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Earth-Science Reviews 234 (2022) 104196
Available online 28 September 2022
0012-8252/© 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-
nc-nd/4.0/).
Impact of the Jenkyns Event (early Toarcian) on dinosaurs: Comparison
with the Triassic/Jurassic transition
M. Reolid
a
,
*
, W. Ruebsam
b
, M.J. Benton
c
a
Departamento de Geología and CEACTEMA, Universidad de Ja´
en, Ja´
en, Spain
b
Department of Organic and Isotope Geochemistry, Institute of Geoscience, University of Kiel, Germany
c
University of Bristol, Bristol, United Kingdom
ARTICLE INFO
Keywords:
Climatic change
Mass extinction
Sauropodomorphs
Theropods
Ornithischians
ABSTRACT
The Early Jurassic Jenkyns Event (~183 Ma) was characterized in terrestrial environments by global warming,
perturbation of the carbon cycle, enhanced weathering and wildres. Heating and acid rain on land caused a loss
of forests and affected diversity and composition of land plant assemblages and the rest of the trophic web. We
suggest that the Jenkyns Event, triggered by the activity of the Karoo-Ferrar Large Igneous Province, was pivotal
in remodelling terrestrial ecosystems, including plants and dinosaurs. Macroplant assemblages and palynological
data show reductions in diversity and richness of conifers, cycadophytes, ginkgophytes, bennetitaleans, and
ferns, and continuation of seasonally dry and warm conditions. Major changes occurred to sauropodomorph
dinosaurs, with extinction of diverse basal families formerly called ‘prosauropods’ as well as some basal sau-
ropods, and diversication of the derived Eusauropoda in the Toarcian in South America, Africa, and Asia, and
wider diversication of new families, including Mamenchisauridae, Cetiosauridae and Neosauropoda
(Dicraeosauridae and Macronaria) in the Middle Jurassic, showing massive increase in size and diversication of
feeding modes. Ornithischian dinosaurs show patchy records; some heterodontosaurids and scelidosaurids dis-
appeared, and major new clades (Stegosauridae, Ankylosauridae, Nodosauridae) emerged soon after the Jenkyns
Event, in the Bajocian and Bathonian worldwide. Among theropod dinosaurs, Coelophysidae and Dilophosaur-
idae died out during the Jenkyns Event and a diversication of theropods (Megalosauroidea, Allosauroidea,
Tyrannosauroidea) occurred after this event with substantial increases in size. We suggest then that the Jenkyns
Event terrestrial crisis was marked especially by oral changes and origins of major new sauropodomorph and
theropod clades, characterized by increasing body size. Comparison with the end Triassic Mass Extinction helps
to understand the incidence of climatic changes driven by activity of large igneous provinces on land ecosystems
and their great impacts on early dinosaur evolution.
1. Introduction
From the Late Triassic to Middle Jurassic, faunas and oras on land
were affected by substantial palaeogeographic and palaeoclimatic
changes as well as extinction crises at the end of the Triassic and in the
early Toarcian. Whereas the end-Triassic mass extinction (ETME) event
is well recognized, there has been little investigation on the impact of
the early Toarcian crisis on terrestrial life, and our aim here is to
compare the effects of both events.
The Triassic–Jurassic transition was associated with one of the ‘big
ve’ largest Phanerozoic extinctions (Sepkoski, 1996; McElwain et al.,
1999; McGhee et al., 2013). Major biotic turnovers occurred in both
marine and terrestrial realms (McElwain et al., 1999, 2007; Palfy et al.,
2000; Hallam, 2002; Hesselbo et al., 2002; Olsen et al., 2002; van de
Schootbrugge et al., 2009; Lindstr¨
om et al., 2012; Wignall and Atkinson,
2020; Opazo and Page, 2021). The volcanism related to the emplace-
ment of the Central Atlantic Magmatic Province (CAMP), with emissions
of CO
2
, CH
4
, SO
2
and Hg, has been considered as the main trigger for the
severe environmental changes leading to the ETME (Gotz et al., 2009;
Deenen et al., 2010; Schoene et al., 2010; Ruhl et al., 2010, 2011; Greene
et al., 2012; Percival et al., 2017; Panli et al., 2019; Lindstr¨
om et al.,
2019; Kaiho et al., 2022).
The early Toarcian witnessed an important environmental change
called the Jenkyns Event (e.g. Müller et al., 2017; Reolid et al., 2020,
* Corresponding author.
E-mail addresses: mreolid@ujaen.es (M. Reolid), wolfgang.ruebsam@googlemail.com (W. Ruebsam), Mike.Benton@bristol.ac.uk (M.J. Benton).
Contents lists available at ScienceDirect
Earth-Science Reviews
journal homepage: www.elsevier.com/locate/earscirev
https://doi.org/10.1016/j.earscirev.2022.104196
Received 4 July 2022; Received in revised form 22 September 2022; Accepted 23 September 2022
Earth-Science Reviews 234 (2022) 104196
2
2021a; Erba et al., 2022), dated at ~183 Ma, that was one of the most
important hyperthermal events of the Mesozoic (e.g. García Joral et al.,
2011; Korte and Hesselbo, 2011; Suan et al., 2011; Danise et al., 2013;
Baghli et al., 2020; Storm et al., 2020; Ruebsam et al., 2020a, 2020b).
Ruebsam et al. (2020b), using TEX86 palaeothermometry proxies for
NW Tethys, estimated a warming of 5 ◦C at the Pliensbachian-Toarcian
boundary and a peak of 10 ◦C warming during the Jenkyns Event.
Documented phenomena during this event include: (1) oxygen depleted
conditions in some marine basins, the Toarcian Oceanic Anoxic Event
(T-OAE, Gill et al., 2011; Fonseca et al., 2018; Izumi et al., 2018;
Ruebsam et al., 2018; Suan et al., 2018); (2) a crisis of marine carbonate
productivity (Bucefalo-Palliani et al., 2002; Mattioli et al., 2004) and
acidication (Müller et al., 2020; Ettinger et al., 2021); (3) a perturba-
tion of the carbon cycle expressed as a negative carbon isotopic excur-
sion (CIE; e.g. Jenkyns and Clayton, 1986; Kemp et al., 2005; Hesselbo
et al., 2007; Ruebsam et al., 2019, 2020a); and (4) a sea-level rise (e.g.
Hallam, 1981; Pittet et al., 2014; Haq, 2018; Krencker et al., 2019).
In this context of environmental change, the early Toarcian is also
characterized by a second-order extinction that affected marine benthos,
including brachiopods, corals, foraminifera and ostracods, and pelagic
forms such as ammonites (e.g. Hallam, 1987; Little and Benton, 1995;
Aberhan and Fursich, 2000; Harries and Little, 1999; Macchioni and
Cecca, 2002; V¨
or¨
os, 2002; Wignall et al., 2005; Arias, 2009, 2013; Dera
et al., 2010; García Joral et al., 2011; Caruthers et al., 2014; Baeza-
Carratal´
a et al., 2017; Reolid et al., 2019; Vasseur et al., 2021).
We now regard the Jenkyns Event as a hyperthermal event, similar to
the end-Permian and end-Triassic events, but at lower intensity. Among
the causes of the Jenkyns Event is the emission of volcanic CO
2
and
thermogenic CH
4
related to the emplacement of the Karoo-Ferrar Large
Igneous Province (LIP) that broadly coincides with the negative CIE
(Hesselbo et al., 2007; Moulin et al., 2017; Fantasia et al., 2019; Font
et al., 2022). However, destabilization of marine methane hydrates
(Hesselbo et al., 2000; Kemp et al., 2005) and deterioration of climate-
sensitive reservoir permafrost areas during the global warming (Rueb-
sam et al., 2019) may have contributed to the input of greenhouse gases
into the atmosphere. This gives a model for the effects on ocean, at-
mosphere and biosphere. We might expect heating and acid rain on land,
leading to a loss of forests and some sediment wash into the sea, together
with aridity and sporadic heavy rainfall conditions on land, all features
of the standard hyperthermal model (Benton and Newell, 2014; Benton,
2018).
The Jenkyns Event also affected emerged lands, and many authors
have identied enhanced weathering (e.g. Brazier et al., 2015; Montero-
Serrano et al., 2015; Them et al., 2017) and aridity (Rodrigues et al.,
2019; Lu et al., 2020; Font et al., 2022). The early Toarcian global
warming also affected terrestrial ecosystems. Rodrigues et al. (2019,
2021) proposed a decreased
13
C fractionation during photosynthesis in
C3 plants, conrming an arid climate for emerged areas of Western
Tethys during the Jenkyns Event. Other changes in terrestrial ecosys-
tems affected diversity and composition of land plant assemblages
(Slater et al., 2019, and references therein) and the increase of wildres
in some areas (Baker et al., 2017).
Dinosaur faunas underwent remarkable evolutionary changes during
the Late Triassic and Early Jurassic (Benton, 1993; Brusatte et al., 2008a,
2008b; Allen et al., 2019; Klausen et al., 2020; Novas et al., 2021; Langer
and Godoy, 2022). However, the discontinuous terrestrial fossil record
and the lack of reliable age constraints have hampered their correlation
to environmental changes or to major events in oral evolution (Barrett,
2014). In any case, the most studied event that had an impact on di-
nosaurs is the ETME (Benton, 1993; Brusatte et al., 2010; Allen et al.,
2019; Singh et al., 2021) whereas the Jenkyns Event remains little
studied (Rauhut et al., 2016; Pol et al., 2020) and poorly understood.
The aim of this work is to identify changes in diversity, size, and
palaeogeographic distribution of dinosaur assemblages in the Early
Jurassic and the impact of early Toarcian global warming but taking into
account the variable quality of the palaeontological record. The
incidence of the Jenkyns Event is compared with the ETME, one of the
‘big ve’ largest Phanerozoic extinctions.
2. Materials and methods
2.1. Palaeontological data
The fossil record of continental organisms, especially vertebrates, is
patchy, with large temporal gaps between sampling horizons (Benton,
1998; Lloyd et al., 2008; Benson and Butler, 2011; Benton et al., 2011,
2013). Further, much of what we know comes from particular horizons
or formations, some of them fossil lagerst¨
atten. In addition, the dating of
continental sedimentary formations is often less certain than for marine
formations.
For the present study, we refer to individual faunas as records of
‘typical’ assemblages of plants and animals of the time, and we explore
diversity-through-time curves. The latter are especially dependent on
homogeneous sampling through time and across all geographic regions
and habitats, which is clearly not possible. Therefore, we distinguish the
narrative evidence of ‘typical’ or ‘exemplar’ faunas and oras, where
evidence is rich and informative, versus uses of the data in which sam-
pling heterogeneity is an issue, including diversity-through-time plots.
Nonetheless, despite suggestions that the amount of error in the data
might make large-scale interpretation risky or awed, we argue instead
that the broad story of the history of life as documented in the fossil
record is roughly correct (Sepkoski et al., 1981; Benton, 1998). We base
this assumption on three lines of evidence, (1) study of collector curves
shows that the application of intense searching by palaeontologists and
even the opening up of new territories such as China, does not materially
affect the large-scale knowledge of stratigraphic ranges of major clades
(Benton, 2008; Benton et al., 2013), (2) comparisons of cladograms with
the fossil record show good correspondence in most cases (Norell and
Novacek, 1992; Benton et al., 2000), and (3) lagerst¨
atten do not
necessarily distort the records (Walker et al., 2019).
For this study, we include a total of 207 species (see Table 1 of the
Supplementary material) after a detailed review of the taxonomic as-
signments, updated ages of the lithostratigraphic formations where
fossil remains were recovered, geographic areas and inferred sizes from
the literature, when available.
We assign the species and genera to widely recognized families and
other small monophyletic groups, except for a few stem taxa that lie at
the bases of major clades, which we term informally “basal Sau-
ropodomorpha”, “basal Sauropoda”, and “stem Neotheropoda”. When
these terms are introduced in the text, we specify their content; in the
current, dened context we can then refer to origins and extinctions of
these paraphyletic groups, but this is for narrative purposes, and we
highlight that such paraphyla do not have origins and extinctions in the
real sense in which clades do.
2.2. Climate trends
Climate records from continental sedimentary archives are sparse,
patchy, and imprecisely dated for the Late Triassic and Early Jurassic.
Therefore, climate trends (global warming/cooling) were reconstructed
from oxygen isotope data measured on belemnite and brachiopod calcite
and conodont phosphates (see Table 2 of the Supplementary Material 2
for data sources). Boxplots with a step size of 2.5 Myr were calculated for
the oxygen isotope data to assess secular climate trends and variability
within a 2.5 Myr interval. Boxplots and smoothing splines were calcu-
lated using PAST software (Hammer et al., 2001). The 2.5 Myr step size
approximates the temporal resolution and dating inaccuracy of the
paleontological data.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
3
3. Results
3.1. Dinosaur assemblages
3.1.1. Sauropodomorpha
The rst dinosaurs, ancestors of sauropods, appearing during the
Carnian (Late Triassic, Fig. 1), were the Guabasauridae (Chromogisaurus,
Pamphagia, Saturnalia) and the basal Sauropodomorpha (Bagualosaurus,
Buriolestes, Pampadromaeus) in the south of Gondwana (Cabreira et al.,
2016; Müller et al., 2018) (Fig. 2). These were bipedal small forms
(1.3–2.5 m long) with slender bodies (<25 kg) (Martínez and Alcober,
2009; Ezcurra, 2010; Cabreira et al., 2016; Müller et al., 2018; Pretto
et al., 2019).
During the Norian (Late Triassic), Sauropodomorpha diversied and
extended to other parts of Pangea with the rst records in Europe
(Agnosphytis, Pantydraco, Efraasia, Plateosaurus, Ruehleia) and India
(Nambalia, Jaklapallisaurus) (Figs. 1 and 2). Diversication is also evi-
denced by new genera of guaibasaurids (Agnosphytis, Guaibasaurus) and
basal Sauropodomorpha (Pantydraco, Nambalia, Efraasia) as well as
appearance of new groups of Sauropodomorpha including Theco-
dontosauridae, Plateosauridae, Massospondylidae and Riojasauridae
(Martínez and Alcober, 2009; Novas et al., 2021) (Figs. 1 and 3). These
families were commonly termed ‘prosauropods’, a paraphyletic assem-
blage of early sauropodomorphs characterized by long necks, small
heads, barrel-shaped bodies and long tails. Plateosauridae include larger
forms with bipedal/quadrupedal posture (Bonnan and Senter, 2007),
forelimbs shorter than hindlimbs, reaching around 8 m length and
>1000 kg (e.g. Plateosaurus longiceps) (Fig. 4), and distributed through
different areas, with Macrocollum and Unaysaurus recorded from South
America (Leal et al., 2004; Müller et al., 2018), Plateosaurus and Ruehleia
from Europe (Yates, 2003) and Jaklapallisaurus from India (Novas et al.,
2011) (Fig. 2). In addition, during the Norian the rst representatives of
basal Sauropoda are Lessemsaurus from South America (Pol and Powell,
2007) and Meroktenos from South of Africa (Peyre de Fabr`
egues and
Allain, 2016). These rst sauropods were quadrupedal with neck and tail
moderately to extremely long, head short, skeleton heavily built and
forelimbs and hindlimbs less exed than in more basal forms.
The Norian/Rhaetian boundary represents the end of guaibasaurids
(Figs. 1 and 3), but also during the Rhaetian basal Sauropodomorpha
diversied, mainly Plateosauridae and the rst Melanorosauridae
(Brusatte et al., 2010; McPhee et al., 2017) (Fig. 3). The size and weight
of these groups increased, with many genera surpassing 10 m length (e.
g. Eucnemesaurus, Euskelosaurus, Riojasaurus, Ingentia, Camelotia; Fig. 4)
and they were quadrupedal when moving normally (Yates and Kitching,
2003; Bonnan and Yates, 2007; Yates et al., 2010; Brusatte et al., 2010).
The end of the Triassic is characterized by the extinction of most
basal Sauropodomorpha (Pantydraco, Nambalia, Asylosaurus, Sefapano-
saurus, Thecodontosaurus), members of Plateosauridae (Plateosaurus,
Plateosauravus, Euskelosaurus) and Melanorosauridae (Camelotia, Mela-
norosaurus), and some genera of basal sauropods (Blikanasaurus, Mer-
oktenos, Ingentia) (Brusatte et al., 2010; McPhee et al., 2017; Novas et al.,
2021) (Fig. 1).
The beginning of the Jurassic is marked by the rst occurrence of
many taxa (Figs. 1–4). Basal sauropodomorphs persist with one genus,
Arcusaurus (South Africa; Yates et al., 2011), and Plateosauridae with
Yimenosaurus (Asia; Bai et al., 1990) and the closely related Xixiposaurus
(Asia, Sekiya, 2010) (Fig. 1). Among basal sauropodomorphs, Anchi-
sauria and Massospondylidae radiated from Hettangian to Pliensba-
chian, anchisaurians mainly in the Hettangian (Figs. 1 and 3). Basal
Sauropoda also diversied at the beginning of the Jurassic (e.g.
Ammosaurus, Yizhousaurus, Pulanesaura, Antetonitrus, Ledumahadi)
(Brusatte et al., 2010; McPhee et al., 2017, 2018). In addition, the rst
eusauropod, Tonganosaurus (Family Mamenchisauridae) is recorded in
the Hettangian of the Yimen Formation (China; Li et al., 2010).
During the earliest Jurassic, sauropodomorphs extended north of the
palaeoequator and are recorded from Asia (Irisosaurus, Jingshanosaurus,
Lufengosaurus, Xingxiulong, Xixiposaurus, Yimenosaurus, Yizhousaurus,
Yunnanosaurus) and North America (Ammosaurus, Anchisaurus, Sar-
ahsaurus, Seitaad) (e.g. Bai et al., 1990; Sertich and Loewen, 2010; Yates,
2010; Rowe et al., 2011; Wang et al., 2017a; Peyre de Fabr`
egues et al.,
2020) (Fig. 2).
The beginning of the Toarcian marks the extinction boundary for the
last basal sauropodomorphs, including Anchisauria and Massospondy-
lidae even though they were diverse during the Sinemurian and
Pliensbachian (Figs. 1 and 3). Only some basal Sauropoda survived the
Jenkyns Event, in Asia with Isanosaurus (Buffetaut et al., 2000), Gong-
xianosaurus (Yaonan and Wang, 2000), Sanpasaurus (McPhee et al.,
2016) and Zizhongosaurus (Hou et al., 1976), in Africa with Vulcanodon
(Cooper, 1984) and Tazoudasaurus (Allain et al., 2004), in India with
Barapasaurus (Jain et al., 1975), and in Europe with Ohmdenosaurus
(Wild, 1978) (Fig. 1). The record of basal Sauropoda is surely incom-
plete, but most of them disappeared before the Aalenian (Middle
Jurassic, Fig. 3), with the exception of Archaeodontosaurus, a possible
basal sauropod from the Bathonian of Madagascar (Buffetaut, 2005)
(Fig. 1).
After the Jenkyns Event, many Eusauropoda (Upchurch, 1995)
appeared, such as Bagualia, Patagosaurus, Volkheimeria (South America;
Pol et al., 2020), Spinophorosaurus (Africa; Remes et al., 2009), and
Nebulasaurus (Asia; Xing et al., 2013) (Figs. 1 and 2). Mamenchisaur-
idae, Cetiosauridae and Neosauropoda (Dicraeosauridae, Macronaria)
appeared and diversied during the Middle Jurassic (Fig. 3). Among the
Macronaria, the end of the Middle Jurassic records the rst camar-
asaurid (Dashanpusaurus, Bathonian) and the rst brachiosaurid (Atlas-
aurus, Callovian). Eusauropods were characterized, among other
features, by massively built skeletons, skeletal pneumacity (with inter-
nal systems of cavities in vertebrae, the pleurocoels), pillar-like limbs,
very robust pelvis bones, and delicate skulls.
Sauropods are noted for their great size, but truly giant forms arose in
the late Middle and Late Jurassic. Large sauropods include African
Macronaria such as Jobaria tigidensis (21 m, Callovian to Oxfordian of
Niger; Sereno et al., 1999) and Atlasaurus imalakei (17 m, Callovian of
Morocco; Monbaron et al., 1999), Asian mamenchisaurids such as
Analong chuanjieensis (20 m, Bathonian of China; Ren et al., 2021),
Anhuilong diboensis (20 m, Aalenian to Bathonian of China; Ren et al.,
2020), Chuanjiesaurus anaensis (25 m, Callovian of China; Sekiya, 2012),
Mamenchisaurus hochuanensis (22 m, Callovian to Oxfordian of
China, Young and Zhao, 1972), and Xinjiangtitan shanshanensis (30 m,
Bathonian to Callovian of China; Wings et al., 2013), and the rst
Turisauria, Narindasaurus thevenini (20 m, Madagascar; Royo-Torres
et al., 2021) (Fig. 4). The estimated weights of these largest sauropods of
the end of the Middle Jurassic ranged between 17 and 22 t (Paul, 2016;
Molina-P´
erez and Larramendi, 2020).
3.1.2. Theropoda
Herrerasaurids have been hypothesized by Sereno et al. (1993),
Sereno (1999) and Nesbitt et al. (2009) as basal members of Theropoda,
and by other authors (summarized, Novas et al., 2021) as basal Sau-
ropodomorpha. Although likely sauropodomorphs, their diets were
carnivorous or omnivorous (Novas et al., 2021), so that Family Her-
rerasauridae (e.g. Herrerasaurus, Caseosaurus, Gnathovorax, Staur-
ikosaurus, Sanjuansaurus) were some of the earliest carnivorous
dinosaurs, as well as the stem Neotheropoda (Nhandumirim, Eoraptor,
Eodromaeus) recorded from the Carnian (Upper Triassic) of South
America (Novas et al., 2021) (Figs. 5–7). They were slightly built forms
with head and neck moderately long, and sizes around 1–2 m and <50
kg. The largest species of the Carnian was Herrerasaurus ischigualastensis,
at 6 m and around 300 kg (Sereno and Novas, 1992) (Fig. 8).
The Norian was a stage of diversication and geographic expansion
of theropods (Figs. 6 and 8), with dominance of Coelophysidae recorded
in Europe (Procompsognathus, Liliensternus) and North America (Gojir-
asaurus, Camposaurus, Coelophysis) and Dilophosauridae in Europe
(Notatesseraeraptor) and South America (Zupaysaurus) (Fig. 5).
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
4
Fig. 1. Distribution of genera of sauropodomorphs from Late Triassic to Middle Jurassic. The early Toarcian biotic crisis is indicated with a gray bar.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
5
Coelophysis, the best representative of Coelophysidae is a medium-size
theropod with a maximum length around 3 m and around 1 m to the
hip (Schwartz and Gillette, 1994; Therrien and Henderson, 2007; Hen-
drickx et al., 2015; Reolid et al., 2021b). However, Liliensternus reached
much larger body size, approaching >5 m (Peczkis, 1994). The neck is
very long and the skull is elongated with big eyes and the deep jaw
presents numerous curved, serrated teeth (Therrien and Henderson,
2007). Coelophysidae were slender runners with a narrow pelvis, fore-
limbs adapted to catch prey, large hindlimbs with very narrow feet and a
long and stiff tail that worked as a counterweight. Despite being an early
dinosaur, the theropod bodyplan is clearly developed in Coelophysis. The
largest coelophysid of the Norian was Gojirasaurus reaching 6.5 m and
around 200 kg (Carpenter, 1997) (Fig. 8). The dilophosaurids were more
robustly constructed than coelophysids, with necks shorter and thicker
than in Coelophysis. Herrerasauridae disappeared at the end of the Car-
nian and only a potential herrerasaurid, Chindesaurus of North America
(Marsh et al., 2019), is recorded in the Norian (Fig. 5).
The record of theropods of the Rhaetian is scarcer but they were
present in many ecosystems as evidenced by trace fossils (Grallator and
Eubrontes ichnogenera; Gierlinski and Ahlberg, 1994; Niedzwiedzki,
2008; Meyer et al., 2015; Szewczyk et al., 2020). Herrerasaurids are not
recorded in the Rhaetian and probably went extinct at the end of the
Norian (Figs. 5 and 7).
The beginning of the Jurassic is dominated by the families Coelo-
physidae (Coelophysis, Panguraptor, Megapnosaurus, Sarcosaurus) and
Dilophosauridae (Shuangbaisaurus, Dracovenator, Dilophosaurus) (Fig. 6).
As for sauropodomorphs, theropods extended during the Early Jurassic.
Both families, Coelophysidae and Dilophosauridae colonized Asia
(Panguraptor, Shuangbaisaurus) and Africa (Megapnosaurus, Dracovena-
tor) during the Hettangian and Sinemurian (Yates, 2006; You et al.,
2014; Wang et al., 2017b) (Figs. 5–7). Dilophosauridae occupied the top
of the trophic system, with Dracovenator and Dilophosaurus (5–6.5 m and
270–390 kg; Therrien and Henderson, 2007; Reolid et al., 2021b) being
among the largest theropods in the Early Jurassic. Recently, Marsh and
Rowe (2020) proposed that Dilophosaurus is a stem-averostran theropod
rather than a member of Coelophysoidea.
New taxonomic groups commenced during the earliest Jurassic,
representing the basal forms of Ceratosauria (Saltriovenator; Dal Sasso
et al., 2018) and Tetanurae (Dracoraptor, Sinosaurus, Kayentavenator,
Cryolophosaurus) (Figs. 5 and 7). They were robuster forms than Coe-
lophysoidea, as for example Saltriovenator zanellai from the Sinemurian
of Italy (around 7 m; Dal Sasso et al., 2018) and Cryolophosaurus ellioti
from the Sinemurian-Pliensbachian of Antarctica (around 6.5 m; Smith
et al., 2007) (Fig. 8).
The beginning of the Toarcian was a major break in the evolution of
theropods. The families Coelophysidae and Dilophosauridae dis-
appeared during the Toarcian, but new basal Ceratosauria are recorded
in the Toarcian such as Berberosaurus from Morocco (Allain et al., 2007)
and Dandakosaurus from India (Yadagiri, 1982) (Figs. 5 and 7). After the
Jenkyns Event, during the late Toarcian the rst species of Allosauroidea
is recorded, Asfaltovenator vialidadi from Ca˜
nad´
on Asfalto Basin
(Argentina; Rauhut and Pol, 2019) at around 8 m length (Figs. 5 and 8)
as well as the rst megalosauroids of Family Piatnitzkysauridae (Con-
dorraptor and Piatnitzkysaurus; Rauhut, 2005; Carrano et al., 2012).
The recovery of theropods occurred during the Middle Jurassic with
the appearance of most basal Tetanurae (Ozraptor, Gasosaurus, Kai-
jangosaurus, Cruxicheiros) and diversication of the clades Mega-
losauroidea (Megalosauridae), Allosauroidea (Metriacanthosauridae)
and Tyrannosauroidea (Proceratosauridae) that dominated during the
Late Jurassic and Cretaceous (Figs. 5 and 7). The size of some theropods
increased during the Middle Jurassic, especially among Mega-
losauroidea and Allosauroidea such as Megalosaurus bucklandii (Mega-
losauridae, 9 m; Benson, 2010), Piveteausaurus divesensis
(Megalosauridae, 11 m; Benson et al., 2018) and Sinraptor dongi (Met-
riacanthosauridae, 8 m; Currie and Zhao, 1993) (Fig. 8).
3.1.3. Ornithischia
The potential rst ornithischian was Pisanosaurus mertii from the
upper Carnian of the Ischigualasto Formation (Argentina; Casamiquela,
1967; Bonaparte, 1976) but some argue it was really a silesaurid dino-
sauriform (Müller and García, 2020). A more convincing earliest
ornithischian is Eocursor parvus from the lower Elliot Formation (Nor-
ian–Rhaetian) of South Africa, represented by a partial skull and rela-
tively complete postcranial skeleton. Eocursor was small, about 1 m long,
with elongate hindlimbs, large hands, and herbivorous, leaf-shaped
teeth. It appears to be a basal ornithischian, occurring before the split
into Heterodontosauridae and Genasauria (Butler, 2010). However,
Olsen et al. (2010) afrmed that the assignment of these deposits to
Upper Triassic is not supported by data, and McPhee et al. (2017) dated
them as lowermost Jurassic.
Late Triassic Heterodontosauridae are represented by two small
forms (<120 cm) from the Rhaetian of South Gondwana, Lycorhinus
(Africa) and Manidens (South America) (Thulborn, 1970; Pol et al.,
2011) (Figs. 9–12). Heterodontosaurids were bipedal, with large canine-
like teeth on both upper and lower jaws, powerful forelimbs and clawed
manus, suggesting they could catch and consume small prey (Norman
et al., 2011), but Sereno (2012) concluded that they were predominantly
or exclusively herbivorous because of the tooth-to-tooth shearing wear
facets in the dentition of Echinodon, Lycorhinus, Pegomastax,
Fig. 2. Record of sauropodomorphs according to different continental masses
from Late Triassic to Middle Jurassic. The thickness of the trends is according to
the number of genera. Note that some components of Gondwana and Laurasia
are differentiated. Main biotic crisis are identied with a red line (end Triassic
Mass Extinction) and gray bar (early Toarcian biotic crisis). (For interpretation
of the references to colour in this gure legend, the reader is referred to the web
version of this article.)
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
6
Abrictosaurus and Heterodontosaurus. The oblique shearing occlusion is a
sophisticated ornithischian adaptation for processing plants, and infer-
red jaw functions also favour an herbivorous diet (Sereno, 2012).
Ornithischians diversied at the beginning of the Jurassic in South
Gondwana with the appearance of new genera of Heterodontosauridae
(Africa; Abrictosaurus, Heterodontosaurus, Pegomastax) but also the origin
of a new family of bipedal herbivores, Fabrosauridae (Africa; Fabro-
saurus and Lesothosaurus) (Figs. 9–11). The clade Thyreophora, repre-
sented by the Family Scelidosauridae, originated and diversied in
Laurasia during the Early Jurassic (Laquintasaura from Central America,
Scutellosaurus from North America, Lusitanosaurus, Scelidosaurus, and
Emausaurus from Europe, and Yuxisaurus and Bienosaurus from Asia)
(Fig. 11). Thyreophorans are characterized by parallel rows of keeled
dermal armour scutes or bony plates (osteoderms) on the dorsal surface
of the body. Scelidosaurids were quadrupedal and had heavily built
bodies, and only Scutellosaurus and Emausaurus were bipedal. The po-
tential rst genus of Neornithischia, Stormbergia, appeared during the
earliest Jurassic (Butler, 2005) (Fig. 9). Therefore, the main divisions of
the Clade Genasauria, Thyreophora and Neornithischia, were estab-
lished in the earliest Jurassic, the former being more diverse (Fig. 11).
The record of ornithischians is scarce from Toarcian to Bajocian.
During the Bathonian and Callovian, a new diversication of ornithis-
chian occurred (Fig. 12). Fabrosaurids are represented by two genera
from China, Xiaosaurus and Agilisaurus (Peng, 1992; Barrett et al., 2005).
Scelidosauridae disappeared during the Toarcian (Fig. 11), but new
families of thyreophorans arose from Bajocian and Bathonian such as
Stegosauridae (Isaberrysaura, Adratiklit, Huayangosaurus, Eoplophysis,
Lexovisaurus, Loricatosaurus), Ankylosauridae (Tianchiasaurus) and
Nodosauridae (Sarcolestes) (Figs. 9 and 11). The new thyreophorans
were widely distributed, having been recorded from Europe (Eoploph-
ysis, Lexovisaurus, Loricatosaurus, Sarcolestes), Asia (Huayangosaurus,
Tianchiasaurus), Africa (Adratiklit) and South America (Isaberrysaura).
Stegosaurids were large quadrupedal thyreophorans characterized by
osteoderms that evolved into plates and spines, forelimbs being sub-
stantially shorter than the hindlimbs, and thin and elongated small
heads in a low position. The biggest recorded species of the Middle
Jurassic were the stegosaurids Adratiklit boulahfa reaching 7 m (Maid-
ment et al., 2019), Isaberrysaura mollensis at 6 m (Salgado et al., 2017)
and Lexovisaurus durobrivensis at 6 m (Paul, 2016) (Fig. 12). Ankylosaurs
(Ankylosauridae and Nodosauridae) were armoured, robust forms
characterized by the presence of shields (from the neck to the tail)
composed of interlocked bony plates, with a very broad body and a head
in a low position.
Neornithischians were represented at the end of the Middle Jurassic
by two small forms from Siberia (Kulindadromeus, 1.5 m; Godefroit et al.,
2014) and Europe (Callovosaurus, ~3.5 m; Ruiz-Ome˜
naca et al., 2007),
compared to Late Jurassic neornithischians such as iguanodontids and
hadrosaurids. Finally, the rst hypsilophodontid (Hexinlusaurus) is also
recorded in the Bathonian and Callovian of China (Barrett et al., 2005).
They were small bipedal herbivores (commonly <2 m) that proliferated
during the Late Jurassic and Cretaceous.
Heterodontosauridae were not recorded, but new genera appeared in
Fig. 3. Temporal distribution of main clades of Sauropodomorpha. Main biotic crisis are identied with a red line (end Triassic Mass Extinction) and gray bar (early
Toarcian biotic crisis). The thickness of the graphic of each clade is according to the number of genera. (For interpretation of the references to colour in this gure
legend, the reader is referred to the web version of this article.)
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
7
the Upper Jurassic and Lower Cretaceous of Laurasia (e.g. Echinodon,
Fruitadens, Tianyulong).
3.2. Vegetation record
3.2.1. Upper Triassic
In the Late Triassic, forests were dominated by the conifer Podoza-
mites, a morphogenus that refers to any broad leaved multi-veined
leaves, probably all being Araucariaceae, which were widespread over
mid-latitudes of eastern Asia, perhaps from 15◦and certainly from 30◦S,
to around 70◦N (Pole et al., 2016).
In some areas, such as the Sichuan Basin in China, Li et al. (2020)
recognise a lowland fern ora and a humid and warm climate in the
Norian, interrupted by a cooler interval at the Norian–Rhaetian transi-
tion, and followed by a mixed mid-storey forest under drier and cooler
conditions in the latest Rhaetian. According to Li et al. (2020), the
Norian palynoora of the Sichuan Basin comprised a ground cover
vegetation of ferns combined with a few lycopsids, mosses and horsetails
whereas the conifer trees consisted of Pinaceae, Araucariaceae and
Podocarpaceae. The macroora in this basin was dominated by horse-
tails (Neocalamites) and ferns (Leptopteris, Dictyophyllum, Phlebopteris).
During the Rhaetian, conifers and ginkgophytes dominated the vegeta-
tion, while the abundance of ferns and horsetails decreased, and seed-
ferns became more abundant.
The Rhaetian record of the North Iberian palaeomargin shows
considerable impoverishment of the xerophytic coniferous forests
(Di´
eguez et al., 2010) and the plant communities were dominated by
cheirolepidiaceans interspersed by an undergrowth vegetation of ferns
and lycophytes adapted to dry environments (Barr´
on et al., 2006;
Di´
eguez et al., 2010).
The uppermost Triassic of North Europe (Germany and Sweden) is
characterized by a conifer forest with Cheirolepidiaceae and Voltziales
(Gravendyck et al., 2020) or by Pinales, cycads and ginkgophytes (van
de Schootbrugge et al., 2009). During the latest Rhaetian, this arbores-
cent vegetation was replaced by a shrubbier and more herbaceous cycad
and ground fern assemblage, with a diverse cryptogam ora (van de
Schootbrugge et al., 2009; Gravendyck et al., 2020).
3.2.2. Triassic/Jurassic transition
The response of terrestrial vegetation to the biotic crisis at the
Triassic/Jurassic transition was major turnovers (McElwain et al.,
2007). Signicant palynooral turnovers reported from both hemi-
spheres (Larsson, 2009; Turner et al., 2009; Vajda and Bercovici, 2014;
Lindstr¨
om, 2016) may be correlated and represent a clear global vege-
tation response to climatic changes in the latest Rhaetian.
The macroora from Sweden and Greenland shows a dramatic
species-level decline of >80%, with the Lepidopteris ora of the Upper
Triassic being replaced by the Thaumatopteris ora of the lowermost
Jurassic (McElwain et al., 1999, 2007; Kustatscher et al., 2018). In Eu-
ropean sedimentary successions, Rhaetian palynological assemblages
were dominated by abundant gymnosperm pollen Ricciisporites tuber-
culatus, then followed by a fern spore spike at the T/J transition, and
nally dominance by Classopollis (Cheirolepidiaceae) in the Lower
Jurassic (Gotz et al., 2009; Larsson, 2009; van de Schootbrugge et al.,
2009; Bonis et al., 2009, 2010; Mander et al., 2010; Pie´
nkowski et al.,
2012; Vajda et al., 2013; Vajda and Bercovici, 2014). The T/J boundary
fern spike and subsequent dominance of Classopollis was also recorded in
North America (Olsen et al., 2002; Whiteside et al., 2007), Greenland
(McElwain et al., 2007), Europe (Fisher and Dunay, 1981; van de
Schootbrugge et al., 2009), and Asia (Lu and Deng, 2009; Li et al., 2020).
In the Sichuan Basin, Li et al. (2020) reported palynological assemblages
dominated by ferns at the T/J transition, with increased abundance of
Cheirolepidiaceae and decrease of cycadophytes/ginkgophytes and co-
nifers. In areas of eastern Asia where fossil leaves of the conifer Podo-
zamites dominated in the Late Triassic, these appear to have remained
untouched during the ETME (Pole et al., 2016).
In the Southern Hemisphere, Rhaetian oras were dominated by
seed-ferns and were replaced by more complex assemblages with co-
nifers (cheirolepids), Bennettitales, and new seed-ferns during the Early
Jurassic (Turner et al., 2009). The palynoora was dominated by lyco-
phyte spores and corystosperm seed-fern pollen with common bryo-
phyte spores in the Rhaetian, whereas the Hettangian was characterized
by common cheirolepidiacean pollen and increased fern spores, and
dominance of Classopollis (Cheirolepidiaceae) in the Sinemurian (Aki-
kuni et al., 2010; de Jersey and McKellar, 2013).
Therefore, at global scale a general trend was a vegetation turnover
characterized by the dominance of ferns and related forms during the T/
J transition, followed by a bloom of Cheirolepidiaceae conifers during
the earliest Jurassic.
3.2.3. Lowermost Jurassic
The T/J fern spike was followed by dominance of Cheirolepidiaceae
in the Hettangian to early Sinemurian in Europe, China, Australia, and
New Zealand (Akikuni et al., 2010; Bonis et al., 2010; Di´
eguez et al.,
2010; de Jersey and McKellar, 2013; Gravendyck et al., 2020; Li et al.,
2020).
In the Sichuan Basin the Lower Jurassic is characterized by high
abundance of fern palynomorphs, but with a lower abundance than at
the T/J transition, whereas the conifers increased (mainly Cheir-
olepidiaceae and Pinaceae). Cycadophytes/ginkgophytes were also
common in the ora, whereas seed-ferns were less abundant (Li et al.,
2020).
In North Germany the palynological record of the lowest Jurassic is
characterized by conifer forests of Pinaceae, Podocarpaceae and Cheir-
olepidiaceae with abundant Selaginellales (Gravendyck et al., 2020).
In the Ca˜
nad´
on Asfalto Basin (Argentina) the pre-Toarcian plant
assemblages consisted of diverse sphenophytes, dipteridacean ferns,
conifers, seed-ferns, bennetitaleans and cycads indicative of humid
conditions (Escapa et al., 2008; Choo et al., 2016; Pol et al., 2020).
3.2.4. Pliensbachian and Toarcian
In the European Pliensbachian, palynological assemblages indicate a
vegetation of high-diversity forests, dominated by a mixture of bisaccate
pollen-producing conifers and seed-ferns as well as spore-producing
Fig. 4. Diversity of sauropodomorpha represented as number of genera and
body-size (length) distribution from late Carnian to Callovian.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
8
mosses (bryophytes) and club mosses (lycophytes) (Slater et al., 2019;
Danise et al., 2021). Higher proportions of spore-producing mosses
(bryophytes) and clubmosses (lycophytes) suggest relatively wetter
conditions on land at this time (Slater et al., 2019). At the Pliensbachian-
Toarcian boundary transition, palynological assemblages decreased in
diversity and richness with a drop in abundance of bisaccate pollen-
producing conifers and seed-ferns and an increase in cycads
(Chasmatosporites spp.) (Pie´
nkowski et al., 2016; Slater et al., 2019).
At the onset of the negative CIE that characterized the Jenkyns Event
(Reolid et al., 2020; Erba et al., 2022), land plants experienced a major
drop in richness and diversity (Slater et al., 2019; Danise et al., 2021).
Forests of bisaccate pollen-producing conifers and seed ferns were
replaced by poorly diversied forests dominated by Cheirolepidiaceae
(represented by Classopollis spp.) and cycads. The later stage of the
Fig. 5. Distribution of genera of theropods (including herrerasaurids) from Late Triassic to Middle Jurassic. The early Toarcian biotic crisis is indicated with a
gray bar.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
9
negative CIE is characterized by a peak of abundance of the conifer
Cerebropollenites macroverrucosus (Koppelhus and Dam, 2003; Slater
et al., 2019).
After the Jenkyns Event, the low diversity of land plant communities
persisted in Europe, with dominance of Cheirolepidiaceae conifers
(Classopollis spp.) and Cupressaceae (Perinopollenites elatoides) whereas
bisaccate pollen-producing conifers and seed-ferns were in a minority,
and Cerebropollenites macroverrucosus abruptly decreased (Slater et al.,
2019).
In the Ca˜
nad´
on Asfalto Basin (Patagonia) the post-Jenkyns Event
plant assemblages were less diverse than those before, as deduced from
pollen and ora, being largely dominated by the conifers Araucariaceae,
Cheirolepidiaceae and Cupressaceae (Escapa et al., 2008; Olivera et al.,
2015; Choo et al., 2016) indicative of seasonally dry and warm condi-
tions (Pol et al., 2020).
Therefore, a general trend in the middle and upper Toarcian included
a decrease in diversity and increase of abundance of thermophilic plant
groups and progressive dominance of the conifers Araucariaceae,
Cheirolepidiaceae and Cupressaceae in both the northern hemisphere
(Deng et al., 2018; Slater et al., 2019) and southern hemisphere (Escapa
et al., 2008; Olivera et al., 2015; Choo et al., 2016; Pol et al., 2020).
Fig. 6. Record of theropods (including herrerasaurids) according to different
continental masses from Late Triassic to Middle Jurassic. The thickness of the
trends is according to the number of genera. Note that some components of
Gondwana and Laurasia are differentiated. Main biotic crisis are identied with
a red line (ETME) and gray bar (early Toarcian biotic crisis). (For interpretation
of the references to colour in this gure legend, the reader is referred to the web
version of this article.)
Fig. 7. Temporal distribution of main clades of theropods (included herrer-
asaurids). Main biotic crisis are identied with a red line (ETME) and gray bar
(early Toarcian biotic crisis). The thickness of the graphic of each clade is ac-
cording to the number of genera. (For interpretation of the references to colour
in this gure legend, the reader is referred to the web version of this article.)
Fig. 8. Distribution of the diversity of Theropoda (included Herrerasauridae)
represented as number of genera and body-size (length) from late Carnian
to Callovian.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
10
3.2.5. Middle Jurassic
Middle Jurassic palynological assemblages were dominated by fern
spores (Deltoidospora, probably produced by the fern Coniopteris; Slater
et al., 2018), with abundant lycophyte spores and seed-ferns (Alispor-
ites). Conifer pollen assemblages indicate dominance of Araucariacea
(Araucariacites), Cupressaceae (Perinopollenites) and Cheirolepidiaceae
(Classopollis) accompanied by gingkoes (Gingko hutonii) (Slater et al.,
2018). This spore-pollen assemblage is widespread through central and
north Europe from the United Kingdom and North Sea (Slater et al.,
2017, 2018), Scandinavia (Guy-Ohlson, 1986, 1989; Mehlqvist et al.,
2009; Vajda, 2001; Vajda and Wigforss-Lange, 2009) and Ukraine
(Shevchuk et al., 2018), evidence for an extensive and homogeneous
vegetation across Europe during the Aalenian and Bajocian.
3.3. Late Triassic to Early-Middle Jurassic climates
Climate conditions and climate change are major drivers of the
evolution of marine and continental organisms and ecosystems (e.g.
Hoffmann and Sgr`
o, 2011; Price et al., 2013). Throughout the Mesozoic,
climate trends are reconstructed from oxygen isotope palae-
othermometry applied to fossilized shell material of marine in-
vertebrates and plankton (e.g. belemnites, brachiopods, oysters,
foraminifera), or conodont phosphate, which allow assessessment of
relative sea water temperature changes (e.g. Grossman, 2012). How-
ever, absolute temperature reconstructions suffer from poor knowledge
of the δ
18
O of sea water, which is also affected by ice mass effects and
local sea water salinity (see discussion in Ruebsam et al., 2020a and
references therein). This limitation can be overcome by clumped isotope
palaeothermometry (Fern´
andez et al., 2021), or molecular palae-
othermometry (e.g. TEX
86
proxy; Schouten et al., 2002) that can be
applied to sediment archives that experienced only a minor degree of
burial diagenesis (e.g. Robinson et al., 2017; Ruebsam et al., 2020b).
Climatic conditions prevailing in continental areas can be inferred
from palaeo-ora characteristics (leaf or plant material, spores, pollen)
and from lithological climate indicators, such as the occurrence and
distribution of evaporites, dune sand, or coals (e.g., Frakes, 1979; Frakes
et al., 1992; Rees et al., 2000; Boucot et al., 2013).
3.3.1. Late Triassic
The Late Triassic climate is described as being mainly warm/hot and
arid (Frakes et al., 1992). In particular, eastern and central parts of
Pangaea, as well as the western Tethys region were characterized by arid
conditions. Higher, but highly seasonal rainfall occurred on the western
margin of Pangaea, as well as the eastern coasts of Laurasia and Gond-
wana. In both hemispheres, high-latitudinal areas were characterized by
more humid conditions and possibly pronounced seasonality, with
freezing conditions during winter (Sellwood and Valdes, 2006; Boucot
et al., 2013; Miller and Baranyi, 2021). According to Sellwood and
Valdes (2006), lower-latitude areas of Pangea experienced summer
temperatures above 35 ◦C with cooler winter temperatures. High-
latitude areas were characterized by warm summers (>20 ◦C) but
near freezing during the winter. Conodont oxygen isotope data indicate
that the Late Triassic was a hothouse time (e.g., Trotter et al., 2015; Sun
et al., 2020). Data indicate high seawater temperatures in the middle
Carnian during the Carnian Pluvial Episode followed by moderate
cooling throughout the early Norian. Minor warming occurred during
the late Norian and was followed by minor cooling throughout the
Rhaetian (Fig. 13). However, climate evolution in or late Triassic is
poorly documented. In particular, absolute temperatures are only
inaccurately reconstructed, which makes climate reconstructions dif-
cult (e.g., Sun et al., 2016a).
Arid climate conditions, dominating at low- and mid-latitudes during
the Late Triassic, were briey interrupted by more humid conditions
during the Carnian Pluvial Episode (Fig. 13) in the Tethyan realm (e.g.,
Simms and Ruffell, 1990; Hornung et al., 2007; Trotter et al., 2015;
Ruffell et al., 2016; Baranyi et al., 2018, 2019; Dal Corso et al., 2020).
The Carnian Pluvial Episode was accompanied by major changes in
continental ecosystems documented by the rst appearance of modern
conifers and Bennettitales (Sun et al., 2016b; Dal Corso et al., 2020;
Miller and Baranyi, 2021). Global warming occurred across the Triassic/
Fig. 9. Distribution of genera of ornothischians from Late Triassic to Middle Jurassic. The early Toarcian biotic crisis is indicated with a gray bar.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
11
Jurassic boundary and continued in the Early Jurassic (e.g., McElwain
et al., 1999; Korte et al., 2009; Dera et al., 2011; Hesselbo et al., 2020;
for a review also see Schoepfer et al., 2022). Periods of major envrion-
mental change associated with the Carnian Pluvial Episode and the
Triassic/Jurassic boundary reconcile with major perturbations of the
global carbon cycle that were potentially related to periods of intensied
volcanism (e.g., Dal Corso et al., 2012; Sun et al., 2019; Ruhl et al.,
2020).
3.3.2. Early Jurassic
The climate in the Early Jurassic was predominantly warm and
humid (Frakes et al., 1992). However, it was also characterized by
higher variability, which included warm and cold periods (e.g. Dera
et al., 2011; Korte and Hesselbo, 2011, Korte et al., 2015; Ruebsam et al.,
2019, 2020a). In addition, differing latitudinal climatic zones developed
(e.g. Rees et al., 2000; Dera and Donnadieu, 2012; Boucot et al., 2013;
Philippe et al., 2017). Low-latitude areas along the Tethys Ocean were
situated in the tropical to subtropical climate belt with high
precipitation rates. Arid to semi-arid conditions prevailed in the interior
of Laurentia and southern America (Parrish et al., 1982; Rees et al.,
2000). High latitudinal areas were characterized by temperate climate
conditions with recurring excursions to warm-temperate, but also to
cold-temperate and cold climates (Fig. 13) (e.g., Vakhrameev, 1991;
Zakharov et al., 2006; Devyatov et al., 2011; Ruebsam and Schwark,
2021).
Global temperatures remained high in the Sinemurian, with equa-
torial sea surface temperatures in the range 30–35 ◦C (Robinson et al.,
2017). Cooling in the late Pliensbachian may have promoted the for-
mation of high-latitudinal glaciation at their most extensive in the latest
Pliensbachian to earliest Toarcian (Dera et al., 2011; Korte et al., 2011;
Krencker et al., 2019; Ruebsam et al., 2019; Ruebsam and Schwark,
2021; Fleischmann et al., 2022). The end Pliensbachian is identied by a
sea-level drop with subsequent ooding and negative CIE related to the
Pliensbachian-Toarcian boundary event (Bodin et al., 2016; Fantasia
et al., 2019; Rodrigues et al., 2019; Al-Suwaidi et al., 2022; Fleischmann
et al., 2022). Latest Pliensbachian to early Toarcian equatorial sea sur-
face temperatures uctuated between 22 and 32 ◦C, attesting to highly
variable and contrasting climate conditions (Ruebsam et al., 2020b).
Fig. 10. Record of ornithischians according to different continental masses
from Late Triassic to Middle Jurassic. The thickness of the trends is according to
the number of genera. Note that some components of Gondwana and Laurasia
are differentiated. Main biotic crisis are identied with a red line (ETME) and
gray bar (early Toarcian biotic crisis). (For interpretation of the references to
colour in this gure legend, the reader is referred to the web version of
this article.)
Fig. 11. Temporal distribution of main clades of ornithischians. Main biotic
crisis are identied with a red line (ETME) and gray bar (early Toarcian biotic
crisis). The thickness of the graphic of each clade is according to the number of
genera. (For interpretation of the references to colour in this gure legend, the
reader is referred to the web version of this article.)
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
12
During the early Toarcian, related to the Jenkyns Event and the carbon
cycle perturbation, sea water temperatures in the tropical to subtropical
latitudes increased by about 10 ◦C (Ruebsam et al., 2020b; Fern´
andez
et al., 2021). Oxygen isotope data suggest that temperatures remained
high during the middle and late Toarcian (Fig. 13) (Dera et al., 2011;
Korte et al., 2015). An increase of warm- and drought-adapted plants
through the Jenkyns Event, suggests a warmer and drier climate. Slater
et al. (2019) interpreted strong seasonality during the Jenkyns Event
with extreme wet and dry seasons, through which drought-adapted
plants were successful.
3.3.3. Middle Jurassic
Following marked cooling at the Early/Middle Jurassic boundary,
overall cooler climates have been reconstructed for the Middle Jurassic
(Dera et al., 2011; Krencker et al., 2014; Korte et al., 2015). Tropical to
subtropical climate conditions dominated at low-mid latitudes, while
mid-latitudes were characterized by warm-temperate climate condi-
tions. Cold temperate to cold climate conditions occurred at high lati-
tudes (Vakhrameev, 1991; Rees et al., 2000; Boucot et al., 2013;
Ruebsam and Schwark, 2021). During the Middle Jurassic, cold-
temperate to cold climate expanded towards lower latitudes, while the
boundary between tropical to subtropical and warm-temperate climates
shifted towards mid-latitudes (Rees et al., 2000). As a consequence, the
latitudinal climate gradient became more pronounced, and the areal
extent of the warm-temperate climate zone declined (Fig. 13). Arid
climate conditions continued to dominate in central parts of the conti-
nents, such as in the interior of Laurentia and South America (Rees et al.,
2000; Boucot et al., 2013; Fig. 13).
4. Discussion
4.1. Dinosaurs and environmental changes during the Late Triassic
The Late Triassic was a key time in the evolution of terrestrial or-
ganisms, when new taxonomic groups arose such as lizards, turtles,
mammals, crocodiles, pterosaurs and dinosaurs (Benton et al., 2014;
Klausen et al., 2020; Benton, 2021; Benton and Wu, 2022). A rst
explosive radiation of dinosaurs occurred following the Carnian Pluvial
Episode (CPE; Benton et al., 2018; Bernardi et al., 2018; Dal Corso et al.,
2020), a climatic change linked to the eruption of the Wrangellia LIP
(see Dal Corso et al., 2012, 2020). The CPE is characterized by a shift
towards more humid condtions and a remarkable enhancement of hy-
drological cycling (Dal Corso et al., 2020; see also section 3.3), and it has
been identied as a driver of major evolutionary innovations along and
diversications of emerging groups (sauropodomorphs, phytosaurs,
aetosaurs and turtles) and Middle Triassic groups (rauisuchians, rhyn-
chocephalians), and the rst appearance of mammals and croc-
odylomorphs (Lucas and Luo, 1993; Datta, 2005; Irmis et al., 2013;
Brocklehurst et al., 2015; Lecuona et al., 2016; Lichtig et al., 2018;
Reolid et al., 2018; Dal Corso et al., 2020). Climatic and oral changes
following the CPE caused the extinctions of some herbivores such as
rhynchosaurs and a major decline of dicynodonts (e.g. Brusatte et al.,
2010; Singh et al., 2021). Plants also radiated and diversied during the
CPE, with the origin of several modern conifer families (Pinaceae,
Cupressaceae, and Cheirolepidiaceae; see Dal Corso et al., 2020). Her-
bivorous insects also expanded (Labandeira, 2006).
Several authors argued that the CPE triggered the initial diversi-
cation of dinosaurs, a clade that had existed undetectably since the end
of the Early Triassic (Ezcurra, 2010; Langer et al., 2010; Benton et al.,
2018; Bernardi et al., 2018; Dal Corso et al., 2020; Benton, 2021; Benton
and Wu, 2022), and this result is conrmed by the Bayesian analysis of
face-value fossil data by Langer and Godoy (2022). However, when they
modelled phylogenetic data, the sharp peaks in diversication are
shifted backwards to the Ladinian, but that is presumably because
phylogenetic modelling assumes constant rates and cannot detect
sharply enhanced rates during explosive diversications.
During the Carnian and early Norian, the main terrestrial herbivores
were rhynchosaurs, large anomodonts, traversodont cynodonts (Olsen
and Galton, 1977; Charig, 1984) and some early aetosaurs (Bonaparte,
1971, 1978). Sauropodomorpha were the rst dinosaurs that diversied
into multiple herbivorous lineages recorded mainly in southern Gond-
wana (Wilson and Sereno, 1998; Barrett and Upchurch, 2007; Barrett,
2014, Novas et al., 2021). According to Singh et al. (2021) these Carnian
and Norian herbivores (Dicynodontia, Cynognathia, Aetosauria, Ortni-
thischia, and Sauropodomorphs) generally avoided competition by
occupying different guilds.
The rst 30 Myr of sauropodomorph evolution (late Carnian to latest
Rhaetian) were characterized by high variability in size, locomotion
(bipedal and quadrupedal) and feeding biomechanics (Barrett and
Upchurch, 2007; Barrett, 2014; Button et al., 2017; McPhee et al., 2017;
Müller and Garcia, 2022) ranging from small (<10 kg) bipedal taxa to
the large (>5 tons) quadrupedal early sauropods (Allain and Aquesbi,
2008; McPhee et al., 2017; Benson et al., 2018; Apaldetti et al., 2018).
Body size increased rapidly, and some taxa reached gigantic sizes,
equivalent to their Jurassic relatives, before the Triassic/Jurassic
boundary (Buffetaut et al., 2002; McPhee et al., 2017; Apaldetti et al.,
2018) (Fig. 4), and this sharp size increase towards the end of the Norian
is demonstrated in modelling results (Langer and Godoy, 2022). Basal
sauropodomorphs, such as Plateosaurus and Massospondylus, were un-
able to pronate their manus and this restricted their capacity to walk
quadrupedally (Bonnan and Senter, 2007), whereas the earliest sauro-
pods such as Melanorosaurus and Antetonitrus, could and probably were
quadrupeds (Yates and Kitching, 2003; Yates et al., 2010), but the manus
still retained some degree of functionality for non-locomotor purposes.
Niche partitioning has been noted already among sauropodomorph di-
nosaurs, expressed in their body size and postural disparity (Singh et al.,
2021) avoiding trophic competition.
The main sauropodomorph morphological and palaeoecological
novelties were established before the Triassic/Jurassic boundary (Bru-
satte et al., 2010; Langer et al., 2010; McPhee et al., 2017; Brusatte,
2019). The success of the sauropodomorph bauplan almost from their
origin is evidenced by their numerical dominance in Upper Triassic
terrestrial assemblages (except in North America) and their persistence
during the Jurassic and Cretaceous (McPhee et al., 2017). However, at
the end of the Norian, six of 17 genera of sauropodomorphs disappeared
(35%), but eight new genera were recorded at the beginning of the
Rhaetian (Figs. 1 and 14).
Fig. 12. Distribution of the diversity of Ornithischia represented as number of
genera and body-size (length) from late Carnian to Callovian.
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Earth-Science Reviews 234 (2022) 104196
13
The ornithischian record of the Upper Triassic is scarce and restricted
to a small geographical area in southern Gondwana (Thulborn, 1970;
Brusatte et al., 2010; Butler, 2010; Pol et al., 2011) (Fig. 10) and they
were less signicant in terrestrial ecosystems than the anomodonts,
traversodont cynodonts, rhynchosaurs, and sauropodomorphs. Howev-
er, Barrett (2000) suggested that early ornithischians may have been
facultatively omnivorous, rather than strictly herbivorous.
Theropods were rare components in Late Triassic ecosystems (Nes-
bitt et al., 2007; Brusatte et al., 2010), except for the Chinle Formation at
Ghost Ranch, New Mexico, where hundreds of skeletons of Coelophysis
bauri were recorded (Colbert, 1989). Theropods were less abundant and
less diverse than contemporary carnivores such as phytosaurs, raui-
suchians and ornithosuchids (Benton, 1983; Welles, 1986; Brusatte
et al., 2008a, 2008b; Benton et al., 2018). At the end of the Norian, 10 of
12 genera of theropods disappeared (83%), most of them coelophysids,
as well as all herrerasaurids. The record of new theropod taxa is poor in
the Rhaetian.
The morphological disparity (range of morphologies and body types)
of Late Triassic dinosaurs, according to Brusatte et al. (2008b), increased
over time but it was lower than the morphological disparity of crur-
otarsan archosaurs that were very abundant and diverse. Crurotarsans
and dinosaurs coexisted for around 30 myr (Benton et al., 2014), and in
some cases crurotarsan morphologies were similar to those of dinosaurs,
for example ornithosuchids such as Ornithosuchus and Riojasuchus, and
poposaurid rauisuchians such as Efgia, Poposaurus, Shuvosaurus and
Sillosuchus (Nesbitt and Norell, 2006; Nesbitt, 2007). This morpholog-
ical convergence suggests that dinosaurs and crurotarsans were com-
petitors for trophic resources during the Late Triassic, and the non-
dinosaurs were not then at a disadvantage (Brusatte et al., 2008a, 2010).
4.2. Crossing the Triassic/Jurassic boundary
The Triassic/Jurassic transition is characterized by severe environ-
mental stress in the ocean and on land, with a sharp increase of atmo-
spheric CO
2
concentrations (McElwain et al., 1999; Cohen and Coe,
2007; Michalík et al., 2007; Whiteside et al., 2010). The eruption of
Fig. 13. Late Triassic to Middle Jurassic climate trends (left panel). Box plots show oxygen isotope data in a 2.5 Myr window (Jurassic data from Ruebsam and
Schwark, 2021; for Triassic data we refer to the supplement; CPE: Carnian Pluvial Episode, T/J: Triassic/Jurassic, l.Pl.-e.Toa.: late Pliensbachian-early Toarcian, T-
OAE: Toarcian Oceanic Anoxic Event, Aal.: Aalenina, B.: Bajocian, Bat.: Bathonian, Call: Callovian; H. Hettangian; Pliensb.: Pliensbachian). The approximate dis-
tribution of climate zones at Stage/Age level (right panel) has been inferred from the distribution climate sensitive deposits and paleo-oral data (e.g., Parrish et al.,
1982; Rees et al., 2000; Boucot et al., 2013). Across the Triassic/Jurassic boundary, climate conditions became more humid. In addition, across the latitudes a more
pronounced climatic gradient was formed in the Early and Middle Jurassic. This is expressed by the formation of different climate zones (A: arid, T-ST: tropical to sub-
tropical, WT: warm temperate, C-CT: cold to cold temperate).
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
14
Fig. 14. Comparison of the distribution of the main clades of dinosaurs from Carnian to Callovian with the temperature uctuations as inferred from δ
18
O values. The width of the bars is proportional to the number of
genera. Note that the ETME and the Jenkyns Event constituted main events in the dinosaur evolution with extinctions and subsequente radiations of new taxa. The Norian/Rhaetian boundary a signicant boundary with
the extinction of Guabasauridae and Herrerasauridae, and decreasing diversity of other groups (e.g. Coelophysoidea). Most of the dinosaur groups that dominated the Late Jurassic and Cretaceous appeared during the
Middle Jurassic after the Toarcian biotic crisis.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
15
ood basalts caused a massive input of greenhouse gases into the at-
mosphere that caused the global warming and biotic extinction both on
land and sea (Whiteside et al., 2010). McElwain et al. (1999) proposed a
global warming of 4 to 5 ◦C, driving the turnover of megaora (see also
section 3.3). Recent studies on sedimentology and biomarkers have
suggested increased wildre activity during the Triassic/Jurassic tran-
sition (Marynowski and Simoneit, 2009; Belcher et al., 2010; Uhl and
Montenari, 2011; Petersen and Lindstr¨
om, 2012; Pole et al., 2018; Song
et al., 2020; Alipour et al., 2021; Zhang et al., 2022), probably as a result
of the warmer and drier climate (see also section 3.3). Zhang et al.
(2022) proposed an extensive deforestation and wildres possibly
caused by acid rain generated by the CAMP eruptions (Blackburn et al.,
2013; Thibodeau et al., 2016; Percival et al., 2017; Ruhl et al., 2020).
At the end of the Rhaetian, a total of 13 of 16 genera of sau-
ropodomorphs disappeared (81%) (Fig. 1). The record of ornithischians
is too poor for analysis. Only ve genera of theropods lived at the end of
the Triassic, according to the updated fossil record, and only three taxa
went extinct at the end of Rhaetian (Daemonosaurus, Lucianovenator and
Pterospondylus) (Fig. 5). According to Allen et al. (2019), for the ETME,
body size was not a selective factor when phylogenetic relationships are
taken into account.
Crurotarsan archosaurs, the main competitors of dinosaurs, suffered
substantial extinction at the end of Triassic and only the croc-
odylomorph lineage persisted (Brusatte et al., 2008a; Benton et al.,
2014). Herbivores such as dicynodonts (Therapsida) and aetosaurs
(Crurotarsi) and carnivores such as poposauroids (Crurotarsi) and phy-
tosaurs disappeared at the end of the Triassic (Benton et al., 2014).
4.3. Early Jurassic diversication of dinosaurs
The second main radiation of dinosaurs occurred following the ETME
(Fig. 14), and dinosaurs became the most successful group of the
Jurassic and Cretaceous with a wide range of adaptations, occupying
many different ecological niches and exhibiting a wide range of body
sizes (Brusatte et al., 2010; Langer et al., 2010; Benton et al., 2014)
(Figs. 4, 8 and 12). According to Lloyd et al. (2008), dinosaur diversity
jumped during the Early Jurassic, conrmed by Langer and Godoy
(2022) whose work shows a distinct jump in diversity in the Hettangian,
although this might partly reect the short duration of this stage (2
myr). Otherwise, they detected only slow increases in diversity of di-
nosaurs through the Early Jurassic, and this is not necessarily an effect of
poor sampling but may be real. For example, Brusatte et al. (2008b,
2010) and Benton et al. (2014) showed that the extinction of potential
competitor groups at the end of the Triassic was not met with an ex-
plosion of dinosaurs in terms of morphological disparity, which would
have suggested some kind of ecological release.
The base of the trophic chains, the primary producers, recovered
slowly after the ETME. Cheirolepidiaceae were among the most common
conifers in the Early Jurassic, distributed over a wide range of habitats
(Akikuni et al., 2010; Bonis et al., 2010; Di´
eguez et al., 2010; de Jersey
and McKellar, 2013; Gravendyck et al., 2020; Li et al., 2020). They are
interpreted as xerophytic and thermophilous shrubs and trees of
subtropical-tropical climates, and some cheirolepidaceans were coastal
plants that tolerated seasonal droughts and saline inuence (Alvin,
1982), having properties that enabled them to dominate disturbed
ecosystems after crises (Tosolini et al., 2015). The Early Jurassic is
characterized by increased diversity and plants indicating overall more
humid conditions and the development of a more pronounced lat-
itudinal climate gradient (Rees et al., 2000; Escapa et al., 2008; Choo
et al., 2016; Philippe et al., 2017; Slater et al., 2019; Gravendyck et al.,
2020; Pol et al., 2020; see also section 3.3).
Early Jurassic sauropodomorph distribution was worldwide (Fig. 2),
and indeed most of their key adaptations (huge size, quadrupedal
locomotion with graviportal specializations, obligate herbivory) arose in
the Late Triassic, and most of Triassic lineages continued into the Early
Jurassic (Fig. 14). Basal sauropods of the Early Jurassic mainly showed
specializations such as U-shaped jaws, spatulate tooth crowns with
reduced denticles and a lateral plate on the dentary (Barrett and
Upchurch, 2007; Yates et al., 2010). When basal sauropods evolved,
they were the same size as the largest basal sauropodomorphs and
shared the same habitats (Apaldetti et al., 2018), and probably avoided
competition for trophic resources through specializations in masticatory
apparatus.
By the Early Jurassic, ornithischians were globally distributed
(Fig. 10) and relatively diverse and abundant, with the radiation of
Heterodontosauridae and the origin of Fabrosauridae, Scelidosauridae
(Thyreophora) and Neornithischia (Fig. 14). This diversication may be
related to the end-Triassic extinction of several herbivorous clades that
left vacated ecological niches for them to occupy (Olsen et al., 2002;
Butler et al., 2007; Brusatte et al., 2008b).
Early Jurassic theropods are much more abundant, taxonomically
diverse and show a greater variability of morphologies than in the Late
Triassic (Figs. 5-8). Theropods extended to all continents and increased
in size. The coelophysoids (Coelophysidae, Dilophosauridae) dominated
during the earliest Jurassic (Brusatte et al., 2010), and basal forms of
Ceratosauria and Tetanurae appeared (Fig. 14), being robust forms
characterized by larger body sizes and more disparate morphology. The
taxonomic and morphological diversication of theropods during the
Early Jurassic points to specializations for different prey and ecological
niches, as sauropodomophs and ornithischians diversied (Fig. 14). The
extinction of many crurotarsan lineages, including carnivores such as
rauisuchians, phytosaurs and ornithosuchids, at the end of Triassic
probably favoured the radiation and expansion of theropods during the
Early Jurassic (Olsen et al., 2002; Benton, 2004; Brusatte et al., 2008b,
2010; Benton et al., 2014).
4.4. The early Toarcian biotic crisis. What about dinosaurs?
Although the record of Toarcian dinosaurs is scarce and many lack
precise ages, it is clear that some clades of herbivores (basal sau-
ropodomorphs, scelidosaurids) and carnivores (coelophysoids) dis-
appeared during the early Toarcian biotic crisis (Fig. 14).
At the Pliensbachian/Toarcian boundary and through the Jenkyns
Event, a total of 10 of 12 genera of sauropodomorphs disappeared
(83%), including all ‘prosauropod’ families (Fig. 14). This is conrmed
by calibrated phylogenetic trees that conrm the extinction of numerous
lineages of early Jurassic sauropodomorphs during the Toarcian (Pol
et al., 2020), mainly affecting Massospondylidae, Anchisauria and basal
Sauropoda (Fig. 14). Some basal Sauropoda survived into the early
Toarcian in Asia (Gongxianosaurus, Isanosaurus, Sanpasaurus, and Ziz-
hongosaurus; Hou et al., 1976; Buffetaut et al., 2000; Yaonan and Wang,
2000; McPhee et al., 2016), India (Barapasaurus; Jain et al., 1975), Af-
rica (Tazoudasaurus and Vulcanodon; Cooper, 1984; Allain et al., 2004),
and Europe (Ohmdenosaurus; Wild, 1978). However, these disappeared
before the Aalenian (Middle Jurassic) (Fig. 14).
The record of ornithischians during the Pliensbachian is poor, but the
beginning of the Toarcian marks the extinction of most species of Het-
erodontosauridae, Fabrosauridae and Scelidosauridae, but new genera
of Heterodontosauridae and Fabrosauridae emerged in the Bathonian
and Callovian (Fig. 14).
Changes in vegetation could have led to extinction of herbivores and
the subsequent extinction of some carnivores. At the onset of the
negative CIE that characterized the Jenkyns Event, land plants experi-
enced a major loss in diversity and richness (Deng et al., 2018; Slater
et al., 2019; Danise et al., 2021). Analysis of spore-pollen assemblages by
Slater et al. (2019) showed that vegetation shifted from a Pliensbachian
high-diversity assemblage with conifers, seed ferns and lycophytes, to an
early Toarcian low-diversity assemblage of cheirolepid conifers, cycads
and Cerebropollenites-producers adapted to warm drought-like
conditions.
In the northern hemisphere, forests were dominated by Cheir-
olepidiaceae (represented by Classopollis spp.) and cycads and a peak of
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
16
the conifer Cerebropollenites macroverrucosus during the more extreme
conditions of the Jenkyns Event (Slater et al., 2019; Danise et al., 2021).
Immediately after the event, a low diversity of land-plant communities
persisted with dominance of Cheirolepidiaceae conifers (Classopollis
spp.) and Cupressaceae (Perinopollenites elatoides), whereas bisaccate
pollen-producing conifers and seed-ferns were in a minority, and Cere-
bropollenites macroverrucosus sharply decreased (Slater et al., 2019).
In Patagonia, close to the Karoo-Ferrar igneous province, before the
Pliensbachian–Toarcian volcanism, plant assemblages were diverse and
indicated humid conditions (sphenophytes, dipteridacean ferns with
large fronds, conifers, seed ferns, Bennetitales and cycads; Escapa et al.,
2008; Choo et al., 2016; Pol et al., 2020). During the Jenkyns Event, the
less diverse fossil pollen and ora, dominated by the conifers Araucar-
iaceae, Cheirolepidiaceae and Cupressaceae, indicate seasonally dry and
warm conditions (Escapa et al., 2008; Olivera et al., 2015; Choo et al.,
2016). This less diverse forest was dominated by plants with small scaly
leaves adapted to dry conditions (Pol et al., 2020).
The disappearance of many elements of the diverse pre-Toarcian
vegetation and the proliferation of plants with small scaly leaves inu-
enced the extinction of diverse lineages of smaller non-sauropod her-
bivores, which lacked adaptations to high-bre herbivory as their
gracile skulls and mandibles were less mechanically efcient (Barrett
and Upchurch, 2007; Button et al., 2017) and their teeth were small,
with thin enamel (<200
μ
m) and lacked tooth–tooth occlusion (Pol
et al., 2020).
As for carnivorous dinosaurs, most Pliensbachian theropods became
extinct during the early Toarcian (Coelophysis, Segisaurus, ‘Podokesau-
rus’, Dilophosaurus, Cryolophosaurus). The Coelophysoidea, which had
survived from the Norian, died out in the early Toarcian, probably
related to the extinction of many of their potential prey (Fig. 14). The
record in the Toarcian is limited, with two basal ceratosaurians, Ber-
berosaurus and Dandakosaurus.
The effects of volcanogenic global warming were severe for conti-
nental ecosystems and the impact on land plant communities recorded at
the start of the CIE are contemporaneous with the main phase of Karoo-
Ferrar LIP (Sell et al., 2014; Burgess et al., 2015; Moulin et al., 2017;
Them et al., 2018; Font et al., 2022) and Chon Aike LIP volcanism
(Pankhurst and Rapela, 1995). However, the early stages of volcanism
occurred at the Pliensbachian/Toarcian boundary (Moulin et al., 2017;
Them et al., 2018; Xu et al., 2018) and were parallel to an initial shift in
land plant communities (Slater et al., 2019). The Pliensbachian/Toar-
cian boundary records about 5 ◦C warming followed by 8 ◦C cooling in
the middle Tenuicostatum (Polymorphum) ammonite Zone. The Jen-
kyns Event itself was accompanied by about 10 ◦C warming. Certainly,
we cannot discuss trends in dinosaur evolution over such a short time-
scale. Therefore, during the early Toarcian, these drastic climate uc-
tuations may have profoundly impacted on continental ecosystems
(Slater et al., 2019; Ruebsam et al., 2020b; see also section 3.3), causing
re-occurring shifts in oral and faunal assemblages.
In addition, wildres during the early Toarcian were probably more
common, mostly in the northern hemisphere (Baker et al., 2017) as
conifers have biochemical and morphological traits that make them
particularly ammable whether dry or alive and ferns are known to be
ammable when fully dry (Hollaar et al., 2021). Baker et al. (2017) has
been alone in documenting charcoal abundances as evidence for wildre
intensities, and conrmation elsewhere is required. However, the
highest temperatures occurred during the negative CIE core, while
wildre activity increased during the onset and recovery of the negative
CIE. The impact of global warming and wildres on stressed ecosystems
occurred at different times but at the available temporal resolution, we
cannot differentiate the impact of global warming and wildres on di-
nosaurs. The vegetation turnover, and in particular, the loss of plant
biomass, which is a common consequence of warming events, not only
affected dinosaurs and trophic changes, but might have resulted in
changes in the hydrological cycle and increased soil erosion and run-off
on land (van de Schootbrugge et al., 2009; Ruebsam et al., 2020c; Vajda
et al., 2020).
4.5. Post-Jenkyns Event radiation of dinosaurs
A general trend in vegetation after the Jenkyns Event global warming
included a decrease in diversity and increase in abundance of thermo-
philic groups and progressive dominance of the conifers Araucariaceae,
Cheirolepidiaceae and Cupressaceae both in the northern (Deng et al.,
2018; Slater et al., 2019) and southern hemispheres (Escapa et al., 2008;
Olivera et al., 2015; Choo et al., 2016; Pol et al., 2020).
Eusauropods were the dominant components of large herbivore
guilds in the post-Jenkyns Event (middle and late Toarcian to Aalenian)
in South America (Bagualia, Patagosaurus and Volkheimeria; Pol et al.,
2020), Africa (Spinophorosaurus; Remes et al., 2009), and Asia (Nebu-
lasaurus; Xing et al., 2013) (Figs. 2 and 14). According to Pol et al.
(2020), the dominant ora of the post-Jenkyns Event showed reduced
plant leaf-sizes, and large conifers with coriaceous leaves were strongly
selective for survival and success of eusauropods. This would seem to be
a good case of plant–herbivore interactions (Barrett, 2014), in which the
new eusaropods had specialized adaptations to exploit the highly
nutritious Araucariaceae and Cheirolepidiaceae conifers (Hummel et al.,
2008; Clauss et al., 2013). Eusauropods are characterized not only by
their large body sizes but also by their deep skulls, robust mandibles and
large spoon-shaped teeth with thick and rugose enamel (Allain and
Aquesbi, 2008; Barrett and Upchurch, 2007; Barrett, 2014; Button et al.,
2017; Pol et al., 2020).
The Middle Jurassic is characterized by overall cooler climatic con-
ditions, in particular at high- and mid-latitudes (e.g., Dera et al., 2011;
Ruebsam and Schwark, 2021; see also section 3.5). In the Middle
Jurassic, eusauropods were the only surviving sauropodomorph lineage,
with the possible exception of Yunnanosaurus youngi (Lu et al., 2007).
Mamenchisauridae, Cetiosauridae and Neosauropoda (Dicraeosauridae
and Macronaria) began to appear in the Middle Jurassic of South
America, Africa, and Asia. These sauropods, with massive skeletons,
skeletal pneumaticity and pillar-like limbs, showed great size increase,
with African Macronaria and Asian mamenchisaurids at >20 m and 17 t.
The record of ornithischians is limited just after the Jenkyns Event,
but new families of thyreophorans debuted from Bajocian and Batho-
nian, including early members of Stegosauridae, Ankylosauridae and
Nodosauridae (Maidment et al., 2008; Thompson et al., 2012) (Fig. 14).
The new thyreophorans were distributed almost worldwide, from
Europe, Africa and South America. The low position of the head with
respect to the body suggests these herbivores specialized in consuming
low plants, probably occupying a different ecological niche than sau-
ropods that exploited upper levels of the forest. However, like
eusauropods, thyreophorans experimented with an increase in size
during the Middle Jurassic, reaching >6 m in some genera such as
Adratiklit, Isaberrysaura and Lexovisaurus (Paul, 2016; Salgado et al.,
2017; Maidment et al., 2019). Fabrosaurids, hypsilophodontids, and
neornithischians diversied during the Middle Jurassic.
The recovery of herbivores after the Jenkyns Event, with increased
diversity and size in many cases, was coupled with the diversication
and increased size of carnivorous theropods (Fig. 15). During the late
Toarcian, Asfaltovenator vialidadi debuted, the rst species of Allosaur-
oidea, at around 8 m length (Ca˜
nad´
on Asfalto Basin, Rauhut and Pol,
2019). First representatives of Megalosauroidea, the piatnitzkysaurids,
are also recorded in Argentina from the same basin (Fig. 5). The Middle
Jurassic witnessed the radiation of theropods, with the appearance and
diversication of basal Tetanurae, including the major clades Mega-
losauroidea, Allosauroidea and Tyrannosauroidea. The biggest speci-
mens of theropods during the Middle Jurassic reached around 10 m
(Megalosaurus bucklandii and Piveteausaurus divesensis; Benson, 2010;
Benson et al., 2018).
Therefore, we identify the Jenkyns Event as pivotal in a major
remodelling of terrestrial ecosystems, including plants and dinosaurs.
The Toarcian was a relevant boundary in the evolutionary history of
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
17
Fig. 15. Correlation between temperature uctuations represented by δ
18
O values, diversity (number of genera) and body-size of Sauropodomorpha, Theropoda (including Herrerasauridae) and Ornithischia, with
average trend of vegetation diversity with episodes of dominance of thermophilic and xerophicitc vegetation (mainly cheirolepidiaceans), potential incidence of wildres and main episodes of eruptive activity of the LIP.
Note the trend of increasing body-size after the Jenkyns Event.
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
18
theropods, as shown by stratigraphically calibrated phylogenies (Car-
rano et al., 2012, Fig. 13; Rauhut et al., 2016, g. 25) with a substantial
radiation after the Jenkyns Event, mainly during the Aalenian-Bajocian.
The Aalenian was also a critical time in the oceans too, associated with a
major phase of the Mesozoic Marine Revolution, when food chains were
substantially reorganised through diversications of calcareous nanno-
plankton, radiolarians, foraminifera, ammonites, bivalves, brachiopods
and planktivorous sh (see Fantasia et al., 2022).
5. Conclusions
Key aspects of the early evolution of dinosaurs were triggered by
environmental crises. For example, the CPE and ETME were hyper-
thermal events associated with sharp global warming, acid rain, and
climatic changes, and both events profoundly affected the course of
dinosaurian evolution. Here we explored the impact of the early Toar-
cian Jenkyns Event, which was characterized in terrestrial environments
by global warming, perturbation of the carbon cycle (negative carbon
isotopic excursion), enhanced weathering and wildres. We might
expect that heating and potential acid rain on land should lead to a loss
of forests and would affect the diversity and composition of land plant
assemblages and the rest of the trophic web.
After the ETME, the Early Jurassic plant assemblage was dominated
by conifers, mainly Cheirolepidiaceae and Pinaceae, and ferns with large
fronds. Cycadophytes, ginkgophytes, and bennetitaleans were also
common, whereas seed-ferns were less abundant. In some areas bryo-
phytes and lycophytes (mosses) suggest wet conditions. In this context,
among terrestrial tetrapods, Sauropodomorpha dominated the herbi-
vore guild and diversied northwards being recorded in outcrops from
Asia to North America. The basal sauropodomorphs (‘prosauropods’)
Anchisauria and Massospondylidae radiated from Hettangian to
Pliensbachian, after the extinction of typical Triassic Plateosauridae.
Basal Sauropoda diversied in the Early Jurassic, with the rst
eusauropod, Tonganosaurus (Mamenchisauridae) from the Hettangian
(China).
Ornithischians diversied in the Early Jurassic in Gondwana with
the radiation of Heterodontosauridae and the origin of Fabrosauridae. A
new suborder, Thyreophora, represented by the Family Scelidosauridae,
diversied in Laurasia. The potential rst genus of Neornithischia,
Stormbergia, appeared during the earliest Jurassic.
Among theropods, Coelophysidae and Dilophosauridae dominated
and colonized Asia and Africa during the Hettangian and Sinemurian.
New in the earliest Jurassic were also basal forms of Ceratosauria and
Tetanurae.
At the onset of the Jenkyns Event, palynological assemblages and
land plants decreased in diversity and richness. Low-diversity forests
were dominated by conifers (Cheirolepidiaceae, Pinaceae) and cycads,
indicating seasonally dry and warm conditions. Climatic and vegetation
changes drove the extinction of all basal sauropodomorphs at the base of
Toarcian and some basal Sauropoda survived across the Jenkyns Event.
Of course, the record is incomplete, but most of these basal Sauropoda
disappeared before the Aalenian. Scelidosauridae disappeared during
the Toarcian, but the record of ornithischians is scarce from Toarcian to
Bajocian. Coelophysidae and Dilophosauridae died out in the Toarcian,
but new genera of basal Ceratosauria were recorded in the Toarcian.
After the Jenkyns Event, low diversity land-plant communities per-
sisted, with dominance of thermophilic groups, and the conifers Arau-
cariaceae, Cheirolepidiaceae and Cupressaceae in the northern and
southern hemispheres, indicating seasonally dry and warm conditions.
Many Eusauropoda appeared in South America, Africa, and Asia.
Mamenchisauridae, Cetiosauridae and Neosauropoda (Dicraeosauridae
and Macronaria) began to appear in the Middle Jurassic. These sauro-
pods, with massive skeletons, skeletal pneumaticity, pillar-like limbs,
and delicate skulls, show great size increase, with African Macronaria
and Asian mamenchisaurids at >20 m and 17 t.
Among ornithischians, new families of thyreophorans debuted from
Bajocian and Bathonian such as Stegosauridae, Ankylosauridae and
Nodosauridae, being recorded from Europe, Asia, Africa and South
America. During the Bathonian and Callovian, ornithischians diversi-
ed: heterodontosaurids and fabrosaurids extended to the north, neo-
rnithischians diversied in Eurasia, and the rst hypsilophodontid
(Hexinlusaurus) occurred in the Bathonian and Callovian of China.
The recovery of theropods after the Jenkyns Event is marked by the
rst allosauroids and megalosauroids (Argentina, Upper Toarcian). A
theropod radiation occurred during Middle Jurassic with the diversi-
cation of basal Tetanurae and superfamilies Megalosauroidea, Allo-
sauroidea and Tyrannosauroidea. The size of some theropods increased
during the Middle Jurassic, especially in Megalosauroidea and Allo-
sauroidea reaching >10 m.
Therefore, we identify the Jenkyns Event as pivotal in a major
remodelling of terrestrial ecosystems, including plants and dinosaurs.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.earscirev.2022.104196.
Declaration of Competing Interest
None.
Data availability
Data will be made available on request.
Acknowledgments
Financial support through the projects PY20_00111 and RNM-200
Research Group (Junta de Andalucía, Spain) and PID2019-104625RB-
100 (Spanish Government) are gratefully acknowledged. We thank the
Editor (Christopher Fielding) and three anonymous reviewers for their
comments and suggestions.
References
Aberhan, M., Fursich, F.T., 2000. Mass origination versus mass extinction: the biological
contribution to the Pliensbachian – Toarcian extinction event. J. Geol. Soc. Lond.
157, 55–60.
Akikuni, K., Hori, R., Vajda, V., Grant-Mackie, J.A., Ikehara, M., 2010. Stratigraphy of
Triassic-Jurassic boundary sequences from the Kawhia coast and Awakino gorge.
Murihiku Terrane, New Zealand. Stratigraphy 7, 7–24.
Al-Suwaidi, A.H., Ruhl, M., Jenkyns, H.C., Damborenea, S.E., Mance˜
nido, M.O.,
Condon, D.J., Angelozzi, G.N., Kamo, S.L., Storm, M., Riccardi, A.C., Hesselbo, S.P.,
2022. New age constraints on the lower Jurassic Pliensbachian-Toarcian Boundary
at Chacay Melehue (Neuquen Basin, Argentina). Sci. Rep. 12, 4975.
Alipour, M., Alizadeh, B., Jahangard, A., Gandomisani, A., 2021. Wildre events at the
Triassic-Jurassic boundary of the Tabas Basin, Central Iran. Int. J. Coal Sci. Technol.
8, 897–907.
Allain, R., Aquesbi, N., 2008. Anatomy and phylogenetic relationships of Tazoudasaurus
naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco. Geodiversitas
30, 345–424.
Allain, R., Aquesbi, N., Dejax, J., Meyer, C., Monbaron, M., Montenat, C., Richir, P.,
Rochdy, M., Russell, D., Taquet, P., M'ghari, M., 2004. A basal sauropod dinosaur
from the early Jurassic of Morocco. Comptes Rendus Palevolution 3, 199–208.
Allain, R., Tykoski, R., Aquesbi, N., Jalil, N.E., Monbaron, M., Russell, D., Taquet, P.,
2007. A basal abelisauroid from the late early Jurassic of the High Atlas Mountains,
Morocco, and the radiation of ceratosaurs. J. Vertebr. Paleontol. 27, 610–624.
Allen, B.J., Stubbs, T., Benton, M.J., Puttick, M.N., 2019. Archosauromorph extinction
selectivity during the Triassic-Jurassic Mass Extinction. Palaeontology 62, 211–224.
Alvin, K.L., 1982. Cheirolepidiaceae: Biology, structure and paleoecology. Rev.
Palaeobot. Palynol. 37, 71–98.
Apaldetti, C., Martínez, R.N., Cerda, I.A., Pol, D., Alcober, O., 2018. An early trend
towards gigantism in Triassic sauropodomorph dinosaurs. Nat. Ecol. Evol. 2,
1227–1232.
Arias, C., 2009. Extinction pattern of marine Ostracoda across the Pliensbachian-
Toarcian boundary in the Cordillera Ib´
erica, NE Spain: causes and consequences.
Geobios 42, 1–15.
Arias, C., 2013. The early Toarcian (early Jurassic) ostracod extinction events in the
Iberian Range: the effect of temperature changes and prolonged exposure to low
dissolved oxygen concentrations. Palaeogeogr. Palaeoclimatol. Palaeoecol. 387,
40–55.
Baeza-Carratal´
a, J.F., Reolid, M., García Joral, F., 2017. New Deep-water brachiopod
resilient assemblage from the South-Iberian Palaeomargin (Western Tethys) and its
M. Reolid et al.
Earth-Science Reviews 234 (2022) 104196
19
signicance for the brachiopod adaptive strategies around the early Toarcian Mass
Extinction Event. Bull. Geosci. 92, 233–256.
Baghli, H., Mattioli, E., Spangenberg, J.E., Bensalah, M., Arnaud-Godet, F., Pittet, B.,
Suan, G., 2020. Early Jurassic climatic trends in the south-Tethyan margin.
Gondwana Res. 77, 67–81.
Bai, Z.Q., Yang, J., Wang, G.H., 1990. Yimenosaurus, a new genus of Prosauropoda from
Yimen County, Yunnan Province. Yuxiwenbo 1, 14–23.
Baker, S.J., Hesselbo, S.P., Lenton, T.M., Duarte, L.V., Belcher, C.M., 2017. Charcoal
evidence that rising atmospheric oxygen terminated early Jurassic Ocean anoxia.
Nat. Commun. 8, 15018. https://doi.org/10.1038/ncomms15018.
Baranyi, V., Miller, C.S., Ruffel, A., Hounslow, M.W., Kürschner, W.M., 2018.
A continental record of the Carnian Pluvial Episode (CPE) from the Mercia Mudstone
Group (UK): palynology and climatic implications. J. Geol. Soc. 176, 149–166.
Baranyi, V., Rost´
asi, `
A., Raucsik, B., Küschner, W.M., 2019. Palynology and weathering
proxies reveal climatic uctuations during the Carnian Pluvial Episode (CPE) (Late
Triassic) from marine successions in the Transdanubian Range (western Hungary).
Glob. Planet. Chang. 177, 157–172.
Barrett, P.M., 2014. Paleobiology of herbivorous dinosaurs. Ann. Rev. Earth Planet.Sci.
42, 207–230.
Barrett, P.M., 2000. Prosauropod dinosaurs and iguanas: speculations on the diets of
extinct reptiles. In: Sues, H.D. (Ed.), Evolution of Herbivory in Terrestrial
Vertebrates. Cambridge Univ. Press, Cambridge, pp. 42–78.
Barrett, P.M., Butler, R.J., Knoll, F., 2005. Small-bodied ornithischian dinosaurs from the
Middle Jurassic of Sichuan, China. J. Vertebr. Paleontol. 25, 823–834.
Barrett, P.M., Upchurch, P., 2007. The evolution of feeding mechanisms in early
sauropodomorph dinosaurs. Spec. Pap. Palaeontol. 77, 91–112.
Barr´
on, E., G´
omez, J.J., Goy, A., Pieren, A.P., 2006. The Triassic-Jurassic boundary in
Asturias (northern Spain): palynological characterisation and facies. Rev. Palaeobot.
Palynol. 138, 187–208.
Belcher, C.M., Mander, L., Rein, G., Jervis, F.X., Haworth, M., Hesselbo, S.P., Glasspool, I.
J., McElwain, J.C., 2010. Increased re activity at the Triassic/Jurassic boundary in
Greenland due to climate-driven oral change. Nat. Geosci. 3, 426–429.
Benson, R.B.J., 2010. A description of Megalosaurus bucklandii (Dinosauria: Theropoda)
from the Bathonian of the UK and the relationships of Middle Jurassic theropods.
Zool. J. Linnean Soc. 158, 882–935.
Benson, R.B.J., Butler, R.J., 2011. Uncovering the diversication history of marine
tetrapods: ecology inuences the effect of geological sampling biases. Geol. Soc.
Lond., Spec. Publ. 358, 191–208.
Benson, R.B.J., Hunt, G., Carrano, M.T., Campione, N.E., 2018. Cope’s rule and the
adaptive landscape of dinosaur body size evolution. Palaeontology 61, 13–48.
Benton, M.J., 1983. Dinosaur success in the Triassic: a noncompetitive ecological model.
Q. Rev. Biol. 58, 29–55.
Benton, M.J., 1993. Late Triassic extinctions and the origin of the dinosaurs. Science 260,
769–770.
Benton, M.J., 1998. The quality of the fossil record of vertebrates. In: Donovan, S.K.,
Paul, C.R. (Eds.), The Adequacy of the Fossil Record. Wiley, New York, NY,
pp. 269–303.
Benton, M.J., 2021. The origin of endothermy in synapsids and archosaurs and arms
races in the Triassic. Gondwana Res. 100, 261–289.
Benton, M.J., 2004. Origin and relationships of Dinosauria. In: Weishampel, D.B.,
Dodson, P., Osm´
olska, H. (Eds.), The Dinosauria, 2nd edition. University of
California Press, Berkeley, CA, pp. 7–24.
Benton, M.J., 2008. How to nd a dinosaur, and the role of synonymy in biodiversity
studies. Paleobiology 34, 516–533.
Benton, M.J., 2018. Hyperthermal-driven mass extinctions: killing models during the
Permian-Triassic mass extinction. Philos. Trans. Roy. Soc. Ser. A 376, 20170076.
Benton, M.J., Wills, M.A., Hitchin