Monday, July 27, 2026

Saber-toothed cats' spinal tumors may show how inbred species struggled to survive

Evidence of spinal nerve tumors and developmental abnormalities in saber-toothed cats from the La Brea Tar Pits indicates that the dwindling species was in poor genetic health

Frontiers

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Lumbar vertebra HC 12233. The left side of the foramen has been widened, and the blue arrow points to a hole in the bone, thought to have been left behind by a tumor that expanded into this space and eroded the bone. Image by Dr Hugo Schmökel.
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Credit: Dr Hugo Schmökel

The fossilized spines of saber-toothed cats in the La Brea Tar Pits reveal evidence for an unexpectedly high prevalence of rare spinal nerve tumors, suggesting that the species became inbred just before extinction. These tumors, which cause significant pain and reduced limb function, could have made the cats particularly vulnerable to the lure of prey animals stuck in the tar pits.

“A trapped prey animal is very attractive for a predator in pain,” said Dr Hugo Schmökel of the Evidensia Academy Sweden and the University of Zürich, lead author of the article in Frontiers in Veterinary Science. “A wounded or sick predator must rely on carcasses for surviving, so they’ll take bigger risks to get to them.”

A death trap

At the La Brea Tar Pits in California, crude oil seeps up through cracks in the ground in the form of ponds of sticky black tar which can trap animals that walk into them. The distress calls of trapped prey attract predators, which then become trapped themselves. During the Pleistocene, this included saber-toothed cats — Smilodon fatalis.

“Smilodon was an ambush hunter, hiding in the lush vegetation of the late Californian Pleistocene, jumping on prey and wrestling it down, until a fatal stab ended the hunt,” said Schmökel. “But scavenging certainly also happened.”

Well-preserved specimens of Smilodon held by the La Brea Tar Pits Museum allow scientists to look for evidence that could help us understand the species’ extinction. Schmökel and his colleagues investigated Smilodon’s spines. They identified 3,722 vertebrae, representing at least 849 adults, in the museum’s collection, and examined these for pathological changes.

They found numerous cases of developmental abnormalities: 32 vertebrae with incompletely developed arches, 48 fused ‘block’ vertebrae, and 226 ‘transitional’ vertebrae, where vertebrae form incorrectly — for example, cervical vertebrae that form like thoracic vertebrae, with a rib.

Even more strikingly, the scientists found widened foramina, holes which allow nerves to travel through the spine, in three vertebrae. Widened foramina with a smooth remodeled surface are a very strong indication that the individual was affected by a spinal nerve tumor: the tumor grows and exerts pressure on the bone over time, increasing the size of the hole.

“Dogs which are brought to my clinic with a spinal nerve tumor mainly have signs of pain, and many human patients with a spinal nerve tumor complain of pain,” said Schmökel. “This was probably also the case in Smilodon. In advanced cases without treatment the nerve and the affected limb eventually lose function, making hunting very difficult.”

Spinal nerve tumors are extremely rare in both humans and modern-day animals. Human cases are caused by specific genetic mutations, either spontaneous or inherited. Doctors see approximately 0.22-0.38 cases for every 100,000 humans. By contrast, the presence of three cases — the affected vertebrae came from three different pits, so must have belonged to different animals — means that the estimated prevalence rate at La Brea Tar Pits is a staggering 353 cases for every 100,000 Smilodons.

Small population, big risks

We can’t be sure why Smilodon was so severely affected by spinal nerve tumors. But the high prevalence of developmental abnormalities leads the team to suspect that the species had become inbred, although this can’t be proven without genetic analysis. As their numbers began to fall, so that fewer potential mates were available, harmful genetic variants could have become concentrated in the population, increasing the likelihood that each litter of kittens inherited health problems. The same spinal malformations have been documented in modern-day inbred grey wolf populations.

The scientists point out that the tumors themselves could have increased the chances that the cats ended up in the tar pits: pain and difficulty hunting might have led them to take greater risks than healthy animals. But for Schmökel, the evidence of inbreeding is a wake-up call regarding our treatment of modern megafauna.

“Reduced fitness and smaller litters don’t help a population under stress,” said Schmökel. “But inbreeding is not the cause of the crash of populations, it is a medical consequence. Loss of habitat, pollution, hunting or poaching, and in some areas today climate change, are the cause of the fall in numbers of wild cats. We can assume that the same happened to Smilodon at the end of the Pleistocene.

“We must take care of living wild animals. We humans reduce their living space, hunt them, pollute them. And when there are only a few left, we start, maybe, to act. But by then these animals are probably affected by inbreeding and saving them is more difficult.”

Lumbar vertebrae HC 12288. The white arrow on the CT scan shows the pathologic widening of the left foramen of the fourth and fifth lumbar vertebrae, and the yellow arrow shows where the third and fourth lumbar vertebrae have fused together. Image by Dr Hugo Schmökel.

Credit

Dr Hugo Schmökel

Journal

Frontiers in Veterinary Science

DOI

10.3389/fvets.2026.1857385

Method of Research

Observational study

Subject of Research

Animals

Article Title

Foraminal widening indicating a spinal nerve tumor in the saber-tooth cat Smilodon fatalis from Rancho La Brea

Article Publication Date

27-Jul-2026

Australia’s first fully integrated bionic arm

University of Melbourne

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*Meablex is addressing technological limitations with conventional bionic prosthetics to improve the quality of life for people with upper limb loss.*
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Credit: Meablex

Almost 24 million people globally live with upper-limb loss, yet access to effective prosthetic arms remains limited.

In high-income countries, only around half of people with upper-limb loss have ever trialled a prosthesis, and 35-40 percent of users ultimately abandon their device, with rejection rates highest among children.

In low-income countries, the access gap is even greater, with only 10 percent of people estimated to trial a prosthetic device.

Senior Research Engineer Dr Alireza Mohammadi and his team interviewed 60 amputees, clinicians and suppliers to identify the limitations associated with current prosthetic devices.

The research team subsequently founded ‘Meablex’ to address these technological limitations and improve the quality of life for people with upper limb loss.

“Bionic hands are typically made out of rigid and heavy materials like metal and therefore can be hazardous if there’s a malfunction,” Dr Mohammadi said.

“Our next-generation prosthetics are much safer as we use lightweight soft robotic materials and advanced 3D-printing technologies.”

Most commercially available forearm sockets that connect a residual limb to a bionic hand, are not designed to be adjustable.

This can create challenges when a person’s limb changes shape due to growth, exercise, temperature, activity levels or natural changes in limb volume throughout the day.

“If someone exercises while wearing a fitted prosthetic socket, their residual limb may temporarily expand due to increased blood flow, causing the socket to become too tight,” Dr Mohammadi said.

“As current sockets are not adjustable, the prosthetic will need to be refitted. For growing children, the challenge is even greater as they need to have their fitted sockets regularly replaced to accommodate changes in their body shape over time. This costly process can take several months and during this time the child can’t use their bionic hand.”

Meablex has addressed this issue by designing adaptable sockets, enabling the user to manually adjust their prosthetic arm in real time.

Current prosthetic arms operate using ElectroMyoGraphy (EMG) sensors that detect electrical activity generated when the user contracts muscles in their residual forearm.

A machine learning model then interprets the electrical activity to decipher the user’s intended hand movement.

The user can make different prosthetic hand movements by contracting specific muscles in their residual forearm.

However, these signals can be affected by sweat, electrode placement and changes in socket fit, which may disrupt signal quality and make the device harder to control.

Meablex has developed a new control approach designed to be more reliable in everyday conditions.

“Our system uses magnetic sensors designed to be less affected by sweat than skin-surface electrical sensors,” said Dr Mohammadi.

“Our technology combines a lightweight 3D-printed prosthetic hand with a new sensorised socket that detects subtle muscle movement, rather than relying only on traditional electrical muscle signals.”

Clinical trials are slated to get underway later this year, with a commercial launch planned for early 2027, following clinical validation and regulatory approval.

Dean of the Faculty of Engineering and Information Technology (FEIT) Professor Thas Nirmalathas said the project exemplified engineering as a critical tool to improving health and wellbeing through new innovations in bionic prosthetics.

“From identifying the problem, to engaging with the community and now to being on the cusp of trialing an innovative state-of-the art fully integrated bionic arm, the team is set to transform the lives of amputees globally,” Professor Nirmalathas said.

Meablex was recently awarded $470,000 through Australia's Economic Accelerator (AEA) Ignite program to support the next stage of development, clinical validation and commercialisation.

Method of Research

Case study

Subject of Research

People

How changing environments can preserve an ancient microbial survival strategy

Theory explains how a seemingly self-destructive behaviour known as “latecomer killing” could persist for hundreds of millions of years

Institute of Science Tokyo

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Schematic diagram of the mechanism for stable evolution of “latecomer killer” discovered in this study
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Credit: Arisa H. Oda, Tetsuhiro S. Hatakeyama

A research group led by Tetsuhiro Hatakeyama from the Earth-Life Science Institute (ELSI) at Institute of Science Tokyo have revealed how a seemingly self-destructive survival strategy could persist in yeast for hundreds of millions of years. By combining population-dynamics theory with comparative experimental observations, the team found that alternating periods of nutrient-rich conditions and starvation can stabilise this unusual behaviour over evolutionary timescales. The findings were published in the Journal of the Royal Society Interface.

The study addresses a long-standing puzzle in evolutionary biology. Budding yeast and fission yeast diverged approximately 300 to 600 million years ago, yet both retain the same "latecomer-killing" strategy and use the same autotoxins. Why such a costly behaviour has been conserved across such distant species has remained unexplained.

When glucose becomes scarce, yeast cells release toxins into their surroundings. Cells that have already adapted to these toxins survive, while genetically identical cells arriving later, before they have adapted, are killed. This phenomenon, known as latecomer killing, allows cells that have already adapted to a starvation environment to exclude late-arriving, toxin-sensitive competitors, even when those competitors are genetically identical clones.

At first glance, however, the strategy appears evolutionarily unstable. Both toxin production and resistance carry costs. Evolutionary theory predicts that "cheaters," cells that retain resistance but avoid the cost of producing toxins, should eventually outcompete toxin-producing cells. If so, the system should disappear over time.

To investigate this paradox, the researchers developed a population-dynamics model that simulated yeast populations under different environmental conditions.

The results revealed that neither constant nutrient-rich conditions nor continuous starvation could maintain the toxin-adaptation system. Instead, evolutionary stability emerged only when the environment alternated between long nutrient-rich periods and shorter episodes of starvation.

During nutrient-rich periods, cells with the toxin-adaptation system behave much like toxin-sensitive cells, while cheaters still pay the cost of maintaining resistance and are gradually removed from the population. When starvation returns, toxin-adaptation cells switch to producing toxins and resisting them, enabling them to eliminate toxin-sensitive cells. In this way, long nutrient-rich periods suppress cheaters, while shorter starvation episodes suppress sensitive cells, together preserving the strategy over long evolutionary timescales.

"The surprising result was that neither constant abundance nor constant starvation could maintain this system," said Hatakeyama. "Only when the environment switched between the two did the toxin-adaptation strategy become evolutionarily stable. This shows that long-term environmental fluctuations can shape the survival of biological strategies that would otherwise disappear."

The findings suggest that environmental fluctuations can play a much greater role in evolution than previously recognised. Rather than simply selecting the fittest strategy under a single condition, changing environments can preserve complex ecological strategies that become advantageous only through the alternation of different conditions.

The team also compared yeast species across the phylogenetic tree. Budding yeast and fission yeast, which diverged approximately 300 to 600 million years ago, both show latecomer killing and use the same autotoxins. In contrast, two yeast species more closely related to budding yeast did not show clear evidence of latecomer killing. This suggests that whether a species retains or loses the system may reflect its long-term ecological history rather than phylogenetic relatedness alone.

The theory predicts that similar toxin-adaptation systems should be found preferentially in microorganisms that inhabit environments which are generally nutrient-rich but occasionally experience starvation. Testing this prediction through environmental surveys and laboratory evolution experiments could reveal whether comparable strategies occur in bacteria and archaea.

More broadly, the work raises the possibility that these systems preserve clues about a species' long-term ecological history. Understanding how cooperation, competition and adaptation evolve under changing environmental conditions may also provide insights into major evolutionary transitions, including the emergence of multicellular life.

Reference

Tetsuhiro S. Hatakeyama1*, Kunihiko Kaneko2, Kunihiro Ohta3,4 and Arisa H. Oda3,4, Evolvability of the toxin-adaptation system in yeast, Journal of the Royal Society Interface, DOI: 10.1098/rsif.2026.0345

Earth-Life Science Institute, Institute of Science Tokyo, Meguro-ku, Tokyo, Japan
Niels Bohr Institute, University of Copenhagen Niels Bohr Institute, Copenhagen, Denmark
Basic Science, The University of Tokyo, Meguro-ku, Tokyo, Japan
Division of Information and Mathematical Sciences, Tokyo Woman’s Christian University, Suginami-ku, Tokyo, Japan

More information

Earth-Life Science Institute (ELSI) is one of Japan’s ambitious World Premiere International research centers, whose aim is to achieve progress in broadly inter-disciplinary scientific areas by inspiring the world’s greatest minds to come to Japan and collaborate on the most challenging scientific problems. ELSI’s primary aim is to address the origin and co-evolution of the Earth and life.

Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”

World Premier International Research Center Initiative (WPI) was launched in 2007 by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).

The yeast phylogenetic tree studied in this study. Although Baker's yeast and fission yeast diverged hundreds of millions of years ago, both exhibit “latecomer killing,” whereas species intermediate between them do not.