19 research outputs found
Sauropod teeth from the Middle Jurassic of Madagascar, and the oldest record of Titanosauriformes
No full textHere we describe 31 fossil teeth, deposited in the palaeontological collections of the Museo di Storia Naturale di Milano (MSNM), that come from the inland portion of the Mahajanga Basin, NW Madagascar, namely from the Sakahara Formation (classically known as Isalo IIIb subunit), which is dated to the Bathonian stage of the Middle Jurassic. Based on detailed morphological characters, the eight morphotypes recognized herein are tentatively referred to four sauropod taxa: Archaeodontosaurus descouensi, 'Bothriospondylus madagascariensis', Lapparentosaurus madagascariensis and an indeterminate specialized eusauropod, which may represent a new species and provides the first evidence of a Bathonian diplodocoid in Madagascar. The identification of the teeth is corroborated by comparative examination of morphometric data. We provide evidence that Titanosauriformes were present in the Bathonian, on the basis of seven specimens referable to this Glade. We also discuss in detail some dental characters that support the existence of a clear niche partitioning between the abovementioned taxa that co-existed in the Malagasy Middle Jurassic terrestrial ecosystem. We hypothesize, for the first time, a direct correlation between the pattern drawn on the tooth crown by the enamel wrinkles and the feeding ecology of sauropod dinosaurs. The enamel wrinkles probably played a structural function: coarse wrinkles were associated with a diet composed mainly of hard foodstuff, whereas fainter wrinkles, which appeared in more derived morphologies, were associated with a diet composed of softer foodstuff
FIRST SKELETAL REMAINS OF HELVETICOSAURUS FROM THE MIDDLE TRIASSIC ITALIAN OUTCROPS OF THE SOUTHERN ALPS, WITH REMARKS ON AN ISOLATED TOOTH
No full textThe enigmatic marine reptile Helveticosaurus zollingeri, from the Middle Triassic Besano Formation of Monte San Giorgio, is known from three specimens found in Swiss territory. This paper describes the first skeletal remains of this taxon recovered from the corresponding Italian outcrops of Besano (Varese). An isolated tooth assigned to the same taxon and coming from the San Salvatore Dolomite, Rasa di Varese (Varese), is also redescribed herein. The skeletal remains have been CT scanned to inspect the preserved morphology of the bones hidden below the surface; CT data also allowed the identification of an associated ammonoid which has been crucial to determine the stratigraphic position of the studied material. The redescription of the tooth has been helped by a digital model of the specimen obtained through photogrammetry. With the additional new data obtained from the two specimens, the first skeletal reconstruction of Helveticosaurus is provided. This is followed by a phylogenetic test of the taxon, assessing its position among marine Triassic diapsids. Finally, in the light of recent studies we discuss the swimming mode and the possible ecological niche occupied by the animal: we suggest a distinction between the function of forelimbs and hindlimbs, and a distinction between different swimming styles likely performed by Helveticosaurus, depending on the speed of movements
STUDY OF THE PALEONTOLOGICAL RECORD OF THE BESANO FORMATION (MIDDLE TRIASSIC) AT ¿SASSO CALDO¿, VARESE, UNESCO WHL MONTE SAN GIORGIO
No full textThe Besano Formation consists of an alternation of laminated dolomitic banks and bituminous shales, and sparse cineritic tuffs that are dated as Late Anisian–Early Ladinian. It is one of the richest fossil-bearing formations from the Monte San Giorgio area; on the Italian side of Monte San Giorgio, the Sasso Caldo site is the one from which the greatest part of the Besano collection housed at the Museo di Storia Naturale di Milano is from. This Ph.D. thesis aims to the study of the Besano Formation macrofauna, through biochronostratigraphic zonation of the Sasso Caldo Site, revision of the large ichthyosaur Besanosaurus leptorhynchus), and study of the most important specimens, chosen for their preservation and rarity, but also to test the hypothesis of variations in the influence of open sea on the Besano basin.
All the available ammonoids and bivalves from the Sasso Caldo site (Besano Formation), housed in the collections of the Museo di Storia Naturale di Milano, were examined and determined. The systematic study led to the recognition of 15 ammonoid taxa belonging to 10 genera, and five species belonging to the bivalve genus Daonella. The study of bed-by-bed collected specimens allowed the biochronostratigraphic classification of the Sasso Caldo section and the time-calibration of invertebrate and vertebrate bioevents. Results evidence that at Sasso Caldo site crops out almost the entire middle to upper Besano Formation. corresponding the Nevadites secedensis ammonoid zone. The trend of distribution of specimens reflects the establishment of an intraplatform basin with discontinuous open-marine influence in the middle Besano Formation, while the upper Besano Formation corresponds to a shallower subtidal restricted platform environment.
Among the terrestrial taxa recovered at Sasso Caldo from the upper Besano Formation, a remarkably well-preserved fossil scorpion (BES SC 1973) is described in this thesis. This finding corroborates the hypothesized existence of a near shoreline during the deposition of the upper Besano Formation. BES SC 1973 is assigned to a new taxon gen. et sp. nov., included in the family Protobuthidae. This finding represents the first arachnid recorded from the Besano Formation, and the second genus attributed to the family Protobuthidae. This specimen is also the first reported Italian Mesozoic fossil scorpion.
Regarding vertebrates, MSNM V927 and 928, a portion of the axial skeleton of a large diapsid, is attributed to Helveticosaurus zollingeri, a rare diapsid known only from the Besano Formation. This animal was recovered in association with the ammonoid Ticinites, at the base of the N. secedensis Zone, in coincidence with the establishment of the intraplatform basin of the middle Besano Formation. This specimen is the first record of skeletal remains and the second specimen assigned to the taxon in Italy. In this work the niche occupied by this animal in the Middle Triassic coastal ecosystems and its swimming style are also revised and discussed.
MSNM V926, and SMNS 50010, respectively a portion of ribcage and an isolated partial forefin of a large ichthyosaur, were attributed to Cymbospondylus buchseri. MSNM V926 represents the first specimen attributed to this taxon and recovered on the Italian side of Monte San Giorgio.
A great part of this thesis is dedicated to the revision of Besanosaurus leptorhynchus. The specimens studied and attributed to Besanosaurus leptorhynchus preserve a remarkably complete cranial and postcranial anatomy so that this taxon can be now accounted among the best-understood Middle Triassic ichthyosaur taxa. The revision of the skull morphology of this taxon clarified long-standing controversies regarding its cranial anatomy and the taxonomy of shastasaurids from Monte San Giorgio. The six specimens here described represent a potential ontogenetic series composed of an embryo (inside the maternal cavity of BES SC 999), likely two subadults, and four adults. They can be ordered by increasing size as follows: embryonic material of BES SC 999, PIMUZ T 4376, PIMUZ T 1895, BES SC 999, BES SC 1016, GPIT 1793/1, PIMUZ T 4847. Also, Besanosaurus resulted the largest Middle Triassic ichthyosaur taxon of the Western Tethys to date, since a full adult size is confidently estimated to be almost 8 m in PIMUZ T 4847. Besanosaurus is characterized by a long, slender, and gracile snout, representing an ecological specialization never seen before the Anisian in a large-sized diapsid. The study of the postcranial anatomy of Besanosaurus leptorhynchus is based on four specimens: PIMUZ T 4376, PIMUZ T 1895, BES SC 999, PIMUZ T 4847. The results suggest that this taxon possesses a peculiar bauplan, which in its proportions fits in between Cymbospondylus and the shastasaur-grade ichthyosaurs. Swimming capabilities of Besanosaurus leptorhynchus were tested and compared with Cymbospondylus and Mixosaurus. Among the ichthyosaurs from the Besano-Monte San Giorgio fauna (Cymbopondylus, mixosaurids, and Besanosaurus), different hunting strategies, demonstrated by different morphologies and dimensions of the rostra, as well as different body proportions and swimming styles, should have led to niche partitioning.
The key phylogenetic position occupied by Besanosausurus leptorhynchus in the ichthyosaurian phylogeny was investigated: the analysis shows that this taxon represents the basalmost member of shastasaur-grade ichthyosaurs, recovered to be a paraphyletic group.
Eventually is addressed a study of the embryonic material preserved in BES SC 999. We deem the material in the body cavity of BES SC 999 unambiguously embryonic and attributable to Besanosaurus leptorhynchus. Here the embryonic material is described in detail and qualitatively compared with the maternal specimen and to other known ichthyosaur prenatal specimens
An exceptionally well-preserved scorpion from the Besano Formation (Monte San Giorgio, Middle Triassic, Southern Alps): preliminary study
No full textCranial anatomy of Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 (Reptilia: Ichthyosauria) from the Middle Triassic Besano formation of Monte San Giorgio, Italy/Switzerland: taxonomic and palaeobiological implications
No full textBesanosaurus leptorhynchus Dal Sasso & Pinna, 1996 was described on the basis of a single fossil excavated near Besano (Italy) nearly three decades ago. Here, we re-examine its cranial osteology and assign five additional specimens to B. leptorhynchus, four of which were so far undescribed. All of the referred specimens were collected from the Middle Triassic outcrops of the Monte San Giorgio area (Italy/Switzerland) and are housed in various museum collections in Europe. The revised diagnosis of the taxon includes the following combination of cranial characters: extreme longirostry; an elongate frontal not participating in the supratemporal fenestra; a prominent ‘triangular process’ of the quadrate; a caudoventral exposure of the postorbital on the skull roof; a prominent coronoid (preglenoid) process of the surangular; tiny conical teeth with coarsely-striated crown surfaces and deeply-grooved roots; mesial maxillary teeth set in sockets; distal maxillary teeth set in a short groove. All these characters are shared with the holotype of Mikadocephalus gracilirostris Maisch & Matzke, 1997, which we consider as a junior synonym of B. leptorhynchus. An updated phylogenetic analysis, which includes revised scores for B. leptorhynchus and several other shastasaurids, recovers B. leptorhynchus as a basal merriamosaurian, but it is unclear if Shastasauridae form a clade, or represent a paraphyletic group. The inferred body length of the examined specimens ranges from 1 m to about 8 m. The extreme longirostry suggests that B. leptorhynchus primarily fed on small and elusive prey, feeding lower in the food web than an apex predator: a novel ecological specialisation never reported before the Anisian in a large diapsid. This specialization might have triggered an increase of body size and helped to maintain low competition among the diverse ichthyosaur fauna of the Besano Formation
Paleogeographic distribution of the Shastasauridae: geological evidence for a waterway connecting the Arctic Sea and Eastern Tethys, during the early/middle Anisian
No full textOntogenetic variation in the cranium of Mixosaurus cornalianus, with implications for the evolution of ichthyosaurian cranial development
No full textRelatively complete ontogenetic series are comparatively rare in the vertebrate fossil record. This can create biases in our understanding of morphology and evolution, since immaturity can represent a source of unrecognized intraspecific variation in both skeletal anatomy and ecology. In the extinct marine reptile clade Ichthyopterygia, ontogenetic series were widely studied only in some Jurassic genera, while the ontogeny of the oldest and most basal members of the clade is very poorly understood. Here, we investigate cranial ontogeny in Mixosaurus cornalianus , from the Middle Triassic Besano Formation of the Swiss and Italian Alps. This small-bodied taxon is represented by a wealth of material from multiple size classes, including fetal material. This allows us to assess ontogenetic changes in cranial morphology, and identify stages in the ontogenetic trajectory where divergence with more derived ichthyosaurs has occurred. Early ontogenetic stages of Mixosaurus show developmental patterns that are reminiscent of the presumed ancestral (early diverging sauropsid) condition. This is prominently visible in the late fetal stage in both the basioccipital, which shows morphology akin to basal tubera, and in the postorbital, which has a triradiate head. The ontogenetic trajectory of at least some of the cranial elements of Mixosaurus is therefore likely still very akin to the ancestral condition, even though the adult cranium diverges from the standard diapsid morphology.Open Access funding enabled and organized by Projekt DEAL.Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung http://dx.doi.org/10.13039/501100001711Staatliches Museum für Naturkunde Stuttgart (SMNS) (4944
Data from: Sauropod teeth from the Middle Jurassic of Madagascar, and the oldest record of Titanosauriformes
No full textHere we describe 31 fossil teeth, deposited in the paleontological collections of the Museo di Storia Naturale di Milano (MSNM), that come from the inland portion of the Mahajanga Basin, NW Madagascar, namely from the Sakahara Formation (classically known as Isalo IIIb subunit), which is dated back to the Middle Jurassic Bathonian stage. Based on detailed morphological characters, the eight morphotypes recognised herein are tentatively referred to four sauropod taxa: Archaeodontosaurus descouensi, ‘Bothriospondylus madagascariensis’, Lapparentosaurus madagascariensis, and an indeterminate specialised eusauropod, which may represent a new species, and the first evidence of a Bathonian diplodocoid in Madagascar.
The identification of the teeth is corroborated by comparative examination of morphometric data. In this paper we provide evidence that Titanosauriformes were present in the Bathonian, on the basis of seven specimens referable to this clade. We also discuss in detail some dental characters that support the existence of a clear niche partitioning between the above mentioned taxa, that co–existed in the Malagasy Middle Jurassic terrestrial ecosystem. We finally hypothesise, for the first time, a direct correlation between the pattern drawn on the tooth crown by the enamel wrinkles and the feeding ecology of sauropod dinosaurs. The enamel wrinkles likely played a structural function: coarse wrinkles were associated to a diet composed mainly by hard foodstuff, whereas fainter wrinkles, which appeared in more derived morphologies, were associated to a diet composed by softer foodstuff
S3 - 3D model of MSNM V6217
No full textSpecimen MSNM V6217 comes from the Sakaraha Formation (Isalo IIIb subunit), which is Bathonian in age (Middle Jurassic). It has been collected in 2003, isolated from other fossils. It is distinguished by a unique elongate, spindle–like shape, and by a transverse section that remains subcircular up to one-third of the crown height. This specimen is the only representative of morphotype J8, taxon D, which should belong to Diplodocoidea (Dicraeosauridae?) or Titanosauria. MSNM V6217 might represent a new taxon, maybe a basal member of Diplodocoidea, and the oldest fossil record of the clade in Africa.
This 3D model has been generated with photogrammetry processing and merging 50 photos together, divided in two groups, to obtain an object with about 1000000 faces.
Description in the main text
S1 - 3D model of MSNM V5801
No full textSpecimen MSNM V5801 comes from the Sakaraha Formation (Isalo IIIb subunit), which is Bathonian in age (Middle Jurassic). It has been collected in 2001, in association with MSNM V5802 and V5803, near the Tsinjorano village school (Majunga Province, NW Madagascar). It was lying near two theropod teeth and two fragmentary sauropod long bones, almost completely powdered by weathering (G. Pasini, pers. com. 2016). This specimen is attributed to morphotype J2 and included in taxon A, which represents a taxon more derived than Mamenchisauridae but not belonging to Titanosauriformes and Diplodocoidea.
This 3D model has been generated with photogrammetry processing and merging 34 photos together; an object with about 180000 faces has been obtained.
Description in the main text
