CT scan of an ancient reptile skull reveals little evolutionary change
over 22 million years
3D imaging analysis shows skull is nearly identical to one much older


Date:
August 25, 2021
Source:
Southern Methodist University
Summary:
A CT scan of the skull of a long-necked plesiosaur shows the cranial
architecture of these long-extinct marine reptiles didn't evolve
much over 22 million years that they lived during the Cretaceous
time. That's very unusual, according to a paleontologist.



FULL STORY ==========================================================================
A CT scan of the skull of a long-necked plesiosaur shows the cranial architecture of these long-extinct marine reptiles didn't evolve much
over 22 million years that they lived during the Cretaceous time.


========================================================================== That's very unusual, said SMU paleontologist Louis Jacobs, an expert on prehistoric creatures and co-author of a study published in PLOS One.

"Basically, in anything except living fossils, you don't go 22 million
years without evolving," said Jacobs, professor emeritus of Earth Sciences
at SMU and president of ISEM at SMU.

Elasmosaurid plesiosaurs, lookalikes of the mythical Loch Ness monster,
were the largest of the long-necked plesiosaurs, growing as long as 43
feet with half of that length deriving from their small heads and very
long necks.

Paleontologists from SMU (Southern Methodist University), as part of an international team called Projecto PaleoAngola, based their findings on a
CT scan of the 71.5 million year old skull from a species of elasmosaurid called Cardiocorax mukulu.

This detailed 3D model allowed the paleontologists to compare the well- preserved skull of C. mukulufound in Angola to that of other species
of elasmosaurids. They found that C. mukululooked nearly identical to
skulls that came from much older elasmosaurids, including one found at
Cedar Hill, Texas, in 1931, whose 93-million-years old remains can be
found at SMU's Shuler Museum of Paleontology.

"The skull shape, organization of muscles, and the shape and arrangement
of the teeth largely reflect how an animal acquired prey," said co-author Michael J.

Polcyn, research associate and director of SMU's Digital Earth Sciences Laboratory "The interesting aspect of Cardiocorax mukuluis that it
appears that this animal's predecessors adopted a particular feeding
style early in their evolutionary history, and then maintained the same
basic skull structure for the next 22 million years" It will take more
research to pinpoint why elasmosaurids might have been different from
other reptiles in their evolutionary journey.



========================================================================== Elasmosaurids lived during the Cretaceous Period, which spanned from 145 million years ago to 66 million years ago. They were predators, thriving
on fish and other marine life. Projecto PaleoAngola paleontologists
first discovered C. mukulu in Angola in 2015.

The lead author of the CT scan study is Miguel P. Marx, who will
be starting a Ph.D. program at Lund University in Sweden later this
month and was a researcher in SMU's Earth Science department during this
study. Other co- authors include Jacobs and Polcyn of SMU.; Octa'vioMateus
of Universidade Nova de Lisboa and Museu da Lourinha~, Portugal; Anne
S. Schulp of the Naturalis Biodiversity Center and Utrecht University in
the Netherlands; and A. Oli'mpio Gonc,alves of the Universidade Agostinho
Neto in Angola.

Skull found in the same area that yielded Smithsonian Museum exhibit
Mateus found the nearly complete cranium and jaw of C. mukulu, along
with 12 associated teeth and other fossilized parts of the reptile's
body in Bentiaba, Angola in 2017. That area is on the coast of Angola
that Jacobs has called a "museum in the ground," because so many fossils
have been found in the rocks there.

Many of those fossils are currently on display at the Smithsonian's
National Museum of Natural History. The museum's "Sea Monsters Unearthed" exhibit, co- produced with SMU, features large marine reptiles from the Cretaceous Period - - mosasaurs, turtles, and plesiosaurs.



========================================================================== Jacobs and Polcyn forged the Projecto PaleoAngola partnership with collaborators in Angola, Portugal, and the Netherlands to explore and
excavate Angola's rich fossil history and began laying the groundwork
for returning the fossils to the West African nation. Back in Dallas,
Jacobs, Polcyn, and research associate Diana Vineyard went to work over
a period of 13 years with a small army of SMU students to prepare the
fossils excavated by Projecto PaleoAngola.

Like the Smithsonian exhibit, the discovery of the Cardiocorax mukulu
remains were the result of that collaboration.

CT scan shows jaws and teeth of elasmosaurids didn't evolve much Marx's computed tomography (CT) scan of the skull was designed to reveal parts of
the skull that are otherwise difficult to see, such as the braincase. Only
part of the skull was actually freed from the Angolan rock in which it
was discovered because elasmosaurids skulls are so fragile. So the CT
scan was taken largely through the rock that preserved the specimen.

However, "the good resolution of the resulting CT images allowed me to discriminate between the bone, the rock matrix, and the plaster jacket
the skull was protected in," Marx said. "Thus, I could build a 3D model
of the skull and be able to study the fragile parts of it, such as the braincase and palate, without touching it." The team's conclusions
about the cranial anatomy of C. mukulu were drawn from comparisons to
the skull of Libonectes morgani,a much older elasmosaurid housed at SMU.

"The skull of L. morgani at SMU is so complete that the sutures between different bones can clearly be delineated," he said. "The skull of
Libonectes morgani worked as a guide for me when making the skull model
of Cardiocorax mukulu. This made the process of building the model much faster." Marx and the PaleoAngola team also compared the 3D imaging
to the skulls of Styxosaurus snowii and Thalassomedon haningtoni --all elasmosaurids from different time periods.

The similarity between the jaws, teeth and other skull anatomy of
C. mukulu and its predecessors was a surprising discovery, Marx said.

For example, the skull of Cardiocorax mukulu and Libonectes morgani both exhibit a tall dorsal ramus of the maxilla, and the organization of the
skull bones around the orbits is identical, Marx said. The skulls of
these two species only differed in a couple of key aspects, including a slightly different number of teeth in the upper and lower tooth rows, the location of the premaxillary-parietal suture, and the presence or absence
of the pterygoids contacting each other beneath the basioccipital bone.

"It appears that the skull of elasmosaurids did not undergo significant evolutionary change throughout their history, which is very cool,"
Marx said.

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


========================================================================== Journal Reference:
1. Miguel P. Marx, Octa'vio Mateus, Michael J. Polcyn, Anne S. Schulp,
A.

Oli'mpio Gonc,alves, Louis L. Jacobs. The cranial anatomy and
relationships of Cardiocorax mukulu (Plesiosauria: Elasmosauridae)
from Bentiaba, Angola. PLOS ONE, 2021; 16 (8): e0255773 DOI:
10.1371/ journal.pone.0255773 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210825101431.htm

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