Hello. Good evening. My name is Diana Munn. I'm Director of Public
Programs at the Harvard Museum of Science and Culture. It's my pleasure to welcome you
to tonight's Evolution Matters Lecture, sponsored
by the Harvard Museum of Natural History. We are delighted to
have Professor Javier Ortega-Hernández
with us tonight, who will discuss some of the
earliest known organisms from the Cambrian period and
their role in the evolution of animals. I would like to take a
moment to recognize Drs. Herman and Joan Suit for
their generous sponsorship of this lecture series. They have sponsored The
Evolution Matters Lecture Series for the past 10 years. And it is their support that
allows us to present and record these lectures. It is now my
pleasure to introduce James Hanken,
Professor of Biology, Curator of Herpetology,
Alexander Agassiz Professor of
Sociology and Director of the Museum of
Comparative Zoology at Harvard University who
will introduce our speaker. Thank you, Diana. I want to welcome
all of you as well to joining us this evening. I look forward to the
lecture as much as you do. Now before I
introduce our speaker, I've been asked to
introduce my background, and then we'll
move on from there. I'm speaking to you from
Arlington, Virginia. And as many of
you may have read, one of the unexpected
consequences or side effects of the
COVID-19 pandemic, following the lack of
activity in our cities is that a lot of wildlife
returned to places where they hadn't been very
conspicuous in a long time. And that was the
case in our house here in Arlington, where
a pair of black vultures set up shop in the attic of our
garage in our home in April. And what were four birds
eventually became-- excuse me, what started out
as two birds about a month ago became four birds. And you see those four birds
in the photo behind me. That's a picture I took just
yesterday on our back porch. They've become quite fond of
us, especially once we started feeding them raw
chicken for breakfast every morning in the backyard. Anyway, that's my
that's my social life, or our social life for
the last few months. And I hope you don't
mind looking at them. Now on to our speaker
for this evening. Javier Ortega-Hernández is a
invertebrate paleontologist who is interested in the evolution
of major groups of animals. Not living animals so much like
the vultures you see behind me, but animals that evolved
right at the dawn of animal evolution. Now to do this, to study
organisms like this, you have to work in typically in
what's called the Paleozoic era and especially focused on events
such as the Cambrian explosion and the so-called Great
Ordovician Biodiversification Event which I suspect
Javier will be talking to us about a lot this evening. Now Javier is originally
from Mexico City, where he received an
undergraduate degree in biology from the Universidad
Nacional Autónoma de México. In 2008, he moved
across the big pond over to the United
Kingdom, where he completed a master's
degree in palaeobiology at the University of Bristol. He then stayed in England. He moved over to the
University of Cambridge, where he completed a PhD
in Earth Sciences in 2013. But then stayed on
another five years when he was offered
a very prestigious postdoctoral research fellowship
called the Herchel Smith Postdoctoral Research Fellowship
in Biological Sciences, also at Cambridge. He joined Harvard in 2019
as an Assistant Professor in the Department of Organismic
and Evolutionary Biology. And at the same time, a curator,
or the curator, of invertebrate paleontology in the Museum
of Comparative Zoology, where I'm director. And it's been a
pleasure to have Javier with us these last couple of
years, together with Stephanie Pearce, our curator of
vertebrate paleontology, who joined the faculty
and the museum only a few years
before Javier did. The two of them have invigorated
the study of paleobiology at Harvard. And they've both been a
wonderful addition to MCZ. Now, as you'll see,
or I suspect you'll see from tonight's
lecture, Javier is quite a
well-rounded scientist. He combines the study of
newly collected fossils that he gets himself during
field work with laboratory investigations that use some
very modern techniques to see things in fossils quite
literally that people haven't been able to see
until a few years ago. So without any further
ado, let's hear what Javier has to say. Javier? Thank you so much, Jim. That was a lovely introduction. I appreciate it and
thank you so much, Diana. It is a real
pleasure to be here. And I am super happy to be able
to talk to all of you today. This is going to be,
I hope, a fun lecture. And can I just check
that everything looks OK on everyone's slide? Cool. OK. So let's get started. So today we want to talk about
Wonderful Cambrian Beasts. But before I do that, I
want to wish all of you a Happy National Fossil Day. Many of you may know,
there is a National Fossil Day in the United
States, and it is celebrated on the second
Wednesday of October. And this particular year, the
artwork for National Fossil Day is this Permian Reefs at
Guadalupe and Glass Mountains in Texas and New Mexico. So it is very
special for me to be able to share this particularly
paleontological day with all of you. And I hope that you will enjoy
the lecture going forward. So as Jim mentioned, I am an
invertebrate paleobiologist. And I specialize on the Cambrian
Explosion and all the events that surround it and
particularly all the animals associated with it. As many people interested
in the Cambrian Explosion, I came to this line of work
through reading Wonderful Life by Steve Jay Gould,
who was the curator of invertebrate paleontology a
few years before myself, also from Harvard. And here we have a
picture of him in 1987. Now Steve Gould became
very influential, even though he didn't actually
work directly on the Cambrian itself, because he did this very
in depth exploration of what all of this study that was
being produced around the '70s and '80s regarding
the Cambrian Explosion animals from the Burgess
Shale and what they meant. And him being kind of
famous for his writing, he did combine a
lot of hyperbole and a little bit of
pop culture in trying to make some of his
writings more accessible, but also to try to make a
point about the importance of these organisms from an
evolutionary point of view. And this is just
something I want to show, one of my favorite paragraphs
from Wonderful Life. Which is where he
sort of emphasizes that many of these
animals in the Cambrian are what we now know very sort
of informally as weird wonders. So in this particular
case, he's talking about what defines the success
of some groups of animals over others. And specifically,
he argues, well, if we extend this
theme, being, again, the difficulties in regarding
what makes an animal be successful or not, beyond the
arthropods to the weird wonders of the Burgess Shale,
we want to ask ourselves why not Opabinia and
Wiwaxia are survivors. Why don't we have a world of
grazing marine herbivores, with sclerites and
not snail shells? Why not anomalocaris, a
very famous common animal, and the world of marine
predators with grasping limbs with a jaw like a nutcracker? And he goes on to say, why don't
we have now a Steven Spielberg movie that features
an anomalocaris that would chomp on a
crusty kind of sailor instead of having a shark? And this is just
a wonderful sort of exploration of what
could have been if history would have taken another route. However, what is
interesting here is that Gould gets
a lot of recognition for writing Wonderful Life. However, it was actually a
fundamentally collaborative effort. Because, of course, Gould
provided the narrative. But one of the reasons Wonderful
Life became so influential was because it really
did bring to life many of these Cambrian, weird
animals for the first time. And that was thanks to the
wonderful illustrations by illustrator Marianne Collins. So a lot of the figures I'm
going to show you right now are Marianne's work. And it was really
instrumental because it helped to bridge this gap
between what is really a very technical, scientific
illustration with a much more lifelike organism that we
can much easily relate to. And this is the only
time I have met Marianne. This was in 2009. And we're standing
in the Walcott Quarry in British Columbia with
[INAUDIBLE] mountain just at my back. So this was a very special
moment for me a few years ago. And it's something that,
again, I want to emphasize. That Marianne did have a
truly impactful contribution to the way that we see the
Cambrian explosion right now. So as I mentioned before,
these are a whole bunch of Cambrian weird wonders,
as we would very informally call them. And this includes forms that are
really difficult, traditionally speaking, to link with
extant diversity nowadays. They are weird and have strange
shapes and peculiar ecologies. And they're just kind of
difficult to figure out. And, again, because we have
these wonderful illustrations, we have a much
better sense of what these look like as animals. So now we jump in
time, and then we can have a lot more research,
a lot more technology forming what life was
like in the Cambrian. And this is just a wonderful
example of a 3D reconstruction, produced by our colleagues
at the Royal Ontario Museum, that shows what the Burgess
Shale environment would have looked like. Again, this marine ecosystem,
full of strange animals that we don't see
around anymore and that are nevertheless still
sparking our imagination. Of course, we have anomalocaris
doing a victory lap after eating a trilobite. So this is what we think about
when we think of the Cambrian explosion nowadays. However, all of this is possible
because of the availability of diverse and very
abundant fossils of non-shelly complex
animals in what we call exceptional deposits. These are sites, again,
like the Burgess Shale and a few more I'm going
to mention in this talk. And what is really
remarkable here is that all of these organisms
are fundamentally soft and fundamentally prone to decay
under normal circumstances. In most of the fossil
record, we will see shells and bones and teeth. But only under the most
special circumstances, we will actually get a
lot of this diversity. So it makes it that this
study of these deposits is actually very important,
because it allows us to have this unique
window into life that we would otherwise never be
able to see and appreciate. And the best part is
that we can actually find these sort of deposits
all around the world. Of course, one of
the more famous ones is the Burgess Shale,
which is Middle Cambrian in British Columbia in
the Canadian Rockies. And, again, we
have Walcott Quarry on the left with [INAUDIBLE]
mountain on the back. And Burgess Shale
fossils are pretty flat. I mean, they are super pancaked. And that makes it so that
they have some difficulties in studying them. But nevertheless,
they still remain some of the best
preserved fossils that anyone can ever see
because of the amount of morphological
detail that they have. However, also we
have a whole bunch of other localities
around the world. One that myself and several
people in my research group are investigating working
on, including [INAUDIBLE] are fossils from
the Western USA, particularly in the area we
call the House range, which housed at least half a dozen
of exceptional [INAUDIBLE] fossils. These may not have the
beautiful, amazing detailed preservation of
the Burgess Shale, but they are
nevertheless providing a much greater geographical
area over which we can find these fossils. And we find very
different organisms that we don't really see
in the Burgess Shale. So it really complements
our view of Cambrian life much more effectively. And of course, that doesn't
stay in North America. We can also go to North
Greenland with the Sirius Passet. We can go to South
Australia in Emu Bay Shale. We can go to several
parts of China. In this particular case,
with the Qinjiang biota. And we have, again, this
very consistent record during the Cambrian in that
we have some sites which are just truly exceptional. And they preserve all
of these weird wonders, these strange animals, sometimes
in great numbers as well. So they are an amazing,
invaluable resource for us to really understand how the
early biosphere came to be and basically how complex life
started which, again, I think has a fundamental intrinsic
value for us to know where everything that is
surrounding us looks like, where does it come from,
and why the biosphere looks the way it does. Now one of the
great complications of working with the Cambrian
Explosion and these kind of organisms and
something that became sort of infamous in his
book, Wonderful Life is, again, emphasizing
the difficulties of linking directly, in an
evolutionary relationship, all of these weird oddballs from the
Cambrian with the biodiversity that we see today. Because we are living
in the present. Of course, we have a
much better understanding of what biodiversity looks
like, works like, feels like, and smells like nowadays. So we can do all
sorts of fancy studies on them, including
molecular biology. And you can dissect
the whole thing. With the Cambrian, that
is not so much possible. We only have the
morphology and maybe a little bit of
chemical information. So it really is difficult
to be able to say, well, are all of these
Cambrian oddballs a whole different thing? Are they these so-called failed
evolutionary experiments? Are they just different
kingdoms or phyla that didn't go anywhere? Or are they something else? And one of the things
I do quite often, and a lot of the people
in our research do, is that we strive to
find the connections that allow us to understand
Cambrian forms in the context of the extant biosphere. So with that in mind, I'm
going to show you a few case studies, which are a
combination of an old classic from the Burgess Shale with
a little bit of a twist. And on the second
half of the talk, I will show some of the
more current research that we are doing to
understand what this Cambrian organisms are and how they can
inform the evolution of life on Earth. So this is important. Because we know that all of
the major groups of animals, or most of the major
groups of animals started in the
Cambrian, or at least have a record in the Cambrian. So being able to tie, again,
all of this extant diversity with all of these wacky
fossils is super useful. Because then one can
inform the other one. So, again, this is
just part of the reason why we spend a lot of our time
and lose some nights of sleep thinking about
flattened fossils that may look really great
in the centerpiece, but they are actually much
more important than that. And they do provide
this, again, invaluable source of information. So with that being
said, the first thing I want to talk about
is this quirky story of Hallucigenia sparsa. Now Hallucigenia's a classic. This has been going on
for a few years now. And it is probably one of
the most famous animals from the Cambrian. And the reason for
that is because it has this kind of really
fun history behind it. So Hallucigenia was
originally found by Charles Doolittle Walcott at
the start of the last century. And it was initially sort
of shoehorned, classified as some sort of worm. When it was revived in the '70s
by colleagues at Cambridge, particularly by
Simon Conway Morris, it was interpreted in this
particular orientation. And, well, as you
can probably tell, it's pretty difficult
to say what it is. It's kind of all over the place. It has some spikes. It has what appears
to be some tentacles. It looks a bit like a
sausage in the middle. It's not super
obvious what it is. So based on this
initial description, Simon produced this, again, now
quite notorious reconstruction and suggested this
name Hallucigenia, because this looks
like a hallucination. So this is one of those
organisms that Gould really drove home that it's so
different and so surreal that it just cannot have any links
with anything living anymore, or anything living today. However, when we look
a little bit closer, we start to find some
characters that actually allow us to link it with
some groups that make a little bit more sense. And just before we
go further, I also want to emphasize
that in the '70s, there was absolutely no
context for interpreting many of these fossils. So it's usually fun to say,
like, oh, well, how silly. People got it wrong. But, again, in the '70s, there
was nothing to compare it to. So any interpretation was
as good as the next one. Some years pass. And then in 1992, someone
had a good measure-- and not someone, Lars
Ramskold, had in good measure to actually take
a dentist's drill and actually prepare
some of the fossils to try to reveal some of the
features hidden within the rock itself. And what he did
is that he started to follow some of these
tentacle-like things on the lower half of the animal. And he discovered claws. This became quite useful. Because during the
'80s and early '90s, a lot of fossils from the
Chengjiang biota in China were discovered. And there was this group of
animals called the lobopodians, which are basically worms with
legs, that started to be found. So this allowed
people to realize, or it allowed Lars Ramskold
to realize, like, well, Hallucigenia is not some
sort of weird thing. It's actually lobopodian. And it was possible to make a
correct side of reconstruction, where now we interpret
this animal as having these dorsal or these
armor spines on the back, having these pairs of legs
with claws at the underside, having a more or less
featureless head, and then doing its own thing. It's still pretty weird. And if we were going
to stop it at that, it would still be
difficult to argue, well, this is clearly related to
anything living around today. So a few years ago, a colleague
of mine, Martin Smith, who is a professor at
Durham University in the UK, we decided to take another
look at Hallucigenia and, specifically, to
use some new techniques to interpret its morphology
or to analyze its morphology. So one of the features
of Hallucigenia, now illustrated on
the right way up, is that it has these
very prominent spines, as I mentioned
before, and it also has these very prominent claws. And you may be able
to see, there's a small hook-like projection
which are very, very dark on the underside. And they look very
dark because they are preserved as carbon films. So the carbon looks-- it's dark. It has been graffitized
because of the way that the Burgess
Shale is formed. And because it's
made of carbon, it is actually possible to analyze
it under an electron microscope to see some of these details. And what you have
here is a really find single claw Hallucigenia. What becomes very obvious
is that, in addition to having this very
distinctive sickle shape, it also has a number of
features inside of it. So we were able to identify up
to three constituent elements. Which, in this
case, you can think of about stacked ice
cream cones, just one inside of the other one. So this was quite fun. But also really
remarkable, because after doing quite a bit of
research on the literature, we only found one
group of animals nowadays that has claws,
that looks like a worm, and has this overall
constitution, and that also has claws with
this particular organization. And the answer is the velvet
worms, or onychophorans. Velvet worms some
of you may know, because they are extremely cute,
as you can probably appreciate. And they are very
small-- well, they're reasonably small invertebrates. They are restricted to
tropical environments. They are exclusively
terrestrial. And even though they look
a bit like caterpillars, they are not insects whatsoever. They are their own thing. They have a very ancient
history and they're just kind of really fun little animals. They [INAUDIBLE]
tail using papillae on their mouth to capture prey. And what was, again,
quite significant is that we were able to find the
link that connects Hallucigenia with onychophorans. So if we see the claws in
the legs of onychophorans and the jaws inside
their mouth, they have this very similar structure
that we see in Hallucigenia. So on the left side, we
have this lovely 3D image of an onychophoran leg, which
has two claws on the tip. And then, on the bottom,
we have a small video of another onychophoran kind of
showing its jaw on the mouth. And what you can
see on the right is just a dissected
version of that. And, again, we have this
very distinctive sort of [INAUDIBLE] claw or
[INAUDIBLE] construction, both in the claws
and in the jaws. The jaws in this case are
a modified set of legs. So it does make sense like
it has the same organization. So because we can find
this complex feature in both of these
animals, we can actually tie Hallucigenia with
the onychophorans. And by default, we
can say something about the early history of
onychophorans themselves, which otherwise have a
very meager fossil record. They only are known from
very few amber deposits and only one decent
carboniferous micro fossil, but it still doesn't
have a lot of detail. So this is telling us that
at least some relatives of onychophorans,
even though they are very distant relatives,
do extend to the Cambrian Explosion. And this is implying
that onychophorans, throughout their history, had
to lose these defensive spines and had to evolve this
internal jaws for feeding, maybe associated with a
terrestrial environment. Again, this is really strange. Because Hallucigenia's marine. And onychophorans are
the only major group of animals that has no aquatic
representatives nowadays. What was really fun about
this is that, well, I mean, that is great for Hallucigenia. But Hallucigenia
actually has a lot of relatives in the Cambrian. And some of the weirdest
animals that you will ever see. And when we published
this a few years ago, you'll notice,
like, when we called it Hallucigenia on steroids. Because it certainly is. It's much bigger. It's much spikier and leggier
and hairier and everything. So in this case, we
have this animal, which is called Collinsium ciliosum. And this is from the
early Cambrian Xiaoshibo biota in South China. So this is an organism that
we worked with our colleagues in Yunnan University
a few years ago. And what you will
notice is that, well, it is also a lobopodian. However, it does have
some other features. It has this very
strong dorsal armature of spines, which are super big. And it has way more
than Hallucigenia. But very prominently,
the legs on the front have these almost tentacular
and feathery-like appearance. They have all of these
setae on the sides that make it look like a
feather, which is super weird. This is a reconstruction
of this animal, and I swear that
every single thing you see in this reconstruction,
you can see on the fossils. This has no artistic
license whatsoever. Every single hair and
leg and claw and spine, you can see in this fossil. So as you can appreciate, this
is, again, like Hallucigenia, but a little bit hyper. It has much more spines. It has these very
peculiar limbs. And it is very
interesting to think why. It is also interesting that
this is not the only one. There's a lot of them. This is another
representative, an animal called Acinocricus stichus from
the Spence Shale in the USA. And this animal was originally
interpreted as a green alga. But then, after the
discovery of some of these other
lobopodians, now we know it is also one of these
very peculiar Hallucigenians. And this one is
particularly metal, because it has rings of
spikes all the way through. This is by far the
thorniest worm that you will find in the Cambrian. More recently, we
have some research by our colleagues in the
UK, by Richard Howard and Xianguang Hou. And this is a redescription
of this organism called Facivermis yunnanicus,
also from the Chengjiang. Now Facivermis is also
related to these animals. And we can tell
it because it has this wormlike body and these
very distinctive feather limbs. But you will notice it has
no spines, unlike [INAUDIBLE] and unlike Collinsium
or Hallucigenia. It is one of these
suspension fitting worms that has become naked and has lost
the legs on its rear side and only has this sort
of pear-shaped bulb. So it is thought that
this animal was actually living sort of like
buried in the sediment and then just kind of did
this movement with its arms to filter feed. And then we have
yet another one, also from the Burgess Shale,
Ovatiovermis cribratus, also described by our
colleagues in Royal Ontario Museum in Toronto. And, again, it is similar to
all of these animals as well. It has no spines. It does have claws on its bum. But it also has these kind
of weird, feathery tentacles. And our colleagues
were so kind to produce this wonderful, animated
reconstruction that illustrates how it is thought
that all of these animals fed. These animals are
collectively known as luolishaniids, which is the
clade that we're talking about. And the idea is that they would
use all of these feathery limbs to sort of, like, hug the water
and basically bring together either small animals or a
little bit of organic matter into their mouths. And you may be
thinking, yeah, right. I mean, this looks like
a complete stretch. But what is really cool
is that this actually happens still today. And you may not appreciate in
which animals it does happen. So here we have a
video of a hermit crab. But the hermit crab has a
cirrhipede, or a barnacle, associated with it,
just kind of attached, which is this kind
of cone-like thing that has this feathery
[INAUDIBLE] things sticking out. Now barnacles are
crustaceans, which are very heavily modified. And they basically swim
around, stick themselves through their head to something. And then form a shell
and start to filter feed. So what we have here
is an arthropod, which is sort of closely related
to the lobopodians, doing exactly the
same thing that we think these weird Cambrian
animals are doing. What happens here is that
this is just an arthropod. And lobopodians are a different
part of the tree of life. But we see fundamentally
the same strategy. So it is not so strange
anymore to think about some of these legged worms doing
basically the same thing, just in a slightly, probably
much slower pace. Because, again,
barnacles are quite tiny. So they can do these
movements much quicker. So what this is telling us
is that these luolishaniids are reflecting great diversity. They are extremely specialized
suspension feeding worm like marine animals. And they had this
global distribution. So they are just a
wonderfully weird group that is doing something
back in the Cambrian. And nevertheless, again,
they share so many characters with hallucegenia. So we have to think, well,
clearly these animals are also related to hallucegenia and
are also related by default with onychophorans. And what really kind
that springs to mind is, well, what happened? Why did onychophora sort of
lose all of these accoutrements? I mean, they were so cool
back in the Cambrian. And now they're cute. They're definitely less
versatile than they once were. And what you see on the left
is a pretty good representation of extant onychophorans. And as you can appreciate,
they are very colorful. And they're adorable. But they are very same. They are a very homogeneous
group of animals. So they did lose a lot
of this complex ecology that they had back
in the Cambrian. So if we put this into
more quantitative terms, we can say that
onychophorans basically became much less variable
throughout their evolution, compared to what
happens in the Cambrian. Again, this graph is showing
that Cambrian representatives occupy a much greater
degree of morphus base, or ecological diversification,
compared to the representatives that we see nowadays. So the take home message
from this part of the talk is that hallucegenia and its kin
do reveal this rich and complex evolutionary history
for onychophorans during the Cambrian explosion. And if it were not because
of these exceptional fossils, we would have no idea
that this happened. Because, again, onychophorans
are really soft and squishy, mushy animals. We had someone
onychophorans in the lab. We didn't look after
them super well. And they turned into snot. They disappeared. There were not even
carcasses left behind. So that gives us a good
idea of how difficult it is for these animals to be
represented in the rock record. And it emphasizes
again the importance of being able to have access
to these particular deposits. Now, a quick kind of
midway information. The next thing I'm going
to talk about deals more with our current
ongoing research. And this is going
to be interactive. So what I want you to do
is to grab your phone. I'm going to assume
that most of you will have a phone
accessible to you. And you will see, in the next
few slides, a number of QR codes, like this
QR code that you see in your lower left corner. Now if you use your phone,
you open your camera app, and you point it
towards the screen, your camera will
recognize this QR code as it does a face, more or less. When prompted, you
will be asked to open a link that is going to lead you
to a website called Sketchfad. And you will be able to
actually see and interact with the models I'm going
to show you in this talk directly at the tip
of your fingers. A little similar to
this representation in the lower right. So again, I invite
you all to do this. It's quite fun. I will still show the
figures in the talk. And all of these links will
be accessible for people after the talk, as
well, in case you don't have a phone next to you. With all that being
said, let's get started. So one of the big complications
of working with Cambrian organisms is that, again,
they are superflat, for the most part. And we have to think about
it a little bit hard. Because, at the end of
the day, these are small invertebrate animals. They have become
buried by thousands of tons of mud and sediment
when they were buried. And then this sediment
has become liquefied, has become rock. Then it is gone into the
Earth's crust a little bit and has experienced all
of these intense tectonic and geological pressures. So it is understandable
that these fossils are less than pristine. So it would be great to be able
to maybe see a little bit more, a little bit more
than meets the eye. And this is what we have strived
to do with some new methods. So what I'm showing you here
is a flyby across a fossil from the Cambrian, from the
early Cambrian Chengjiang biota. So what we have been developing
in close collaboration with our colleagues in Yunnan
University in South China is the use of
computer tomography to be able to understand the
3D morphology of these very flattened, but not completely
2D fossils for the first time. And to be able to
basically observe what is going on inside of the rock. Like the dark side of
the moon, if you may. This part that we would never be
able to see with our eyes alone but that we can get to
using X-ray technology. We can do this because
the fossils themselves are enriched in iron. The iron is a different density
compared to the rock itself. It's a little bit
similar to the way that we see ourselves in X-rays. Our bones are much
denser than our flesh. So we can see, for
example, right about now, you will start to see the fossil
as this very bright white spot at the top of the image. So that is what we look for. And we are then
able to reconstruct into a 3D model that
allows us to understand the morphology of these
animals in amazing detail. So let me show you some
cool fossils again. In this particular case,
we have been working with a few arthropods lately. And this has been useful
for a number of reasons. One of them is that
this technique allows us to re-study animals that were
very poorly known that either are extremely rare or animals
that are super well known and that we still can find
some new features-- to say, we can find some new
features in them. And that is going
to give us, again, that little extra
information to understand them a little bit better. The first one I
want to talk about is this organism called
ercaicunia multinodosa, which was described in 1999. So a little bit
over 20 years ago. And as you can appreciate
from this drawing, this is as it was
originally described. Granted, it is not the
most detailed drawing. And it was a different
time, 20 years ago. But there it is. So again, you can use a QR
code to scan this fossil and check it out in
your mobile device. And again, just to
emphasize the point, ercaicunia is a
reasonably rare animal. It is not the rarest. But it is not super
abundant, which is part of the reason
it was sort of ignored for a long time. However, in the
last few years, we were able to start
this collaboration with our colleagues in China. A colleague of mine, Joanna Gold
and myself went to South China, to Kunming to Yunnan University
to do this collaboration. And we were able to essentially
again get an amazing glimpse into the hidden morphology
of this animal that would not be possible based
on its fossil alone. Again, on the left side, we
have how the fossil looks, which is OK. I mean, it's not the best. But it's not horrible. But then on the right
side, what we have is this tomographic
virtual model. This is what we get when we
actually process the data and we are able to study the
other side of the material. And this is what you will be
seeing in the tomographic model in Sketchfad, as well. If we take a closer
look, ercaicunia is full to the brim with lovely
morphology, amazing detail, and really informative features. So we were able to identify
that the antenna have this very sort of complex
flattened CT, which look a little bit
similar to some features that we see in
crustaceans nowadays, which are used for sensing
both by touching and chemical sensation. We were able to find a number
of additional limbs on the head. So for example, this
feature in green is actually a secondary antenna. We were able to see mandible
and another mouthparts. And we were also able
to see the trunk limbs in really exceptional detail. And the trunk limbs is where
ercaicunia absolutely shines. Because it's possible to
actually dissect them out individually because all
of this is done virtually. And one of the things that you
will notice is that it is flat, but it is still pretty
three-dimensional. So what you're seeing on
the right and the left side is a model of the
middle of the body. It's the trunk. And this has not
been modified by us. This is as flat
as the animal is. Now, it is a tiny specimen. So, for our size, it is
essentially two dimensional. But when we look
close enough, you can see that there
is a little bit of three dimensionality in it. And that is quite valuable. Because it allows us to
have a much better idea of the spatial organization
of all of these different features. Now, on the right side, what we
have is one dissected biramous limb of ercaicunia. And this is where it becomes
a really interesting story. Because we can
identify the components of the limb in great detail. We have the green part,
which is basically what we call the endpod
or the walking leg. We have the blue bit,
which is the exopod, which has something like a gill
or a respiratory structure. And then, we found
another feature that we don't usually see
in many of these organisms. And that is this feature
called the epipodites. Now, the epipodite looks a bit
like a teardrop shaped lobe. And it may not look like much. But it is actually
super significant. Because epipodites
are features that have a respiratory and also
more regulatory function. And as far as we know,
from extant arthropods, they are only ever
found in crustaceans. In this case, we have some
lovely electronoscopy images of branchiopod
larvae, or juveniles, that are showing the
limbs developing. And what you can see,
again, is this kind of leafy teardrop
shaped lobes basically at the shoulder of
the limb, if you may. If my arm was a
limb, they are just kind of sticking out over here. And again, this is something
we see in several groups of crustaceans nowadays. And we don't see them
in any other group. We do not see them in insects. We do not see them in myriapods. We do not see them
in [INAUDIBLE].. So being able to find
this complex feature, again, is telling us something
significant about ercaicunia. And in particular, this
is super important. Because it is going to
produce this direct link between ercaicunia and
crustaceans nowadays. There is a lot of people doing
kind of really interesting work on molecular clock
analysis and phylogeny, trying to understand what is the
precise timing for the origin of all of these
groups of animals. And many studies
suggest that crustaceans did originate in the Cambrian. This particular case,
this is true for decapods. But again, there is
some uncertainty there. And they may have at
least [INAUDIBLE],, maybe Cambrian origin. But decapods are one of
the groups of crustaceans that you have epipodites. So again, being able to find
this feature in ercaicunia is really giving us this very
strong signal that, not only do we have the epipodites,
we have the head structure and the trunk appendages. So all of these features come
together to tell us ercaicunia is very likely related
to crustaceans. And this, again, comes
in nice agreement with these molecular
clock estimates. And it is always
wonderful to have agreement between
different sources of data. Be it molecular, morphological,
or developmental. When we have all the data
telling the same story, this is very powerful. Because it does help strengthen
the argument a lot more. So it just makes for a much
more robust hypothesis. The second animal I want to tell
you about today with these 3D methods is this organism
called cambrorastor. And you might think,
oh, cambrorastor is this shrimpy looking
thing, of which there are two in this lab. But you would be wrong. Cambrorastor is actually
that little smirk of orange on the lower left
side that looks like not much. But I swear it's actually
super interesting. And this is, again, a
really useful demonstration of how micro CT can bring
up some details in fossils which are again poorly
preserved or super rare. And you cannot get more
rare than cambrorastor, which is known from
these only specimen. So this is what
cambrorastor looks like. And admittedly, micro
CT didn't actually reveal the amazing
details on the under side that we were hoping for. But it did help us to have
a much better view of what the outline of this
animal looks like and have a much better idea
of the original complexity. As you can tell, both
from the light photograph and from the micro
CT model, there are a lot of compaction
wrinkles associated with this. And this happens when we have
a very complex structure. Think about it like
a bowl or a helmet. And this gets flat. And that flattening, we
have lines of weakness that are going to just kind of-- because of the
compression, they're going to be expressed
in the fossil. So this is telling us
that this animal in life was quite voluminous
in its shape. Now, even though we do not have
a lot of limb information-- we only have this one
piece of exoskeleton-- we know for sure
it is cambrorastor. because there was some really
amazing research published last year, which
actually described the first cambrorastor species,
cambrorastor [INAUDIBLE] from the Burgess Shale. And some of you who might
subscribe to Science may remember this journal
cover from a few years ago. So what we have
on the lower right is this lovely 3D model of
cambrorastor from the Burgess Shale. And this shows how we
understand its morphology. So the fossil I showed
you before is basically the head, the shield
of this animal that has this very
peculiar shape that is hosting the animal underneath. And the animal itself is what
we would call a radiodont. This is an animal related
to animal [INAUDIBLE],, which is, again, very
famous and well known. But it is a little
bit different. It has its frontal appendages,
which, in this case, have these kind of long spines. And we will discuss that
in a bit more detail. And what's also really fun
is that, again, similar to the luolishaniids,
there are several instances of cambrorastor since
its discovery last year. So on the upper right, we have
Jean-Bernard Caron, the creator of invertebrate
paleontology at the ROM, holding this very large fossil
that, as my understanding, is affectionately known
as the mothership. Because it certainly looks
a bit like a spaceship. And that is another
relative of cambrorastor. It may be a different species
or a different genus altogether. But the shape of this
head is unmistakable. So we are able to make this
link directly because again, the preservation
of this organism and the use of computer
tomography quite effectively. Now what is really interesting
is, when we put cambrorastor into a larger context, as I
mentioned before, cambrorastor was first known from
the Burgess Shale, which is this red star, in the
middle Cambrian, which is approximately 580
million years old. And our new cambrorastor is
from from the early Cambrian of China, Chengjiang,
which is approximately 10 million years older. So 518. Now, one of the
things that they share is having this very distinctive
horseshoe shaped outline. And they are not alone
in this distinction. Horseshoe shaped outlines
are also known in trilobites, like the one in the upper right,
in this [INAUDIBLE] trilobite. But also it is the namesake
of this animal in the lower left in panel C, which is
the horseshoe crab, which is neither a horseshoe nor crab. It's actually a chelicerid. It is more related to arachnids. But the point here
being is that we have these animals
that are belonging to very different parts
of the tree of life. And all of them have this very
peculiar horseshoe shaped head. And we have to ask ourselves,
well, why are they doing that? Why it is so advantageous to
have a horseshoe shaped head? And this comes to
demonstrate one of the more interesting
aspects of radiodont evolution in the Cambrian in that they are
amazingly ecologically diverse. So radiodonts come in
all sorts of sizes. They go from the cambrorastor
size, which is super tiny-- the fossil is just around
a centimeter long-- and we go all the
way to the size of adriochasis,
which is actually an Ordovician radiodont
from Morocco, which can be essentially two meters long. Like, the actual specimens. And they are very difficult to
carry in the field, of course. And everything in between. But there is not only
the size differential. There is also the
ecology difference. And basically, radiodonts
come in three main flavors. They can either be filter
feeders in that they have these very elongated bodies. And they have these frontal
limbs that they use for, again, swimming in
the water column and eating, basically
filtering the water as it goes. We have raptorial predators,
like anomalocaris, which is again the more famous one. And they have more of the stubby
frontal appendages with spines. So they would just kind
of go and eat animals, either soft bodied or maybe
a bit lightly shelled. And then we have the
sediment sifters, as it is the case
of cambrorastor. And these sediment
sifters would actually swim very close to the
bottom of the sea floor. And they would use their
limbs to basically rake up the sediment and capture any
animals or small organisms living there and
then consume them. So this is quite interesting. Because what I'm essentially
trying to explain is that, back in
the Cambrian, we have this group of
arthropod relatives, which are essentially behaving
on one end of the spectrum like basking sharks or Baleen
whales, in that they are quite large animals swimming
in the water column and filling their mouth
with filtered water to get all the tiny animals out. But then, on the same
group of Cambrian animals, we also have the whole
other end of the spectrum. We have these very
distinctive horseshoe shaped organisms that
are living very close to the bottom of the ocean or
at the bottom of the ocean, just basically again
sweeping the Cambrian sea floor looking for food. And all of these belong
to the same group. So we have this, again,
amazing ecological diversity within a single
group of organisms. So the take home
message here is that, even though we only know this
animal cambrorastor in China from a single specimen-- and
a single not great specimen-- we can still tell a lot about
how this group diversified and how they live. And it demonstrates
that, very early on during the evolution
of radiodonts, they had already
basically explored either most or all of
the ecological options available to them that we will
see much later in the Cambrian, as well, which is,
again, quite exciting. Now, the last thing I will
talk about rather briefly is this animal called
leanchoilia illecebrosa. And what I like to say
at this point of the talk is that, if there is just one
QR code that you want to scan, it's this one. Because this animal
came out absolutely beautifully in the scan. So it is really worth
your time if, again, you are into this sort of thing. Now, one of the things with
leanchoilia illecebrosa, also from the Chengjiang,
is that it is actually very well known. Leanchoilia has been,
this particular taxon is known from
hundreds of specimens. There are at least half a
dozen publications that deal with its morphology,
ontogeny, ecology. So it is really one of those
animals that we would think, well, why even bother? We know everything there is
to know about this organism. So let's put it in a drawer. Let's move on to the next one. But again, one of
the beauties of using this approach of micro
CT to Chengjiang fossils is that it still can
provide some surprises, even in specimens which are species
that are so well known. And in this particular case, one
of the stunning controversies with leanchoilia and other
animals related to it, called [INAUDIBLE],, is, where
do they go in the tree of life? Now, what we see
on the left is yet another of these great videos
by the ROM website showing the leanchoilia superlata. It is a close relative
from the Burgess Shale. But it basically has
the same bits and bobs. It's this animal that looks
a bit like a woodlouse. But it lives in the oceans. And they have this very
distinctive, very, very big what we call great appendages
that, in this case, look like whippy
things on the front. Now, the origin of
these great appendages has been super debated
and really, really, really controversial. And the reason for
that is that, depending on where they go or depending
on the interpretations of where these animals go in
the tree of life, we have to make entirely
different reconstructions of the evolution of arthropods. So we have a vested
interest in kind of straightening the record
and being able to say where actually these animals go. And the two main
interpretations are, well, either they are related to
arthropods but distantly. Or there may be closer
relatives to chelicerids. And all of that
basically depends on how we interpret
the origin in the head of this pair of limbs. And that can be very
difficult to assess. Because we do not have, again,
developmental information or embryonic information. And we only have
so many fossils. And they're usually flat. And it's difficult
to identify them. So again, micro
CT to the rescue. So, in this particular
study, we were able to actually scan small
juveniles of these leanchoilia animals. And the one kind of doing
the video on the left side is a seven millimeter
long juvenile larva. Now, you will see that
again it has wonderfully preserved morphology. You can see every single
limb, every single tiny spine on the limbs. It is just fantastic. And again, because this
is a virtual model, we can actually modify
and remove certain parts if we want to take a closer look
at some parts of the anatomy. And what we have is that we
can see the mouth in, again, completely unprecedented
detail for this kind of fossil. What we have here is
leanchoilia showing that there is a
mouth opening, which is what you see in panel D with
an narrow, which is basically just a hole. But then, associated
with the mouth, we have this structure
called the labrum. Now, the labrum is
a flaplike feature in the mouth of all
arthropods nowadays. And whether this was present
or not in leanchoilia was actually extremely debated. Finding it allows us to
actually make some correlations with the mouth of older
kinds of arthropods. So, for example,
in panel D, you can see the mouth
region of a spider, of a developing
spider, of an embryo. And in panel E, you can
see that of a cricket. So based on this
information, we were able to tell that this animal
leanchoilia does have a labrum. And the labrum is
quite reduced compared to what we see in the cricket. So this is supporting
the interpretation that leanchoilia really has a
labrum which is quite reduced. It helps us to clarify were
these great appendages come from, which would be from the
second segment of the head. And it provides additional
support for the interpretation that this animal is closely
related to chelicerids. It is not a chelicerid. It is not a spider at all. But it is more, it is closer
to that particular evolutionary line than to any other
line, as far as we can tell. And again, this kind
of comes together quite nicely with
data from morphology from the nervous system
in some other specimens. So this is basically
my last slide. But what I hope to have
achieved in this talk is to give you a sense of
how much we do not know and how much these amazing
fossils from the Cambrian can tell us. And just simply how
amazing they are. Because they truly
are fantastic. This, what I'm
showing right now, is an ongoing work by one of
our local Illustrators, Holly Sullivan, that is working
with us in the MCC to produce some of these
wonderful reconstructions to bring these animals to life. Similar to the one
I have behind me. And this is basically a
middle Cambrian environment from the Marjum Formation
in the House Range of Utah. It is one of those
deposits that have started to get more attention
lately, particularly-- not exclusively-- but particularly
because of the research we do in our group. And, again, we were
able to reconstruct yet another one of these
fascinating deposits in so much greater detail than
ever possible before. So this is always
a work in progress. And there is just so much
more to come and so much work to be done. So hopefully we will
have a lot of Cambrian for many, many years
still ahead of us. With all that being said, I
just want to thank all of you for joining me today on
this National Fossil Day, to thank all the
wonderful people that make up the lab for Invertebrate
Paleontology at Harvard. And all of which contribute in
their own way to this research and to basically our collective
experience and expertise. So with all that
being said, I am very happy to answer any questions. And thank you so much
again for your time. Javier, thank you so much
for a wonderful presentation. First, let me ask if you
can close your presentation. I don't know if that's possible. Yep. Ah, very good. Let's say we have several-- actually, what I'd
like to do is not pay attention to the
questions so I can just play with the Sketchfad
graphics that I've downloaded onto my iPad. But I'll take a few
minutes away from that to moderate the questions. So we have several
outstanding questions submitted by several people. Let's kind of set this
up like a TV game show. We have some questions
which are real softballs. They should be very
easy for you to answer. And then they go in
degree of difficulty. So let's start with
first from George. He asks, was anomalocaris a
predator or filter feeder? Anomalocaris would fall
within the predator category. That being said, there are
many species of anomalocaris. And some of them have
been misinterpreted when they were first described. So, for example, there is one
called anomalocaris briggsi, which, even though
it is currently classified as anomalocaris,
it will very likely change classification. Because it is an
actual filter feeder. But the correct
anomalocaris is definitely on the predatory side. OK. Let's try another
hopefully short one. We've got a lot of
questions to answer here. So what kind of
animal was wiwaxia? Wiwaxia is currently regarded
as being very likely a close relative of either mollusks
or annelids, or the group that joins both of them together,
which are collectively known as spiralians. Wiwaxia had a muscular foot,
a little bit like a snail. And it also has this kind
of really intense armor of little platelets,
which are not shelly. They are more hardened,
like a nut shell. And they do have
the mouthparts that look very similar to the
mouth parts of a snail. So if anyone has ever
bought, for example, those little aquatic snails that
you can get and have as pets, and they go and stick
basically on the plastic, you can see how
they're scraping. Something very similar
is going on with wiwaxia. So it is definitely on
that part of the tree. But it is also a
particularly difficult animal to work with because
it's so squashed. And it has so much morphology. It can be very difficult
to tease it apart and have a clear look at what's going on. Thank you. Now here's a very
interesting general question, which I suspect a lot of people
are interested in the answer. This comes from Michael. Wonderful Life was
published 31 years ago. In view of all the more
recent developments, is it still a
valuable book to read? And if not, what
book do you recommend for non-paleontologists? That's a great question. I still read Wonderful
Life because I think it's a wonderful book. It's great. But let's increase
our vocabulary here. It is a great time capsule of
how evolutionary thinking was during the 90s. And indeed, I use it as part
of a course I teach in Harvard. Because it helps to
make the point of how our understanding of these
animals has changed and matured and how context is so
important for understanding this kind of data. Because paleontology
has a peculiarity that it has a very strong
historical component to it. So understanding what
people said before and why can be as useful as
making the analysis. So just for that, I think it's
still very worthwhile reading. It is just a fun
thing to read, too. In terms of other books
that you can consult for more up to date
perspective, there is a book called The Cambrian
Explosion by Doug Irwin and Jim Valentine. I think it was published either
last year or two years ago. And that one does provide a
much more modern view of what these animals are
and their diversity and how we interpret them. OK. Thank you. Now, let's see. Let's do this one here. This is your 100 point question. Spiders do not have
by biramous limbs. But early in
development, they do have a second axis on
their embryonic legs called nathandites. Are crustaceans'
epipodites homologous to chelicerid nathandites? Wow. That is a great question. So actually, when I
showed the figure, that one was showing one
of those nathandites. And now, the difference
is that spiders, early in their
evolutionary history-- so they're related to
horseshoe crabs, which do have these spines
which would be homologous to the nathandite. The difference is that
all of these projections originate in different
parts of the limb. The epipodites-- So again, if you have
my arm, the epipodites come out on the
dorsal, on the back, on the dorsal side like this. Because they have to be
external for water contact. The endites, which
are spines usually-- not usually-- always
on the ventral side, have a fitting function. So they have to be
closer to the midline because the mouth
faces backwards. So they have to produce
this medial foot group. So they will actually
be on this orientation because they are used for
chomping down on food. So what do you see
on the spider is, to some extent, a vestigial
feature or hangover from these earlier ancestry. Because spiders
nowadays have shifted all of their feeding
functions to their fangs, their chelicera on the front. But if you see arachnids
or spider relatives from the Paleozoic,
some of them do still have some of these spines
on their more proximal parts of the limb. So they're not
homologous to epipodites. But they are rather a vestigial
part of their feeding apparatus that is not present anymore in
adult extant representatives. OK. Thank you. Now, here's a good one. This is more speculative,
so you get the 100 points. The more speculative
general question from Abel. What caused the
Cambrian explosion? I could sit here for
10 hours and still not have a definitive answer. And it is a fantastic question. But it's also
incredibly complicated to answer because, the
more we research into it, the more confounding
factors there are. Some people suggest
that there were environmental triggers that
caused the Cambrian explosion. Like, for example,
there is a correlation of increased oxygen in
the environment close to the Cambrian explosion. There is evidence of
strong tectonics happening before that would have
input a lot of nutrients into the ocean waters. That could have caused
the Cambrian explosion. There are events known
as snowball earth, which are global glaciations just
before the current explosion. There are even
supernovas, polar wonders happening before the explosion. So it is very difficult to say,
oh clearly, any of those alone is the result. Other people
argue that the Cambrian explosion was basically a
result of the increasing ecological complexity of the
organisms that were already there that just happened
to reach a critical mass. And then boom, everything just
went sort of super accelerated in terms of competition. Before the Cambrian,
in the [INAUDIBLE],, we do have evidence
for microscopic life. But yeah, I mean
the precise reason why we see animals
at the Cambrian is still a little bit elusive. It has also been
suggested that it may be that the Cambrian wasn't
very conducive to preservation because of the changes in
the seawater chemistry. And what we see as the
Cambrian explosion is more of an explosion of fossils,
rather than an explosion of animals themselves. But again, the true
answer probably lies in a combination of all
of these different factors. So again, there is
no one golden ticket for the Cambrian explosion. It's more of a
multitude of events coming together to produce this
period in the history of life. OK. Here's actually a
question that follows up the idea of
preservation, from Craig. Is there a chance of finding
an unsquashed version of any of these critters someday? I suppose it depends how much
are you happy to settle for. At present, what I
have shown is as close as we can possibly get to being
able to take these fossils out virtually from the rock as
unsquashed as they can be, considering that there are
still reasonably flattened. But these are microfossils. So these are large fossils that
we can see with our own eyes. During the Cambrian, there are
other modes of preservation that do fossilize very,
very tiny organisms in 3D. Like, in complete 3D. And this is a process
called phosphorization. So they basically become
kind of replicated by phosphate, by sulfur
released from bacteria. And in those cases, we have
amazingly 3D preservation. But they're tiny. So you need to have an
electron microscope to see them in any meaningful detail. And they also have
a number of issues. They provide
amazing information. But we do not know if they are
the adults or the juveniles. Or they're are just so immature
that we cannot really tell that much about some aspects
of their phylogeny. So with exceptional
preservation, it's always a trade off. Either we have
something awesome and we suffer in some other way. So it is very useful,
for that reason, to investigate the
fossil record from as many different
perspectives as possible. Because we can put all of this
together and say something much more complete than
the sum of the parts alone. Here's just a
technical question. Someone who's asking you to
repeat the name of the book by Doug Irwin and
James Valentine. So the book is called
The Cambrian Explosion. The Cambrian Explosion? Yes. My understanding is that there
will be a follow up email with [INAUDIBLE]
of this lecture. So we can include a link
to that book in that email, as well, for all of those
that are interested. Great. OK. Let's see. We've got some more. Are you game to do a few
more questions, Javier? Oh, absolutely. Yes. OK. What has been done recently
in the past year in terms of research on the
Chengjiang biota? The new one? Not Chengjiang? The Quingjiang? Q-U-I-N-G-J-I-A-N-G. So it's difficult to tell. Because of the current
situation we live in, I would imagine that
my colleagues have not been able to go to the field
as they normally would. So I would imagine that field
work has stopped significantly for the time being. However, there are tons
of material existing at the moment at Northwest
University in Quingjiang. And I know that there are some
of these projects ongoing. I am involved in a few of them. But again, things have
slowed a little bit because of the disruptions around. But I can definitely assure
that there are a lot of fossils. And Quingjiang is very peculiar. Because it does preserve animals
that we don't usually see, even in exceptional deposits. Like cone jellies, or jellyfish. So truly stuff that [INAUDIBLE]. And yet, our
colleagues have them in pretty healthy
numbers in Quingjiang. So it is going to really
become one of the deposits to attract more attention in
the following years to come. Great. Here are two, I think,
related questions. One from Fabrizio. How do you think the Cambrian
feeding habits evolved? Did the carnivorous habit come
first, then suspension feeders? I guess it depends on what
organism we are talking about. If we're talking
chronologically, let's go chicken and egg. I would say-- well, I would
say it's a fact that suspension feeding came first. Because sponges are
extremely powerful suspension feeders in
the oceans nowadays. They are animals. They do not have kind of
complex bells and whistles. But basically, all they
do is sit and filter feed or suspension feed
nonstop, all the time, all day, every single day to the
extent that they are basically a major ocean pump. So definitely suspension
feeding came first in animals. It depends, when we look at
specific groups of animals, whether predation is more of an
ancestral feature or suspension feeding is more of
a direct feature. I imagine this may be more
geared towards the radiodonts. And I would argue
that, for radiodonts, I think that maybe predation
may have come out first. Because we have some
relatives of radiodonts that are a little bit
different and similar enough. And they do have
more of the grabby, stubby frontal appendages than
the suspension feeding ones. But again, it will be very
dependent on the group of organisms we're
talking about. OK. Thank you. This next question, I think,
also follows on to that. It's related. Very general, but it applies
to what you just said. How are convergent
traits distinguished from inherited from a
common ancestor? So that is another
excellent question. And it is difficult.
The more data we have, the better informed
hypotheses we can make to make to
establish this distinction. The problem is that
we are constantly struggling with this point
in the fossil record. Simply because we only
have morphology to go with. Right? So if we see two things that
look very similar, well, is this similarity a
result of convergence or a result of inheritance? In the case of cambrorastor
that I talked about, we have this very distinctive
horseshoe shaped headshield. Now we can be pretty
confident that that is a result of
convergent evolution because we have other parts of
the animal in the Burgess Shale specimens that show that this
is definitely a radiodont. It has the frontal appendages. It has the circular mouth. It has the body flaps. And it is not a
horseshoe crab, which has legs and has gills and
has other parts and other bits and pieces. So the more data we
put into the equation, the easier it is for us to say
whether something is convergent or not. In other cases, when
we have uncertainties or simply we do not
have enough information to be able to make
this distinction, it is very difficult to
tell or even impossible. Because both hypotheses
may be as equally valued. OK? So to give you another
example, one may argue or-- Javier, I'm going to ask
you to actually stop there. Because we want to get another
two questions in before we have to shut
down for the night. As you say, you
could go on for hours about some of these things. So just two more
questions-- and I want to apologize for those
people who submitted questions that we weren't able to
answer through the talk. So the first one, from Mark. Instead of looking
forward from the Cambrian, have you also looked
back and attempted to make evolutionary connections
to any ediacaran fauna? Great question. I have not done this myself. Because I am quite
specialized and have a lot of work still to do with the
arthropods and their relatives. But other colleagues
have actually been much more
involved in doing this. For example, a colleague
called Jennifer [INAUDIBLE] has been able to identify
links between Cambrian fossils in Chengjiang and
some of the [INAUDIBLE] from around the world. And so, it is being done. Just not by myself at present. OK. This will be the last question. Again, thank you again, Javier,
for a wonderful presentation. Thank you, audience, for
some great questions. From Jayden. Seeing all this
diversity so early in Earth's history makes me
think, how fast can nature fill in a niche? It's cool seeing, just in one
branch of life, filter feeders, predators, and bottom
feeders all at once. Do you think these niches
were filled earlier, and anomalocaris and others
outcompeted previous animals? Or did the Cambrian explosion
initiate most of it? So just for a bit of
context there, actually the Cambrian explosion
comes in really late in the history of the Earth. For most of the Earth's life,
most of the Earth's history, life is unicellular
and mostly prokaryotic. There is even this
period of time called the boring billion
because, again, we have tiny things. And not a lot goes on
in terms of fossils. So the Cambrian explosion
is actually much later event, which means that actually
having complex ecologies is something really
difficult to achieve. And it takes a lot of
time, a lot of evolution to accumulate, to be able to
interact with the environment in this particular way. In the case of the radiodonts
or the anomalocaris, actually what happens is that
some of the work by people in the lab, like Stephen Bates,
is suggesting that actually anomalocaris, the predators,
were outcompeted by the filter feeders, based on the
distribution of fossils we see in the upper Cambrian
and even in the Ordovician. But again, this is more
interesting research to come out that will
clarify this question. Well, you did a
wonderful job, Javier, both in your presentation
and in fielding all of these questions. So thanks very much to
you for giving this talk. We look forward to hearing a
sequel sometime in the future. And thank you all again at home
for joining us this evening. Have a good night. Bye bye. Thank you for watching.
