Early dinosaurs may have lived in social herds as early as 193 million
years ago
Fossils indicate a communal nesting ground and adults who foraged and
took care of the young as a herd, scientists say
Date:
October 21, 2021
Source:
Massachusetts Institute of Technology
Summary:
Scientists believe they have found the earliest evidence for
complex herd behavior in dinosaurs. Researchers say Mussaurus
patagonicus may have lived in herds some 193 million years ago --
40 million years earlier than other records of dinosaur herding.
FULL STORY ==========================================================================
To borrow a line from the movie "Jurassic Park:" Dinosaurs do move
in herds.
And a new study shows that the prehistoric creatures lived in herds much earlier than previously thought.
==========================================================================
In a paper appearing in Scientific Reports, researchers from MIT,
Argentina, and South Africa detail their discovery of an exceptionally preserved group of early dinosaurs that shows signs of complex herd
behavior as early as 193 million years ago -- 40 million years earlier
than other records of dinosaur herding.
Since 2013, members of the team have excavated more than 100 dinosaur
eggs (about the size of chicken eggs) and the partial skeletons of 80
juvenile and adult dinosaurs from a rich fossil bed in southern Patagonia.
Using X-ray imaging, they were able to examine the eggs' contents
without breaking them apart, and discovered preserved embryos within,
which they used to confirm that the fossils were all members of Mussaurus patagonicus -- a plant-eating dinosaur that lived in the early Jurassic
period and is classified as a sauropodomorph, a predecessor of the
massive, long-necked sauropods that later roamed the Earth.
Surprisingly, the researchers observed that the fossils were grouped by
age: Dinosaur eggs and hatchlings were found in one area, while skeletons
of juveniles were grouped in a nearby location. Meanwhile, remains of
adult dinosaurs were found alone or in pairs throughout the field site.
This "age segregation," the researchers believe, is a strong sign of
a complex, herd-like social structure. The dinosaurs likely worked as
a community, laying their eggs in a common nesting ground. Juveniles congregated in "schools," while adults roamed and foraged for the herd.
========================================================================== "This may mean that the young were not following their parents in a
small family structure," says team member Jahandar Ramezani, a research scientist in MIT's Department of Earth, Atmospheric and Planetary
Sciences. "There's a larger community structure, where adults shared
and took part in raising the whole community." Ramezani dated ancient sediments among the fossils and determined that the dinosaur herd
dates back to around 193 million years ago, during the early Jurassic
period. The team's results represent the earliest evidence of social
herding among dinosaurs.
Living in herds may have given Mussaurus and other social sauropodomorphs
an evolutionary advantage. These early dinosaurs originated in the
late Triassic, shortly before an extinction event wiped out many other
animals. For whatever reason, sauropodomorphs held on and eventually
dominated the terrestrial ecosystem in the early Jurassic.
"We've now observed and documented this earliest social behavior in
dinosaurs," Ramezani says. "This raises the question now of whether living
in a herd may have had a major role in dinosaurs' early evolutionary
success. This gives us some clues to how dinosaurs evolved." A fossil
flood Since 2013, paleontologists on the team have worked in the Laguna Colorada Formation, a site in southern Patagonia that is known for bearing fossils of early sauropodomorphs. When scientists first discovered fossils within this formation in the 1970s, they named them Mussaurus for "mouse lizard," as they assumed the skeletons were of miniature dinosaurs.
==========================================================================
Only much later did scientists, including members of the Argentinian team, discover bigger skeletons, indicating Mussaurus adults were much larger
than their rodent namesakes. The name stuck, however, and the team has continued to unearth a rich collection of Mussaurus fossils from a small, square kilometer of the formation.
The fossils they have identified so far were found in three sedimentary
layers spaced close together, indicating that the region may have been
a common breeding ground where the dinosaurs returned regularly, perhaps
to take advantage of favorable seasonal conditions.
Among the fossils they uncovered, the team discovered a group of 11
articulated juvenile skeletons, intertwined and overlapping each other,
as if they had been suddenly thrown together. In fact, judging from the remarkably preserved nature of the entire collection, the team believes
this particular herd of Mussaurusdied "synchronously," perhaps quickly
buried by sediments.
Based on evidence of ancient flora in the nearby outcrops, the Laguna
Colorada Formation has long been assumed to be relatively old on the
dinosaur timescale.
The team wondered: Could these dinosaurs have been herding from early on? "People already knew that in the late Jurassic and Cretaceous, the large herbivore dinosaurs exhibited social behavior -- they lived in herds and
had nesting spots," Ramezani says. "But the question has always been,
when was the earliest time for such herding behavior?" A gregarious
line To find out, Diego Pol, a paleontologist at the Egidio Feruglio Paleontological Museum in Argentina who led the study, looked for
samples of volcanic ash among the fossils to send to Ramezani's lab
at MIT. Volcanic ash can contain zircon - - mineral grains contaning
uranium and lead, the isotopic ratios of which Ramezani can precisely
measure. Based on uranium's half-life, or the time it takes for half of
the element to decay into lead, he can calculate the age of the zircon and
the ash in which it was found. Ramezani successfully identified zircons
in two ash samples, all of which he dated to around 193 million years old.
Since the volcanic ash was found in the same sediment layers as the
fossils, Ramezani's analyses strongly suggest that the dinosaurs were
buried at the same time the ash was deposited. A likely scenario may
have involved a flash flood or windblown dust that buried the herd,
while ash from a distant eruption happened to drift over and, luckily
for science, deposit zircons in the sediments.
Taken together, the team's results show that Mussaurus and possibly
other dinosaurs evolved to live in complex social herds as early as 193
million years ago, around the dawn of the Jurassic period.
Scientists suspect that two other types of early dinosaurs --
Massospondylus from South Africa and Lufengosaurus from China -- also
lived in herds around the same time, although the dating for these
dinosaurs has been less precise.
If multiple separate lines of dinosaurs lived in herds, the researchers
believe the social behavior may have evolved earlier, perhaps as far
back as their common ancestor, in the late Triassic.
"Now we know herding was going on 193 million years ago," Ramezani
says. "This is the earliest confirmed evidence of gregarious behavior
in dinosaurs. But paleontological understanding says, if you find
social behavior in this type of dinosaur at this time, it must have
originated earlier." This research was supported, in part, by National
Science Foundation in the U.S. and the National Scientific and Technical Research Council of Argentina.
========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Jennifer
Chu. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Pol, D., Mancuso, A.C., Smith, R.M.H. et al. Earliest evidence
of herd-
living and age segregation amongst dinosaurs. Sci Rep, 2021 DOI:
10.1038/ s41598-021-99176-1 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/10/211021120921.htm
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