Description
Geosites, or geotopes, are places that bear particularly significant witness to the evolution of the earth's crust or the influence this has had on the development of life and man. They thus include outcrops of rocks, soils, fluids, minerals and fossils or even particular landscape forms and natural phenomena.
These sites are characterised by particular significance for their exemplarity, uniqueness, beauty, scientific or didactic interest, or for the particular importance they have had in the anthropic and cultural development of the place. In general, geosites constitute non-renewable resources, which is why their valorisation and protection is of great importance.
When the dinosaurs populated our planet (230 to 65 million years ago), Trentino was very different from what we see today; the rocks that make up its mountains tell us of the slow transformation of a muddy coastal plain into a tropical sea, the shaking of the earth under the thrust of submarine volcanoes, the subsequent uplift of the seabed into mountain ranges.
Over the last few decades, palaeontologists have discovered many new dinosaurs and have given increasing importance to the study of their footprints.
Precisely because it is rich in areas that bear witness to traces of large extinct reptiles, Trentino has become a very interesting territory in just a few years. Dinosaur footprints can be found in various locations, all of which, however, are preserved in rocks from the Jurassic period (between 202 and 140 million years ago) included in the Grey Limestone Formation (geologists call the Formation a package of rock layers with a similar appearance, composition and fossiliferous content).
But why are the footprints left by these large reptiles so interesting?
From their analysis, millions of years later, we can learn a lot of information that allows us to reconstruct the appearance, way of life, evolution and adaptation to the territory of the animals that left them.
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The discovery
One morning, in the late 1980s, Luciano Chemini, a passionate naturalist from Rovereto, was walking through the 'laste' of Lizzana, upstream of Lavini di Marco. The sun was low and its grazing light highlighted, along a corridor cleared of debris (colatoio), three series of rounded cavities, surrounded by a raised rim. Although some of the cavities were filled with soil, Chemini guessed that they might be the footprints imprinted in the limestone by some ancient animal.
The discovery was reported to the Tridentine Museum of Natural Sciences and the inspection carried out in the summer of 1991 confirmed his intuition: the tracks reported belonged to dinosaurs without a doubt! Systematic research conducted from 1992 onwards and directed by Giuseppe Leonardi and Paolo Mietto gradually led to the discovery of footprints and tracks of more than 200 individuals. Today, dinosaur footprints are no longer a rare fossil in Italy, yet the Lavini di Marco site remains the best known and undoubtedly the most significant due to its high number of specimens, size and the exceptionality of some tracks. The extent of the outcrop, the splendour of the surrounding natural environment and the year-round accessibility contribute to its notoriety
Who left the footprints?
A footprint provides us with a lot of interesting information. It is first of all its shape that tells us whether the author was a carnivorous or herbivorous animal, whether he walked on two or four legs, whether he was a cub or an adult. By comparing the footprint with fossil skeletons, it is possible to get an indication of the appearance, weight and size of the animal that produced it. By studying the distance between footprints in fossilised tracks, palaeontologists can calculate how fast dinosaurs moved. We can understand how they behaved, whether they were alone or in company, whether they were running away or chasing prey.
The field of palaeontology that deals with the study of footprints and their classification is called ichnology (from the Greek ichnos, trace). One of the main difficulties of this discipline is to recognise the author of a trace, which is why the classification of footprints is separate from that of the organisms that produced them, and footprints have different names from the animal that impressed them into the ground. Only in very few cases is it possible to link fossil tracks to their authors with certainty, in which case the name of the footprint corresponds, at least in part, to the name of the animal. This is the case, for example, for the Tyrannosauripus (from the Latin, Tyrannosaurus foot) footprint, which immediately gives us an idea of the animal to which it belonged (Tyrannosarus). Much more often these similarities in terms are not there and so the names of the footprints are completely disconnected from their origin. The way that is usually used to identify the author of a track is to compare the fossil skeleton of animals with fossil footprints of the same age. A footprint researcher, after all, does not behave much differently from the prince in the fairy tale when looking for Cinderella. Once the slipper (the footprint) is found, it is necessary to find the right foot to fit it (the dinosaur's foot). The problem is that we do not possess the skeletons of all the animals that lived in the Jurassic period and sometimes, even if we do have the bones, it is not easy to work out how the calloused pads and muscle bundles that left their mark on the ground were distributed. For this reason, for many of the footprints identified at the Sinks of Mark, it has not been possible to identify the corresponding animal with certainty.
But who were the dinosaurs at the Sinks?
The most numerous were theropod carnivores of varying sizes (their footprints number in the hundreds), probably attributable to Ceratosaurus, but possibly also to primitive Tetanurus.
Herbivore tracks follow: among them are some 20 very ancient sauropods Vulcanodontidae, considered to date the oldest sauropod tracks ever discovered.
Some footprints belonged to small primitive herbivores (Ornithischia) and a few tracks may have been left by large Ornithopoda, bipedal herbivores.
The presence of much smaller animals belonging to groups other than dinosaurs is also documented at Lavini. Their traces are small and difficult to recognise, sometimes preserved in inaccessible places. Such evidence indicates the presence of invertebrates similar to large snails, crustaceans similar to lobsters, large lizards and small primitive mammals no bigger than a cat.
How were the footprints preserved?
How is it possible that footprints imprinted in the mud of an ancient beach have been preserved for hundreds of millions of years?
Generally, the footprints that we find fossils in rocks today are those that managed to harden before being buried by a subsequent layer of sediment. Many of the fossil footprints that are discovered, however, are not those left directly on the ancient muddy surface, but are actually sub-footprints. In fact, for every footprint that is formed on the muddy surface (the footprint in the narrow sense), many more are formed in the lower layers of sediment deformed by the weight of the animal, less and less detailed as one goes deeper; these are called sub-footprints.
At the Lavini di Marco the initial hardening of the footprints is linked to the particular environmental conditions existing in the Lower Jurassic. At that time, in fact, today's Adige Valley was part of a vast muddy plain on the eastern edge of an arid continent. Dinosaurs populated the entire expanse, with the large herbivores probably preferring the small coastal ponds, where they perhaps found food more easily. Carnivores, on the other hand, left numerous footprints in the drier areas where they could evidently move better.
In the most superficial part of the soil, mineral salts, such as dolomite, were concentrated, which, with their subsequent crystallisation, bound the sediment granules together like a kind of cement. These processes allowed the formation of a hard surface crust that helped save the footprints from being erased by the advancing sea until they were completely buried.
The tour
All the tracks are distributed over a vast area that, to make the route clearer, has been divided into 5 sectors, some of which are equipped for the visit (each track studied is marked by a number preceded by the acronym ROLM (=Rivereto Lavini di Marco)
The forest road
From the car park at Grotta Damiano Chiesa, one returns to the first bend, at which (on a barred forest road) the palaeontological trail begins, marked by special signs. A number of tracks and isolated footprints left mainly by carnivorous dinosaurs are visible along the forest road.
Two three-toed footprints of the Kayentapus type are visible on the left side of the road. These are footprints of a bipedal carnivorous dinosaur that walked by placing its feet in front of each other along an almost straight line. This dinosaur is probably similar to Sarcosaurus from the Jurassic period (discovered in England), which can be attributed with a length of almost 4 m and a weight of around 70 kg. The footprints are sparsely spaced, a sign that the animal moved slowly; in fact, it can be established that the speed at which it moved was less than 2 km per hour, i.e. it walked slower than we do when we move around the city looking at shop windows.
A little further on, again on the left-hand side of the road, two more three-fingered footprints are visible. They are larger than the previous ones left by a larger carnivorous dinosaur. The animal probably had the build and size of the Jurassic Dilophosaurus (discovered in Arizona), 6 to 7 m long and weighing an estimated 280 to 500 kg. It is interesting to note that the distance between the footprints is much greater than before, a sign that this animal was running at around 10 km per hour, undoubtedly a respectable speed for a large predator
A little further on, on the same side of the road, a depression (possibly the footprint of a herbivore) is surrounded by small, parallel, sinuous furrows. These are possibly the tracks left on the soft mud by a gastropod (=marine mollusc) moving in search of food.
The main colander or 'Chemini colander'
This is a long, debris-free corridor that rises almost perpendicular to the forest road. A path runs alongside it and two wooden turrets provide a panoramic view of the area. Some thirty tracks or isolated footprints of sauropods, theropods and possible ornithopods have been discovered on this area.
ROLM 12: This is the first track encountered when ascending the path to the "Colatoio Chemini" and can be seen just upstream of the small wooden bridge that crosses it. The footprints are just shapeless holes imprinted in the soft mud, but their arrangement along a straight line is enough to tell us that this is the track of a carnivorous bipedal dinosaur.
ROLM 1: It is a track arranged diagonally to the colander, near the first wooden turret. It consists of a succession of slightly elongated footprints with a more dilated part corresponding to the toe area. In some of the footprints the fingers are still discernible in the form of three or four rounded lobes. This is the track of a quadrupedal sauropod, but the hands (i.e. the front legs) are absent, perhaps completely covered by the footprints (the hind legs) or eroded. The animal was large and heavy (more than eight metres long) and proceeded with a rather slow gait. The curious thing is that in the final part of the track the footprints become closer together and the pace is clearly irregular. The last footprint of the regular sequence shows a long arched furrow in the rear. It is possible that the animal has put a foot wrong by slipping a little in the mud (creating a furrow) and has decomposed its gait (the less regular and closer steps) by getting back into balance. If you look closely at the bottom of some of the footprints, you can see that there are small flat fragments of clear, now petrified mud. These bits, similar to breadcrumbs, are what remains of the hard crust of mud, trampled and crushed by the weight of the dinosaurs.
ROLM1 and ROLM2 seem to have been left by the same animal bending upstream, but on closer inspection they turn out to belong to two different animals that proceeded in the opposite direction. A closer look at the footprints also shows that the sauropods making ROLM1 and ROLM2 did not transit at the same time. We can now see the wide and shallow footprints of ROLM1 cross those of ROLM2, which are smaller and better defined, with clear edges of mud raised by the weight of the animal. But how much time elapsed between the passage of the two animals? A day, a season, hundreds or thousands of years? It is difficult to determine. A layer of rock one millimetre thick could correspond to a time interval of several months, even when we can identify the very thin layer on which the animal had stepped, it is practically impossible to follow it laterally in a continuous manner. In other words, today we cannot have a snapshot of the plain but a series of photos taken at different times. Therefore two tracks, although close together in the case of ROLM1 and 2, could have been left by animals that lived at different times, even several tens of years apart.
About halfway along the trail linking the two turrets, the footprints left by the fingertips of a three-toed paw have been identified: three parallel grooves are visible. The rock in which these tracks are preserved is characterised by the presence of small bivalves (=shells), gastropods and fossil oolites (=small limestone spherules). These elements indicate that the sediment from which these rocks were formed was a mud typical of a seabed that was not too deep (a few metres). The simultaneous presence of dinosaur tracks finally reveals to us that the depth of this ancient seabed could not have been significant: the animal in fact while swimming sometimes touched the seabed with its fingertips, thus leaving its footprints there.
ROLM 9: This is the most obvious track in this sector and cuts a long diagonal across the colliery near the second viewing tower. From time to time some footprints seem to be missing, perhaps completely filled in with mud when the animal's feet were lifted, some are very shallow and only recognisable when the light is shining. The author of this track is still unknown. The shape of the footprints and their arrangement differs from other known tracks in the Lower Jurassic. It has been suggested that this may be a large bipedal herbivore of an as yet unknown species, but not all scholars agree with this hypothesis.
ROLM 11: This track cuts through Colatoio Chemini just upstream of the second viewing tower. The footprints are slightly elongated and with a more dilated part corresponding to the finger area. The hands are poorly imprinted, recognisable only by the presence of faint round depressions on the outside and in front of the feet. It too was left by a slowly proceeding herbivorous sauropod, some features of the track allow us to understand why. The footprints are very deep with large muddy edges raised by the weight of the animal and particularly marked at the end of the track. The mud must therefore have been very soft and water-soaked. Geological data even indicate that in the area of today's Colatoio Chemini there was a kind of small pond and that the surface trodden by the dinosaurs was below the water surface. The animals sank into the soft bottom, which sometimes closed as soon as they lifted their paws, and we can understand this by looking at the second of the footprints from the side of the turret, for example. This left footprint is reduced to a thin furrow, a sign that the mud has fallen in, closing it almost completely.
The large fold
It can be reached from the high forest path connected to the Colatoio Chemini, along the way back to the parking area. Two sauropod tracks are preserved on an almost vertical wall: one 'climbs' the wall, while the other is crossed by that of a large theropod; here and there are other tracks and isolated footprints. In this area, the rock layers form a large fold, along whose axis (the fold zone) these tracks are clearly visible. Dinosaurs did not walk on vertical rocks! The rocks underwent this deformation as a result of the compressive forces associated with the dynamics of the Earth's crust.
On the surface of a quadrangular boulder, along the path leading towards the high fold, the isolated footprint of the largest carnivorous dinosaur so far found at Lavini can be observed: the footprint is not complete, but the foot measures at least 38 centimetres in length. The animal must have been a large and massive predator weighing about a tonne and over 7 metres long, similar to Saltriosaurus, the Tetanurus dinosaur recently found in Jurassic rocks in Lombardy.
ROLM 26: This is a track that in suitable light conditions can be seen from afar, apparently climbing up the wall, giving the impression that a 'rock-climbing' dinosaur left it. It is attributed to a quadrupedal sauropod dinosaur with inconspicuous hand tracks. Its strange position is linked to the intense movements that this whole area underwent after the footprints were imprinted on the Jurassic beach. The dynamics of our planet meant that, starting around 60 million years ago, the superficial layers of the earth's crust subjected to enormous pressure broke and folded. Thus, these ancient seabeds and coastal areas were uplifted and turned into mountains. During the uplift, the rock layers were folded and fractured, and large fractures, called faults, were formed that shattered and displaced huge portions of rock. Finally, about a thousand years ago, a large landslide slid down the mountainside, exposing the fossiliferous layers.
ROLM 28: This is a track preserved at the base of the long fold of rock strata that runs along the highest path and is just to the left of track ROLM 26. It is a short trackway of five incomplete pairs of footprints and is intersected by track ROLM 159 of a large theropod, without it being clear which of the two dinosaurs passed first. The rock surface is unfortunately damaged, right at the intersection of the two tracks. The herbivore must have been very large, more than 10 metres long, probably the largest of the Sinks. The handprints are much more lateral than the footprints, they are crescent-shaped and vary in size; one hand is reduced to a narrow slit because the footprints have been filled with mud. The footprints have a wider and deeper front, and are largely surrounded by wide borders of petrified mud.
The lower culverts
They run downhill from the forest road and occupy the entire lower part of the site. They are arranged in a 'Y' shape and are conventionally called 'sauropod colander' (lower leg), 'theropod colander' (northern arm) and 'ornithopod colander' (southern arm). Along the collieries are: a small sauropod track, a few tracks of possible large bipedal ornithopods, a few dozen tracks and more often isolated theropod footprints.
ROLM 75 (the first sauropod): This is located in the lower part of the Lavini area and is accessed either from the lower forest road or from the path indicated by the signs, which branches off to the right and downhill from the upper road. It is a poorly preserved quadruped track, approximately 7 metres long, slightly curved and with at least 10 hand-foot pairs. Sauropod tracks can be divided into two basic types: broad-gauge and narrow-gauge (a terminology borrowed from railway jargon). This is the narrow-gauge type; that is, a track in which the axis of the track (mean line) cuts across the footprints while the handprints are located outside and in front of the footprints. The distance between steps and the angles between steps indicate a slow, 'strolling' gait. The footprints are sometimes surrounded by wide borders of petrified mud, but these have more often been eroded. The footprints are pear-shaped with the front wider. Those of the hands, on the other hand, are variable in shape, generally crescent-shaped. The track is somewhat irregular, a sign that the animal was advancing in an uncertain manner on slippery ground.
ROLM 64(a wounded animal?): This is located in the upper part of the Ornithopod Colony and is reached via the visitor trail that runs along the lower part of the site. It is a straight, apparently bipedal track, about 14 metres long. The animal walked at a slow pace, but in a rather peculiar way: the strides are alternately short and long; in such a way that the stride (=the distance) between the right and the left foot is much longer than that between the left and the next right. This must be a peculiarity of the gait, but it cannot be excluded that it is the track of a limping animal. All the footprints are surrounded by a wide, high raised edge that gives the impression of a wave of soft mud, spilling outwards from the footprint. Some of these edges have small grooves carved by water on the rock (karstification). This indicates that, prior to the discovery, large sections of the track were exposed to the weather and runoff water along the culverts for a few centuries. The footprints are generally oval in shape, with the trace of four fingers; in some of them, the upper layer of cover, laid down after the passage of animals, is still visible. As with track ROLM 9 at Colatoio Chemini, the mystery of the animal to which it should be attributed still remains: a sauropod or a large herbivorous biped of an unknown species?
ROLM 33 (duck feet): This is a bipedal track located just upstream of the previous one, consisting of three large three-toed footprints. The first two footprints are adjacent, one right and one left respectively; the next right is missing, and a partially buried left follows, then the track disappears. The missing footprint was not eroded, but for some reason was not preserved. Perhaps in this place the mud had already dried out completely, so as to support the weight of the animal without sinking it, or more likely it was so soft that it fell into the footprint, closing it. The first footprint, a right-hand one, shows three rounded fingers. In making this footprint, the animal had slipped slightly with its 'heel'. The second footprint is flattened at the third toe, which is thus very narrow, with an appearance that does not correspond to the original shape. This track is also difficult to determine. It has been suggested that it may be a walk of a large herbivore but it is possible that it is the deformed track of a large carnivore.
The 'high slabs'
These are above the forest road, located further south than Colatoio Chemini, and are less accessible because they are uncomfortable and slippery in an area not equipped for visiting. Other tracks and footprints of numerous dinosaurs, as well as bipedal and quadrupedal herbivores, can be observed here. Some of these tracks and footprints are among the most beautiful present at Lavini.
Predatory dinosaurs, represented by three-toed footprints with claws, are by far the most numerous in the upper right-hand sector of the Chemini Colatoio. This site is unfortunately not accessible to the public, due to the steep slope of the rock strata. The footprints are generally shallow, indicating that the authors of the footprints were light and quick animals. Footprints of various sizes and shapes can be found on the 'high slabs', which are still being studied, due to trampling by a large number of animals. This is where the footprints of the smallest dinosaur in the Sinks come from, just 7 cm long. This was a ceratosaurus (Grallator-type footprint), about 1.5 m long, more than half of which was occupied by the tail and which must have weighed about 4 kg. One of these surfaces has been called 'the ballroom' by scholars, due to the large number of footprints imprinted at various depths and in all directions! It is an extraordinary spectacle to see these surfaces in the early morning, with the sun low and the light grazing, imagining a beach teeming with life.
Amongst the hundreds of footprints on the 'Laste alte', one pair of footprints left by a herbivorous bipedal dinosaur, 1.5 to perhaps 2 metres long and weighing no doubt a few kilograms, perhaps a dozen at most, is of particular interest. The footprints can be classified as Anomoepus. The word Anomoepus means different rear and front feet. Roland T. Bird, an American scholar, pointed out one of the most interesting and captivating examples of dinosaur behaviour when he formulated the interpretation of an Anomoepus track. This track shows an animal walking, then crouching and squatting on the ground, getting up and finally resuming its walk. Exceptionally, however, in that case, the reason for this behaviour was clear: the animal was taking shelter from a storm. The tracks leading up to the crouching traces, like all the sediment around it, bear the marks left by the raindrops, which are missing at the point where the animal stood up again, thus indicating that it remained in that position until the downpour subsided. After the storm had passed, the animal erased the marks that the rain had just left under its steps. The tracks in the Lavini di Marco also document this type of behaviour: a short walk followed by a pause with the legs almost parallel and a subsequent crouching. We do not know the reason for this behaviour and the poor preservation of the tracks will hardly allow us to understand it in the future. Nevertheless, we have the extraordinary opportunity to step back in time and observe a snapshot in the life of an animal from almost two hundred million years ago.
And the tail? Unlike the fossil tracks of crawling animals, where the presence of the tail impression is normal, in the case of dinosaurs, whether biped or quadruped, the tail impression is practically never found on the ground. It can be deduced from this that dinosaurs, whether bipedal or quadrupedal, practically never rested their tails on the ground, let alone crawled with them. Instead, they kept it high, also to act as a counterweight to the body, which remained very low, almost parallel to the ground or slightly inclined; the tail also moved from right to left to balance the change of foot and from top to bottom to balance the movement of the torso.
Texts: M.Avanzini, M.Galetto, C.Lauro, G.Tommasi
Drawings and photos: M.Avanzini, MTSN archive