Field Guide Lavini di Marco - 1 LAVINI DI MARCO

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1 Field Guide Lavini di Marco - 1 LAVINI DI MARCO Objectives: To observe traces left in the geologic record by once-living animals, such as dinosaurs To relate the fossil evidence to a short chronology scenario Highlight for the site: See footprints left by dinosaurs General Information The Lavini di Marco site, where the dinosaur footprints were discovered, is located on the left flank of the Adige Valley. Rocks on this side of the valley consist of steeply inclined layers of limestone, which dip at an angle very similar to that of the hill slope (Fig. 1). The pull of gravity acting on the inclined layers has caused repeated rockfalls through time, one of which was even mention by the poet Dante in the Divina Commedia. The rockfalls have left an accumulation of rock rubble on the valley floor and extensive scarps in the area from where the slid layers have detached (Figs. 1, 2). In 1989, an amateur paleontologist, hiking on the inclined surfaces exposed by the Lavini rockfalls, noted some regularly spaced depressions which looked like trails left by a walking animal and were later determined as being made by dinosaurs (Fig. 2). The discovery sparked a more systematic survey of the area which led to the identification of tens of dinosaur footprints and tracks. The paleoenvironment The rock formation in which the footprints are found is named Gray Limestones (see Appendix B) and has been determined to be part of the Lower Jurassic (Avanzini et al. 1997) (see Appendix A). The sediments consist of stratified limestone and dolomite containing structures (such as mud cracks) and fossils (ostracods and mollusks) considered indicative of very shallow marine water, with periodic phases of exposure. Chemical analysis of the sediment paired with detailed observation of the sedimentary structures has led researchers to suggest that the paleoenvironment in which the dinosaurs left their traces was a tidal flat (coastal wetland periodically inundated by tides) in a semiarid climate (Avanzini et al., 1997). Fig. 1: View of the Lavini di Marco site. Inclined layers dipping at the same angle as the hill slope (dashed lines show orientation of stratification) slid downward during catastrophic rockfalls. Rock rubble accumulated at the foot of the slope, and large surface exposures were left in the detachment area on the valley flank.

2 Lavini di Marco Field Conference Fig. 2: Left: Rubble from a rockfall at Lavini di Marco. Note how the layers still in place show high inclination (dashed lines) at an angle similar to that of the hill slope. Right: surface exposure of one of the inclined layers uncovered by the Lavini rockfalls, with one of the trackways (ROLM9) first noticed in The footprints More than 1000 footprints, with sizes varying from 7 to 38 cm, have been identified to date on a surface area of about 1 km 2 (Avanzini, 2002). They are distributed in 7 distinct horizons within a 7 m thick interval (Avanzini & Petti, 2008). Some prints are arranged in trackways (the longest of which consists of 26 sequential tracks) (Avan zini, 2002). A general distinction can be made between tridactyl (three digits) and subcircular to elliptical footprints, the former left by bipedal, the latter by quadrupedal dinosaurs. It seems that the different track types are not distributed randomly, but larger tracks of quadrupeds are associated with sediment which was originally water impregnated, whereas smaller bipedal tracks are more common on sediment indicative of harder and drier surfaces (Avanzini et al., 1997). The trace makers As observed in many other fossil localities, the occurrence of abundant tracks at Lavini di Marco is not accompanied by the preservation of dinosaur bones. This means that the affinity of the trace makers can only be generally inferred by comparison of the tracks with fossil specimens and other tracks from fossil sites around the world. Most of the tridactyl prints can be attributed to bipedal carnivorous theropods, probably belonging to the Ceratosauria and Tetanurae groups. A few subordinate tridactyl prints are attributed to small and large herbivores of the order Ornithischia. The subcircular prints were left by large, herbivorous, quadrupedal dinosaurs of the sauropod group. These represent some of the earliest sauropod tracks found in the geologic record (Avanzini & Petti, 2008). By looking at the distance cast or mold Filling of a footprint True footprint underprints Fig. 3: Ways in which a dino saur track can be preserved: true print, under print (concavity in the deformed underlying layers), and cast (sediment filling the depression left by the track).

3 Field Guide Lavini di Marco - 3 between prints in a trackway and by measuring the size of the tracks, it is possible to re construct the speed and size of the animals which left them. These calculations applied to the Lavini di Marco tracks result in dinosaur sizes ranging from 1 to 11 m (Avanzini, 2002). The process of preservation How did the traces get preserved? When the dinosaurs walked on the surfaces which now form the layers of the Lavini di Marco, they left some depressions by deforming the sediment with their weight. This deformation can be ob served in the layers below the print (Fig. 3). How deep the depressions went depended on the weight of the animal but also on the degree of induration of the sediment. In some cases, it is clear that the sediment trampled by the dinosaurs was soft and water impregnated because it flowed back in the print after the animal lifted its foot. In others, the fill of the prints consists of cracked chips of sediment, indicating a certain degree of induration. In any case, for the prints to be preserved from subse quent de struction, an early cemen tation of the sediment seems to be required. This process of early cementation (by dolo mite) has been suggested for the Lavini tracks by Avanzini et al. (1997). Unsolved questions Probably the most puzzling aspect of the Lavini track is the question of what were these dinosaurs doing in a semi-arid tidal flat. Large-sized herbivorous dinosaurs needed large amounts of vegetation for nutrition and the sediments where the tracks are preserved lack almost any trace of plant remains. Furthermore, chemical analysis of the sediment shows the absence of soil formation and clear pre ponderance of marine over fresh water (Avanzini et al., 1997). While the carnivorous dinosaurs could have survived by eating other animals, it is difficult to understand how the herbivorous dinosaurs could have sustained themselves in the absence of plants for food and fresh water. Stop 1 What: Large broken blocks of limestone and rubble accumulation visible along the first stretch of the path (Fig. 2). Why: Rockfalls are catastrophic processes which challenge the uniformitarian view of geologic change. Notes: There are four different possible combinations of rates of change in geologic phenomena: gradual periodic, gradual episodic, catastrophic periodic, and catastrophic episodic (Huggett, 1990). Think of where rockfalls should be placed in this scheme. Which of these processes do you think were more influential in creating the landscape we observe today? A complex story of multiple events is told by these simple blocks of rock: deposition of soft sediments, cementation, uplift, erosion. Fig. 4: Trackway ROLM200. Note how the lower print shows two bulges of mud that flowed inside the print after the animal lifted its foot. Scale is 10 cm long. Think of the differences you would expect in gravitational collapse of hard rocks vs soft sediment. What would you look for to identify similar catastrophic events in the record of the flood? Stop 2 What: Trackway ROLM200 Why: Learn how the fossil record opens a window into the past, revealing details about organisms, their behavior, and the environment in which they lived or died. Any model of origins needs to incorporate the information provided by the fossil record. Notes: This trackway consists of two tridactyl footprints (Fig. 4). Their alignment indicates this dinosaur walked by placing its feet along a straight line. Note how the farther track preserves the impression of the claw. By measuring the length of the track, it is possible to get an estimate of the size of the dinosaur. This animal was almost 4 meters long and about 70 kg in weight. The fact that the tracks are close to each other indicates that this individual was moving at low speed.

4 Lavini di Marco Field Conference Stop 3 What: Trackway ROLM201 Notes: This trackway also consists of two tridactyl footprints left by a bipedal carnivorous dinosaur and arranged in straight line (Fig. 5). The prints are larger than ROLM200 and the estimated size of the animal is between 6-7 m and kg. The spacing between prints is also much larger than that observed in ROLM200, indicating that this dinosaur was moving at higher speed (about 10km/h) (Avanzini, 2002). Fig. 6: Trackway ROLM1. This track documents the dynamic of a Jurassic slippage. Pen for scale is 15 cm long. The estimated size for this animal is large (about 8m) and its speed was low. When observing the succession of the steps of ROLM1, it is possible to re construct the dynamic of a Jurassic slippage (Fig. 6)! The first tracks are regularly spaced, but the last track of this regular sequence shows to its side a long curved rim which documents a misstep taken by the dinosaur on the slippery muddy surface. The following tracks are less regular and closer, as if the animal was trying to re-adjust its walk. Fig. 5: Trackway ROLM201. Dashed line indicates trajectory of movement. Scale bar is 30 cm long. ROLM2 (Fig. 7) seems to be the continuation of ROLM1 in a different direction, but upon closer look it is clear that this is a separate trackway left by another animal. First, the expanded portion of the prints of ROLM2 is on the opposite side than those of ROLM1. This means that the animals were walking in opposite directions. Second, the ROLM2 prints are deeper, smaller and better defined, with clear rims of mud around the tracks, expelled under the weight of the walking dinosaur. Even if both prints were left by sauropod-like animals, it is not possible to know how much time elapsed between the transits of these two individuals in the same area. Stop 4 What: Trackways ROLM1 and ROLM2 Notes: These two trackways are found along a steep surface named Colatoio Chemini, the site where the footprints were first discovered. ROLM1 was left by a sauropodlike dinosaur and the shape of the prints is elliptical, slightly elongated, with one side more ex panded than the other. The more expanded portion of the tracks corresponds to the location of the toes, which can still be inferred from four small lobate depressions in some of the prints. Even if the animal was a quadruped, the tracks left by the forefeet are not present, maybe because they were overprinted by the larger tracks of the hindfeet. Fig. 7: Trackways ROLM1 and ROLM2, showing the opposite directions of movement of the two dinosaurs. Scale bar is 40 cm long. Stop 5A (optional) What: Trackway ROLM9

5 Field Guide Lavini di Marco - 5 once the animal lifted its foot. The spacing and shape of the tracks indicate that they were left by a bipedal animal. However, the identity of the track-maker is still debated because these tracks have a unique shape not found in any other Jurassic deposit (Avanzini, 2002). Stop 5B (optional) What: Trackway ROLM11 Notes: ROLM11 was also left by a quadrupedal sauropodlike dinosaur, moving at a slow pace. The tracks are elongated, with a more expanded portion in the area of the digits. The prints of the forefeet are smaller and shallower, placed in front and to the outside of the prints of the hindfeet. The prints are deep and well marked, with mud expulsion rims, especially in the distal part of the trackway. However, the second print to the left on the side of the viewing platform is reduced to an elongated notch in the sediment, indicating that the mud flowed back in the depression immediately after the dinosaur stepped out (Fig. 8). These observations suggest that the sediment was water-impregnated, and possibly covered by a thin sheet of water. Fig. 8: Trackway ROLM11. The white dashed line highlights the elongated footprint partially filled by mud, which flowed back after the animal stepped away. Notes: ROLM9 is one of the most obvious trackways along the Colatoio Chemini. Even if most of the prints are deep and well defined, some tracks in the succession are missing and others are detectable only from a very shallow depression in the sediment. One explanation for the missing tracks is that they were filled by mud Stop 6 (optional) What: Isolated track on detached block Notes: This individual footprint is notable because it is the biggest discovered to date in the Lavini area. It is a tridactyl track, 38 cm long, left by a bipedal carnivore Fig. 9: Left: trackway ROLM26, found on a steeply inclined surface. Right: trackway ROLM28, with outlines and indication of tracks left by hindfeet (right: rf; left: lf) and forefeet (right: rh; left: lh) respectively.

6 Lavini di Marco Field Conference of impressive dimensions (estimated length: 7 m; estimated weight: 1 ton) (Avanzini, 2002). Stop 7A (optional) What: ROLM 26 Notes: ROLM26 is a very visible trackway (Fig. 9), left by a quadrupedal sauropod-like dinosaur with poorly evident impressions of the forefeet. The most eye-catching detail about this trackway is that it is found on a steeply inclined surface. Obviously, this is due to subsequent tilting of the rock layers and does not imply that this dinosaur was climbing on a rock wall. Stop 7B (optional) What: ROLM28 Notes: ROLM28 is a short trackway, consisting of both forefeet and hindfeet impressions of a quadrupedal dinosaur (Fig. 9). The tracks left by the forefeet are smaller, placed more laterally and in some cases almost completely filled with mud. The tracks left by the hindfeet are larger and deeper, with well-defined mud expulsion rims. Given the large size of the prints, this is estimated to be the largest animal documented at the Lavini site, possibly more than 10 m long (Avanzini, 2002). Questions for reflection 1) In the geologic record, body fossils of terrestrial vertebrates are only very rarely found preserved with their tracks at the same site. Creationist researchers have also suggested that, for some vertebrate groups, tracks are found consistently lower in the geologic record than fossil parts of the corresponding trace-makers (Brand & Florence, 1982). How can these patterns be explained from a short-age and a long-age perspective? 2) Fossils are not randomly distributed in the rock record. For example, dinosaurs and their tracks are only found in Mesozoic rocks. The tracks of Lavini di Marco are an example of consistency with this general scheme, because they occur in Jurassic rocks, which are part of the Mesozoic (Appendix A). How is this consistent distribution explained in the short-chronology and in the long-ages approaches? 3) It is difficult to estimate how much time elapsed during the deposition of this interval of sediments and their trampling by different dinosaurs. A traditional geologist will give an answer biased by a view of geologic processes as slow and gradual. For example, even if Avanzini et al. (1997) find some evidence for relatively rapid cementation of the tracks, their suggested short time interval is one encompassing only several tens of thousands of years (p. 548). On the contrary, creationist geologists will be biased toward fast, non-uniformitarian processes and would likely suggest a time interval of hours for deposition of this track-containing rock package. What are some of the observations which could be used to support one or the other of these scenarios? 4) Why does the lack of plant remains in the deposits represent a problem for the uniformitarian interpretation of this fossil site? 5) Mesozoic rocks are commonly considered by creationists as having been deposited during the flood. At Lavini, there are tens of meters of Mesozoic limestone above and below the track-bearing layers. If deposition of these layers was related to the flood, how does the evidence for walking animals impact our conception of flood dynamics?