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January 09, 2013

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Toe tracks said to come from many little, swimming dinos

Jan. 9, 2013
Courtesy of the University of Queensland
and World Science staff

Doz­ens of lit­tle di­no­saurs, swim­ming in shall­ow riv­er wa­ters, left a group of track marks in Aus­tral­ia pre­vi­ously thought to be ev­i­dence of a di­no­saur stam­pede, a new study claims.

Re­search­ers say the marks sug­gest cer­tain or­nith­o­pods—plant-eating di­no­saurs whose name means “bird-footed”—liked to get around by swim­ming or wad­ing, per­haps us­ing riv­er cur­rents for help. These crea­tures seem to have been in no par­tic­u­lar hur­ry, as the tracks were made over a pe­ri­od long enough that the wa­ter lev­el changed quite a bit, said the re­search­ers.

“It’s dif­fi­cult to see how tracks such as these could have been made by run­ning or walk­ing an­i­mals. If that was the case we would ex­pect to see a much flat­ter im­pres­sion of the foot.”

Romilio added that similar-looking traces left by dif­fer­ent-sized di­no­saurs sig­naled fluctua­t­ions in wa­ter depth. “The small­est swim traces in­di­cate a min­i­mum wa­ter depth of about 14 cm (a­bout six inch­es), while much larg­er ones in­di­cate depths of more than 40 cm” (16 inch­es,) he said.

“Un­less the wa­ter lev­el fluc­tu­at­ed, it’s hard to en­vis­age how the dif­fer­ent sized swim traces could have been pre­served on the one sur­face. Some of the larg­er tracks are much more con­sist­ent with walk­ing an­i­mals, and we sus­pect these di­no­saurs were wad­ing through the shal­low wa­ter.”

Romilio said the swim­ming tracks be­longed to or­nith­o­pods, small, two-legged plant-eaters whose feet and hip structure re­sem­ble those of birds. “Some of the smaller ones were no larg­er than chick­ens, while some of the wad­ing an­i­mals were as big as emus.”

The often large spac­ing among many con­sec­u­tive tracks sug­gest the crea­tures were mov­ing down­stream, per­haps us­ing the cur­rent to help push them along, the in­ves­ti­ga­tors said. Giv­en the likely fluctua­t­ions in wa­ter depth, the re­search­ers think the tracks were formed over sev­er­al days, may­be even weeks.

Pre­vi­ous re­search had iden­ti­fied two types of small di­no­saur tracks at Lark Quar­ry: long-toed tracks, from a crea­ture called Skar­to­pus, and short-toed tracks from an an­i­mal known as Wintono­pus. But the new ana­lysis sug­gests they are both made by a short-toed di­no­saur, though some indi­vid­uals made long tracks by drag­ging their toes through the bottom.

Salis­bury said re­gard­less of how it’s in­ter­preted, “Lark Quar­ry is, and will al­ways re­main, one of Aus­tral­ia’s most im­por­tant di­no­saur track­sites.”

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Dozens of little swimming dinosaurs in a river environment left a group of track marks in Australia previously thought to be evidence of a dinosaur stampede, a new study claims. Researchers say the marks suggest certain ornithopods—plant-eating dinosaurs whose name means “bird-footed”—liked to get around by swimming or wading, perhaps using river currents for help. These creatures seem to have been in no particular hurry, as the tracks were made over a period long enough that the water level changed quite a bit, said the researchers. “Many of the tracks are nothing more than elongated grooves, and probably formed when the claws of swimming dinosaurs scratched the river bottom,” said Anthony Romilio of the University of Queensland in Australia, a doctoral candidate who led the study. The findings are published in the January issue of Journal of Vertebrate Paleontology. The investigation drew on new techniques that allow 3-D analysis of tracks once examined mostly as two-dimensional outlines, added Romilio’s supervisor and coauthor of the paper, Steve Salisbury. The work is “allowing us to learn more about how these dinosaurs moved and behaved in different environments,” Salisbury remarked. Romilio said the 95-98 million-year-old tracks lie in thin beds of rock made from silt and sand deposited in a shallow river when the area was part of a vast, forested flood plain. The site is now part of Lark Quarry Conservation Park in central-western Queensland, Australia. “Many of the tracks are nothing more than elongated grooves, and probably formed when the claws of swimming dinosaurs scratched the river bottom,” Romilio said. “Some of the more unusual tracks include ‘tippy-toe’ traces – this is where fully buoyed dinosaurs made deep, near vertical scratch marks with their toes as they propelled themselves through the water. “It’s difficult to see how tracks such as these could have been made by running or walking animals. If that was the case we would expect to see a much flatter impression of the foot.” Romilio added that similar-looking traces left by different-sized dinosaurs signaled fluctuations in water depth. “The smallest swim traces indicate a minimum water depth of about 14 cm (about six inches), while much larger ones indicate depths of more than 40 cm” (16 inches,) he said. “Unless the water level fluctuated, it’s hard to envisage how the different sized swim traces could have been preserved on the one surface. Some of the larger tracks are much more consistent with walking animals, and we suspect these dinosaurs were wading through the shallow water.” Romilio said the swimming dinosaur tracks at Lark Quarry belonged to small, two-legged herbivorous dinosaurs known as ornithopods. “Some of the smaller ones were no larger than chickens, while some of the wading animals were as big as emus.” Sometimes large spacing among many consecutive tracks suggest the creatures were moving downstream, perhaps using the current to help push them along, the investigators said. Given the likely fluctuations in water depth, the researchers think the tracks were formed over several days, maybe even weeks. Previous research had identified two types of small dinosaur tracks at Lark Quarry: long-toed tracks, from a creature called Skartopus, and short-toed tracks from an animal known as Wintonopus. But the new study suggests they are both made by a short-toed dinosaur, just that some were dragging their toes through the sediment and thereby elongating the tracks. Salisbury said regardless of how it was interpreted, these findings took nothing away from the importance of the site. “Lark Quarry is, and will always remain, one of Australia’s most important dinosaur tracksites.”