Long before current whales made it fashionable, Triassic-era marine
reptiles were filtering minute foodstuffs from vast volumes of water,
according to new fossils discovered in China.
Researchers from China and the UK analyzed the skulls of two recently
discovered specimens of Hupehsuchus nanchangensis and found features that
allowed the creatures to sweep up vast volumes of water to sift out food, a
method known as
filter feeding.
Although this is how
baleen whales today feed,
Hupehsuchus, a species of prehistoric marine reptiles that measured one meter (three
feet) long and were closely related to
ichthyosaurs, may have discovered it as much as 250 million years ago.
Lead author of the study and paleontologist Zichen Fang from the Wuhan
Center of China Geological Survey state, "We were shocked to discover these
adaptations in such an early marine reptile.
Both fossil relics originate in China's
Jialingjiang Formation. One of them is a nearly full skeleton, while the other is substantially
intact from the skull to the clavicle region.
Fang and his colleagues analyzed the head of the whole skeleton specimen
and compared it to skulls from 130
amniote
species, including as baleen whales (mysticetes),
toothed whales (odontocetes),
seals
(pinnipeds), crocodilians, birds, and
platypus.
According to the study, Hupehsuchus's skull anatomy suggests that it
evolved
convergently
with contemporary baleen whales, meaning the two species acquired comparable
characteristics through time.
According to Li Tian from the University of Geosciences Wuhan, a biogeologist, "We
suggest it had independently evolved some form of baleen."
Hupehsuchus possessed a big mouth and long, thin, flexible lower jaws,
which were excellent for more effectively filter-feeding.
According
to Long Cheng, a paleontologist at the China Geological Survey's Wuhan
Center, "the long snout was composed of unfused, strap-like bones with a
long space between them running the length of the snout."
This arrangement is unique to contemporary baleen whales, whose floppy
snout and lower jaw structures enable them to hold a massive throat area
that enlarges dramatically as they move forward and swallow little
fish.
The researchers discovered that the margins of the jaws of Hupehsuchus
feature grooves and notches, which suggests that the animal employed soft
tissues like baleen to force water out of its relatively large mouth.
Tian
argues
that modern baleen whales are toothless in contrast to toothed whales like
dolphins and orcas.
Baleen whales have grooves along their mouths to maintain baleen curtains,
which are made of keratin, a protein that is used to form hair, feathers,
and fingernails.
The
best evidence is that early whale ancestors possessed both teeth and baleen before losing
all of their teeth to become the filter-feeding baleen whales we know today.
It is uncertain where baleen originated in the whale's evolutionary
past.
According to Fang and colleagues, Hupehsuchus was a sluggish swimmer who
most likely employed a continuous ram filter feeding technique, similar to
bowhead and right whales, to graze on dense concentrations of plankton near
the water's surface.
Hupehsuchus could have adopted this diet so early in its evolutionary
history due to fierce competition for food.
The severe global extinction event known as the "Great Dying" that occurred
approximately 252 million years ago was accompanied by increasing
temperatures and acid rain, and only around 4% of marine species managed to
survive. Hupehsuchus soon after appeared.
According to paleontologist Michael Benton of the University of Bristol in the UK,
"the hupehsuchians lived in the Early Triassic, about 248 million years ago,
in China and they were part of a huge and rapid re-population of the
oceans."
According to the scientists, it took whales over 30 million years to
acquire adaptations for filter-feeding, thus Hupehsuchus' accomplishments
are impressive.
This period was turbulent, Benton
claims. It was astounding to learn how quickly these big marine reptiles sprang
on the scene and fundamentally altered the marine ecosystems of the
time.
The study has been published in
BMC Ecology and Evolution.
