Monday, 12 May 2014

Grakalovac theropod tracks mystery (1)

 Kamenjak theropod lineup

When comparing my finds, photographs and measurements from Kamenjak 1 and 3 (I had discovered two more tracksites on Kamenjak, so I have named the sites K1, K2 and K3), with the data and conclusions from Fabio's (Dalla Vecchia et all, 2001) paper Dinosaur track sites in the upper Cenomanian (Late Cretaceous) of istrian peninsula (Croatia), describing the tracks from Grakalovac promontory (Kamenjak 1 or K1) something just doesn't add up. Many new questions and speculations appear. Here are some of my thoughts regarding this problem:
1. The theropod morphotype with a relatively very long  middle toe (#3) is reminiscent of an ancient theropod trait going all the way from the late Triassic and early Jurassic (Anchisauripus, Grallator, Brontozoum). Given that in general theropod feet are rather conservative and that they have not changed much over the 100 million year span, this can be plausible. I have already concluded that the tracks on Grakalovac were probably left by a ceratosaur or a compsognathid.
2. Dalla Vecchia has noticed and featured in his paper two size classes of theropod tracks on Grakalovac (K1), both being the same or very similar morphotype.  It seems that Fabio and his colleagues either didn't notice the other tracks, or more likely that the erosion has uncovered these new tracks during the past 14 years. I have noticed several new tracks, some of which were quite unusual. Among them are the ones that look like belonging to a baby hadrosaur.
3. It is a consensus that Istria and some other parts of ADCP was by the Cenomanian (Late Cretaceous) large island with the dwarf insular dinosaurs inhabiting it. That's where my large-foot theropods from K1 and especially K2 don't quite fit in. Or do they?
In the diagram below is the Kamenjak theropods lineup. The little brown silhouette is the Chinese "large compsognathid", with the foot about 11-12,5 cm long (A); marked with (B) is the small Grakalovac (K1) theropod from Fabio's paper and my photographs with a foot 16,5-17 cm long; (C) is the larger specimen from the paper (K1) and (D) is the largest track maker from K1 with the foot 38-40 cm long. The yellow silhouette (E) is the giant with the similar foot shape from the K3 track site, I had discovered last year. Its foot was around 65-67 cm long. 

3. So what is strange with this "insular" ichnocenosis is the obvious presence of very large theropods. I could settle with the 5-meters long one as one of a plausible size (D), but my discovery of the footprints which translate into a 8-10 meters huge beast (E) made me wonder: Am I seeing things? Are my interpretations wrong? Maybe the tracks were deformed? Maybe these were over sized under tracks? So far the evidence speaks in favour of true tracks.
4. Diminishing size or regression in growth of once large insular herbivores in order to compensate for the reduced food sources and maintain the viable population is a well documented biological scenario. So far, the evidence (tracks of herbivorous dinosaurs in Cenomanian rocks of Istria) speaks in favour of the pygmy island dwellers.Those were the small sauropods and small ornithopods.
How do the large theropods fit in here? Maybe they were oriented towards the sea based food? Fish eating dinosaurs? Like the spinosaurids. In any case, I do speculate that the small sauropods had to have some form of defence against the fierce giant predators. Maybe they were heavily armoured like the ankylosaurs? It is even possible that we still didn't find the tracks of the larger Cenomanian Istrian herbivorous dinosaurs.
One thing is certain: We will continue researching and learning new things about dinosaurs and their fantastic, mysterious world.

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