Giant dinos may
have migrated
Seasonal roaming perhaps
helped sauropods get big
By Nick Bascom
Recalling the trek made by the cartoon
Apatosaurus Littlefoot in The Land
Before Time, real sauropod dinosaurs
in prehistoric western North America
may have fled the summer drought conditions of lowland river floodplains for
the lush vegetation of upland settings.
Such migrations, if they occurred, might
explain how long-necked sauropods
reached their immense size, researchers suggest online October 26 in Nature.
With fearsome Jurassic preda-
tors about, the bigger sauropods grew,
the safer they were. “Once sauropods
reached their full size, they were effec-
tively immune to predation,” says study
leader and geochemist Henry Fricke of
Colorado College. An allosaur attack
would have been as harmless as “a bunch
of hyenas trying to attack an elephant.”
Some paleontologists believe that sau-
ropods grew so large because they had
difficulty chewing and so needed huge
stomachs to digest food. As the animals’
stomachs evolved to bigger sizes, so did
the rest of them, the theory goes. While
Fricke doesn’t discount this theory, he
believes that seasonal sojourns to areas
rich in vegetation also played a part in
the evolution of gigantism in sauropods.
Chemical differences between sauropod
teeth and nearby sediment suggest the
dinosaurs migrated seasonally.
between the enamel and sediments,
Fricke believes that sauropods must have
been leaving the basin itself and going to
the adjacent highlands to eat and drink.
“Food may not have been the sole
reason the sauropods moved,” says
George Engelmann of the University
of Nebraska at Omaha, who was not
involved in the study. “But the isotopic
variation suggests, at least, that they
were moving around.”
Fricke plans to test the tooth enamel
of other nonsauropod dinosaur spe-
cies, such as Stegosaurus, so that he
can provide a more complete picture of
sauropod feeding behavior. If the oxygen
isotope levels of smaller herbivores indi-
cate that they remained in the lowlands
year-round to feed, then Fricke will have
more evidence that a higher nutrient
demand was the central factor driving
the sauropods to migrate. s
Toothy ancestors found
Tiny but seemingly ;erce, these members of a now-extinct group
of mammals called dryolestoids scrabbled for existence nearly
100 million years ago in the shadows of dinosaurs. Paleontologists recently unearthed rare skulls and other bones of a
previously unknown species in Argentina; in the Nov. 3 Nature,
Guillermo Rougier of the University of Louisville in Kentucky
and colleagues name the species Cronopio dentiacutus, its
name in part a nod to its acutely sharp teeth. Few mammal
fossils have been found in South America from this time
period, before the age of dinosaurs gave way to the age of
mammals. Scientists hope the discovery will reveal more
about whether early mammals evolved differently in North
and South America. Dryolestoids are most closely related to
a modern group of mammals called therians, which includes
marsupials such as opossums and placental mammals such
as people. —Alexandra Witze
FROM TOP: HENRY FRICKE/COLORADO COLLEGE; JORGE GONZALEZ, © GUILLERMO ROUGIER
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