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Journal ArticleDOI

Co-occurrence of Neusticosaurus edwardsii and N. peyeri (Reptilia) in the Lower Meride Limestone (Middle Triassic, Monte San Giorgio)

12 Nov 2011-Swiss Journal of Geosciences (SP Birkhäuser Verlag Basel)-Vol. 104, Iss: 1, pp 167-178

Abstract: A newly opened excavation in the Cassina beds of the Lower Meride Limestone (Monte San Giorgio UNESCO World Heritage List, Canton Ticino, Switzerland), has yielded a pachypleurosaurid (Reptilia: Sauropterygia) specimen which is identified as Neusticosaurus peyeri. The resulting co-occurrence of N. peyeri and N. edwardsii, the latter so far regarded as the sole species of the genus present in this horizon, challenges the hypothesis of a single anagenetic lineage in Neusticosaurus species from Monte San Giorgio. In addition, it leads to a reconsideration of the phylogenetic inferences about Neusticosaurus evolution in the Monte San Giorgio area. The stratigraphic distribution of the Neusticosaurus species in the Monte San Giorgio basin is updated on the basis of recent finds.
Topics: Neusticosaurus (50%)

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Co-occurrence of Neusticosaurus edwardsii and N. peyeri
(Reptilia) in the Lower Meride Limestone (Middle Triassic,
Monte San Giorgio)
Rudolf Stockar
Silvio Renesto
Received: 4 March 2010 / Accepted: 7 February 2011 / Published online: 12 November 2011
Ó Swiss Geological Society 2011
Abstract A newly opened excavation in the Cassina beds
of the Lower Meride Limestone (Monte San Giorgio UNE-
SCO World Heritage List, Canton Ticino, Switzerland), has
yielded a pachypleurosaurid (Reptilia: Sauropterygia)
specimen which is identified as Neusticosaurus peyeri. The
resulting co-occurrence of N. peyeri and N. edwardsii, the
latter so far regarded as the sole species of the genus present
in this horizon, challenges the hypothesis of a single ana-
genetic lineage in Neusticosaurus species from Monte San
Giorgio. In addition, it leads to a reconsideration of the
phylogenetic inferences about Neusticosaurus evolution in
the Monte San Giorgio area. The stratigraphic distribution of
the Neusticosaurus species in the Monte San Giorgio basin is
updated on the basis of recent finds.
Keywords Neusticosaurus Lower Meride Limestone
Monte San Giorgio Middle Triassic Biostratigraphy
Phylogeny
Institutional abbreviations
MCSN Museo Cantonale di Storia Naturale, Lugano,
Switzerland
PIMUZ Pala
¨
ontologisches Institut und Museum der
Universita
¨
tZu
¨
rich, Switzerland
MUMSG Museo del Monte San Giorgio, Meride,
Switzerland
Introduction
The Cassina (also known as ‘alla Cascina’’) beds belong to
the world-renowned fossiliferous levels of the Middle
Triassic Monte San Giorgio Lagersta
¨
tte (UNESCO World
Heritage List, Canton Ticino, Southern Alps; Fig. 1), par-
ticularly famous for its rich and diverse fauna of Middle
Triassic marine vertebrates (e.g. Kuhn-Schnyder 1974;
Bu
¨
rgin et al. 1989).
In 2006 a new excavation (Fig. 1) was started by the
Museo Cantonale di Storia Naturale (MCSN), Lugano in
this fossiliferous horizon, first discovered in 1933 by the
University of Zurich which carried out several subsequent
excavations in 1937, between 1971 and 1973, and again in
1975 (see Stockar 2010 for a review). The aim of the
ongoing excavation is to carefully re-document the level in
order to provide a better characterization of the basin.
Besides over three hundred fish specimens, a new pac-
hypleurosaurid (Reptilia, Sauropterygia) specimen of the
genus Neusticosaurus was found, which is described and
discussed below.
Geological setting
The Middle Triassic succession at Monte San Giorgio
(Figs. 1, 2) starts with a fluvio-deltaic sequence dated to
the late Anisian (Bellano Formation, Illyrian; Sommaruga
Editorial handling: Jean-Paul Billon-Bruyat.
R. Stockar (&)
Museo Cantonale di Storia Naturale, Viale Cattaneo 4,
6900 Lugano, Switzerland
e-mail: rudolf.stockar@ti.ch
R. Stockar
Institut de Ge
´
ologie et Pale
´
ontologie, Universite
´
de Lausanne,
Anthropole, 1015 Lausanne, Switzerland
S. Renesto
Department of Structural and Functional Biology, Universita
`
degli Studi dell’Insubria, via Dunant 3, 21100 Varese, Italy
Swiss J Geosci (2011) 104 (Suppl 1):S167–S178
DOI 10.1007/s00015-011-0077-x

et al. 1997), overlying a Permian volcanic succession. The
upper Anisian sediments testify to the progressive trans-
gression of a shallow epicontinental sea and the related
growth of carbonate platforms (Salvatore Dolomite; Zorn
1971) north of a land area buried today under the Po Plain
(Brusca et al. 1981; Picotti et al. 2007). During the latest
Anisian and Ladinian, whereas in the north shallow-water
sedimentation continued, in the Monte San Giorgio area the
formation of a 30–100 m deep and 10–20 km wide intra-
platform basin with restricted circulation (Furrer 1995)
resulted in the deposition of the Besano Formation, the San
Giorgio Dolomite and the Meride Limestone.
The Besano Formation (‘‘Grenzbitumenzone’’; Frau-
enfelder 1916), is an alternation of black shales and
dolomites up to 16 m thick, including in its uppermost part
the Anisian–Ladinian boundary (Brack et al. 2005); a
volcanic ash layer lying a few metres below this boundary
resulted in an U–Pb minimum age of 242.1 ± 0.6 Ma
(Mundil et al. 2010). The Besano Formation, which yielded
most of the spectacular vertebrate fossils (fishes and rep-
tiles) together with important index fossils such as
ammonoids and daonellid bivalves, grades upwards into
the 60 m thick San Giorgio Dolomite. The overlying
400–600 m thick Meride Limestone (Furrer 1995) begins
with the Lower Meride Limestone, 90 m (Wirz 1945)to
150 m thick (Furrer 1995), which bears three fossil tetra-
pod beds (Cava inferiore, Cava superiore and Cassina
beds), each yielding different vertebrate assemblages
(Sander 1989;Bu
¨
rgin et al. 1989) and consisting of finely
laminated limestones with intercalated volcanic ash layers.
The top of the Lower Meride Limestone is defined by a
dolomite bed (‘‘Dolomitband’’; Frauenfelder 1916), reach-
ing a thickness of about 30 m (Wirz 1945). The overlying
Upper Meride Limestone is made up of alternating well-
bedded limestones and marlstones with an increasing clay
content towards the top, where strong seasonal variations of
salinity and water level together with the influence from a
neighbouring emerged area are documented. The uppermost
part comprises the so-called ‘Kalkschieferzone’’, which is
120 m thick and which represents the late evolution of the
intraplatform basin, followed by the Carnian regressive
phase (Pizzella Marls; Furrer 1995).
The pachypleurosaurids from Monte San Giorgio
Pachypleurosaurids (Sauropterygia) are generally small
Middle Triassic marine reptiles, restricted to shallow-water
habitats and widely reported from western Tethyan and
eastern Tethyan faunal provinces. According to Rieppel
(2000), the family Pachypleurosauridae N
OPCSA 1928 con-
stitutes a monophyletic taxon. Pachypleurosaurid genera
from China (Keichousaurus, Hanosaurus) are the sister-taxa
of European pachypleurosaurids (Rieppel 1998, 2000, but
Lower Salvatore Dolomite
San Giorgio Dolomite
Besano Formation
50m
Meride
Limestone
Switzerland
Italy
Arzo
Meride
Besano
Serpiano
Porto Ceresio
Poncione d'Arzo
Monte San Giorgio
Lake Lugano
Cassina beds / locality
Cassina
45°54' N
8°57' E
Fig. 1 Map of the Monte San
Giorgio area showing the
Middle Triassic carbonate
sequence and the location of the
excavation site of the Cassina
beds near Cassina (after Stockar
2010). Scale bar 1km
S168 R. Stockar, S. Renesto

Holmes et al. 2008 suggested that Keichousaurus is instead a
basal nothosauroid); amongst the latter, the central European
Muschelkalk (Germanic Triassic) pachypleurosaurids
(Anarosaurus, Dactylosaurus) are the sister-taxa of those
from the Alpine Triassic. Cladistic relationships thus indicate
a diversification from the eastern Tethyan faunal province into
the western Tethys (Rieppel 2000, 2010). The first diversi-
fication of pachypleurosaurids in the western Tethyan realm
followed the marine transgression that began in the late Early
Triassic and proceeded from east to west across central
Europe. This enabled the colonization of the central Euro-
pean Muschelkalk basin by pachypleurosaurids (and by
other sauropterygians and protorosaurs) from the eastern
Tethyan faunal province via the East Carpathian gate fol-
lowing the northern Paleotethys branch (Rieppel and
Hagdorn 1997; Rieppel 2010). The opening of southern
gateways (the Silesian–Moravian gate in the east and, above
all, subsequently by the late Anisian and early Ladinian the
Burgundy gate in the west) allowed pachypleurosaurids to
disperse into the southern Alpine intraplatform basins
(Rieppel and Hagdorn 1997; Rieppel 2010), where the
crown-group pachypleurosaurs (SerpianosaurusNeustico-
saurus clade) further diversified. Admittedly, some isolated
remains from the middle Muschelkalk might be referred to
Serpianosaurus, but conclusive diagnostic remains are
missing (Rieppel and Hagdorn 1997). The increased taxic
diversity observed in Monte San Giorgio deposits might be
correlated with a greater habitat fragmentation in the intra-
platform southern Alpine basin facies, which from the late
Anisian is included in the ‘unstable shelf area’ (Mostler
1993), compared to the habitat of the Muschelkalk basin
(Rieppel and Lin 1995).
The Alpine pachypleurosaurid genera Serpianosaurus
and Neusticosaurus occur in the Monte San Giorgio
sequence as abundant vertebrate fossils in the Besano
Formation and in all three tetrapod-bearing beds of the
Lower Meride Limestone (e.g. Cornalia 1854; Zangerl
1935; Sander 1989). According to Rieppel and Lin (1995),
Serpianosaurus R
IEPPEL 1989 is the sister-taxon of the
genus Neusticosaurus S
EELEY 1882. In his monographic
description, Sander (1989) stated that, at Monte San
Giorgio, four species occur in stratigraphic superimposition
(Fig. 2), namely, Serpianosaurus mirigiolensis R
IEPPEL
1989 (Besano Formation, Anisian–Ladinian boundary)
followed through the Ladinian by Neusticosaurus pusillus
S
EELEY 1882 (Cava inferiore beds), Neusticosaurus peyeri
S
ANDER 1989 (Cava superiore beds) and, finally, Neusti-
cosaurus edwardsii C
ORNALIA 1854 (Cassina beds), the
latter being the largest species, reaching 120 cm in length.
According to the same author, different species have never
been found together in the same horizon, suggesting that
their stratigraphic ranges never overlap; consequently, he
interpreted the genus Neusticosaurus not only as forming a
monophyletic taxon but also as possibly constituting a
single lineage undergoing anagenetic change within the
Monte San Giorgio sequence. Sander’s assumptions were
challenged by Kuhn-Schnyder (1994), but the treatment of
the three Neusticosaurus species as segments of an ana-
genetic lineage has subsequently been supported by
O’Keefe and Sander (1999). The implications of these
conclusions are discussed in Rieppel (2000, p. 52). Even
from a not strictly palaeontological point of view, the
assumption of a sequential temporal appearance such as
this, ruling out species co-occurrence, is particularly
intriguing, since it lends a biostratigraphic potential to
these commonly occurring tetrapods, even though limited
to the Monte San Giorgio where both N. peyeri and N.
edwardsii are found to be endemic. Elsewhere, N. pusillus
seems to have persisted virtually without morphological
change throughout the late Ladinian in both the Alpine and
Germanic Triassic (O’Keefe and Sander 1999; Rieppel 2000).
In the Germanic Triassic N. pusillus is the only diagnosable
Neusticosaurus species (Rieppel and Hagdorn 1997)and
*
*
Permian Triassic
Liassic
Anisian
Rhyolithe and
associated
volcaniclastics
Bellano Fm.
Cassina beds
Cava superiore beds
Cava inferiore beds
Kalkschieferzone
Pizzella Marls
Meride Limestone
Dolomia Principale
Tremona Series
"Dolomitband"
Lower Salvatore
Dolomite
Besano Fm.
Rhaet
Carnian
Ladinian
Norian
100 m
0 m
242.1 +/- 0.6 Ma
(U-Pb age; Mundil et al. 2010)
San Giorgio
Dolomite
S. mirigiolensis
N. pusillus
N. peyeri
N. edwardsii
Figure 8
Fig. 2 Stratigraphic distribution of the pachypleurosaurids from
Monte San Giorgio, according to Sander (1989) and O’Keefe and
Sander (1999). Stratigraphic log modified from Furrer (1995)
Neusticosaurus from Monte San Giorgio S169

occurs in the Hohenecker Limestone, a lateral equivalent of
the ‘Lingula Beds’ of the upper part of Lower Keuper.
According to Brack et al. (1999), this time interval is
possibly somewhat younger than the Protrachyceras
gredleri ammonoid zone to which, in turn, occurrences of
N. pusillus from Monte San Giorgio (Cava inferiore beds)
are restricted (Stockar 2010, p. 105), being later substituted
by those of N. peyeri and N. edwardsii (at least in part still
within the P. gredleri zone; Stockar 2010, p. 105). If cor-
rect, the geographic and temporal distribution pattern of
N. pusillus described above would support the view of Rieppel
and Hagdorn (1997), according to which the Serpiano-
saurusNeusticosaurus clade diversified in the southern
Alpine intraplatform basin facies and later (N. pusillus)
returned to the Germanic basin during the Ladinian via the
Burgundy gate. However, caution is necessary. As admit-
ted by Rieppel and Lin (1995), unequivocal identification
of Neusticosaurus species depends on the availability of
fairly complete specimens, which is not usually the case as
far as the upper Muschelkalk facies of the Germanic basin
is concerned, even though disarticulated pachypleurosaur
remains are abundant there. Consequently, the opposite
scenario of an initial migration of N. pusillus during the
early Ladinian from the Germanic to the Alpine basin,
where the genus subsequently further diversified, cannot be
ruled out a priori.
Materials and methods
The new excavation site lies to the south of the summit of
Monte San Giorgio, a little way out of the outcrop where
the Cassina beds were originally discovered in 1933
(Fig. 1). Here, the Cassina beds (Stockar 2010) form an
almost 3 m thick interval, mainly consisting of interbed-
ded, finely laminated, organic-rich shales and limestones
(laminite lithofacies) with intercalated thicker limestones
(turbidite lithofacies) and volcaniclastic layers derived
from volcanic ash suspension-fall (tephra lithofacies). The
sequence grades upwards into the thick-bedded dolomitic
limestones and dolomites belonging to the ‘Dolomitband’’.
So far, the upper third of the succession (Fig. 3) has been
excavated bed by bed over a surface of around 40 m
2
,
yielding a well-preserved vertebrate fauna mainly com-
posed of fishes belonging to at least six species, dominated
by the large predatory actinopterygian Saurichthys. Reptiles
turned out to be rare in the upper part of the Cassina beds
and the specimen belonging to the genus Neusticosaurus
described here is the only articulated find recovered so far.
The Cassina beds are traditionally regarded as early
Ladinian in age (e.g. Hellmann and Lippolt 1981; O’Keefe
et al. 1999) but reliable index fossils such as ammonoids
and conodonts have never been reported from this horizon.
Furrer et al. (2008) tentatively correlated the Cassina beds
with the lowermost Wengen Formation of the GSSP sec-
tion at Bagolino (Protrachyceras archelaus ammonoid
zone, late Ladinian; Brack et al. 2005). This correlation is
consistent with the occurrence of Echinitosporites iliaco-
ides (Scheuring 1978), a palynomorph which is regarded as
limited to the late Ladinian P. archelaus zone (see Stockar
2010 for a review of biostratigraphic data).
The Neusticosaurus specimen is mostly articulated and
exposed in ventral view, as reported for most pachypleu-
rosaurids from Cava inferiore and Cava superiore beds.
This preservation pattern is ascribed to the development of
decay gas in the wide abdominal cavity which held the
body with the ventral side upward (Furrer 2003). The
specimen was recovered from a 8 mm thick bed belonging
to the laminite lithofacies which, according to Stockar
(2010), testifies to anoxic to suboxic bottom-water condi-
tions with possible growth of benthic microbial mats and
consequent bio-armouring effect of carcasses.
According to our examination of the historical collection
stored at the Pala
¨
ontologisches Institut und Museum der
Universita
¨
tZu
¨
rich (PIMUZ) and to unpublished field data
(both courtesy Heinz Furrer, PIMUZ), the bulk of Neusti-
cosaurus material from the Cassina beds comes from just the
base of the sequence, which lies approximately 2 m below
the bed bearing the specimen described here. Consequently,
the latter is slightly younger than most (if not all) known
pachypleurosaurid specimens from the Cassina beds.
The specimen was mechanically prepared with the aid of
vibrotools and sharpened needles.
Systematic palaeontology
Class Reptilia L
AURENTI 1768
Superorder Sauropterygia O
WEN 1860
Order Eosauropterygia R
IEPPEL 1994
Infraorder Pachypleurosauroidea H
UENE 1956
Family Pachypleurosauridae N
OPCSA 1928
Genus Neusticosaurus S
EELEY 1882
Neusticosaurus peyeri S
ANDER 1989
Type species: PIMUZ T3615 (Sander 1989), a complete
specimen from Cava superiore beds.
See Sander (1989, p. 601–602) for synonymy.
Material: specimen MCSN 8076 of the collection of the
Museo Cantonale di Storia Naturale, Lugano, Switzerland,
collected from bed 34, Cassina beds, Lower Meride
Limestone (Figs. 4, 5, 6, 7).
Measurements (in mm):
Skull length (from the tip of the snout to the occipital
condyle): 22.3
S170 R. Stockar, S. Renesto

Fig. 3 Detailed
sedimentological log of the
upper part of the Cassina beds
being investigated, with an
indication of the distribution
and abundance of vertebrate
fossils (after Stockar 2010,
modified)
Neusticosaurus from Monte San Giorgio S171

Figures (8)
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Abstract: The new neopterygian genus Ticinolepis, including two new species T. longaeva and T. crassidens is described from Middle Triassic carbonate platform deposits of the Monte San Giorgio. The anatomy of this fish shows a mosaic of halecomorph and ginglymodian characters and, thus, the new taxon probably represents a basal holostean. During the latest Anisian to earliest Ladinian the two new species coexisted in the intraplatform basin represented by the uppermost Besano Formation, but only T. longaeva sp. nov. inhabited the more restricted basin represented by the Ladinian Meride Limestone (except for the Kalkschieferzone). The more widely distributed type species shows interesting patterns of intraspecific variation including ontogenetic changes and morphological variation over time. The second species presents anatomical features that strongly indicate a strictly durophagous diet. The different distribution of the species is interpreted as a result of habitat partitioning and different adaptability to palaeoenvironmental changes.

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Cristina Lombardo1Institutions (1)
TL;DR: The species is characterized by a single plate-like branchiostegal, a suboperculum larger than the operculum, a maxillary fixed and posteriorly expanded, a large and rectangular dermopterotic and a large triangular dermosphenotic.
Abstract: A new taxon of Late Ladinian basal actinopterygian is described on the basis of a single specimen from the Meride Limestone (Kalkschieferzone) of Meride (Canton Ticino, Switzerland). The species is characterized by a single plate-like branchiostegal, a suboperculum larger than the operculum, a maxillary fixed and posteriorly expanded, a large and rectangular dermopterotic and a large triangular dermosphenotic; the scales are rectangular to rhomboidal, the lepidotrichia of median fins are segmented from their base and the caudal fin shows epaxial rays. These features resemble the condition of the Redfieldiiformes, a freshwater fish group, whose presence in Europe is still controversial, owing to poor preservation of specimens found so far.

9 citations


Cites background from "Co-occurrence of Neusticosaurus edw..."

  • ...…the uppermost levels of Meride Limestone, the Kalkschieferzone (=KSZ), dating from the Late Ladinian, turned out to be very interesting for their faunal composition, and also for paleoenvironmental studies (Lombardo and Tintori 2002; Stockar 2010; Stockar and Renesto 2011; Stockar et al. 2012)....

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  • ...In particular, the uppermost levels of Meride Limestone, the Kalkschieferzone (=KSZ), dating from the Late Ladinian, turned out to be very interesting for their faunal composition, and also for paleoenvironmental studies (Lombardo and Tintori 2002; Stockar 2010; Stockar and Renesto 2011; Stockar et al. 2012)....

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References
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Journal ArticleDOI
03 Feb 1998-Copeia
TL;DR: J.M. Moody, The Paleogeography of Marine and Coastal Turtles of the North Atlantic and Trans-Saharan Regions and G.L. Bell, Jr., Phylogenetic Revision of North American and Adriatic Mosasauridea.
Abstract: M.A. Taylor, Foreword. Ichthyosauria: J.M. Callaway, Introduction. P.M. Sander, The paleobiogeography of Shastasaurus. J.M. Callaway, A New Look at Mixosaurus. C. McGowan, A Transitional Ichthyosaur Fauna. R. Motani, Temporal and Spatial Distribution of Tooth Implantation in Ichthyosaurs. Sauropterygia: O.C. Rieppel, Introduction. O.C. Rieppel and H. Hagdorn, Paleobiology of Middle Triassic Sauropterygia in Central and Western Europe. G.W. Storrs, Morphologic and Taxonomic Clarification of the Genus Plesiosaurus. K. Carpenter, Comparative Cranial Anatomy of Two North American Cretaceous Plesiosaurs. Testudines: E.L. Nicholls, Introduction. R. Hirayama, Distribution and Diversity of Cretaceous Chelonoids. D.K. Elliott, G.V. Irby, and J.H. Hutchison, Desmatochelys Iowa, a Marine Turtle from the Upper Cretaceous. R.T.J. Moody, The Paleogeography of Marine and Coastal Turtles of the North Atlantic and Trans-Saharan Regions. Mosasauridae: G.L. Bell, Jr., Introduction. G.L. Bell, Jr., Phylogenetic Revision of North American and Adriatic Mosasauridea. A. Sheldon, Ecological Implications of Mosasaur Bone Microstructure. Crocodylia: S. Hua and E. Buffetaut, Introduction. R.K. Denton, Jr., J.L. Dobie, and D.C. Parris, The Marine Crocodile, Hyposaurus, in North America. Faunas, Behavior, and Evolution: J.A. Massare, Introduction. S.G. Lucas, Marine Reptiles and Mesozoic Biochronology. Z. Gasparini and M. Fernandez, Tithonian Marine Reptiles of the Eastern Pacific. R. Collin and C.M. Janis, Morphological Constraints on Tetropod Feeding Mechanisms: Why Were There No Suspenion-Feeding Marine Reptiles? R.L. Carroll, Mesozoic Marine Reptiles as Models of Long Term, Large-Scale Evolutionary Phenomena. Subject Index.

174 citations


Peter, Brack, Hans, Riebe  +4 more
01 Jan 2005

152 citations


"Co-occurrence of Neusticosaurus edw..." refers background in this paper

  • ...…Frauenfelder 1916), is an alternation of black shales and dolomites up to 16 m thick, including in its uppermost part the Anisian–Ladinian boundary (Brack et al. 2005); a volcanic ash layer lying a few metres below this boundary resulted in an U–Pb minimum age of 242.1 ± 0.6 Ma (Mundil et al.…...

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  • ...Furrer et al. (2008) tentatively correlated the Cassina beds with the lowermost Wengen Formation of the GSSP section at Bagolino (Protrachyceras archelaus ammonoid zone, late Ladinian; Brack et al. 2005)....

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Journal ArticleDOI
Roland Mundil1, József Pálfy2, Paul R. Renne3, Paul R. Renne1  +1 moreInstitutions (4)
Abstract: A review of geochronological data underlying the geological time-scale for the Triassic yields a significantly different time-scale calibration than that published in the most recent compi- lation (Geologic Time Scale 2004). This is partly due to the availability of new radio -isotopic data, but mostly because strict selection criteria are applied and complications arising from biases (both systematic and random) are accounted for in this contribution. The ages for the base and the top of the Triassic are constrained by U- Pb ages to 252.3 and 201.5 Ma, respectively. These dates also constrain the ages of major extinction events at the Permian- Triassic and Triassic- Jurassic bound- aries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K -Ar ( 40 Ar/ 39 Ar) system, which requires accounting and correcting for a systematic bias of c. 1% between U -Pb and 40 Ar/ 39 Ar isotopic ages (the 40 Ar/ 39 Ar ages being younger). Robust age constraints also exist for the Induan- Olenekian boundary (251.2 Ma) and the Early- Middle Triassic (Olenekian-Anisian) boundary (247.2 Ma), resulting in a surprisingly short dur- ation of the Early Triassic, which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time. Furthermore, the Anisian-Ladinian boundary is con- strained to 242.0 Ma by new U- Pb and 40 Ar/ 39 Ar ages. Radio- isotopic ages for the Late Triassic are scarce, and the only reliable and biostratigraphically-controlled age is from an upper Carnian tuff dated to 230.9 Ma, yielding a duration of more than 35 Ma for the Late Triassic. All of these ages are from U-Pb analyses applied to zircons with uncertainties at the permil level or better. The resulting compilation can only serve as a guideline and must be considered a snapshot, resolving some of the issues mainly associated with inaccurate and misinterpreted data in previous publi- cations. However, further advances will require revision of some of the data presented here.

150 citations


Journal ArticleDOI
P. M. Sander1Institutions (1)
TL;DR: Morphometric comparison of all four pachypleurosaurids indicates that the changing vertebral numbers between species are largely due to a change in number of segments, and taphonomic analysis of the small species indicates attritional mortality and suggests weak bottom currents in the Monte San Giorgio basin during early Ladinian times.
Abstract: The largest and most diverse collection of Pachypleurosauridae (Nothosauria, Reptilia) comes from Monte San Giorgio, Switzerland. Several hundred complete skeletons were collected from four distinct horizons of bituminous limestones and shales of Anisian-Ladinian boundary to early Ladinian age (Middle Triassic). Serpianosaurus mirigiolensis comes from the oldest strata, the Grenzbitumenzone Beds. The three younger strata, all in the Lower Meride Limestone, yield three species of Neusticosaurus. Neusticosaurus pusillus comes from the Cava Inferiore horizon, Neusticosaurus peyeri, new species, from the Cava Superiore horizon, and Neusticosaurus edwardsii, new combination, from the Alla Cascina horizon. Neusticosaurus pusillus is biostratigraphically important because it is one of the rare species reported from both the Germanic and the Alpine Triassic. Neusticosaurus pusillus and N. peyeri are small and very similar in their anatomy. Neusticosaurus species are easiest separated by their number of presacral vertebrae. Ornamentation of the bone surface is distinctive for all four pachypleurosaurids. Soft parts are rarely preserved, except for one partial squamation. The biological age of Neusticosaurus individuals can be determined by skeletochronology (aging by bone annuli). Small species of Neusticosaurus were sexually mature after three to four years and lived for six to nine years. Taphonomic analysis of the small species indicates attritional mortality and suggests weak bottom currents in the Monte San Giorgio basin during early Ladinian times. Morphometric comparison of all four pachypleurosaurids indicates that the changing vertebral numbers between species are largely due to a change in number of segments. All Monte San Giorgio pachypleurosaurids are sexually dimorphic in forelimb development. Sex x has poorly differentiated and relatively short humeri whereas sex y has well differentiated and relatively long humeri. The sexes are of about the same size and represented in roughly equal numbers. Identification of gender was not possible. Good growth series, especially of Neusticosaurus peyeri, from embryo to large adult permitted qualitative and quantitative study of ontogeny. The skull grows with negative allometry; the humerus grows isometrically or with positive allometry, depending on sex and species; the femur grows isometrically. The adult size range in N. peyeri is considerably larger than in modern reptiles. The Monte San Giorgio pachypleurosaurids are a monophyletic group. The phylogeny of this group is congruent with the stratigraphic distribution of its members.

139 citations


"Co-occurrence of Neusticosaurus edw..." refers background or methods or result in this paper

  • ...…evidence of habitat partitioning, based on the marked differences in adult size (up to 550 mm and up to 1,200 mm in overall length, respectively, according to Rieppel 2000), as well as in dentition (the tooth count is higher in N. edwardsii, which also shows more functional teeth; Sander 1989)....

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  • ...Along with a large collection of specimens attributed to N. peyeri (according to Sander 1989 the only species occurring in this horizon) one specimen was recovered and ascribed to N. edwardsii (MCSN 5624; Heinz Furrer, PIMUZ, personal communication, 2009)....

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  • ...In addition, the dorsal vertebrae count (probably 20) is lower than in N. pusillus (22–24; Sander 1989, p. 578; Rieppel and Lin 1995, p. 35; Rieppel 2000, p. 53)....

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  • ...…(Wirz 1945) to 150 m thick (Furrer 1995), which bears three fossil tetrapod beds (Cava inferiore, Cava superiore and Cassina beds), each yielding different vertebrate assemblages (Sander 1989; Bürgin et al. 1989) and consisting of finely laminated limestones with intercalated volcanic ash layers....

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  • ...Medially, the long, thin splenial is visible, followed by the slim prearticular which lies below a deep surangular; a small coronoid bone seems to be present, as in N. pusillus and N. peyeri (Sander 1989), but no coronoid process is visible....

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