April 20, 2007
A Utah site frozen in Early Jurassic time recently yielded discoveries that include an enormous, previously unknown carnivorous dinosaur, a new shark species, at least three other new fish and three new trees.
All of the now-extinct organisms once thrived in or around a giant lake 200 million years ago, according to paleontologists who made the finds.
Anatomical features and track marks linked to the dinosaur suggest it specialized in eating and catching fish, including sharks and huge bony fish that, when consumed, would have been "like biting through chain mail," Utah State paleontologist James Kirkland told Discovery News.
The fish-loving dino, which the researchers believe was a cousin of the crested dino Dilophosaurus, would have been a formidable adversary to its fearsome prey.
"These (dinosaurs) got up to 18-20 feet in length, 6-7 feet high at the hips, and weighed between 750-1,000 pounds," explained Andrew Milner, city paleontologist at the St. George Dinosaur Discovery Site on Johnson Farm, Utah, where the excavations took place.
Long, sharp teeth at the front of the dinosaur's mouth helped to keep fish from flying out, said Kirkland, while other, more slender teeth had "steak-knife serration" wear patterns between the tip and the gum line.
"The only other meat-eating dinosaurs with teeth worn like that are the spinosaurs Spinosaurus and Suchimimus from North Africa where large...fish dominated," said Kirkland.
One of the fish species discovered at the site, now called Lake Dixie, was indeed a semionotid — an early type of fish that usually had an elongated body, gills, jaws and scales or bony plates.
"Fish in the past were more armored than they are today," Kirkland explained.
The new shark species, named Lissodus johnsonorum, would have been an easier dinner, since its skeleton was made of cartilage and not hard bone, but the crunchy fish were more prevalent in the lake and outnumbered sharks 10 to one.
The Dilophosaurus relative also possessed nasal openings that retracted back from the end of its snout so, like today's crocodiles and alligators, it could still breath when its mouth was underwater.
Perhaps the most dramatic finds at the site are the dinosaur track marks. Milner said these belonged to several creatures including other dinosaur species, other reptiles and early ancestors of mammals.
The tracks show how the fish-eating dinosaur would wade out into the lake, sometimes "chest deep," according to Kirkland.
It's likely the dinosaur went into the lake to catch sharks and other fish, said Kirkland. This was no easy task, as indicated by "floundering" dinosaur claw scrapes and other marks found at the bottom of Lake Dixie.
"We have counted over 3,000 individual claw marks and toe scrapes that show incredibly detailed preservation," Milner told Discovery News. "We can see details of cuticle on the tips of claws, skin impressions, scale scratch lines and where claw cuticle was overlapped by the fleshy toe pads at the end of the toes."
There initially was some skepticism from other experts that these could include evidence for dinosaur swimming and fishing but, when the latest discoveries were announced near the site, British vertebrate paleontologist Peter Galton said "this has finally put to rest" the prior doubts.
The New Mexico Museum of Natural History and Science has just published a book, "The Triassic-Jurassic Terrestrial Transition," which provides brief mentions of many of the recent finds.
Visitors to the St. George site may also view some of the discoveries while literally walking in the footsteps of dinosaurs.