Earth's first giant

Date:
December 23, 2021
Source:
Natural History Museum of Los Angeles County
Summary:
The two-meter skull of an enormous new ichthyosaur species, Earth's
first known giant creature, reveals how both the extinct marine
reptiles and modern whales became giants.



FULL STORY ==========================================================================
The two-meter skull of a newly discovered species of giant ichthyosaur,
the earliest known, is shedding new light on the marine reptiles'
rapid growth into behemoths of the Dinosaurian oceans, and helping us
better understand the journey of modern cetaceans (whales and dolphins)
to becoming the largest animals to ever inhabit the Earth.


========================================================================== While dinosaurs ruled the land, ichthyosaurs and other aquatic reptiles
(that were emphatically not dinosaurs) ruled the waves, reaching similarly gargantuan sizes and species diversity. Evolving fins and hydrodynamic body-shapes seen in both fish and whales, ichthyosaurs swam the ancient
oceans for nearly the entirety of the Age of Dinosaurs.

"Ichthyosaurs derive from an as yet unknown group of land-living reptiles
and were air-breathing themselves," says lead author Dr. Martin Sander, paleontologist at the University of Bonn and Research Associate with the Dinosaur Institute at the Natural History Museum of Los Angeles County
(NHM).

"From the first skeleton discoveries in southern England and Germany
over 250 years ago, these 'fish-saurians' were among the first large
fossil reptiles known to science, long before the dinosaurs, and they
have captured the popular imagination ever since." Excavated from a rock
unit called the Fossil Hill Member in the Augusta Mountains of Nevada,
the well-preserved skull, along with part of the backbone, shoulder,
and forefin, date back to the Middle Triassic (247.2-237 million years
ago), representing the earliest case of an ichthyosaur reaching epic proportions. As big as a large sperm whale at more than 17 meters (55.78
feet) long, the newly named Cymbospondylus youngorum is the largest animal
yet discovered from that time period, on land or in the sea. In fact,
it was the first giant creature to ever inhabit the Earth that we know of.

"The importance of the find was not immediately apparent," notes
Dr. Sander, "because only a few vertebrae were exposed on the side of
the canyon. However, the anatomy of the vertebrae suggested that the
front end of the animal might still be hidden in the rocks. Then, one
cold September day in 2011, the crew needed a warm-up and tested this suggestion by excavation, finding the skull, forelimbs, and chest region."
The new name for the species, C. youngorum, honors a happy coincidence,
the sponsoring of the fieldwork by Great Basin Brewery of Reno, owned
and operated by Tom and Bonda Young, the inventors of the locally famous
Icky beer which features an ichthyosaur on its label.



==========================================================================
In other mountain ranges of Nevada, paleontologists have been recovering fossils from the Fossil Hill Member's limestone, shale, and siltstone
since 1902, opening a window into the Triassic. The mountains connect our present to ancient oceans and have produced many species of ammonites,
shelled ancestors of modern cephalopods like cuttlefish and octopuses,
as well as marine reptiles. All these animal specimens are collectively
known as the Fossil Hill Fauna, representing many of C. youngorum's prey
and competitors.

C. youngorumstalked the oceans some 246 million years ago, or only about
three million years after the first ichthyosaurs got their fins wet,
an amazingly short time to get this big. The elongated snout and conical
teeth suggest that C. youngorum preyed on squid and fish, but its size
meant that it could have hunted smaller and juvenile marine reptiles
as well.

The giant predator probably had some hefty competition. Through
sophisticated computational modeling, the authors examined the likely
energy running through the Fossil Hill Fauna's food web, recreating the
ancient environment through data, finding that marine food webs were able
to support a few more colossal meat-eating ichthyosaurs. Ichthyosaurs of different sizes and survival strategies proliferated, comparable to modern cetaceans' -- from relatively small dolphins to massive filter-feeding
baleen whales, and giant squid-hunting sperm whales.

Co-author and ecological modeler Dr. Eva Maria Griebeler from the
University of Mainz in Germany notes, "due to their large size and
resulting energy demands, the densities of the largest ichthyosaurs from
the Fossil Hill Fauna including C. youngourum must have been substantially lower than suggested by our field census. The ecological functioning
of this food web from ecological modeling was very exciting as modern
highly productive primary producers were absent in Mesozoic food webs and
were an important driver in the size evolution of whales." Whales and ichthyosaurs share more than a size range. They have similar body plans,
and both initially arose after mass extinctions. These similarities make
them scientifically valuable for comparative study. The authors combined computer modeling and traditional paleontology to study how these marine animals reached record-setting sizes independently.



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"One rather unique aspect of this project is the integrative nature of
our approach. We first had to describe the anatomy of the giant skull in
detail and determine how this animal is related to other ichthyosaurs,"
says senior author Dr. Lars Schmitz, Associate Professor of Biology
at Scripps College and Dinosaur Institute Research Associate. "We did
not stop there, as we wanted to understand the significance of the
new discovery in the context of the large- scale evolutionary pattern
of ichthyosaur and whale body sizes, and how the fossil ecosystem of
the Fossil Hill Fauna may have functioned. Both the evolutionary and
ecological analyses required a substantial amount of computation,
ultimately leading to a confluence of modeling with traditional
paleontology." They found that while both cetaceans and ichthyosaurs
evolved very large body sizes, their respective evolutionary trajectories toward gigantism were different. Ichthyosaurs had an initial boom in
size, becoming giants early on in their evolutionary history, while
whales took much longer to reach the outer limits of huge. They found a connection between large size and raptorial hunting -- think of a sperm
whale diving down to hunt giant squid -- and a connection between large
size and a loss of teeth -- think of the giant filter- feeding whales
that are the largest animals ever to live on Earth.

Ichthyosaurs' initial foray into gigantism was likely thanks to the
boom in ammonites and jawless eel-like conodonts filling the ecological
void following the end-Permian mass extinction. While their evolutionary
routes were different, both whales and ichthyosaurs relied on exploiting
niches in the food chain to make it really big.

"As researchers, we often talk about similarities between ichthyosaurs
and cetaceans, but rarely dive into the details. That's one way this
study stands out, as it allowed us to explore and gain some additional
insight into body size evolution within these groups of marine tetrapods,"
says NHM's Associate Curator of Mammalogy (Marine Mammals), Dr. Jorge Velez-Juarbe. "Another interesting aspect is that Cymbospondylus
youngorumand the rest of the Fossil Hill Fauna are a testament to the resilience of life in the oceans after the worst mass extinction in
Earth's history. You can say this is the first big splash for tetrapods
in the oceans." C. youngorumwill be permanently housed at the Natural
History Museum of Los Angeles County, where it is currently on view.

========================================================================== Story Source: Materials provided by Natural_History_Museum_of_Los_Angeles_County. Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* Illustrations_of_the_enormous_new_ichthyosaur_species ========================================================================== Journal Reference:
1. P. Martin Sander, Eva Maria Griebeler, Nicole Klein, Jorge Velez
Juarbe,
Tanja Wintrich, Liam J. Revell, Lars Schmitz. Early giant reveals
faster evolution of large body size in ichthyosaurs than in
cetaceans. Science, 2021; 374 (6575) DOI: 10.1126/science.abf5787 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211223143055.htm

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