Descoberta arqueológica em Minas Gerais revela práticas funerárias pré-históricas no Brasil
A
descoberta de 39 esqueletos humanos na região de Lagoa Santa indica que
os povos que viviam no território do país tinham hábitos mais complexos
do que se imaginava.
Por BBC
Os esqueletos encontrados na Lapa do Santo indicam que os povos que
viviam ali eram muito mais complexos do que se imaginava — Foto: André
Strauss/Divulgação
A descoberta de 39 esqueletos humanos, com idades entre 8 mil e 11 mil
anos na região metropolitana de Belo Horizonte, está ajudando a
redefinir o que se sabia sobre os primeiros brasileiros. O achado
ocorreu na Lapa do Santo, uma pequena caverna no município de Lagoa
Santa.
São os ossos mais antigos do Brasil e revelam que, ao contrário do que
se pensava até agora, os povos que viviam no local naquela época eram
complexos e tinham práticas funerárias altamente elaboradas.
A novidade é resultado do projeto Morte e vida na Lapa do Santo: uma
biografia arqueológica dos povos de Luzia, coordenado pelos
pesquisadores André Strauss, do Museu de Arqueologia e Etnologia (MAE), e
Rodrigo de Oliveira, do Instituto de Biociências (IB), ambos da
Universidade de São Paulo (USP).
É um trabalho de pesquisa interdisciplinar, que tem como objetivo
caracterizar como viviam as populações que estavam no Brasil central
durante o Holoceno Inicial (Holoceno é o período geológico que começou
há 11.500 anos e se estende até o presente).
De acordo com Strauss, os esqueletos desencavados eram de idosos,
crianças, homens e mulheres. "Todos tinham sinais de rituais
mortuários", revela.
"Alguns estavam queimados, outros pintados de vermelho e alguns
combinavam crânios de crianças com corpos de adultos, ou dentes de uma
pessoa com a arcada de outra. O que chamou a atenção também é que esses
sinais variavam dependendo da idade arqueológica dos ossos. Isso pode
significar que os povos que habitavam a região alteraram sua forma de
tratar os corpos dos mortos ao longo do tempo. Essa descoberta é inédita
na arqueologia brasileira."
Os primeiros americanos
A região tem dezenas de sítios arqueológicos que vêm sendo escavados e pesquisados desde 1843 — Foto: André Strauss/Divulgação
A região onde trabalham os arqueólogos, Lagoa Santa, está entre as mais
ricas em restos de culturas pré-históricas do Brasil. Ali, dezenas de
sítios arqueológicos vêm sendo escavados e pesquisados desde 1843,
quando o naturalista dinamarquês Peter Wilhelm Lund (1801-1880),
considerado o pai da paleontologia brasileira, descobriu ossadas humanas
misturadas com as de animais já extintos. Desde então, centenas de
crânios e outros ossos humanos foram desenterrados do local.
Entre eles, o mais antigo de que se tem registro no Brasil, com 11.300
anos, descoberto em 1974, pela arqueóloga francesa Annette
Laming-Emperaire, no sítio chamado Lapa Vermelha IV.
Como era de um indivíduo do sexo feminino, foi batizada de Luzia pelo
bioantropólogo Walter Alves Neves, também da USP, que foi orientador de
Strauss e Oliveira, que agora dão continuidade ao seu trabalho.
Em 1995, ele fez medidas antropométricas do crânio, que mostraram que
Luzia tinha mais a ver com os africanos do que com os índios atuais.
Com base nisso e em outras descobertas, ele elaborou sua hipótese para a
ocupação das Américas, apresentada no livro O povo de Luzia - em busca
dos primeiros americanos, em coautoria com o geógrafo Luís Beethoven
Piló.
A hipótese propõe que os primeiros americanos chegaram ao continente em
duas levas migratórias, uma há 14 mil anos e a segunda há 11 mil,
vindas da Ásia pelo estreito de Bering. A primeira seria composta por
uma população com traços semelhante aos dos africanos e aborígines
australianos. A segunda era de indivíduos parecidos com asiáticos e
índios americanos atuais.
Ao longo do tempo, os dois povos se miscigenaram no novo mundo.
Para outros estudiosos, no entanto, os indígenas atuais ou ameríndios e
os primeiros que chegaram à região de Lagoa Santa fazem parte de um
mesmo tipo, cujas diferenças morfológicas podem ser explicadas pela
variabilidade natural que existe dentro de qualquer população. A
pesquisas de Strauss e Oliveira poderão ajudar a elucidar a questão.
Segundo Strauss, o projeto segue em pleno andamento com a escavação da
Lapa do Santo e a análise do material encontrado. "Isso inclui estudos
morfológicos, de microvestígios, isótopos, datação, antropologia
virtual, micromorfologia e DNA", conta.
"Até o momento, nossos estudos não dialogam diretamente com o tema dos
primeiros americanos. Quando sair o resultado do DNA poderemos
determinar se o modelo dos dois componentes está correto ou não."
As escavações realizadas até agora já revelaram vários aspectos dos
grupos, desconhecidos até agora — Foto: André Strauss/Divulgação
Práticas funerárias surpreendentes
As escavações realizadas até agora já revelaram, no entanto, vários
aspectos dos grupos que eram desconhecidos até agora. "Apesar das
centenas de esqueletos exumados em Lagoa Santa em quase dois séculos de
pesquisa, muito pouco foi discutido em relação às práticas funerárias na
região", diz Strauss.
"De acordo com as poucas descrições disponíveis na literatura, elas
sempre foram caracterizadas como simples e homogêneas, incluindo apenas
enterros primários de um único indivíduo e sem nenhum tipo de
acompanhamento funerário."
As descobertas de Strauss e Oliveira mudam radicalmente esse quadro. De
acordo com eles, os sepultamentos da Lapa do Santo tinham uma alta
variabilidade, o que contradiz a visão tradicional sobre as práticas
mortuárias na região.
"Além dessa retificação histórica, a diversidade delas no local ganha
relevância, porque contraria a homogeneidade de outros componentes do
sítio, tais como os artefatos de pedra, os remanescentes faunísticos, a
morfologia craniana e a própria composição da matriz sedimentar."
Segundo Strauss, os sepultamentos também permitem inferir que ao longo
do Holoceno Inicial grupos distintos que, possivelmente, não se
reconheciam como parte de um mesmo povo habitaram a região. "Na ausência
de mais datações diretas para os esqueletos, não é possível descartar a
hipótese de que, em um mesmo momento, diferentes povos tenham ocupado a
região", acrescenta.
Simplificando, ele diz que é possível que, durante o Holoceno Inicial,
não tenha existido "um único 'povo de Luzia'", expressão cunhada por
Walter Neves para se referir aos grupos humanos que habitaram a região
de Lagoa Santa na época, "mas sim muitos 'povos' e muitas 'Luzias', cada
um único em suas idiossincrasias simbólicas, culturais e, por que não,
linguísticas".
"Assim, o registro funerário da Lapa do Santo contribui para retratar
uma pré-história plural e dinâmica, onde a diversidade é a regra e
elemento interpretativo fundamental", diz.
terça-feira, 27 de novembro de 2018
Artist’s reconstruction of Stromatoveris, an ancient marine animal
J. Hoyal Cuthill
These half-billion-year-old creatures were animals—but unlike any known today
So-called Ediacaran organisms have puzzled biologists for
decades. To the untrained eye they look like fossilized plants, in tube
or frond shapes up to 2 meters long. These strange life forms dominated
Earth’s seas half a billion years ago, and scientists have long
struggled to figure out whether they’re algae, fungi, or even an entirely different kingdom of life that failed to survive.
Now, two paleontologists think they have finally established the
identity of the mysterious creatures: They were animals, some of which
could move around, but they were unlike any living on Earth today.
Scientists first discovered the Ediacaran organisms in 1946 in South
Australia’s Ediacara Hills. To date, researchers have identified about
200 different types in ancient rocks across the world. Almost all appear
to have died out by 541 million years ago, just before fossils of
familiar animals like sponges and the ancestors of crabs and lobsters
appeared in an event dubbed the Cambrian explosion. One reason these
creatures have proved so tricky to place in the tree of life is that
some of them had an anatomy unique in nature. Their bodies were made up
of branched fronds with a strange fractal architecture, in which the frond subunits resembled small versions of the whole frond.
Jennifer Hoyal Cuthill at the Tokyo Institute of Technology and the
University of Cambridge in the United Kingdom and Jian Han at Northwest
University in Xi’an, China, have now found key evidence that the
Ediacaran organisms were animals. They analyzed more than 200 fossils of
a 518-million-year-old marine species named Stromatoverispsygmoglena.
Paleontologists had previously concluded that the 10-centimeter-tall
species was some sort of animal—in part, says Hoyal Cuthill, because it
was found alongside other known animals, and all of the fossils are
preserved in a similar way. Hoyal Cuthill and Han argue S. psygmoglena was also an Ediacaran organism, a rare “survivor” that somehow clung on through the Cambrian explosion.
The Stromatoveris fossils, which were all unearthed in
Yunnan province in southwestern China, are beautifully preserved, Hoyal
Cuthill says. As she examined specimen after specimen she became
increasingly excited. “I began thinking: My goodness, I’ve seen these
features before.” Like some of the strange Ediacaran organisms, Stromatoveris was made up of several radially repeated, branched fronds with a fractal internal architecture.
A fossil of one of the 200 or so types of Stromatoveris
J. Hoyal Cuthill
To find out what sort of animals Stromatoveris and the
other Ediacaran organisms were, Hoyal Cuthill and Han ran a computer
analysis that uses anatomical features to reconstruct evolutionary
relationships. They found that Stromatoveris and the other Ediacaran organisms don’t belong to any living animal group or “phylum.” Instead, they cluster on their own branch in the animal evolutionary tree,
between the sponges and complex animals with a digestive cavity like
worms, mollusks, and vertebrates, the team reports today in Palaeontology.
“This branch, the Petalonamae, could well be its own phylum, and it
apparently lacks any living descendants,” Hoyal Cuthill says.
“It looks very likely [the Ediacaran organisms] are animals,” says
Simon Conway Morris, a paleontologist at the University of Cambridge,
who worked with Han on the first description of Stromatoveris in 2006, but who was not involved in the current study. At that point there were just a handful of known Stromatoveris fossils. The researchers argued that they were similar to some Ediacaran organisms, although others later questioned that link. Conway Morris says the new study “extends the story very nicely” by exploring the Ediacaran nature of Stromatoveris in more detail.
Geobiologist Simon Darroch at Vanderbilt University in Nashville is
also comfortable with the idea that the Ediacaran organisms were animals
and that a few survived into the Cambrian. But on a first look he is
not convinced that Stromatoveris was one such survivor; he
thinks the evidence that it had the fractal architecture of an Ediacaran
organism isn’t strong—yet he’s open to persuasion.
If the new conclusion settles one mystery, though, it introduces
another. The Ediacaran organisms represent the first major explosion of
complex life on Earth, and they thrived for 30 million years. Their
demise has been linked to the appearance of animals in the Cambrian
Explosion, Hoyal Cuthill says. But that simple explanation doesn’t work
as well if Ediacaran organisms were animals themselves, and some were
still alive tens of millions of years later. “It’s not quite so neat
anymore,” she says. “As to what led to their eventual extinction I think
it’s very hard to say.”
Por mais de 70 anos, os cientistas têm intrigado as formas desconcertantes de fósseis de meio bilhão de anos que não se parecem com nenhum outro organismo que já viveu na Terra. Os paleontólogos não foram capazes de dizer se muitos desses fósseis de forma estranha de oceanos antigos representam plantas, animais ou alguma outra forma de vida. Agora, vestígios de colesterol - uma assinatura da vida animal - de um conjunto de fósseis incrivelmente bem preservados confirmam que uma criatura chamada Dickinsonia, que se parece um pouco com um tapete de banho acolchoado, era na verdade um animal estranho.
These chemical traces “are giving us a completely different way of
understanding what is happening” in very ancient ecosystems, says
paleontologist Douglas Erwin of the Smithsonian Institution’s National
Museum of Natural History in Washington, D.C.
As formas de vida que viveram na Terra há meio bilhão de anos deixaram para trás alguns dos mais estranhos fósseis conhecidos. Chamados de Ediacarans - batizados com o nome de Ediacara Hills da Austrália, onde alguns dos primeiros foram encontrados - eles viveram nos oceanos entre 570 milhões e 541 milhões de anos atrás, pouco antes da explosão cambriana, quando surgiram os primeiros animais reconhecíveis. Até quase um metro de comprimento, algumas das 200 espécies descritas de Ediacaran têm frondes em forma de fractal. Outros, como Dickinsonia, parecem ter módulos cheios de fluido que lhes davam uma aparência “acolchoada”. Teorias sobre o que eles eram abundantes: protistas gigantes? Liquens? Algas? Algum tipo de esponja? Ou alguma outra forma de vida que desapareceu desde então?
Ilya Bobrovskiy, a geologist who now works at the Australian National
University (ANU) in Canberra, wondered whether he might be able to get
clues from some exceptional fossils that still preserve a film of what
looks like organic material. These fossils come from a cliff on the
shore of the White Sea in northwestern Russia, where for 550 million
years, the rocks have escaped the heat and pressure that can obliterate
molecular traces. “They are some of the least cooked rocks of this age
that anyone has found,” Erwin says.
A film of organic matter from an unusual ancient fossil
Ilya Bobrovskiy/Australian National University
Bobrovskiy contacted Jochen Brocks, an expert in ancient
biomolecules at ANU, to ask whether he thought the film might still
contain molecules that could reveal clues to the organism. “Jochen said I
was completely insane,” Bobrovskiy says. (Brocks’s version of the
story: “I said, ‘Right. That’s the most stupid idea I’ve ever heard.’
But I told him he should find out for himself.”)
Bobrovskiy moved from Russia to Australia to join Brocks’s lab.
There, he first tested his idea on a collection of small round Ediacaran
fossils called Beltanelliformis. The researchers removed the
film from the rock, dissolved it, and used gas chromatography and mass
spectrometry to look for preserved organic molecules. They found high
levels of hopanes, a molecule that suggested the Beltanelliformiswere colonies of cyanobacteria, the researchers reported earlier this year.
Buoyed by that result, the researchers had the nerve to try the technique with the much larger Dickinsonia fossils.
(“They would have brought $30,000 on eBay,” Brocks says. “But we sliced
them up and dissolved them.”) The results, reported today in Science, were striking. In the Dickinsonia fossil, 93% of the organic molecules had 27 carbon molecules;
that makes them members of a family called cholesteroids, which
includes cholesterol and is a signature of animal cells. Samples from
immediately above and below the Dickinsonia fossil had a
different mix of steroids: Only 11% were cholesteroids and more than 70%
were stigmasteroids, molecules with 29 carbon atoms, which are a
signature of green algae.
“It’s a very unusual style of organic preservation,” says Gordon
Love, a geochemist at the University of California (UC), Riverside. “We
don’t usually expect to find these organic films, so there are a few
quirky features that require more evaluation.” Still, he says, the
conclusion that Dickinsonia produced cholesterol—and was
therefore an animal—“is the most parsimonious explanation at this stage.
I would say it’s plausible.”
“If this were the only evidence we had, it wouldn’t be enough,” says
Mary Droser, a paleontologist and expert on Ediacarans at UC Riverside.
“But along with the other evidence, it’s great.” She says it’s
especially satisfying that the biochemical evidence came from Dickinsonia. “I won’t say it’s the [Tyrannosaurus] rex of
the Ediacarans—it’s not a predator. But it has that sort of standing,”
she says, as an iconic representative of its ecosystem. “It is a special
one, and it’s wonderful to have evidence from the geochemical world
that it was an animal.”
KOOTENAY NATIONAL PARK IN CANADA—The drumming
of the jackhammer deepens. Then, a block of shale butterflies open,
exposing to crisp mountain air a surface that hasn't seen sunlight in
half a billion years. "Woo!" says paleontologist Cédric Aria of the
Nanjing Institute of Geology and Palaeontology in China, bracing the top
slab of rock upright.
Its underside bears charcoal-colored smudges that look vaguely like horseshoe crabs or the Millennium Falcon from Star Wars.
"It's a spaceship landing area here," says expedition leader
Jean-Bernard Caron, curator of invertebrate paleontology at the Royal
Ontario Museum (ROM) in Toronto, Canada.
Those "spaceships" are carapaces, molted onto a long-vanished ocean
floor by a species new to science. This field season they've been
spilling out of the rocks here, where Caron's team has spent the past
few years unearthing groundbreaking animal fossils from the Cambrian
period, the coming-out party for animal life on Earth. During the
Cambrian, which began about 540 million years ago, nearly all modern
animal groups—as diverse as mollusks and chordates—leapt into the fossil
record. Those early marine animals exhibited a dazzling array of body
plans, as though evolution needed to indulge a creative streak before
buckling down. For more than a century, scientists have struggled to
make heads or tails—sometimes literally—of those specimens, figure out
how they relate to life today, and understand what fueled the
evolutionary explosion.
Com cuidado, Aria e Caron colocam a parte de cima da laje de lado. O espaço é difícil de encontrar na pedreira, empoleirado em uma saliência do tamanho de um pequeno quarto a uma altitude de 2500 metros, muito acima de Tokumm Creek. Durante anos, um local igualmente ameaçador, a cerca de 40 quilômetros a noroeste desse vale, oferecia a janela mais clara do Cambriano. Lá, em 1909, o paleontologista norte-americano Charles Doolittle Walcott descobriu o Burgess Shale, uma formação fóssil que preserva não apenas conchas duras, mas também características suaves como as pernas, os olhos e as entranhas dos creepy crawlies.
But in recent years, Caron has shown that the richest fossil-bearing
rock extends many kilometers beyond Walcott's site. This summer's
excavation marks his latest visit to this long Cambrian tapestry. Each
new stop has offered striking views of unfamiliar animals, many already
described in high-profile papers: the little fish relative Metaspriggina, a vertebrate ancestor that Caron now speculates clustered in schools; the pincered Tokummia;
and the ice cream cone–shaped fossils called hyoliths, which Caron's
Ph.D. student Joseph Moysiuk last year linked to shelled animals called
brachiopods, some of which persist today.
Other sites around the world are also opening new vistas of the
Cambrian. Scientists can now explore the animal explosion with a
highlight reel of specimens, along with results from new imaging
technologies and genetic and developmental studies of living organisms.
"There have been a host of new discoveries," says paleontologist Doug
Erwin of the Smithsonian Institution's National Museum of Natural
History in Washington, D.C. Researchers may be closer than ever to
fitting these strange creatures into their proper places in the tree of
life—and understanding the "explosion" that birthed them.
Jean-Bernard Caron shows off the "mothership," an enigmatic
Cambrian life form his team found in the Canadian Rockies this summer.
(PHOTO) JOHN LEHMANN; (FOSSIL) ROYAL ONTARIO MUSEUM
Each new find brings the simple joy of unearthing and imagining
a seemingly alien creature. On a break, Caron cautiously shows off this
year's crown jewel, found about a week earlier. It's an intact,
hand-size carapace with a center spine, like a Prussian spiked helmet
frozen in ancient rock. Another undescribed species, it seems to be
related to the spaceships. Caron's team calls it the mothership.
He's nervous just holding it. Burgess Shale fossils are so valuable
that Parks Canada keeps the exact locations of Caron's sites secret,
monitors them with cameras, and prosecutes fossil poachers. ROM once
insured a Burgess Shale specimen for half a million Canadian dollars
when it went on loan, he says—and that was an animal known through
multiple fossils. This is one of a kind.
"It's going to be iconic," Caron says. "It's the most extraordinary fossil I've ever found."
For years, Caron suspected Walcott's site might be rivaled elsewhere
in the Rocky Mountains. The breakthrough came in 2012, near an area
called Marble Canyon, where a 2003 wildfire had burned off the trees.
While crossing an avalanche chute filled with broken tiles of rock, his
reconnaissance party found itself surrounded by impressions of
soft-bodied creatures, many with unfamiliar shapes. "It was clear that
nobody had ever been walking over this pile of rocks before with this
purpose in mind," says Bob Gaines, a geochemist from Pomona College in
Claremont, California, who has joined Caron's expeditions since the
beginning.
They returned to excavate in 2014. At least one in five of the
animals they found at Marble Canyon belongs to species new to science,
the team concluded. Now, they've moved on to other sites along the
valley.
How Cambrian species are related to today's animals has been debated
since the fossils first came to light. Walcott classified his oddities
within known groups, noting that some Burgess Shale fossils, such as the
brachiopods, persisted after the Cambrian or even into the present. So,
for example, he concluded almost all the creatures resembling today's
arthropods were crustaceans.
But later paleontologists had other ideas. Harvard University's
Stephen Jay Gould perhaps best captured the charisma of Cambrian life in
his 1989 book Wonderful Life: The Burgess Shale and the Nature of History,
in which he lavished attention on the "weird wonders" excavated from
Walcott's city block–size quarry. Gould argued that oddballs such as the
aptly named Hallucigenia, a worm with legs and hard spines,
seem unrelated to later animals. He slotted the unusual forms into their
own phyla and argued that they were evolution's forgotten experiments,
later cast aside by contingencies of fate.
Contemporary paleontologists have settled on yet another way to
understand them. Consider the arthropods, arguably Earth's most
successful animals. In a family tree, the spray of recent branches that
end in living arthropods—spiders, insects, crustaceans—constitutes a
"crown" group. But some animals in the Burgess Shale probably come from
earlier "stems" that branched off before the crown arthropods. These
branches of the tree don't have surviving descendants, like a childless
great-uncle grinning out from a family photo. In that view, many of
Gould's weird wonders are stem group organisms, related to the ancestors
of current creatures although not ancestors themselves. Newer fossils
from the Canadian Rockies help support that view. Caron argued in 2015,
for example, that his specimens of Hallucigenia have features
suggesting the animal belongs on a stem group of the velvet worms,
creatures that still crawl around in tropical forests spitting slime.
All in the family
A partial schematic of a proposed
family tree of arthropods shows the complex relations among living and
extinct groups. Some extinct Cambrian creatures (red) may belong to
"stem" groups that branched off the arthropod tree before the common
ancestor of living groups like arachnids and insects.
(GRAPHIC) N. DESAI/SCIENCE; (DATA) JO WOLFE, MIT
Similar analysis awaits the spaceships. At first glance,
Caron's team thinks they are a new species or group of radiodontans,
stem arthropods that also include Anomalocaris, the Cambrian's
charismatic apex predator—a clawed, fearsome-jawed swimmer half a meter
long. Filling out the branches of that stem group gives a "step-by-step
view of how an arthropod built its body" through evolutionary time, says
paleontologist Allison Daley at the University of Lausanne in
Switzerland.
Throughout much of Cambrian paleontology, that's the game—a
high-stakes, sometimes contentious race to find diagnostic body parts on
known or new fossils, make arguments about what taxonomic groups they
belong to, and maybe revise evolutionary history in the process.
In the past few years, paleontologists have approached the problem
with an array of new techniques. Those include scanning electron
microscopes, which can discern a specimen's chemical makeup as well as
image it, and computerized tomography (CT) scans, which can penetrate
fossils without scraping away material. Those tools have also
illuminated a startling series of internal features: fossilized Cambrian
brains. Beginning in 2011, paleontologist Xiaoya Ma, now at the
University of Exeter in the United Kingdom, published a string of papers
tracing nervous tissue in exceptionally preserved Chinese fossils.
Those nervous system architectures offer a parallel way to sort animals
into evolutionary groups, beyond the usual anatomical structures, and
other teams have presented their own compelling specimens.
In fossils of the shrimplike Chengjiangocaris kunmingensis
from southwest China, for example, "we have this structure that looks
almost like a pearl necklace," running almost head to tail, says Javier
Ortega-Hernández, an incoming professor at Harvard. His team, led by Jie
Yang at Yunnan University in Kunming, China, argued in 2016 that the
necklace is a nerve cord studded with smaller clusters of neurons,
themselves sprouting tiny nerve fibers. Living arthropods no longer have
those fibers. But today's velvet worms and priapulid worms do, implying
kinship between long-vanished stem arthropods and those groups.
Critics argue that paleontologists such as Ma and Ortega-Hernández
overinterpret some fossils, spotting nervous tissues that aren't there.
Many of those structures, the critics say, might just be "halos,"
biofilms formed when microbes broke down internal parts like muscles or
guts after death. But other researchers are convinced. "If you look at
the best-preserved nervous systems, there's no doubt" that the features
are real, says Graham Budd, a paleontologist at Uppsala University in
Sweden and an architect of the current stem-and-crown concept.
Bold claims that use anatomy to revise family trees engender similar controversy throughout the field. One argument that Hallucigenia
fits with the velvet worms, for example, depends on the exact shape of
its claws. But other teams counter that the claws aren't diagnostic of
ancestry.
The uncertainties leave paleontologists ever hungry for newer, better
specimens. "When there is a debate, you bring a new fossil and say,
‘Look, this is the feature we see,’" Caron says, warming up in a tent
perched high above Tokumm Creek. "Without fossils, it's speculation."
Banff
Lake Louise
Bow River
Columbia River
Tokumm Creek
Walcott Quarry
Yoho National Park
Yoko National Park
Banff National Park
Kootenay National Park
0
25
Km
FRANCE
FRANCE
Alberta
British Columbia
Bilbao
Madrid
Marble Canyon
N. DESAI/SCIENCE
The fossils make up for the discomfort: 6 weeks in tents above
the tree line warding off grizzlies with an electrified fence,
contending with hot days and snow days and wildfire smoke, obeying the
smelly requirement to carry everything—everything—out of the national
park at the expedition's end.
It's a chilly August morning, 1 day before a helicopter comes to take
all human traces away. Today is the last chance to stumble on a fossil
that could crack a mystery—say, to find the body that belongs in the
mothership carapace.
The nine-member team hikes from camp to their quarry, up steep,
rock-littered slopes. Ridged trilobite fossils poke out from exposed
layers, but on this expedition, they don't even warrant a second glance.
At the quarry, most people split rock while Caron's grad students help
ROM curator Maryam Akrami pack away the most recent finds in
swimming-pool noodles. "It's the last day," Caron says. "No injuries!"
Each successive excavation in this valley has targeted the same band
of rock, which records a single slice of geologic time. But each dig has
yielded a different array of new species. That's because conditions
varied across the ancient sea floor, favoring different animals. Such
variation is "not a shock to anybody that has ever strapped on a snorkel
and swum around," Gaines says. But this vast, wide-open valley captures
that kind of diversity at a single moment, allowing glimpses of how the
earliest animal ecosystems were structured.
As Caron's quarries bring this moment into ever-sharper focus, other
sites have opened portals on other stages of the Cambrian. Nearly
everywhere, the fossils preserve levels of squishy detail that are
absent in specimens from later in Earth's fossil record. In 2012, Gaines
and colleagues proposed a reason: Perhaps unique chemical conditions
suffused Cambrian seas. After dead animals settled into mud on the sea
floor, low levels of sulfates could have slowed decay by sulfur-loving
bacteria while alkaline chemistry encased the dead animals in coats of
carbonate, sealing soft tissues inside.
In summer 1984, for example, paleontologist Hou Xian-guang of Yunnan
University uncovered an arthropod glistening in Cambrian mudstone, its
legs seemingly alive. He had discovered the Chengjiang biota, a trove of
immaculate fossils that sprawls over a region in southwest China.
Perched in their quarry 2500 meters up, paleontologists hammer open slabs of shale to expose the rare fossils inside.
JOHN LEHMANN
Slightly older than the Burgess Shale—about 518 million years
old compared with the Burgess's roughly 507 million years—those deposits
showcase related animals in a different style of preservation. Unlike
Caron's sites, where geologic processes have squashed the fossils almost
flat, the Chengjiang animals still retain some depth. Since 2015,
Chinese researchers, including Hou, have capitalized on that by using CT
scans to make 3D images of the specimens without destroying them.
Today, three rival Chinese teams, each with international collaborators,
compete to pull out new discoveries from the site. "There is an
absolute landslide of material," Ortega-Hernández says.
Add to that sites such as Emu Bay in Australia, where paleontologists
announced in 2011 that they had unearthed radiodontan fossils revealing
their complex, multifaceted eyes; and Morocco's Fezouata Formation,
which paleontologist Peter Van Roy at Ghent University in Belgium
reported in 2010. Each site offers distinct insights. "Every fossil
assemblage is horrifically biased," says paleontologist Nick Butterfield
of the University of Cambridge in the United Kingdom, "but they're
horrifically biased in different ways."
The Moroccan samples, for example, date to a little after the
Cambrian, and they show a blend between the Cambrian's signature
oddities and the more familiar fauna that dominated later periods. "We
are still at the point of unpacking fossils," says Daley, a collaborator
on that research. "This is a chance to study why some taxa go extinct
and why others are able to replace them."
Although show-stopping animals keep falling out of the strata, the
full significance of the Cambrian explosion remains a mystery.
Arthropods, the most diverse and common creatures known from the time,
littered Cambrian ecosystems. Judging by the fossils, Daley argued in a
paper in May, the Cambrian witnessed both the birth and step-by-step
diversification of many modern groups. Another approach yields a
different answer, however. Geneticists use a tool called molecular
clocks to trace back down the tree of life. By starting with genetic
differences between living animals, which have accrued as a result of
random mutations over the eons, molecular clocks can rewind time to the
point where branches diverged.
According to recent studies using that method, modern animals began
to march off into their separate phyla some 100 million years before the
Cambrian. The finding implies that those groups then hung out,
inconspicuous or unnoticed in the fossil record, before suddenly
stepping on stage.
Paleontologists have a cryptic set of clues about life before the
explosion. Long before the odd beasts of the Cambrian evolved, an even
more alien set of ocean organisms left impressions on sedimentary rocks
now seen in Namibia and Australia. The Ediacarans, as those fossils are
called, taunt paleontologists with the same kind of interpretive
challenge as the Cambrian's weird wonders. But they're even weirder.
Their imprints suggest some grew in fractal patterns; others had
three-part symmetry. Unhelpfully, they don't have obvious mouths, guts,
or appendages. "That's where the freak flags are going now," says Jo
Wolfe, a paleontologist at the Massachusetts Institute of Technology in
Cambridge.
A lace crab—a long-extinct "stem" arthropod called Marrella splendens—turns up in a slab.
(PHOTO) JOHN LEHMANN; (FOSSIL) ROYAL ONTARIO MUSEUM
Most Ediacarans vanished before Cambrian deposits, perhaps
perishing in the world's first mass extinction. But many researchers
suspect some belong on the tree of animal life, perhaps as early stems.
One Ediacaran, Kimberella, looks like an animal: a snail or slug that grazed along the sea floor. In August, Stromatoveris,
a frondlike Cambrian creature already thought to be an animal, was
pegged as an Ediacaran survivor on the basis of its fractal branches.
That would make its Ediacaran relatives animals, too. And in September,
researchers announced that an iconic Ediacaran fossil called Dickinsonia, which looks like a halved Christmas ham, contained lipid molecules that resemble those of living animals.
"We're seeing the beginning of the advent of animals in the
Ediacaran," says paleobiologist Mary Droser of the University of
California, Riverside. "It's more fun and exciting than just the
Cambrian explosion."
And yet even as the Ediacarans shove Cambrian creatures off their
perch as the first animals, Cambrian science itself continues to
explode. Caron and others keep hunting for fossil features that could
reveal the relationships among Ediacaran, Cambrian, and present-day
groups. Other researchers struggle to explain what caused the explosion
of animal forms. Atmospheric oxygen may have spiked, enabling animals to
grow bigger, stronger, and more active. Or erosion could have dumped
toxic calcium into the oceans, prompting organisms to shunt it into
building hard skeletons.
Or biology itself could have led the way. Inventions such as
predation, free swimming, and burrowing into the sea floor—all first
seen in or shortly before the Cambrian—could have transformed a placid
global ecology into a high-stakes contest, spurring waves of
call-and-response innovation between groups. The explosion might also
mark the moment when, after millions of years of quiet progress, animals
had finally accrued the developmental recipes to build body parts and
improvise on basic themes. That genetic toolkit, Butterfield argues, is
"absolutely, astronomically, inconceivably complex. It just took a while
to figure that out." Or, of course, multiple causes could have piled up
together.
After a lunch break, the paleontologists chisel into a few more
slabs. Gaines takes rock samples from each layer of their quarries,
hoping to reconstruct each environment's chemistry. Then Caron delivers
the announcement: "It's over, guys. No more digging."
The next day, its last, the ROM team breaks camp. Over several hours,
a helicopter ferries nets sagging with fossils toward a staging area by
the highway, making the roughly 10-minute trip again and again. Some
specimens, like the spaceships, will be rushed to publication in coming
months, now that visiting journalists have seen them. Other finds will
sit in drawers, awaiting new techniques or the graduate student who asks
the right question.
As the team huddles, waiting for its helicopter ride, tiny,
rabbitlike mammals called pikas cry out from the hills. Each helicopter
trip erases the signs of human presence one by one, until only
carved-out quarries remain. More fossils still rest inside, pressed
between folio sheets of rock, waiting for the next season.
/i.s3.glbimg.com/v1/AUTH_59edd422c0c84a879bd37670ae4f538a/internal_photos/bs/2018/J/a/0pqwBFSuWXfXGZ05N7kQ/102151950-esqueleto1andrstrauss.jpg "Os esqueletos encontrados na Lapa do Santo indicam que os povos que viviam ali eram muito mais complexos do que se imaginava — Foto: André Strauss/Divulgação")
/i.s3.glbimg.com/v1/AUTH_59edd422c0c84a879bd37670ae4f538a/internal_photos/bs/2018/5/J/iHbbTJTI2qsnVdA1vOiw/102152083-tcnicolimpaesqueletoandrestrauss.jpg "A região tem dezenas de sítios arqueológicos que vêm sendo escavados e pesquisados desde 1843 — Foto: André Strauss/Divulgação")
/i.s3.glbimg.com/v1/AUTH_59edd422c0c84a879bd37670ae4f538a/internal_photos/bs/2018/w/C/fBc6P2TaO2k4KBUw6dQg/102152085-pesquisadoresemstioarqueolgico.jpg "As escavações realizadas até agora já revelaram vários aspectos dos grupos, desconhecidos até agora — Foto: André Strauss/Divulgação")
