The unusual prehistoric herbivore Lalieudorhynchus is thought to have been the Permian Period’s
equivalent of a hippopotamus, although its ecology is currently a source of controversy.
Despite its reptilian appearance, Lalieudorhynchus was a synapsid, making it a closer, if still
distant, relative of mammals. Only named in 2022, it remains fairly obscure, to the extent that
this is one of the few life reconstructions of this long dead proto-mammal. Fortunately,
its close relatives, like Cotylorhynchus, are much better known. Named caseids, they are famous for
their massive bodies and disproportionally tiny heads. Caseids were pelycosaurs,
the term used for basal synapsids who still looked very much like reptiles. Although pelycosaurs
like Dimetrodon had been abundant during the Early Permian, the more mammal-like therapsids
had almost entirely replaced them by the Middle Permian. Lalieudorhynchus is the youngest member
of Caseidae, and might very well have been the last pelycosaur. It lived during either
the late Wordian or early Capitanian, roughly two hundred and sixty-four million years ago.
It was once thought a group of synapsids called the varanopids outlasted them. However,
in recent years, the synapsid identify of the varanopids has come under doubt, and
they instead seem to have been actual reptiles. The only known Lalieudorhynchus skeleton is from
the La Lieude Formation in France, which is the source of part of Lalieudorhynchus’s name. The
other half, “rhynchus”, means “nose”, even though Lalieudorhynchus’s skull hasn’t yet been found.
It was chosen because it is the suffix of Cotylorhynchus, a close relative of
Lalieudorhynchus and perhaps the most famous caseid. The species name “gandi” is in honor
of paleontologist Georges Gand, who helped organize the expeditions which unearthed the
Lalieudorhynchus holotype. It was first found in 2001, but wasn’t fully excavated until 2008.
Preparing the fossils took years, and Lalieudorhynchus was only described in 2022.
Altogether, the holotype consists of about fifty bones. Although much
of the skeleton remains missing, these bones are exceptionally well preserved.
The Lalieudorhynchus holotype is estimated to come from an animal that was 3.75 meters long when it
died. The skeleton has a mixture of mature and immature traits, so it is thought to have been
a subadult or late-stage juvenile. However, it is possible the holotype specimen was an adult,
since some semi-aquatic animals like spinosaurid dinosaurs retained juvenile characteristics into
adulthood. Although most of its skeleton remains missing, enough of Lalieudorhynchus has been
found to confirm its anatomy was similar to derived caseids like Cotylorhynchus.
As a side note, early members of Caseidae like Eocasea differed substantially from
Lalieudorhynchus, and were instead small, lizard-like insectivores.
The term “caseid” in this video mostly refers to the larger, more derived herbivores,
since there is no term for these creatures that also excludes the more basal forms.
Caseid rib cages were massive. They expanded over their evolution, presumably to accommodate
massive intestines. Herbivores with such huge guts are adapted to ingest huge quantities of
low-quality plant matter. To carry these massive bodies, caseids evolved robust forelimbs.
It has been proposed caseids may have also used these impressive limbs in intraspecies battles,
to protect themselves from predators, or to uncover roots.
Their toes were short and broad, particularly in the case of Lalieudorhynchus. Unlike therapsids,
caseid limbs remained firmly in a lizard-like sprawling posture. Combined with their weight,
Lalieudorhynchus and other caseids would not have been able to move quickly when on land.
The only major part of caseid anatomy that is not preserved in the Lalieudorhynchus holotype is the
skull. However, since the rest of the body is the same as derived caseids like Cotylorhynchus,
it almost certainly shared their unusually tiny skulls. It is not yet clear why caseid heads
were so small, but this shape would have hampered their ability to forage from ground level plants.
Their teeth were tall and rounded, with cuspules at the ends. The number of cuspules varies between
different species, so without a skull it is unclear how many Lalieudorhynchus had.
In addition to these teeth, caseids also had teeth on their palates and lower jaws. Besides being
an uncomfortable sight for Cenozoic mammals, they were also useful for efficiently grinding up food.
The caseids’s massive tongue, whose size is inferred from their enlarged hyoid apparatus,
are thought to have pressed plant matter against them until the food was ready to be swallowed.
Similar teeth evolved in the sail-backed edaphosaurids, who were also herbivorous
Permian pelycosaurs. Although they been regarded as terrestrial animals for over a century,
some paleontologists now think that the large, herbivorous caseids were semi-aquatic animals.
Lalieudorhynchus is not unique in this regard, but it has the strongest of the supposed aquatic
adaptations. One of the primary forms of evidence for amphibious caseids is their bone histology.
Their bones lack distinct medulla or growth rings and are very spongy,
particularly in Lalieudorhynchus. These traits are found in some aquatic animals,
although as will be explained later on, there are serious concerns regarding these conclusions.
Besides their bone histology, caseids seem to have been uniquely challenged when it came to foraging
in a terrestrial environment. The long necks of the later sauropod dinosaurs allowed them to
forage vast distances while expending very little energy moving. In contrast, the short necks of the
large caseids meant their necks had a much more restricted range of movement than those of modern
grazers. They would have had to partially immerse themselves in the water to even drink. Foraging
on land would require them to move constantly, which would have been energetically expensive.
Furthermore, caseids like Lalieudorhynchus were specialized towards a diet of hard to digest
plants. They would have needed to consume a lot of food to make up for its low quality,
and the arid environment of the time meant there wouldn’t have been that much food available.
The amount of energy expended for each meager bite may have simply been unsustainable.
On the other hand, forging in the water would have been energetically less expensive and
this environment may have offered a richer food supply. They may have even been able to use their
forelimbs to move plants into the reach of their mouths. Not all paleontologists agree that the
caseids were semi-aquatic. One of the criticisms of this hypothesis is their low bone density.
Semi-aquatic animals typically have very dense bones, which allows them to sink under the water.
Aquatic animals with spongy bones instead live in the open ocean, and have evolved them as a result
of prioritizing speed and maneuverability. These words do apply to caseids under any circumstances.
Spongy bone has a variety of other uses that doesn’t imply an amphibious lifestyle. Of note,
it can be used as a weight saving measure, which would have been very helpful for these
plump synapsids. The authors of the paper which named Lalieudorhynchus suggested something a bit
different from the prior hypothesis. Rather than being a specialized swimmer, the paper suggested
that, much like today’s hippos, Lalieudorhynchus was more of a bottom-walker. Its broad toes
would have been well suited for this, although the authors still believe that it would have
been a better swimmer than its mammalian counterparts given its paddle-like feet.
Although hippopotamuses are semi-aquatic, they primarily consume terrestrial plants near the
shore rather than water plants and algae. Given the presence of terrestrial plants close to the
Lalieudorhynchus skeleton, the authors suggested the same for it, although Lalieudorhynchus doesn’t
seem to have been any better at foraging on land than other caseids. The authors did caution that
aquatic flora is less likely to be preserved, so it remains possible that it primarily fed in the
water. However, there are still some problems with Lalieudorhynchus’s proposed ecology.
Hippos have dense bones likes most other semi-aquatic tetrapods, which helps them sink to
the bottom of rivers and lakes. Lalieudorhynchus’s spongier bones may have compromised its ability to
do the same. Additionally, if Lalieudorhynchus was semi-aquatic, its preferred habitat may
have not existed for much of the year. Two hundred and sixty-four million years ago,
Lalieudorhynchus’s home in southern France was at the equator of the increasing arid Permian world.
The climate had distinct wet and dry seasons, and many bodies of water repeatably dried up
each year. A counterargument is that hippopotamus fossils have been found from arid and seasonally
arid paleoenvironments, even though they are predominantly aquatic creatures. Some caseids may
have likewise died in environments different from where they typically lived. On the other hand,
other paleontologists have noted that caseids like Cotylorhynchus seem to be consistently found
in seasonally dry environments unsuitable for the proposed semi-aquatic lifestyle.
However, the Lalieudorhynchus holotype was found alongside the fossils of an aquatic tupilakosaurid
amphibian, a creature whose survival was dependent on the presence of large bodies of water.
An amphibious population of Lalieudorhynchus would have also needed less suitable habitat than
an equally large population of hippos. Like most other mammals, hippopotamuses are endotherms, who
spend most of their energy maintaining their body temperature. As some of the most basal synapsids,
caseids never developed a high metabolism, meaning they needed a lot less food to survive.
While Lalieudorhynchus’s low metabolism may help to counter one criticism of the semi-aquatic
hypothesis, it creates another. Hippos spend most of the day in the water to avoid overheating.
In contrast, as an ectotherm, Lalieudorhynchus was reliant on the external environment to stay
warm and active. With its large, rotund body, Lalieudorhynchus was still vulnerable enough
to overheating to benefit from the opportunity to cool down in the water, but it would have
struggled to remain active at night. Even if it was semi-aquatic, Lalieudorhynchus’s ecology
may have been less hippo-like, with it primarily feeding upon aquatic plants while coming ashore
to bask in the sun. However, assuming it did forage on land, the changing world of the
Middle Perriman would have given Lalieudorhynchus a very good reason to adopt a hippo-like strategy,
but in reverse: foraging on land during the day while resting at night. During the Early Permian,
the top predators were ectotherms who would have been as lethargic during the night as their
potential victims. The therapsids which replaced them did not have this weakness. Most pelycosaurs
would have been nearly defenseless against such foes, and unlike most modern ectotherms,
they were too large to hide during the night, potentially explaining their disappearance.
However, an inverted hippo-like lifestyle would have given Caseidae a fighting chance.
If attacked during the day, they would have had enough energy to either whack then with
their giant forelimbs or escape into the safety of the nearby water. The caseids could stay in
their aquatic sanctuaries during the night, when they would have otherwise lacked the energy to
properly defend themselves. Lalieudorhynchus may have been better suited for spending its resting
hours in the water than hippos. A hippopotamus must surface to breath at least every six minutes.
As an ectotherm, Lalieudorhynchus’s oxygen supply could have lasted much longer.
Of course, the herbivorous caseids may instead survived by focusing on consuming aquatic flora,
which they seem to have been adapted for anyway.
Overall, a lot remains to be learned about how Lalieudorhynchus lived. However, the
traditional model of terrestrial caseids doesn’t seem very plausible anymore, and Lalieudorhynchus
at least seems to have been better suited for an aquatic, hippo-like ecology than its relatives.
A phylogenetic analysis in the paper that described Lalieudorhynchus found it, along
with the caseid Alierasaurus, to be nested within the genus Cotylorhynchus. Of the three species of
Cotylorhynchus, Lalieudorhynchus was found to be most closely related to Cotylorhynchus hancocki.
Notably, although the last of the caseids are found exclusively in Europe,
Cotylorhynchus was native to North America. Much like Lalieudorhynchus’s lifestyle,
the paper’s conclusions regarding caseid taxonomy have not seen universal acceptance.
Since the phylogenetic tree found Lalieudorhynchus to be nested within Cotylorhynchus, the authors
concluded that the three species of Cotylorhynchus should be split up into separate genera.
This seems to be based on the idea that a genus should be monophyletic, when it would make more
sense to simply consider Lalieudorhynchus a descendent of the Cotylorhynchus genus.
Paleontologist Dr. Christian Kammerer, an expert of Permian synapsids, considered splitting up the
Cotylorhynchus genus to be unnecessary. He also said that Lalieudorhynchus should be considered
a new species of Cotylorhynchus instead of its own distinct genus. If this opinion wins out,
then in the future Lalieudorhynchus gandi will be called Cotylorhynchus gandi.
As perhaps the last caseid, and possibly even the last pelycosaur, the extinction of
Lalieudorhynchus is of particular interest. It, or its as of yet undiscovered descendants, may have
been victims of the end Capitanian extinction, which marked the end of the Middle Permian. This
was a major extinction event that, as the name implies, transpired at the end of the Capitanian
age, about two hundred and fifty-nine million years ago. Although its cause and scope are still
debated, it is generally thought to have been at least partially the result of volcanic activity,
much like the later and more devastating Great Dying at the end of the Permian Period.
There is a gap of several million years between Lalieudorhynchus and the end of the Capitanian
age, but the last caseids seem to have been restricted to Europe, which would make it easy
for their fossils to have so far eluded science. Instead of falling victim to a global extinction,
Lalieudorhynchus may have instead died out due to being unable to keep up in the evolutionary arms
race with the new therapsid carnivores. During the Middle Perriman, predatory dinocephalians called
anteosaurs became well suited towards pursing prey into the water. As anteosaurs grew in size,
Lalieudorhynchus would have eventually found the water was no longer the refuge it once was.
Another possibility is that the remaining caseids may have instead have outcompeted by new
herbivores called pareiasaurs. These armored plant eaters appeared just after Lalieudorhynchus, and
their teeth were similar to those of herbivorous caseids, implying they ate the same plants.
Pareiasaurs were reptiles, but had semi-erect limbs and elevated metabolic rates like the
contemporary therapsids. This may have given them an edge over Lalieudorhynchus. Of course,
instead of being responsible for their demise, the pareiasaurs may have opportunistically replaced
the caseids after they succumbed to something else. Either way, although they had a presumably
similar diet to the caseids, pareiasaurs do not seem to have been hippo analogues.
An isotopic analysis of pareiasaurs and other local Permian fauna found they were primarily
terrestrial animals, while it was herbivorous species of dinocephalians who spent more time in
the water. If such a study could be conducted on Lalieudorhynchus or other closely related caseids,
it could help to clear up much of the current confusion surrounding them. At least for now,
a lot of questions remain regarding this bizarre pelycosaur. Was it semi-aquatic or terrestrial?
If it was amphibious, did it primarily consume aquatic or terrestrial plants?
If the latter, how did Lalieudorhynchus manage to efficiently eat them with its short neck?
Besides its lifestyle, there is also debate as to whether Lalieudorhynchus is a valid genus
or simply a new species of Cotylorhynchus. In spite of all the uncertainty regarding this
potentially hippo-like caseid, Lalieudorhynchus is certainly an important part of the history
of the Permian Period. It was the last known member of the first stage of synapsid evolution.
It also provides a lesson regarding evolution as whole. What is often regarded as more “advanced”
is not always strictly better. Although mammals and birds dominate a variety of niches today,
ectothermic reptiles continue to thrive by filling others. Likewise, the last of the pelycosaurs in
the therapsid dominated world were not their closest relatives, who were more like them,
but instead some of the most basal synapsids, and arguably the goofiest among them.
Thank you for watching, and a thank you to the themattalorian for narrating this video.
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