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Archosauria from the Dolomites

Authors:
  • Museum Dolomythos

Abstract

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.
1
Archosauria from the Dolomites
DOLOMYTHOS-Museum
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
by
Thomas Perner
Oregon Institute of Geological Research, 32 SE 139th Ave, Portland, OR 97233-1844, USA
Abstract
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
1cm
2
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
Posidonomya.
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)
Etymology
Dedicated to Michael Wachtler honouring his
intensive and long-lasting research in the
Dolomites.
Type horizon and ages
Southern Dolomites, Pessina, Middle Trias-
sic, Ladinian (Fassanian-Langobardian).
Wachtlerosaurus ladinicus sp. n.
(PERNER, 2018)
Etymology
After the Ladinian (Middle Triassic) strata
where the fossil was found.
Holotype
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
Diagnosis
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.
Description
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
inclined.
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.
Remarks
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-
4
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
1
4 5
3
2
1cm
1cm
5mm
1cm
5mm
5Archosauria from the Dolomites
2
1
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.
2cm
2cm
6
Archosauria from the Dolomites
3
78
6
5
4
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
1cm
1cm 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
feature.
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.
Conclusion
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
1
2
3
6
5
4
8
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
required.
References
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:
10.1111/j.1475-4983.2007.00723.x
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. https://doi.org/10.1206/352.1
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
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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
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