The Rotzo Formation is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

, dating to roughly between 189 and 183

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...

and covering the

Pliensbachian The Pliensbachian is an age of the geologic timescale and stage in the stratigraphic column. It is part of the Early or Lower Jurassic Epoch or Series and spans the time between 190.8 ± 1.5 Ma and 182.7 ± 1.5 Ma (million years ago). The ...

stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * Sta ...

of the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

Period in the

Mesozoic Era The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

. Has been traditionally classified as a Sinemurian-Pliensbachian Formation, but a large and detailed dataset of isotopic ¹³C and ⁸⁷Sr/⁸⁶Sr data, estimated the Rotzo Formation to span only over the whole Pliensbachian. The Rotzo Formation represented the

Carbonate Platform A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonic calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms (usually mic ...

, being located over the Trento Platform and surrounded by the Massone Oolite (marginal calcarenitic bodies), the Fanes Piccola Encrinite (condensed deposits and emerged lands), the Lombadian Basin Medolo Group and Belluno Basin Soverzene Formation (open marine), and finally towards the south, deep water deposits of the

Adriatic Basin The Adriatic Abyssal Plain, more commonly referred to as the Adriatic Basin, is an oceanic basin under the Adriatic Sea. The Adriatic Sea's average depth is , and its maximum depth is ; however, the North Adriatic basin rarely exceeds a depth of ...

. Fossil

prosauropod Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had ...

tracks have been reported from the formation. This formation was deposited within a tropical lagoon environment which was protected by oolitic shoals and bars from the open deep sea located to the east ( Belluno Basin) and towards the west (

Lombardia Basin (man), (woman) lmo, lumbard, links=no (man), (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = , demographics1_footnotes = , demographics1_title1 = , ...

). It is characterized by a rich paleontological content. It is notable mostly thanks to its great amount of big aberrant bivalves, among which is the genus '' Lithiotis'', described in the second half of the nineteenth century. The unusual shape of ''Lithiotis'' and '' Cochlearites'' shells, extremely elongated and narrow, characterized by a spoon-like body space placed in a high position, rarely preserved, seems to suggest their adaptation to soft and muddy bottoms with a high sedimentation rate. The Bellori outcrop displays about 20 m of limestones with intercalated clays and marls rich in organic matter and sometimes fossil wood (coal) and amber. The limestones are well stratified, with beds 10 cm to more than one metre thick, whereas the clayey levels range between 3 and 40 cm in thickness. __TOC__

Invertebrata

Microfossils of the Rotzo Formation consist of benthic foraminifera,

calcareous algae Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adj ...

Ostracoda Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

and

coprolites A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is de ...

Foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

are mainly benthic agglutinated species belonging to the superfamily Lituolacea (suborder Textulariina), while lamellar and porcellaneous-walled species are very rare. The bivalve ''Opisoma excavatum'' is very common.

Ichnofossils

In the Western Venetian Prealps a shallow-water, oceanic carbonate platform system, the

Trento Trento ( or ; Ladin and lmo, Trent; german: Trient ; cim, Tria; , ), also anglicized as Trent, is a city on the Adige River in Trentino-Alto Adige/Südtirol in Italy. It is the capital of the autonomous province of Trento. In the 16th cen ...

platform, developed on the Early Jurassic, producing a large succession of massive to well-bedded white

Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

s, several 100 m thick that are part of the ''Calcari Grigi Group'', where the ''Rotzo Formation'' is the Upper Member. On the local limestone of the Rotzo Formation deep burrowing is a very common type of biogenic activity, as is shown due to the presence of a large characteristic network of burrows which reach down to the lagoonal, marly-clayey assigned strata, suggesting intense bioturbation by large unknown organisms, perhaps giant decapod crustaceans (Probably members of the family

Erymidae Erymidae is a family of decapod crustaceans known only from fossils. They survived for 100 million years, from the Permo-Triassic boundary to the Albian. Eleven genera are recognised: *'' Clytiella'' Glaessner, 1931 – 1 species *'' Clyti ...

), although, the burrows found are not closely related to the ones of

Shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

s or other decapods, but resemble those of

Stomatopoda Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in length ...

and

Malacostraca Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobs ...

. Other includes abandoned burrows, vertical biogenic action and infilling on the sea substrate.

Bivalves

The Rotzo Formation is known mostly due to its massive bivalve associations of the genera '' Lithiotis'', '' Cochlearites'' and '' Lithioperna'' that extended all along the Pliensbachian Trento Platform forming mass accumulations of specimens that formed Reef-Like structures. This fauna appeared after the early Pliensbachian C-cycle perturbation, that triggered the diffusion of the Lithiotis Fauna, noted on the rapid widespread of this biota after the event layers. All of the genera related with this fauna appeared on the lower Jurassic, and all but one became extinct before the Middle Jurassic. This "Reefs" had a strong zonation, starting with the bivalves '' Gervilleioperna'' and '' Mytiloperna'', restricted to intertidal and shallow-subtidal facies. '' Lithioperna'' is limited to lagoonal subtidal facies and even in some low-oxygen environments. Finally '' Lithiotis'' and '' Cochlearites'' are found in subtidal facies, constructing buildups. This sections formed various kinds of ecosystems on the Trento platform, where it appeared in branched corals filled with ( Spongiomorpha), Domal corals ( Stromatoporida), tubular corals, Styllophyllidae corals, unidentified Cerioidea colonial corals, regular echinoid debris, sponges, and the solitary coral '' Opelismilia'' sp., with also aggregated snail shells.

Ammonoidea

Gasteropoda

Echinoidea

Thylacocephala

Crustacea

Vertebrata

Chondrichthyes

Episodic surficial bioturbation is common on the ''Rotzo Formation'', due to invertebrates or fishes which alter intensely but rapidly the substrate for many cm in depth. It this case the Bioturbation is assigned to mollusc predatory Chondrichthyes, such as

Hybodontidae Hybodontidae is an extinct Family (biology), family of sharks that first appeared in the Mississippian age, Mississippian subperiod of the Carboniferous and disappeared at the end of the Late Cretaceous.

and Heterodontidae. It also resembles present day flat angel sharks or Squatinidae and Guitarfish such as

Rhinobatos ''Rhinobatos'' is a genus of fish in the Rhinobatidae family. Although previously used to encompass all guitarfishes, it was found to be polyphyletic, and recent authorities have transferred many species included in the genus to ''Acroteriobatu ...

Actinopterygii

Unidentified fish scales are known from the formation.

Crocodyliformes

Dinosaurs

On the Inter-supratidal levels show that on the ''Rotzo Formation'' the Tracksites were rarely hit by Storm Waves. Bella Lastra Tracksite recovers this environment, where the shales present (Where Fish & Crocodrylomorph Remains where found) are filled with plant roots, pollen grains, spores, freshwater ostracodes and the bivalve Eomiodon. This was deposited mostly on a Lagoonar environment with abundant shed vegetation. The main local Track record recovers specially

Theropoda Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...

and

Sauropoda Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their ...

, where the Sauropods are the most abundant tracks present (70%), moving the Otozum-like Sauropodomorphs of lower levels, with the climate changing from arid to humid. The Coste dell’Anglone ichnosite is considered as derived from semi-arid tidal flat deposits, due to the abundance of Cheirolepidiaceae Pollen. As the Pliensbachian Trento Platform is considered to be formed by a channelized barrier formed by sand, with reiterate tide emersions. The dinosaurs living here probably trampled on the subtidal flats looking for fishes trapped on tidal-derived ponds.

Flora

The Rotzo Formation was deposited on a Lagoon on the emerged Trento Platform, leading to a well preserved fossil flora record, collected and studied since the 19th century. The great level of floral fossilization has even allow to discovery fossil amber on the

Bellori Giovanni Pietro Bellori (15 January 1613 – 19 February 1696), also known as Giovan Pietro Bellori or Gian Pietro Bellori, was an Italian painter and antiquarian, but, more famously, a prominent biographer of artists of the 17th century, equiva ...

section. This amber has allowed to determine that the environment was a shallow tropical lagoon, only a few metres deep, closed seawards by oolitic shoals and bars. This levels are dominated by a high abundance of '' Classopollis'' sp. (

Cheirolepidiaceae Cheirolepidiaceae is an extinct family of conifers. They first appeared in the Triassic, and were widespread during most of the Mesozoic era. They are united by the possession of a distinctive pollen type assigned to the form genus '' Classopoll ...

), associated with dry and wet climates in coastal areas. The abundance of this group of conifers is also proven by the high presence of cuticles of ''

Pagiophyllum ''Pagiophyllum'' is a form genus of fossil coniferous plant foliage. Plants of the genus have been variously assigned to several different conifer groups including Araucariaceae and Cheirolepidiaceae. They were found around the globe during the ...

cf. rotzoanum''. Beyond this genera, spores are highly diversified, including from

Sphenophyta Equisetidae is one of the four subclasses of Polypodiopsida (ferns), a group of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. They typically grow in wet areas, with whorls of needle-like ...

Selaginellales ''Selaginella'' is the sole genus of vascular plants in the family Selaginellaceae, the spikemosses or lesser clubmosses. This family is distinguished from Lycopodiaceae (the clubmosses) by having scale-leaves bearing a ligule and by having ...

Fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except ...

s, with abundance (more than 50%) of trilete spores ('' Deltoidospora''), what suggest a good freshwater availability corresponding to a wet climate, proven also by the presence of aquatic miospores of algae such as ''

Botryococcus ''Botryococcus'' is a genus of green algae. The cells form an irregularly shaped aggregate. Thin filaments connect the cells. The cell body is ovoid, 6 to 10 μm long, and 3 to 6 μm wide. Fossils of the genus are known since Precambrian times, a ...

'' and '' Pseudoschizaea''. The climate was arid on some seasons with monsoon months. The abundance of marine fauna on this sediments, including fragments of corals, bryozoans, bivalves, echinoids, and foraminifera, suggest transport from brackish lagoons and marshes, probably occurred during storm events. Overall data points to a marshy and/or submerged paleoenvironment, comparable to the present-day ''

Taxodium ''Taxodium'' is a genus of one to three species (depending on taxonomic opinion) of extremely flood-tolerant conifers in the cypress family, Cupressaceae. The generic name is derived from the Latin word ''taxus'', meaning "yew", and the Greek ...

'' swamp or cypress swamp and a Bahamian-type marine environment in a rather wet monsoonal climate as in the modern southeastern Asia.