Welcome, everyone. We're really thrilled to have
you joining us today for another custom -tailored
deep dive into your source material. Yeah, thanks
for tuning in. We have a really fascinating puzzle
to put together today. We really do. So the mission
for this session takes us... Plunging headfirst
into the murky, highly competitive depths of
paleontological history. Right into the deep
end. Exactly. We are setting out to solve an
identity crisis that is literally millions of
years in the making. Yeah. And along the way,
we're looking at how a notoriously crowded ecosystem.
I mean, an ocean packed wall to wall with massive
apex predators somehow managed to avoid collapsing
under the weight of its own biodiversity. It's
a great setup. And the material we are drawing
from to explore this is a comprehensive Wikipedia
article detailing a very specific extinct marine
reptile, a creature known to the scientific community
as Pliosaurus and Druduci. And you obviously
can't see us in the studio right now, but we
are absolutely putting air quotes around that
genus name. Oh, heavily utilizing the air quotes.
quotes today. Okay, let's unpack this. Because
the most glaring detail at the very top of our
source material is that typographical mystery.
The animal's official current scientific name
features quotation marks around the genus. Pleiosaurus
and Drususii. And seeing punctuation like that
in peer -reviewed taxonomy usually signals a
really fascinating historical mess. It's essentially
a taxonomic white flag. In the strict, highly
regulated world of zoological nomenclature, those
quotation marks indicate that the scientific
community knows the current classification is
phylogenetically incorrect. But a formal reassignment
just hasn't been published yet. Exactly. The
story of this particular animal represents a
150 -year -long string of revisions. It all starts
back in the late 1800s, when Charles Leeds first
excavated its fossils from the Oxford Clay Formation
over in England. And the initial naming attempt
was made in 1871 by John Phillips. He examined
a jawbone and a swimming paddle from Leeds' collection,
and he cataloged it as Pleiosaurus grandus. But
he actually included a question mark right there
in the publication. Which tells you a lot about
the confidence level at the time. Right. I mean,
Victorian paleontologists were often working
with... really fragmentary remains, and they
knew they were making highly educated guesses.
The field back then relied heavily on overall
morphological similarities. You know, the general
gestalt of the animal. They didn't have the rigorous
statistical character matrices we use today.
So consequently, the specimen was bounced around
constantly. Just constantly relabeled. Yeah.
In 1889, Richard Lidecker examined the remains
and assigned them to a newly established genus
calling it Pellinistes phylarchus. But his own
assessment didn't even last a full calendar year.
No, it didn't. By 1890, Lidecker noticed the
immense size discrepancy between this specimen
and typical Pellinistes material, which prompted
him to propose a new species entirely. Polonistes
avanci. The nomenclature of this animal was shifting
almost seasonally at that point. And then Charles
William Andrews stepped in a few decades later,
right? In 1913. Yes. Andrews analyzed a secondary,
more complete partial skeleton that Leeds had
recovered. And he noted that the osteological
features of the mandible and the vertebrae deviated
far too significantly from the established Polonistes
baseline. So he theorized it represented a distinct
transitional form. Right. A bridge between Polonistes
and the... Which brings us to the supposed end
of the taxonomic ping pong in 1960. Lambert Beverly
Tarlow published a definitive reassessment declaring
the animal a distinct species within the Pleiosaurus
genus. And he named it Pleiosaurus angiosephi
to honor Andrew's earlier diagnostic work. Tarlow
even designated a specific, highly complete partial
skeleton as the holotype. It had the mandible,
teeth, a full vertebral column, and portions
of the appendicular skeleton. But what's fascinating
here is the methodology of paleontology experienced
a massive paradigm shift between 1960 and the
2010s. The digital revolution, basically. Essentially,
yes. The advent of modern phylogenetic analysis
allowed researchers to input hundreds of specific
osteological characters into computational models.
This generates cliograms based on shared derived
traits, rather than just relying on a scientist
looking at it and making a qualitative visual
assessment. And when paleontologists ran the
matrix for Pliosaurus and Drusii, Tarlow's classification
completely fell apart. It really did. And the
defining features of the teeth were the smoking
gun. Right, because all valid, recognized species
within the true Pliosaurus genus exhibit a highly
distinct dental morphology. Their teeth are trihedral.
Which means the cross -section of a true Pliosaurus
tooth shows a definitive triangular shape. It
has three distinct faces. But the dental array
of our creature is completely conical. Yeah,
the cross -sections are round. It fundamentally
lacks the primary synapomorphy, the shared trait
of the genus it was assigned to. So the phylogenetic
models ultimately placed it outside the pliosaurus
genus entirely. The data shows it is a basal
member of the Thalassophonia clade. These are
the classic short -necked pliosaurs. It sits
much further down the evolutionary tree, wedged
somewhere phylogenetically. Between Polonistes
and Simulastes. Which leaves it in taxonomic
purgatory. It requires an entirely new genus
designation. But until a dedicated paper is published
officially minting that new name, it retains
the old one, quarantined in those quotation marks.
And for you, the listener, I think it serves
as a stellar reminder that scientific knowledge
is inherently iterative. I mean, fossilized bone
doesn't change, but the analytical frameworks
we use to interpret those bones. are constantly
evolving. It demands that we revise old assumptions.
Exactly. So you've established what it isn't.
Let's construct what it actually was. Because
the cranial measurements alone are staggering.
The holotype features a skull measuring a full
meter in length. That's over three feet of jaw.
It utilized a classic pliosoromorph body plan.
If you are familiar with the plesiosoromorph
build, you know, the elongated, highly flexible
necks and diminutive little skulls, you will
recognize this as the complete biomechanical
inversion of that. The pliosoromorphs invested
heavily in cranial capacity. The source material
indicates the cervical vertebral column on this
holotype was exceptionally abbreviated. It measured
only 78 .3 centimeters. So that massive meter
-long skull sat on a remarkably short neck, which
was attached to a robust barrel -shaped torso.
And locomotion was achieved through four massive
hydrofoils, right? Yeah, four huge flippers.
Plesiosaurian underwater flight is a really unique
biomechanical adaptation. They didn't rely on
tail -driven propulsion like ichthyosaurs or
mosasaurs did. And interestingly, in this specific
species, the posterior flippers, the back ones,
were significantly larger than the anterior ones.
They needed to generate immense thrust from the
rear just to propel that massive head through
the water column. Here's where it gets really
interesting. The structural engineering of that
one meter skull presents a massive biomechanical
contradiction. It's one of the weirdest things
about this animal. The mandibular symphysis,
which is the fused front portion of the lower
jaw, held up to 12 pairs of teeth. The mandible
as a whole contained roughly 64 teeth, and the
seventh pair were heavily pronounced. They were
broad caniform fangs, essentially. And the contradiction
lies entirely between the morphology of the snout
and the morphology of those teeth. Walk us through
that. Well, the animal possessed a highly elongated,
attenuated rostrum, a very long, narrow snout.
In aquatic environments, a narrow snout is a
highly specialized adaptation to reduce hydrodynamic
drag. It allows the predator to rapidly snap
its jaws laterally through the water. Exactly.
It is an evolutionary design highly optimized
for capturing small, evasive, agile prey. Like
a modern gharial or a river dolphin. They utilize
that exact same hydrodynamic principle to catch
quick fish. You do not evolve an attenuated rostrum
to grapple with massive, heavily armored macro
predators. No, you'd snap your jaw. But the dental
morphology tells a completely different story.
The teeth are conical, with smooth enamel interrupted
by distinct longitudinal ridges. But most importantly,
their structural geometry is specifically adapted
for cutting. And cutting teeth are required for
processing large prey. You need them for shearing
chunks of flesh from animals that are just too
massive to be swallowed whole. So the snout is
engineered for evasive micro -prey, but the teeth
are engineered for large game processors. That's
completely contradictory. And it's compounded
by the taphonomic evidence. The source material
highlights an extreme degree of dental wear on
the crowns of these teeth. The abrasion extends
considerably further down the tooth shaft than
in any other known representative of the entire
plesiosaurian order. So the mechanical stress
it was subjected to was entirely unique within
its clade. To contextualize why an animal would
evolve such a hyper -specific, contradictory
set of tools, we really have to look at the environment
that was shaping it. We are looking at the middle
Jurassic period, specifically the Calovian stage.
That spans roughly 166 to 164 million years ago.
If we connect this to the bigger picture. The
ecosystem preserved in the Peterborough member
of the Oxford Clay Formation wasn't a pelagic
open ocean environment. It was an epicontinental
sea. Effectively, a flooded continental shelf.
Right. The bathymetry data suggests it was remarkably
shallow, averaging only 30 to 50 meters in depth.
And situated at a paleolatitude of roughly 35
degrees north. The surrounding landmasses experienced
a Mediterranean climate. They had distinct wet
and dry seasons. We even have highly granular
data regarding the marine climate itself. Paleoclimatologists
have analyzed oxygen isotopes preserved within
the fossilized shells of bivalves from this specific
stratigraphic layer. And what did they find?
They determined the water maintained a mild average
temperature of about 15 degrees Celsius. So nearly
60 degrees Fahrenheit. The biomass sustained
within that warm, shallow... 50 -meter -deep
water column is almost difficult to comprehend.
I mean, the benthic zone on the seafloor was
just blanketed with diverse invertebrates, ammonites,
nautiloids, bivalves. And moving up the water
column, you encounter Pachycormid filter feeders
like Leedsichthys. Those were massive. They were
essentially operating as the baleen whales of
the Jurassic ecosystem. And the reptilian diversity
alongside them is staggering. You have Opsalmosaurus
inhabiting these waters. That's an ichthyosaur
featuring these massive sclerotic rings adapted
for extreme deep diving. Which suggests they
likely hunted squid nocturnally or maybe ventured
into deeper adjacent basins off the shelf. The
ecosystem also supported multiple clades of marine
crocodiles. Teleosauroids hunted with their gharial
-like rostra, while metrier hinkids exhibited
extreme marine adaptations. They shed their armor,
their osteoderms, and developed hypocircle tail
flukes like fish. You also have the smaller long
-necked plesiosaurs like Cryptoclytus darting
through the shallows. But the most pressing ecological
issue in the source material, the real anomaly
that demands an explanation, is the presence
of the pliosaurids. The massive apex macro predators.
Yes. The Peterborough member yields a higher
diversity of pliosaurid species than any other
fossil assemblage on the entire planet. Which
introduces a massive problem regarding the competitive
exclusion principle. You have a shallow, geographically
constrained sea that is packed with multiple
species of giant apex predators. And basic ecology
tells us two species competing for the exact
same resources in the exact same environment.
cannot stably coexist. One always outcompetes
the other. This raises an important question
regarding how this immense predator density avoided
immediate ecological collapse. And the stabilization
mechanism here is extreme niche partitioning.
The pliosaurids didn't engage in direct competition
because each species evolved morphological extremes.
Right. They effectively siloed themselves into
highly specific trophic distinctives. Let's actually
break down that resource allocation among these
predators. Let's look at the roommates in this
flat share, starting with the top tier, the predators
hunting other massive marine reptiles. Myopleurodon
phyrox and Erdosaurus occupied that macro predator
niche. Their cranial robusticity and their immense
bite force allowed them to target large plesiosaurs
and massive ichthyosaurs. They claimed the absolute
top of the trophic web. The bruisers. Exactly.
then moving to the hard -shelled prey, the massive
cephalopods and ammonites, populating the water
column. Semelestes vorax exploited that specific
resource. It evolved a remarkably wide, deep
skull, capable of generating the immense crushing
force necessary to shatter dense cephalopod shells.
It was operating essentially as a marine nutcracker.
Which leaves the small, rapid -evation fish.
Peloninistes claimed the agile prey. Its highly
attenuated rostrum and piercing, rather than
crushing or cutting teeth, made it the optimal
pursuit predator for small, evasive targets.
And finally, down to the benthic zone, hunting
directly along the mud. Pachycystosaurus doni
utilized pachyostosis. That's a densification
of the bone structure to provide natural ballast.
Like a diver's weight belt. Exactly. It possessed
a relatively fragile skull, which indicates it
avoided struggling prey. Instead, it used its
dense skeleton to stabilize itself while foraging
along the sea floor. It completely avoided the
pelagic hunting grounds of the larger pliosaurids
above it. So what does this all mean? Well, when
we look at our friend Pleiosaurus and Drusii,
in air quotes, its contradictory anatomy suddenly
makes perfect sense. It was substantially larger
than the fish -snatching Pelonistes, and it retained
a similarly elongated snout for hydrodynamic
speed. Yet it possessed cutting teeth and exhibited
extreme dental wear. It was exploiting a very
narrow trophic margin. It was capable of processing
prey that was too large or heavily armored for
Pelonistes to handle. But its hydrodynamic snout
allowed it to capture agile prey that the massive,
bulky Liopleurodon could never catch. It essentially
threaded the needle between two separate apex
niches. And the lesson here for you, the listener,
isn't some forced business metaphor about finding
your market niche. It is a profound realization
about evolutionary biology. Life's capacity for
morphological plasticity means biodiversity isn't
strictly limited by the physical volume of an
environment. It's limited by biomechanical ingenuity.
Nature can pack a half dozen apes. The deep dive
into this one creature ultimately serves as a
masterclass in synthesis. It demonstrates how
phylogenetic modeling corrects the assumptions
of 19th century taxonomy. And how analyzing the
biomechanics of a single mandible can map the
trophic structure of an entire vanished ecosystem.
It underscores that the fossil record isn't just
a catalog of dead animals. It is a complex, interactive
puzzle of biomechanics and paleoclimatology.
It really is. But before we wrap up this session,
there is one final detail from the source material
regarding the fate of this perfectly tuned ecosystem.
Despite their incredible morphological plasticity
and their flawless niche partitioning, these
long -snouted, fish -eating pliosaurs experienced
an abrupt extinction at the boundary between
the Middle and Upper Jurassic periods. It marked
the beginning of a gradual, sustained decline
in overall plesiosaurian diversity globally.
And the paleontological consensus suggests their
demise wasn't driven by biological competition.
They weren't out -hunted or out -maneuvered by
some new apex predator. No, their extinction
was driven... by shifting ocean chemistry and
rapidly fluctuating sea levels. The very environment
they had perfectly adapted to simply ceased to
exist. It leaves you with a fascinating dynamic
to consider moving forward. How does a highly
specialized apex predator, a creature perfectly
engineered to exploit a hyperspecific margin
of its ecosystem, survive when the fundamental
chemistry of its world turns against it? It is
a sobering perspective on the limits of specialization.
It really is. Thank you so much for joining us
for this deep dive into the source material.
Keep analyzing the data, keep questioning the
consensus, and we will catch you on the next
one.