Exhibition "25 years, 25 fossils"
The exhibition "25 years, 25 fossils" celebrates the 25th anniversary of the Natural History Society of Torres Vedras. Come with us on this journey, to discover our paleontological heritage.
The Natural History Society: who are we?
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The Sociedade de História Natural is a scientific institution founded in 1998 and based in Torres Vedras. It has one of the largest vertebrates palaeontological collections of Upper Jurassic in Portugal, as a resulte from 25 years of field work and research in the Western region, particularly in the municipality of Torres Vedras.
In addition to the important collection resulting from excavations and palaeontological prospecting, a protocol established between Torres Vedras City Council and SHN enabled the acquisition of a private palaeontological collection, of collected for decades by two palaeontology enthusiasts, José Santos and Luís Francisco.
One of the SHN´s objectives is to set up and manage a Palaeontological Museum in Torres Vedras where this vast collection can be displayed, serving in essence as a vehicle for transmitting knowledge and scientific research.
In this exhibition, we will be able to see a small part of this important collection.
Join us on this adventure.…
What is a fossil?
Fossils are traces of organisms from the past, of which in most cases only the most resistant parts (bones, shells, etc.) reach us, as the soft parts are generally not preserved, except in very special circumstances. These traces of past life on earth can be divided into two types of record: somatofossils fossils (bones, shells and other biomineralised structures) and ichnofossils (eggs, footprints, invertebrate tracks or galleries, etc.).
All these traces are important for understanding the history of life on earth and its evolution.
How fossils are formed:
After the death of an organism, its remains are subject to a series of physical, chemical and biological processes that determine its potential for fossilisation, as well as its state of preservation.
The action of biological agents can cause the total or partial destruction of organic remains. For example, predators and/or scavengers that feed on organisms or their remains, destroying or disarticulating the skeleton, and microorganisms that contribute to the disintegration. In turn, meteoric agents such as exposure to the sun, rain and wind also contribute to the disintegration of the remains of the organism. Finally, after burial, these rests are affected by a series of processes that alter the sediments. This phase is called fossil-diagenesis, in which processes of compaction, cementation and recrystallisation of the sediments take place, which can lead to the destruction of a shell or the skeletal remains of a dinosaur.
What kinds of fossilization are there?
Unaltered traces
The living being is partially or completely preserved. This type of fossilization occurs in very specific environments, such as oil, resin or frozen soil, which isolate it from agents of physical, chemical or biological alteration.
Mineralization
Process that results in the preservation of a given organic or biomineral remnant by means of mineralogical alterations (e.g. mineral precipitation and recrystallisation).
Incarbonization
Process consisting of the progressive enrichment of carbon in relation to other chemical elements that make up organic matter.
Moulding
This process consists of reproducing the internal or external morphology of an organism by the sediment that fills or surrounds it.
Ichnofossils
Traces of the activity of living beings, such as footprints and fossilised excrements (coprolites). They are an important source of information about the behaviour of organisms in the past.
Geological framework. What is the Lusitanian Basin?
The Lusitanian Basin is the result of the distension of the earth's crust associated with the fragmentation of the supercontinent Pangea, which occurred at the beginning of the Mesozoic period. This Basin is located along the western Iberian margin and is about 225 kilometres long and 70 kilometres wide. The islands of Berlenga and Farilhões represent part of its western boundary.
An important phase in the evolution of this basin took place in the Upper Jurassic, resulting in its continentalisation, i.e. the progressive establishment of terrestrial environments.
The Upper Jurassic sediments of the Lusitanian Basin stand out for his richness of vertebrate fossils, which include dinosaurs, crocodiles, turtles, mammals and pterosaurs. The dinosaur record is abundant and includes ornithopods, ankylosaurs, stegosaurs, sauropods and theropods.
In the Lower Cretaceous, more precisely in the Aptian (≈120M.y.) to the west of this Basin, the opening of the North Atlantic Ocean began, with the formation of oceanic crust.
In this exhibition, we will explore several of these geological moments represented in the Torres Vedras region.
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Torres Vedras Paleontology
Torres Vedras is composed by sediments that belong to the different geological members that make up the Lourinhã Formation. This geological unit dates from the Upper Jurassic (Middle Kimmeridgian to Upper Tithonian) and is known for its abundance of vertebrate fossils, particularly dinosaurs. This geological formation is made up of sediments deposited in ancient continental or transitional environments, i.e. those with a marine-terrestrial influence (deltaic, estuarine, lagoonal, etc.).
The existence of this type of environments in the Upper Jurassic allowed the development of terrestrial fauna, which today are preserved in the form of fossils in this region. The small variations in the environments that existed during this period gave rise to different members: Praia da Amoreira, Porto Novo, Praia Azul, Assenta and Santa Rita.
Praia da Amoreira and Porto Novo members (Late Jurassic: Upper Kimmeridgian)
The depositional environment of these geological members corresponded to a meandering fluvial environment, which developed over flood plains. This fluvial system was made up of main river channels (5 to 9 meters deep) and small tributaries.
These geological members, particularly the Porto Novo Member, show a considerable diversity of fossils, with several discoveries of dinosaurs, among other vertebrate groups.
Ornithopods
Within the dinosaur lineage, ornithopods are one of the most diverse, numerous and longest-lived groups, known from the Jurassic to the end of the Cretaceous. Today, ornithopods are found on all continents, including latitudes close to the poles. Ornithopods are phytophagous forms (they feed on plants) and vary widely in size, from one to two meters in length, like the driosaurids, to forms that can exceed 10 meters in size, like the hadrosaurs.
The ornithopod faunas from the Upper Jurassic of Portugal are mainly composed of members belonging to Iguanodontia. Within this group, forms close to camptosaurs and driosaurs have been identified. Material related to Camptosaurus, a genus of ornithopods known from the Upper Jurassic of the Morrison Formation (USA), was first described in sediments from the Lusitanian Basin in the 1980s and was subsequently identified in the municipality of Torres de Vedras.
As far as driosaurs are concerned, a new species, exclusive to the Portuguese record, has been described, called Eousdryosaurus nanohallucis.
Stegosaurus
Stegosaurs were medium-sized animals, reaching between three and ten metres in length. They were quadrupedal, phytophagous animals with very primitive dental morphology that didn't allow them to effectively process the food they ate. They are characterised by the presence of a double row of vertical plates on the dorsal spine and two pairs of pointed spikes at the end of the tail. This group of dinosaurs is not common in the fossil record, being restricted in practice only to the Jurassic, with a greater incidence in the Late Jurassic. The most significant fossil record of stegosaurs is currently found in North America and Asia. However, they have been recorded on continents such as Europe, Africa and South America.
The stegosaur faunas described in the Upper Jurassic of Portugal are represented by three forms: Stegosaurus, Dacentrurus and Miragaia. Of the taxa mentioned, Dacentrurus is the one with the most abundant record, comprising several specimens from different localities, including the municipality of Torres de Vedras. Less numerous are the remains attributed to Stegosaurus, a common genus in the Upper Jurassic of the Morrison Formation (USA), and Miragaia.
Theropods
Theropods are a group of bipedal dinosaurs, mostly carnivorous but which could also have had an omnivorous or even phytophagous diet. They are known on all continents and are represented by a great diversity of forms, from very small individuals (such as the troodontids) to the largest predators that ever lived on earth (such as Tyrannosaurus and Spinosaurus). The oldest evidence of this group of dinosaurs known today comes from the Triassic and corresponds to small to medium-sized forms. During the Jurassic period, large carnivores appeared. The theropod group also includes the lineage that gave rise to birds, descendants of a clade of small specialised theropods, the coelurosaurs.
The record of theropod dinosaurs currently known in the Western region consists mainly of a group of large carnivore forms, also found in North American West, such as Ceratosaurus, Torvosaurus and Allosaurus. However, this record also includes forms that have so far been considered exclusive to the Portuguese record, such as Lourinhanosaurus.
Although less frequent, there are also some isolated fossils, mainly teeth, identified with small coelurosaurs.
Sauropods
The sauropods are a group of dinosaurs in which you can find the largest land animals that have ever lived on planet Earth, such as Brachiosaurus and Turiasaurus. These dinosaurs had a wide geographical distribution and are especially well known in the Upper Jurassic and Upper Cretaceous, being found on all continental masses.
In addition to the considerable size that some of these animals could reach, sauropods are generally known for their columnar limbs, elongated neck and tail and small skulls when compared to their overall body size.
In Portugal, sauropods are one of the most abundant dinosaur groups from the Upper Jurassic. There are several known examples in the municipality of Torres de Vedras. To date, four distinct species have been identified in the Lusitanian Basin: Lourinhasaurus alenquerensis, Oceanotitan dantasi, Lusotitan atalaiensis, Dinheirosaurus lourinhanensis and Zby atlanticus, as well as several remains of Camarasaurids, Turiasaurids and Diplodocids, which have yet to be determined.
Praia Azul Member (Late Jurassic: Lower Tithonian)
The Praia Azul member corresponds to an ancient deltaic plain with a strong marine influence, where areas with protected bays and lagoons have developed. Certain levels are made up almost exclusively of brackish water bivalve molluscs, such as the genus Isognomon. Vertebrate remains can also be found in these levels, particularly the remains of turtles, crocodiles, fishes and dinosaurs.
Crocodiles
The crocodiliforms are represented by forms belonging to the Atoposauridae, Goniopholididae and Thallatosuchia.
One of the most abundant crocodiliforms in Portugal is the genus Goniopholis, a close relative of today's crocodiles with semi-aquatic habits, similar to the American alligator and nile crocodile. Goniopholis baryglyphaeus from the Portuguese Kimmeridgian is the oldest known species of this genus.
Turtles
Turtles are a well-represented group of reptiles in the Portuguese Upper Jurassic. Two groups stand out for their abundance: one that lived in rivers and other freshwater environments (Pleurosternidae), and another distributed in coastal marine environments (Plesiochelyidae).
One of the few regions of the Iberian Peninsula where articulated shells of Pleurosternidae turtles are currently known is in western Portugal. The study of this record made it possible to identify a new genus and species: Selenemys lusitanica. This species corresponds to a small-sized form (less than 30 cm) and is the oldest known pleurosternid in Europe. The study of this turtle also made it possible to recognise that, after the separation of North America and Europe, these reptiles evolved rapidly, generating two different lineages, separated by the opening of the North Atlantic.
The Plesiochelyidae correspond to relatively larger forms, which can exceed 50 cm in length. Although they lived in marine environments, the extremities of these turtles were not adapted to swimming in deep water, which suggests that they lived in shallow waters near the coast. This group is exclusive to the Jurassic.
Another turtle of great importance found in the Portuguese Upper Jurassic record was the Hylaeochelys kappa, which corresponds to the only genus of European turtle recognised in both the Jurassic and Cretaceous. Although related to the abundant plesiochelids, the adaptation of Hylaeochelys to freshwater environments allowed it to survive after the extinction of this group.
Fishes
Rivers and lakes are populated by different groups of fish, including sharks. The best-known fish belong to the actinopterygian group, such as the extinct bony fish genus Lepidotes. As far as sharks are concerned, the most common belong to the Hybondontidae group.
Assenta Member (Late Jurassic: Tithonian)
This member is represented by layers that formed in fluvial and deltaic environments, where extensive alluvial plains developed. In this unit there are levels with marine influence, allowing the establishment of small coral reefs.
The continental levels are extremely rich in plant and vertebrate remains, especially dinosaurs, as was the case in the Porto Novo member.
Allosauroid from Cambelas
In 2001, during palaeontological prospecting work, some bone fragments were discovered in a layer of clay. Their morphology suggested that they were ventral ribs (gastralia).
That same year and in 2002, palaeontological campaigns were carried out to excavate this specimen, which was later identified as belonging to the carnivorous dinosaur genus Lusovenator, being the oldest Charcarodontosaurid outside Gondwana.
They are large bipedal dinosaurs with long, narrow skulls, usually decorated with crests. They had robust hind limbs while their forelimbs were relatively small, with three fingers on their hands equipped with robust claws. As adults they could reach between eight and twelve metres in length and weigh around 2 tonnes.
Indirect traces: Ichnofossils
Dinosaur footprints
Fieldwork often leads to the discovery of dinosaur footprints. These are of great value to palaeontologists, as they provide a lot of information about the way and speed at which these animals moved.
Diagram of the formation of a footprint:
a)The footstep of an animal forms an imprint in the substrate;
b) Subsequent sedimentation covers the footprint in such a way that it is preserved as a discontinuity between the two layers;
c) On surfacing we can find the footprint in two parts: C1- the countermould, in the material that covered the impression and or C2 - the mould of the footprint.
Ichnofossils of invertebrates
In the prospecting carried out in the Assenta Member, galleries, perforations and tracks produced by invertebrates were found. Extensive areas filled with galleries are not uncommon. Since these organisms have not been preserved, we have access to their fossilised behaviour.
Sedimentary Structures
Ripple Marks
Non-organic sedimentary structures such as ripple marks are formed in sandy or clayey sediment, caused by the undulating movements of river, sea or wind currents. They provide information about sedimentary environments, such as the direction of palaeocurrents.
Santa Rita Member (Late Jurassic: Middle-Upper Tithonian)
A continental terrestrial member where a river system rich in plant remains and vertebrates has been installed. This river system is different from the Porto Novo and Assenta members, being characterised by greater energy and the absence of extensive flood plains.