Tag Archives: jaw

Two Similar Jurassic Mammals Featured Distinctively Shaped Jaw Joints

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According to recent analyses of fossils from two mammalian forms, the development of jaws in modern mammals proves to be more intricate than previously understood. (i) Polystodon chuananensis, a mid-Jurassic herbivorous tritylodont known for its relatively large size and possibly fossilized lifestyle, and (ii) Camulochondylus rufengensis, a newly identified Morganucodontan from the Early Jurassic.

Reconstructed illustration of Polystodon chuananensis. Image credit: Chuang Zhao / PNSO.

“In mammals, the joint connecting the skull to the lower jaw consists of two bones: the squamous bone and the dentary bone, where the lower jaw teeth are situated,” stated Dr. Jin Meng, a curator at the American Museum of Natural History and a researcher at the City University of New York, along with colleagues.

“This configuration replaced the older temporomandibular joint seen in reptiles, which is composed of two different bones: the quadrate and the articular bone.”

“As organisms transitioned from early mammal-like reptiles to true mammals, various ‘experimental’ versions of this new temporomandibular joint arose to withstand the forces of mastication.”

“Ultimately, this culminated in the formation of the bimandibular joint, with the new dentosquamous joint handling most of the chewing pressure, maintaining the joint functionality in reptiles, and establishing an initial system for detecting airborne sounds.”

“Over time, the dentate squamosal became the sole joint, transforming the quadratoid joint into a diminutive bone within the mammal’s middle ear, a critical feature that aids in hearing.”

However, scientists still lack a comprehensive understanding of how this new temporomandibular joint evolved, primarily due to the scarcity of fossils from this era.

“The evolution of the mammalian temporomandibular joint represents one of the most fascinating yet incomplete chapters in vertebrate history, with gaps in fossil records obscuring significant transitions,” remarked Dr. Meng.

Researchers utilized high-resolution computed tomography scans from the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences.

One of these species, Polystodon chuananensis, is an opossum-sized creature featuring “horns” potentially used for digging.

The other, Camulochondylus rufengensis, is a newly described squirrel-sized animal that lived during the Early Jurassic, approximately 174 to 201 million years ago.

Paleontologists identified new jaw structures in both ancient species.

In Polystodon chuananensis, they discovered a uniquely formed secondary temporomandibular joint located between the zygoma and dentary. This marks the first identification of this joint structure in a tetrapod.

In Camulochondylus rufengensis, they characterized a simple articular head of the dentary bone that likely indicates an evolutionary step towards a morphology adaptable to the new temporomandibular joint socket.

“These discoveries enhance the diversity of temporomandibular joints in mammalian evolution and broaden our comprehension of the evolutionary lineage of key mammalian features crucial for understanding how mammals process food and perceive airborne sounds,” the authors concluded.

Their study was published in the journal Nature in September 2025.

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F. Mao et al. Convergent evolution of diverse temporomandibular joints in mammals. Nature published online on September 24, 2025. doi: 10.1038/s41586-025-09572-0

Source: www.sci.news

New Species of Dinosaur Discovered Within Crocodile Jaw

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Reconstruction of the artist’s dinosaur Joaquinraptor Casali

Andrew McAfee, Carnegie Museum of Natural History

During the Cretaceous period, South America was a site of significant dinosaur discoveries.

Named the dinosaur species Joaquinraptor Casali, this megaraptor was uncovered in 2019 along the banks of the Liochico River in Patagonia, Argentina. It is believed to have existed just before the mass extinction of non-avian dinosaurs 66 million years ago.

Recently, Lucio Ibiricu from the National Council on Science and Technology Research in Tubat, Argentina, and his team conducted an in-depth analysis of the fossil, revealing unexpected findings in the nearly complete skull.

“A relative humerus, likely belonging to an extinct crocodile, was found between the jaws of Joaquinraptor and was in direct contact with its teeth,” states Ibiricu. “This indicates a unique ecological interaction at the time of death.”

Further investigations of the crocodilian humerus are ongoing to ascertain its size, but initial assessments suggest it is considerable, according to Ibiricu.

In addition to the recovered skull, the excavation yielded vertebrae, feet, two claws, arms, legs, and hands. Notably, the thumb claw—approximately the size of a human forearm—could have been effective for tearing the flesh of its prey, according to Ibiricu.

Fossils of other megaraptors have been discovered across Asia, Australia, and South America. Joaquinraptor was first identified close to the Cretaceous period’s end, and it is among the more complete specimens found.

The thumb claw of the dinosaur

Matt Lamanna

The scientific team concluded that the dinosaur was at least 19 years old at the time of its demise, based on the microstructure of the tibia. It measured approximately 7 meters in length and weighed a minimum of 1 tonne.

Meanwhile, Tyrannosaurus Rex was considerably larger and boasted a massive head, as noted by Ibiricu. Nonetheless, he emphasizes that both species represented apex predators within their respective environments.

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Source: www.newscientist.com

Entire Mastodon Jaw Fossil Discovered in New York Backyard

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A momentous (or more accurately prehistoric) finding was unearthed just below the Earth’s surface on a New York homeowner’s lawn.

A full mastodon jaw was found in the backyard of a house in Scotchtown, a town in Orange County, as confirmed by state officials. The New York State Museum and the State University of New York at Orange researchers retrieved the jaw and additional bone fragments, as announced by the state Department of Education in a press release on Tuesday.

It has been over 11 years since a discovery of this kind has been made in New York.

The mastodon jaw, presumed to belong to an adult, was discovered by researchers after a homeowner noticed it surfacing on his lawn. Initially, the homeowner found two teeth hidden in plants on the property, and after some digging, two more teeth were discovered.

“Upon finding the tooth and examining it closely, we knew it was unique and decided to seek out an expert,” stated the homeowner.

Following this, museum and university staff conducted an excavation that led to the unveiling of the well-preserved jaw of a mastodon, an ancient relative of present-day elephants. Additionally, part of a toe bone and rib fragments were found.

Mastodon jaw unearthed in backyard in Scotchtown, New York new york state museum

“Though the jaw is the highlight, the additional toe and rib fragments provide valuable context and possibilities for further research,” said Dr. Corey Harris, chair of the Department of Behavioral Sciences at New York University at Orange. “We are also keen on exploring the surrounding area to look for more preserved bones.”

The fossil will undergo carbon dating and analysis to determine the mammal’s time of existence in the area, its dietary habits, and habitat details. The discovery will be showcased on public television as of 2025 and is expected to be featured in magazines.

“This finding proves New York’s rich paleontological history and our persistent efforts to understand the past,” said Robert Ferra, Director of Research and Collections and Curator of Ice Age Animals at the New York State Museum. Dr. Neck mentioned, “This mastodon jaw offers a unique chance to study the ecology of this extraordinary species and enhance our comprehension of the ice age ecosystems in the region.”

To date, approximately 150 mastodon fossils have been found in New York, with about one-third of them located in Orange County.

Source: www.nbcnews.com