has been argued to be convergent between interrelationships of these major clades, however, have long been controversial and are still not fully resolved. Particularly problematic for sorting out therapsid relationships is the long-branch issue-like the modern mammalian orders, all the major therapsid subclades appear within a short span of time in the fossil record and are already clearly recognizable in their first appearances in the middle Permian (i.e., there are no taxa that bridge the morphological gaps between the major clades-with the possible exception of the enigmatic Chinese taxon Raranimus, even the earliest therapsid fossils are each referable to one of these groups) (Rubidge 1991, Liu et al. 2009, 2010. Hence, therapsids may have experienced an explosive radiation similar to that of mammals following the K-Pg extinction, and it has even been suggested that the major subclades diverged so rapidly as to represent an insoluble polytomy (Kemp 2006(Kemp , 2009. ...
... Despite these problems, many studies of therapsid phylogeny do exist, in both precladistic (e.g., Watson 1921, Broom 1932, Olson 1944, 1962, Watson and Romer 1956, Romer 1966, Boonstra 1972) and modern frameworks (e.g., Hopson and Barghusen 1986, Kemp 1988a, b, Gauthier et al. 1988, Rowe 1986, Hopson 1991, Sidor and Hopson 1998, Modesto et al. 1999, Sidor 2000, Liu et al. 2009, 2010, and numerous hypotheses of relationship between the six major clades have been proposed. Two of these studies have had particularly lasting influence on our understanding of therapsid phylogeny: those of Watson and Romer (1956;refined and canonized in Romer 1966) and Hopson and Barghusen (1986;expanded in Hopson 1991expanded in Hopson , 1994. ...
... Dicynodonts were first used extensively in the subdivision of the middle Permian to Middle Triassic rocks of the Beaufort Group in the Karoo Basin of South Africa (e.g., Seeley 1892, Broom 1906a, b, Watson 1914c, d, Kitching 1977, Keyser and Smith 1977, South African Committee for Stratigraphy 1980, Rubidge 1995; see Day 2013a for a historical review of Karoo biostratigraphy), and work continues on this topic to the present day (e.g., Hancox et al. 1995, Hancox and Rubidge 2001, Neveling 2004, van der Walt et al. 2010, Day 2013b, Day et al. 2015a, Viglietti et al. 2016. Because of the richness and extensive study of those deposits, the Karoo has served as the standard of comparison for other Permo-Triassic assemblages, leading dicynodonts to have a key position in terrestrial Permian and Triassic biostratigraphy globally (e.g., von Huene 1940, Chudinov 1965, Anderson and Cruickshank 1978, Cooper 1982, Cox 1991, Lucas 1993, 1998a, b, 2006, 2010, Lucas and Wild 1995, Golubev 2005, Rubidge 2005, Lucas et al. 2007. Two comparatively recent developments promise to have important implications for dicynodont-based biostratigraphy. ...
... Sedimentological work within the Upper Karoo Group of the MZB has established a progressive shift in depositional environments through time from alluvial fan and braidplain deposits, through the fluvio-lacustrine and sheet-flood systems to fluvio-aeolian deposits. In combination with the biostratigraphical record, the Upper Karoo Group of the MZB exhibits the same long-term climatic trends as the Stormberg Group of the MKB (Smith & Kitching, 1997;Bordy et al. 2004;Sciscio & Bordy, 2016) and the Triassic globally (Lucas, 2018), with temperate, humid regimes succeeded by increasingly arid climates. ...
... In recent years, the true age of South Africa's Early-Middle Triassic record, which plays a central role in global tetrapod biostratigraphy (Lucas, 1998), has been called into question by SHRIMP isotope dilutionthermal ionization mass spectrometry (ID-TIMS) dates retrieved from the Gondwanan record in Argentina (Ottone et al. 2014). However, these ages are disputed (see Lucas, 2018). ...
The Triassic–Jurassic Upper Karoo Group of the Mid-Zambezi Basin (MZB; Zimbabwe) includes a thick succession of terrestrial sediments with high palaeontological potential that has been neglected since the 1970s. Here, we review the Upper Karoo Group stratigraphy, present detailed sedimentological work and identify new vertebrate-bearing sites at several measured sections along the southern shore of Lake Kariba. These fossil-bearing sites fall within the Pebbly Arkose and Forest Sandstone formations, and are the first to be recorded from the region since the discovery of Vulcanodon karibaensis nearly 50 years ago. The unique and diverse assemblage of aquatic and terrestrial fauna reported includes phytosaurs, metoposaurid amphibians, lungfish, non-dinosaurian archosauromorphs and non-sauropod sauropodomorph dinosaurs. This improvement of Upper Karoo Group biostratigraphy is important in refining its temporal resolution, and impacts both regional and global studies. Finally, the new fossil sites demonstrate the palaeontological importance of the MZB and its role in providing a holistic understanding of early Mesozoic ecosystems in southern Gondwana.
A new Mystriosuchinae phytosaur, Colossosuchus techniensis, is described from the Upper Triassic Tiki Formation of India. Colossosuchus is diagnosed by multiple apomorphies, including a strongly downturned terminal rosette (c. 70°), closely spaced mediolateral band‐like ornamentation on dorsal surface of the nasal, dorsolaterally oriented supratemporal fenestra, ventrolaterally inclined postorbital–squamosal bars depressed below the skull table, dorsally convex parietal–squamosal bar that descends ventrolaterally below the skull roof, dome‐shaped skull in lateral view, prominent neural arch laminae and fossae, three sacral vertebrae, robust proximal end of the tibia, and fibula with high anteroposterior flaring of the distal end. The total body length of the largest individual recovered from the bonebed is estimated to be more than 8 m, suggesting that Colossosuchus is one of the largest phytosaurs known. Phylogenetic analysis nests Colossosuchus and other undescribed specimens from India within Mystriosuchinae. These form a distinct clade and represent the earliest record of endemism among Gondwanan phytosaurs. This clade is recovered as sister taxa to ((Volcanosuchus + Rutiodon) + Leptosuchomorpha), where the depressed supratemporal fenestra first appeared in the phytosaur lineage, a feature previously used to diagnose the derived leptosuchomorphs. Early‐diverging phytosaur diversification may have coincided with the final stages of the Carnian Pluvial Event with their possible migratory routes along the circum‐Tethyan coastline. The lineage continued to evolve mostly through endemic radiations and experienced an extinction event during early Norian, which marked the disappearance of most of the non‐leptosuchomorph taxa. This is attributed to post‐CPE aridification, although more study is required.
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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.
Abundant conodont faunas from the subsurface of British Columbia, Canada, allow the correlation of Lower and Middle Triassic strata with outcrop sections in British Columbia, the Canadian Arctic and the western USA, as well as recording the previously recognized radiation of neogondolellin conodonts in the early Spathian. Twenty-eight samples collected from the Progress Hz Caribou D-040-H/094-G-07 and Progress Hz Laprise A-082-I/094-G-01 wells yielded more than 1100 conodont specimens, representing twenty-nine pectiniform species belonging to fourteen genera. These faunas enable the recognition of the Dienerian–Smithian, Smithian–Spathian, and Spathian–Anisian boundaries in these wells. Five of the conodont species recognized in the Smithian and Spathian samples are new: Neogondolella n. sp. A, Borinella n. sp. A, Magnigondolella. n. sp. A, Columbitella n. sp. A, and Co. talpa sp. nov. Together with these new segminiplanate species, several other neogondolellin conodonts occur. These faunas are the manifestation in British Columbia of the previously recognized increase in abundance of neogondolellin conodonts in the early Spathian, and they are consistent with hypotheses in which the earliest species of Magnigondolella evolved from Borinella by a progressive fusion of the denticles of the carina. These conodonts help to characterize the events around the globally significant Smithian–Spathian boundary, and to correlate this boundary in North America.
Detailed description and phylogenetic assessment of a phytosaur skull collected from the Tiki Formation of the Rewa Gondwana Basin of India and earlier diagnosed as Parasuchus hislopi, show that it pertains to a new genus and species, Volcanosuchus statisticae. The new taxon is characterized by marginal overlapping of the nostrils by the antorbital fenestrae, external nares situated on a bulbous and raised dome, the lateral surface of the jugal ornamented by a prominent ridge defined by multiple tubercles and radiating thread‐like structures, and distinct ornamentation patterns on the rostrum and skull table. Phylogenetic analysis nests Volcanosuchus within Mystriosuchinae, where it forms a sister taxon to (Rutiodon + Leptosuchomorpha) and marks the transition between the basal Parasuchidae and more derived Mystriosuchinae phytosaurs. Evolution of the phytosaur skulls resulted in changes from non‐overlapping nostril and antorbital fenestra to an overlapping state, anteroposterior elongation of the exoccipital–supraoccipital shelf, appearance of a median ridge on the basioccipital, and reduction of the supratemporal fenestra. Considerable faunal overlap of the Tiki Formation is evident with the lower Maleri Formation, which is late Carnian based on the occurrence of Hyperodapedon, Parasuchus and Exaeretodon. The Tiki Formation correlates with the Ischigualasto Formation of Argentina, the upper part of the Santa Maria Formation, and the overlying lower Caturrita Formation of Brazil, the Isalo II Beds of Madagascar, Lossiemouth Sandstone of Scotland, and the lower Tecovas Formation of the Chinle Group of North America, and ranges from late Carnian to early/middle Norian.
Multiple, small, cylindrical scroll coprolites having rounded and tapering ends and pertaining to a new ichnotaxon have been recovered from the Upper Triassic Tiki Formation of India. This is the first record of scroll coprolites from the Mesozoic. Based on cross‐sectional geometry, external surface textures, and internal morphology, these coprolites are subdivided into three morphotypes. The coprolites contain several kinds of undigested food material in the form of ganoid fish scales, teeth, lower jaw and skeletal remains of various osteichthyans, chondrichthyans, archosauriforms and indeterminate reptiles. These inclusions are embedded in the groundmass separated by thin mucosal layers. The groundmass contains abundant gas vesicles, and secondarily‐filled shrinkage cracks. EDS analysis shows that the overall composition of the coprolites reflects Ca, P, C and O, suggesting calcium phosphate mineralogy, though other elements such as Fe, Mn, Al, Si are present in lesser proportions. Based on their similarity with the scrolled faeces of extant euryhaline hammerhead sharks, it is deduced that these coprolites were produced by euryhaline hybodontid sharks. At least two hybodontid taxa, Lonchidion and Pristrisodus, show high prevalence in the Tiki vertebrate fauna, suggesting that these were the possible producers. As the coprolite inclusions contain remains of other aquatic animals, these carnivorous hybodonts constituted the dominant predators of the Tiki aquatic ecosystem.
Late Triassic ammonoids have been studied for nearly 200 years. Their most extensive fossil records come from Canada (British Columbia), the USA (Nevada), Mexico (Sonora), the Alpine regions of southern Europe (especially Austria and northern Italy), the Himalayas and Russia (Siberia). At least two provinces (Tethyan and Boreal) can be identified using Late Triassic ammonoids, but the cosmopolitanism of selected genera allows Late Triassic ammonoid correlations between provinces. The official definition of the base of the Carnian stage is based on a GSSP (global stratotype section and point) in northern Italy with its primary signal the lowest occurrence of the ammonoid Daxatina canadensis (Whiteaves). Ammonoids are also used (less formally) to define the bases of the Carnian and Norian substages, the (ascending order) Julian, Tuvalian, Lacian, Alaunian and Sevatian. The LO of the ammonoid Psiloceras spelae Guex is the primary signal for the GSSP of the base of the Hettangian (base of Jurassic = top of Triassic) in Austria. The Late Triassic evolutionary history of the Ammonoidea was punctuated by a series of events: (1) the near extinction of the trachyceratids at the beginning of the Tuvalian, followed by the diversification of the Tropitidae; (2) the extinction of the Tropitidae at the beginning of the Norian followed by the diversification of the Thisbitidae and Juvavitinae; (3) a drop in diversity and the appearance of heteromorphs during the Sevatian; (4) a substantial extinction across the Norian-Rhaetian boundary; (5) a final extinction of most of the remaining Rhaetian ammonoids followed by their Early Jurassic recovery. The Late Triassic ammonoid extinction thus was stepwise, with the most substantial drop in diversity at the end of the Norian, not at the end of the Triassic.
Ammonoid faunas representative of every major part of Triassic time occur at one place or another in the marine Triassic strata of western and arctic North America. Though some intracontinental provincialism is evident, particularly among Lower and Middle Triassic ammonoid faunas, various local sections where parts of the faunal sequence are preserved—sections in southeastern Idaho, western Nevada, northern California, northeastern Oregon, northeastern British Columbia, southwestern British Columbia, southeastern and southern Alaska, and the Arctic Islands of Canada—can be pieced together in overlapping fashion into a unified sequential framework of biostratigraphic units presented in an annotated zonal chart. At least 35 zonal units of demonstrably different age are now recognized; these units are apportioned among the Griesbachian, Dienerian, Smithian, and Spathian Stages of the Lower Triassic; the Anisian and Ladinian Stages of the Middle Triassic; and the Karnian, Norian and Rhaetian Stages of the Upper Triassic. This zonation based on North American ammonoid faunas for the first time provides an objective and reasonably detailed standard of reference for expressing the age and correlation of the marine Triassic rocks of Canada and the United States.