Sono giunti tardi, alla fine del Giurassico, dopo i piccoli Ceratosauri ed i mastodontici Allosauri, ma certamente sono quelli che hanno maggiormente stuzzicato la fantasia di tutti: i Tirannosauri.
Su di essi si è molto favoleggiato e molto studiato. Ad un certo punto si è perfino sostenuto che fossero 'scavengers', cioé che si nutrissero di animali già morti, uccisi da altri predatori più veloci.
Oggi, da una squadra di ricercatori canadesi che hanno scavato in una località rigorosamente tenuta segreta della British Columbia, giunge la notizia che il Tirannosauro era un cacciatore di prede viventi e che cacciava in branco, più o meno come oggi fanno i lupi ed i leoni.
La squadra ha rilevato 30/40 impronte chiare e inconfondibili, oggi stampate sulla roccia (un tempo il fondo doveva essere fangoso: sono visibili persino le scaglie dei grandi rettili) a dimostrare il lavoro del branco contro una preda mobile (probabilmente un Adrosauro, un dinosauro erbivoro con un buffo muso d'anatra).
A conti fatti, doveva trattarsi di tre animali pesanti circa tre tonnellate ciascuno, alti all'incirca 2,5 metri e dell'età di meno di trent'anni, capaci di muoversi a 8.5 km/ora, camminando normalmente.
Sono stati fatti stampi delle impronte e la località è stata secretata e ricoperta di terra.
Il Canada non possiede leggi che proteggono la zona dai ricercatori non autorizzati e non ci sono i fondi per proseguire gli scavi, né per staccare le zone delle impronte dal sito e portarle via in elicottero.
L'unica cosa sicura per il momento è seppellirle e proteggerle dall'uomo e dal clima.
Forse dovremmo fare la stessa cosa con Pompei....
Fossil footprints suggest
tyrannosaurs hunted in packs
They were the king of the carnivores that ruled the Earth 70 million years ago but maybe tyrannosaurs were friendlier than their reputations have allowed.
A team of paleontologists in British Columbia uncovered the preserved footprints of three tyrannosaurs, suggesting they might have hunted in packs
[Credit: The Canadian Press/Richard McCrea]
A trio of fossilized footprint tracks discovered near Tumbler Ridge, in northeastern British Columbia, offer compelling evidence that the beasts were not solitary but travelled in packs. The footprints were found by a local guide outfitter in October 2011. "I was hunting with a client and we were just walking along, and I didn't want to cross the river again for the millionth time," said Aaron Fredlund.
As he made his way across a ledge along the river, he stumbled across two unmistakable footprints etched into the rock. "These tracks are really distinct. There was no doubt what we found," he said. That was almost the end of it.
Fredlund began to leave, thought better of it, and went back for photos. A few days later he showed his wife the photos and she urged him to report his discovery. Those photos set Richard McCrea's heart racing half a world away. McCrea, curator of the Peace Region Palaeontology Research Centre in Tumbler Ridge, was in Australia at the time. The picture showed Fredlund's own foot beside the half-metre dinosaur fossil.
The dinosaur footprints preserved in the rock near Tumbler Ridge provide a glimpse at the beasts that roamed the region 70 million years ago
[Credit: The Canadian Press/ HO-Peace Region Palaeontology Research Centre]
By the end of the month, McCrea and his colleagues were at the site themselves.
Over the next year, they found five more prints belonging to three tyrannosaurs.
In total, the site has 30 to 40 dinosaur footprints, including hadrosaurs, or duck-billed dinosaurs, and a smaller dinosaur called Szurexallopus cordata. And the fossils are close to perfect, McCrea said. The surface the animals trod was "pretty much the consistency of Play-Doh," he said, with a very high clay content.
That was then covered by a thick layer of volcanic ash. Conditions were so ideal that impressions of the dinosaurs' rough skin are clearly visible.
"This is the most ideal situation you could almost ask for," he said. Once believed to be solitary creatures, evidence has grown that tyrannosaurs were more "gregarious" than thought, according to McCrea's study published in the scientific journal PLOS One.
Many solitary tyrannosaur tracks have been unearthed but these are the first trackways with multiple prints that show several travelling in close proximity.
"We have extremely compelling evidence that tyrannosaurs travelled in groups. This was suspected and this is probably the most definitive evidence to come out to date on that topic," McCrea said.
Tyrannosaur footprints are outlined at Tumbler Ridge, B.C. following the discovery that the meat-eating dinosaur might have hunted in packs
[Credit: The Canadian Press/Richard McCrea]
The trackways also provide the first record of tyrannosaur's walking gait, which the team calculated to be about 8.5 kilometres an hour.
Paleontologists estimate the three were 25, 26 and 29 years old and stood about 2.35 metres high at the hip. They would have weighed about three tonnes each.
At the time the footprints were made in the Cretaceous period, the area was about 1,100 kilometres further north than it is now but the temperature much milder.
It was also closer to sea level than it is now. McCrea believes the discovery was serendipitous.
The tracks survived millennia because they were covered by earth and they may not have made it through a freezing northern British Columbia winter exposed to the elements, he said.
The team made castings of the footprints but the centre, which is locally funded, cannot afford to excavate the site.
The team covered the tracks to protect them from treasure hunters and the weather and McCrea is searching for grants to retrieve and permanently preserve them. That would involve cutting the rock and flying the fossils out via helicopter.
The location is a well-guarded secret. Unfortunately, despite numerous fossil beds throughout the province, British Columbia does not have a management plan for paleontological sites. The area is not protected under the law.
Author: Dene Moore | Source:
The Canadian Press
[July 23, 2014]
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