ChapterPDF Available

Archosauria from the Dolomites

  • Museum Dolomythos


A small-sized archosaur from the Ladinian (Fassanian-Langobardian) stage of the Southern Dolomites is described. The skeleton is mostly complete; the skull is characterized by its powerful teeth, the ribs are slender, and the prominent pelvis including the ilium, ischium, and pubis suggests a classification in an early group of avian-line archosaurs. Fore limbs and hind limbs are equally long. Since very little is known about the phylogenetically earliest members of the Avemetatarsalia, this new animal helps to fill a gap in the knowledge. It will be named Wachtlerosaurus ladinicus gen. nov. sp. n.
Archosauria from the Dolomites
Oregon Institute of Geological Research
Some new and exciting Triassic Archosauria
from the Dolomites (Northern Italy)
Edited by
Thomas Perner and Michael Wachtler
1Archosauria from the Dolomites
A new interesting archosaur from the Ladinian (Middle Triassic)
of the Dolomites (Northern Italy)
Preliminary report
Thomas Perner
Oregon Institute of Geological Research, 32 SE 139th Ave, Portland, OR 97233-1844, USA
A small-sized archosaur from the Ladinian (Fassanian-Langobardian) stage of the Southern
Dolomites is described. The skeleton is mostly complete; the skull is characterized by its
powerful teeth, the ribs are slender, and the prominent pelvis including the ilium, ischium,
and pubis suggests a classification in an early group of avian-line archosaurs. Fore limbs
and hind limbs are equally long. Since very little is known about the phylogenetically earliest
members of the Avemetatarsalia, this new animal helps to fill a gap in the knowledge. It will
be named Wachtlerosaurus ladinicus gen. nov. sp. n.
Online: August 2018
Archosaurs, new genus, Ladinian, Middle Triassic, Dolomites, Northern Italy
Wachtlerosaurus ladinicus nov. gen. sp n.
Entire slab
Archosauria from the Dolomites
Stratigraphical setting and age
The skeleton was collected between a rich
plant horizon pertaining to the Ladinian stage
(Fassanian-Langobardian) on the Southern
part of the Parco Naturale Adamello-Brenta
in the World Heritage site of Dolomites, but
outside the area of the nature park. The
horizon could be defined well as the Global
boundary Stratotype Section and Point
(GSSP) between the Anisian and Ladinian
stage (upper Middle Triassic) is exposed
on the nearby Ponte di Romanterra, south
of Bagolino (Brack et al., 2005). The older
Buchenstein-Formation is still characterized
with predominantly air-borne volcaniclastic
material (Pietra Verde), whereas a marked
change in sedimentation follows with an
abrupt switch to the volcanoclastic to the
siliciclastic Wengen Formation. This stratum
named by Heinrich Ludolf Wissmann
(1841) after the village Wengen (La Valle)
in the Gader-Valley, encompasses various
vulcanite deposits with changing amounts
of tuffs, clays and limestones. The name
Wengen-Formation was later extended to
the whole Southern Alps indicating basinal
terrigenous and volcanoclastic sediments
and conglomerates, followed sometimes
by submarine fine-grained volcaniclastic
turbiditic sandstones and dark mudstones.
The layers can be observed in many parts
of the Dolomites, from Corvara, till Braies,
Gardena Valley, Passo Giau, Zoldo, staying
in this form till the Lombardian Alps. Their
colour is usually dark-brown to greyish.
The first formal recognition of a stratigraphic
interval, comprising what is now called
Ladinian, originates from the subdivisions of
the Triassic System proposed by Edmund von
Mojsisovics. Ammonoids served as the main
biostratigraphic tool for these divisions. After
that, Bittner (1892) introduced the term
“‘ladinisch” (Ladinian, after the “‘Ladin”’-
people of the Dolomites area) as a new label
for the stratigraphic interval comprising
the South Alpine Buchenstein and Wengen
beds. The base of the Ladinian Stage (Middle
Triassic) is defined by the first occurrence of
the ammonoid Eoprotrachyceras curionii. The
Wengen-Formation is known for its richness
in the brackisch water-shell Daonella and
A late Ladinian (Longobardian) for the
Wengen-Formation is also supported with
Dijkstraisporites beutleri and Maexisporites
meditectatus (Wachtler & Van Konijnenburg-
Van Cittert, 2000). The macro-plant
assemblage is characterized especially by
the conifer Voltzia dolomitica, and also
holding other conifers (Alpia ladinica) like
the cycads Bjuvia dolomitica, Nilssonia
faustinii and Apoldia wengensis, some
ferns (Neuropteridium, Gordonopteris) and
horsetails (Equisetites arenaceus).
Even in a layer of the Wengen-Formation
holding spectacular Voltzia dolomitica twigs
and Daonella-shells, a complete skeleton
of an archosaur, probably belonging to the
base of the avian stem lineage (Avemetatar-
salia) conducting to the dinosaurs and birds,
was found.
Systematic Paleontology
Subclass DIAPSIDA Osborn, 1903
Infraclass NEODIAPSIDA Benton, 1985
Division ARCHOSAUROMORPHA Huene, 1946
Subdivision ARCHOSAURIA Cope, 1869
Infradivision AVEMETATARSALIA Benton, 1999
Wachtlerosaurus gen. n.
(PERNER, 2018)
Dedicated to Michael Wachtler honouring his
intensive and long-lasting research in the
Type horizon and ages
Southern Dolomites, Pessina, Middle Trias-
sic, Ladinian (Fassanian-Langobardian).
Wachtlerosaurus ladinicus sp. n.
(PERNER, 2018)
After the Ladinian (Middle Triassic) strata
where the fossil was found.
PRE 01, is a disassociated skeleton of one
individual, including: complete skull, cervi-
cal, trunk, and caudal vertebrae, forelimb
and hind limbs, pelvis and most part of the
tail. Coll. Wachtler, Dolomythos Museum, In-
nichen, Südtirol.
3Archosauria from the Dolomites
Small Archosauria, with a diapsid skull.
Dentary and premaxillary ending elongated
and holding powerful and robust teeth.
Humerus and femur mainly equal long.
Presence of incurved sharp claws. Ribs
thin and fragile. Pubis and ischium mainly
isometric and pointed backwards.
Skull: The skull is 35 mm long, 20 mm
wide, and consists of several major bones:
the dentary measures 20 mm, the surangu-
lar is separated, the premaxilla is partly bro-
ken by fossilisation, but evidence presents
a nasal aperture. Both hold prominent and
powerful teeth, approximately 1 mm long
and not recurved. The orbita is distinctive
and rounded and 10 mm in diameter.
Cervical vertebrae: The upper spinal col-
umn is hidden in the rock and only visible
on X-Ray: 7 vertebrae can be observed at-
tached, 3 probably lie separate.
Ribs: They could reach a maximum length
of 45 mm and are long and slender.
Fore legs: The humerus is 26 mm long
and flattened in an anteroposterior direc-
tion, the proximal portion is expanded more
than twice the width of the midshaft of the
humerus. The ulna is 11 mm long, and the
distal ends the convex. Digits approximately
are 5 mm, whereas the claws reach a length
of 5 mm and are incurved.
Pelvis: Ilium, ischium and pubis fused to-
gether. Pubis 35 mm long, ischium probably
1 mm shorter. Ilium crest dorsal to the su-
praacetabular crest/rim and anterodorsally
Hind legs: Left and right femur are 26 mm
long and powerful. The femur has expanded
proximal and distal heads and a narrow
shaft with a sygmoidal curvature. The tibia
is 11 mm long and the tarsus 11 mm.
The archosaurs have a 250-million-
year record that originated shortly after
the Permian-Triassic boundary and is
continued today by two extant clades – the
crocodylians and the avians. The phylogeny
of Archosauriformes indicates that an
initial diversification occurred during the
Early Triassic. Early archosaur evolution is
characterized by high rates of homoplasy,
long ghost lineages, and high rates of
character evolution (Nesbitt et al., 2017).
Archosaurs were diverse by the Middle
Triassic and had there a cosmopolitan
distribution. During the Triassic,
archosauriforms settled in many different
habitats from terrestrial (e.g., dinosaur,
‘‘rauisuchian,’’ aetosaur, crocodylomorph),
aquatic terrestrial (phytosaur), till aerial
(pterosaur). Following the Triassic, two main
lineages remained – the Crocodylomorpha
and the Dinosauria.
The early members of Crocodylomorpha
from the Triassic and the Early Jurassic
were lumped into the Sphenosuchia prior
to explicit phylogenetic analyses (Nesbitt,
2011). The other comprise the Avian-
line archosaurs consisting of pterosaurs,
dinosaurs, and a range of intermediate
forms. Today, the only surviving members
are modern birds. Benton proposed the
name Avemetatarsalia in 1999 to include
all bird-line archosaurs – referring to all
archosaurs more closely related to dinosaurs
than to crocodilians. The Avemetatarsalians
first appeared in the Middle Triassic but they
remained a rare component until the origin
of the dinosaurs in the Late Triassic. Even in
the Late Triassic, avian-line archosaurs were
dominated in number of taxa, body types,
and overall abundance by the crocodylian-
line archosaurs (Nesbitt, 2011).
It is thought that the basal archosaurs
changed their posture from sprawling to
erect and showed decreases in femur stress
with a more upright walking way (Kobe &
Benton, 2007). All theropods share several
common features; they have a gracile body,
slender and hollow limb bones, a foot with
three main toes, and they were bipeds,
where the long neck was cantilevered over
the hindlimbs. The ilium has a low, convex
dorsal border and a long preacetabular
process. The ischium and pubis are
elongated and rod-like. The femur and tibia
are strong bones. The forelimbs are different
from the hind limbs. The humerus and femur
are equally long and powerful, whereas the
ulna is more fragile and slenderer than the
tibia. This is also valid for metacarpus and
tarsus (Kubo & Benton, 2007).
It is not easy to insert Wachtlerosaurus in
one of the known families. Therefore, maybe
it is more useful to study the same. From
this point of view, it can be established that
Wachtlerosaurus was only a little rhyncho-
Archosauria from the Dolomites
Wachtlerosaurus ladinicus nov. gen. sp n.
1. Skull; 2. Detail of the teeth; 3. Pelvis, pubis and ilium; 4. Humerus, ulna, and part of the hand bones with claws;
5. Detail of the hand bones and the claws
4 5
5Archosauria from the Dolomites
Wachtlerosaurus ladinicus: X-Ray-Images:
1. Whole slab measuring 24 cm; 2. Back view with image of the pelvis, and the hind legs. Also detail of the verte-
brae and the costae.
Archosauria from the Dolomites
Wachtlerosaurus ladinicus: X-Ray-Images:
3. Detail of the cervical vertebra; 4. Detail of the claws and the hand-bones; 5. Humerus and ulna; 6. Femur and
tibia; 7. Vertebra and ribs; 8. Two dorsal vertebra.
1cm 1cm
7Archosauria from the Dolomites
cephalians); the squamosal lacks an anteri-
orly concave articulatory facet for the pos-
torbital; a well-developed alar process of the
prootic and a radial condyle on the humerus;
an ulnar patella; a secondary curvature of
the clavicles; and an expanded epiphysis of
the first metacarpal along with the absence
of the first distal carpal (suggesting its fu-
sion with the first metacarpal, as observed
in modern squamates (Simōes et al., 2018).
Many of these features are not visible in
Wachtlerosaurus ladinicus. Also, the ribs are
more fragile, whereas the elongated pubis is
not preserved in Megachirella wachtleri.
Another line is the Pseudosuchia, which first
appeared in the Early Triassic. Their ankles,
the astragalus, were joined to the tibia by
a suture, and the joint rotated around a
peg on the astragalus, which fitted into a
socket in the calcaneum. It doesn’t seem
that Wachtlerosaurus was equipped with this
The Ornithodira include the last common
ancestor of pterosaurs and dinosaurs and
also the birds; the Crurotarsi comprise the
ancestors of crocodilians but also some
group of Triassic archosaurs like the ornitho-
suchids, aetosaurs, and phytosaurs.
Early Crurotarsans walked with sprawling
limbs but some later developed fully erect
limbs (most notably the Rauisuchia), where-
as modern crocodilians can walk with their
limbs sprawling or erect depending on the
speed of locomotion.
Wachtlerosaurus ladinicus leaves open
probably only a very early line of the
Avemetatarsalia, although it is suggested
that they appeared in the Carnian age
of the late Triassic (Benton, 1999). Like
Wachtlerosaurus, they were lightly built and
usually adapted to a biped life. This small
archosaur was probably about 25-30 cm long
but had not assimilated to a life in water. So,
a nothosaurian line can be excluded. It holds
no mammalian features; the skeleton was
light-weighty, but no shadows of the skin or
feathers are visible. The animal would have
adapted to a climbing and arboreal lifestyle
with the miniaturization of body size to
evade predation.
Scleromochlus taylori, about 18 cm long,
from the late Carnian Lossiemouth Sand-
stone Formation, provides evidence of a
primitive ankle structure, and it has a slen-
Wachtlerosaurus ladinicus drawings: 1. Whole slab; 2. Skull; 3. Pubis and ilium; 4. Dorsal vertebrae; 5. Humerus and
Ulna; 6. Femur and Tibia
Archosauria from the Dolomites
Measurements taken on the Wachtlerosau-
rus ladinicus
Length of the preserved slab: 240 mm
Skull: 35 mm long x 20 mm high
Orbit 10 mm length x 9 mm wide
Length of the ribs: Longest 45 mm
Humerus: 26 mm
Ulna: 14 mm
Claws: 5 mm
Pubis: 35 mm
Illium: 40 mm
Femur left: 26 mm
Femur right: 25 mm
Tibia: 11 mm
squamosal (not tetraradiate as in most other
diapsids, including small; their necks were
long and had an S-shaped curve; and their
skulls were much more lightly built. Only
the bipedal movement was not very good
evolved in Wachtlerosaurus. Altogether it
can be stated, that this Ladinian animal
opens a window to the evolution of the
birdlike dinosaurs, many further studies are
Benton, MJ., 1999. Scleromochlus taylori and the origin
of dinosaurs and pterosaurs. Philosophical Transactions
B: Biological Sciences, vol 354, pp. 1423-1446.
Brack, P., Rieber, H., Nicora, A., Mundil, R., 2005. The
Global boundary Stratotype Section and Point (GSSP) of
the Ladinian Stage (Middle Triassic) at Bagolino (South-
ern Alps, Northern Italy) and its implications for the Tri-
assic time scale: Episodes, v. 28/4, pp. 233-244
Kubo, T., Benton, MJ., 2007. Evolution of hindlimb
Posture in Archosaurs: Limb Stresses in Extinct Verte-
brates’ Palaeontology, vol 50 (6), pp. 1519-1529. DOI:
Nesbitt, S. 2011. The Early Evolution of Archosaurs:
Relationships and the Origin of Major Clades, Bulletin
of the American Museum of Natural History Number
352: 1-292.
Nesbitt, S., Butler, R., Ezcurra, M., Barrett, P., Stocker,
M., Angielczyk, K., Smith, R., Sidor, C., Niedzwiedzki,
G., Sennikov, A., Charig, A., 2017. The earliest bird-
line archosaurs and the assembly of the dinosaur body
plan. Nature, vol 544, no. 7651, pp. 484-487. DOI:
10.1038/Nature 22037
Renesto, S., Posenato, R., 2003. A new lepidosauromorph
reptile from the Middle Triassic of the Dolomites (North-
ern Italy). Riv. Ital. Paleontol. Stratigr. 109, 463–474
Simōes, T., Caldwell, M., Talanda, M., Bernardi, M.,
Palci, A., Vernygora, O., Bernardini, F., Mancini, L., Ny-
dam, R., 2018. The origin of squamates revealed by
a Middle Triassic lizard from the Italian Alps”. Nature.
557 (7707): 706–709. doi:10.1038/s41586-018-0093-
3. PMID 29849156
Wachtler M., Van Konijnenburg-Van Cittert J.H.A., 2000.
The fossil flora of the Wengen Formation (Ladinian) in
the Dolomites (Italy). Beitr. Paläont., 25: 105-141
der humerus, femur, and fibula having ad-
ditionally the classic bird-like characters of
a tibia that is longer than the femur, and
a closely appressed group of four elongate
metatarsals (Benton, 1999). These char-
acters are only partly recorded in Wachtle-
rosaurus. However, the poor preservation of
Scleromochlus could not be scored for many
of the important characters that optimize
near the base of Avemetatarsalia.
The synapsids, mammal-like reptiles, were
the dominant land vertebrates throughout
the Permian, but they perished mostly be-
tween the Permian-Triassic border. Only a
few synapsids, especially Lystrosaurus, an
herbivorous dicynodont, survived, but in the
Early Triassic, the archosaurs were just the
dominant land vertebrates.
Otherwise, it is difficult to establish when
the archosaurs first appeared. The Permian
reptiles Archosaurus rossicus from Russia
and Poland or Protorosaurus speneri from
Germany appeared in the late Permian, but
there is some doubt if they can be classified
as true archosaurs or only archosauriforms.
Also, early members of the rauisuchians,
such as Scythosuchus basileus from the
Lower Triassic of the Donskaya Luka locality
(Russia) or Tsylmosuchus jakovlevi found
in the Pechora region in the Urals do not fit
well in the blueprint of Wachtlerosaurus.
Another interesting fossil, Megachirella
wachtleri, found in the Anisian layers of the
Dolomites, is the first unequivocal squamate
from the Triassic worldwide (Renesto &
Posenato, 2003; Simōes et al., 2018). It
preserves traits that indicate a lepidosaurian
reptile, such as the presence of a well-
developed quadrate conch, an ectepicondylar
foramen in the humerus and pleurodont
dentition. But results from the micro-CT
scans include a combination of features that
are found uniquely in squamates: a triradiate
Suggested reconstruction of Wachtlerosaurus ladinicus
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
Modern squamates (lizards, snakes and amphisbaenians) are the world's most diverse group of tetrapods along with birds 1 and have a long evolutionary history, with the oldest known fossils dating from the Middle Jurassic period-168 million years ago2-4. The evolutionary origin of squamates is contentious because of several issues: (1) a fossil gap of approximately 70 million years exists between the oldest known fossils and their estimated origin5-7; (2) limited sampling of squamates in reptile phylogenies; and (3) conflicts between morphological and molecular hypotheses regarding the origin of crown squamates6,8,9. Here we shed light on these problems by using high-resolution microfocus X-ray computed tomography data from the articulated fossil reptile Megachirella wachtleri (Middle Triassic period, Italian Alps 10 ). We also present a phylogenetic dataset, combining fossils and extant taxa, and morphological and molecular data. We analysed this dataset under different optimality criteria to assess diapsid reptile relationships and the origins of squamates. Our results re-shape the diapsid phylogeny and present evidence that M. wachtleri is the oldest known stem squamate. Megachirella is 75 million years older than the previously known oldest squamate fossils, partially filling the fossil gap in the origin of lizards, and indicates a more gradual acquisition of squamatan features in diapsid evolution than previously thought. For the first time, to our knowledge, morphological and molecular data are in agreement regarding early squamate evolution, with geckoes-and not iguanians-as the earliest crown clade squamates. Divergence time estimates using relaxed combined morphological and molecular clocks show that lepidosaurs and most other diapsids originated before the Permian/Triassic extinction event, indicating that the Triassic was a period of radiation, not origin, for several diapsid lineages.
Full-text available
The relationship between dinosaurs and other reptiles is well established, but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies. The closest extinct relatives of dinosaurs either have highly derived morphologies or are known from poorly preserved or incomplete material. Here we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch. The anatomy of T. rhadinus provides key information that unites several enigmatic taxa from across Pangaea into a previously unrecognized clade, Aphanosauria. This clade is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia. We demonstrate that several anatomical features long thought to characterize Dinosauria and dinosauriforms evolved much earlier, soon after the bird–crocodylian split, and that the earliest avemetatarsalians retained the crocodylian-like ankle morphology and hindlimb proportions of stem archosaurs and early pseudosuchians. Early avemetatarsalians were substantially more species-rich, widely geographically distributed and morphologically diverse than previously recognized. Moreover, several early dinosauromorphs that were previously used as models to understand dinosaur origins may represent specialized forms rather than the ancestral avemetatarsalian morphology.
Full-text available
A new genus and species of diapsid reptile is described. The specimen was collected from the Anisian (Middle Triassic) succession of Monte Pra della Vacca (Kiihwiesenkopf) in the Dolomites of Braies (Bolzano/Bozen, Northern Italy). Despite being incomplete, the specimen shows enough characters to allow its placement within Lepidosauriformes, close to the Middle Jurassic genus Marmoretta. The importance of this find lies in the great rarity of lepidosauriforms of Anisian age, an epoch approximating the appearance of the first members of the true Lepidosauria (rhyncocephalians and squamates). The new genus may thus add knowledge to the diversity of early lepidosaurians. Some characters of the skeleton, mainly of the forelimb, suggest a terrestrial, perhaps arboreal life style.
Full-text available
The Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian Stage (Middle Triassic) is defined in the Caffaro river bed (45°49'09.5"N, 10°28'15.5"E), south of the village of Bagolino (Province of Brescia, northem Italy), at the base of a 15-20-cm-thick limestone bed overlying a distinct groove ("Chiesense groove") of limestone nodules in a shaly matrix, located about 5 m above the base of the Buchenstein Formation. The lower surface of the thick limestone bed has the lowest occurrence of the ammonoid Eoprotrachyceras curionii (base of the E. curionii Zone; onset of the Trachyceratidae ammonoid family). Secondary global markers in the uppermost Anisian include the lowest occurrence of conodont Neogondolella praehungarica and a brief normal-polarity magnetic zone recognized in closely correlated sections including the principal auxiliary section at Seceda in the Dolomites. The GSSP-level is bracketed by U-Pb single zircon age data from volcaniclastic horizons, indicating a boundary age of ca 241 Ma.
Full-text available
Archosaurs have a nearly 250 million year record that originated shortly after the Permian-Triassic extinction event and is continued today by two extant clades, the crocodylians and the avians. The two extant lineages exemplify two bauplan extremes among a diverse and complex evolutionary history, but little is known about the common ancestor of these lineages. Renewed interest in early archosaurs has led to nearly a doubling of the known taxa in the last 20 years. This study presents a thorough phylogenetic analysis of 80 species-level taxa ranging from the latest Permian to the early part of the Jurassic using a dataset of 412 characters. Each terminal taxon is explicitly described and all specimens used in the analysis are clearly stated. Additionally, each character is discussed in detail and nearly all of the character states are illustrated in either a drawing or highlighted on a specimen photograph. A combination of novel characters and comprehensive character sampling has bridged previously published analyses that focus on particular archosauriform subclades. A well-resolved, robustly supported consensus tree (MPTs  =   360) found a monophyletic Archosauria consisting of two major branches, the crocodylian-line and avian-line lineages. The monophyly of clades such as Ornithosuchidae, Phytosauria, Aetosauria, Crocodylomorpha, and Dinosauria is supported in this analysis. However, phytosaurs are recovered as the closest sister taxon to Archosauria, rather than basal crocodylian-line archosaurs, for the first time. Among taxa classically termed as "rauisuchians," a monophyletic poposauroid clade was found as the sister taxon to a group of paraphyletic "rauisuchians" and monophyletic crocodylomorphs. Hence, crocodylomorphs are well nested within a clade of "rauisuchians," and are not more closely related to aetosaurs than to taxa such as Postosuchus. Basal crocodylomorphs such as Hesperosuchus and similar forms ("Sphenosuchia") were found as a paraphyletic grade leading to the clade Crocodyliformes. Among avian-line archosaurs, Dinosauria is well supported. A monophyletic clade containing Silesaurus and similar forms is well supported as the sister taxon to Dinosauria. Pterosaurs are robustly supported at the base of the avian line. A time-calibrated phylogeny of Archosauriformes indicates that the origin and initial diversification of Archosauria occurred during the Early Triassic following the Permian-Triassic extinction. Furthermore, all major basal archosaur lineages except Crocodylomorpha were established by the end of the Anisian. Early archosaur evolution is characterized by high rates of homoplasy, long ghost lineages, and high rates of character evolution. These data imply that much of the early history of Archosauria has not been recovered from the fossil record. Not only were archosaurs diverse by the Middle Triassic, but they had nearly a cosmopolitan biogeographic distribution by the end of the Anisian.
Full-text available
The phylogenetic position of Scleromochlus taylori has been disputed recently, in terms of whether it is a basal sister group of Pterosauria or of Dinosauromorpha. The seve specimens, all from the Lossiemouth Sandstone Formation (late Carnian, Late Triassic) of Lossiemouth, near Elgin, north–eas Scotland, suggest that Scleromochlus shares no unique features with either Pterosauria or Dinosauromorpha, together the Ornithodira, but is a close outgroup. Scleromochlus retains a primitive ankle structure, and it has a slender humerus, femur and fibula. Scleromochlus shows the classic bird–like characters of a tibia that is longer than the femur, and a closely appressed group of four elongat metatarsals. A new group name, Avemetatarsalia (‘bird feet’), is established here for the clade consisting of Scleromochlus and Ornithodira, and their descendants. A reanalysis of crown–group archosaur relationships confirms the split into Crurotars (crocodile relatives) and Ornithodira (bird relatives), as well as the clear division of Ornithodira into Pterosauria an Dinosauromorpha. Relationships within Crurotarsi are, however, much less clear: Ornithosuchidae probably reside within tha clade, and there might be a clade ‘Rauisuchia’ consisting of Prestosuchidae and Postosuchus, but support for these relationships is weak. Scleromochlus was probably a bipedal cursor that could adopt a digitigrade stance. However, it is possible that Scleromochlus was also a saltator, capable of leaping long distances.
During the Triassic, some 250–200 million years ago, the basal archosaurs showed a transition from sprawling to erect posture. Past studies focused on changes in bone morphology, especially on the joints, as they reorientated from a sprawling to an erect posture. Here we introduce a biomechanical model to estimate the magnitude of femur stress in different postures, in order to determine the most reasonable postures for five basal archosaurs along the line to crocodiliforms (the rhynchosaur Stenaulorhynchus, the basal archosaur Erythrosuchus, the ‘rauisuchian’Batrachotomus, the aetosaurs Desmatosuchus and Typothorax). The results confirm a sprawling posture in basal taxa and an erect posture in derived taxa. Erect posture may have evolved as a strategy to reduce large bending stresses on the limb bone caused by heavy body weights in larger forms.
The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps"
  • T Simōes
  • M Caldwell
  • M Talanda
  • M Bernardi
  • A Palci
  • O Vernygora
  • F Bernardini
  • L Mancini
  • R Nydam
Simōes, T., Caldwell, M., Talanda, M., Bernardi, M., Palci, A., Vernygora, O., Bernardini, F., Mancini, L., Nydam, R., 2018. The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps". Nature. 557 (7707): 706-709. doi:10.1038/s41586-018-00933. PMID 29849156