On October 19th, 2017 we learned about

New evidence necessitates the reevaluation of species that survived past their supposed extinctions

It seems like it’d be hard to miss an animal the size of a lion named for its serrated, sword-like teeth. An animal like Homotherium latidens, or the European scimitar cat, was once one of Europe’s most formidable predators, at least until 300,000 years ago, when it seemed to have gone extinct. However, a jawbone pulled from the North Sea is rewriting that timeline by 270,000 years, as both carbon dating and genetic evidence suggests it was alive as recently as 28,000 years ago. This younger specimen is now raising a lot of questions, as new causes for extinction, new ecological niches and that giant gap in the fossil record all need to be reconsidered.

Homotherium were like slightly scaled-down versions of their more famous saber-toothed cousins, like Smilodon. Nonetheless, this cat still had two large, canine teeth, and their knife-edge shapes suggest they were probably used for cutting and slashing rather than simply impaling prey. It’s hard to know for sure, because the humans that we now know lived as neighbors to these scimitar cats unfortunately didn’t leave any good field notes behind. Even cave paintings of predatory cats found in norther France somehow omit any solid portraits of H. latidens.

Missing, or migrating?

One of the possible explanations for Homotherium’s absence in the fossil and written record may be that they just weren’t around much. One hypothesis to explain how the cats could be alive without leaving behind more evidence is that they had gone on a very long migration, possibly even around the world. This idea is slightly bolstered by some the fact that the cats’ closest relatives are known to have turned up in North America, although that relationship is also being reexamined.

Looking at the mitochondrial DNA recovered from the new jawbone, researchers were able to not only date the specimen, but also see where it fits in the larger cat family tree. They found that H. latidens is remarkably similar to its North American kin, Homotherium serum— so much so that it’s been suggested that they might be the same species in a new location. This similarity is in contrast to H. latidens’ relationship with other cat species, which forked away from each other 20 million years ago. While they do share a common ancestor, your house cat is more closely related to a modern tiger than Homotherium is to other saber-toothed cats like Smilodon.

Assuming that we’ve now found the most recent H. latidens bone on the planet, scientists now have to think about what caused its final extinction 28,000 years ago. As presumptuous as it sounds, there’s a fair chance that these cats really did go extinct at that point (really!) if only because so many other animals were being removed from the food chain around the same time. Europe was experiencing an ice age at that point and coming to grips with more efficient human hunters. The combined ecological stresses likely explain not only the extinction of these saber-toothed cats, but other megafauna like mammoths and cave bears as well.

Other exaggerated extinctions

Balbaroo fangaroo
Balbaroo fangaroo, who’s name may never be topped

As big an upheaval as this new bone has caused, it’s worth remembering that this isn’t the first time paleontologists have had to rethink extinctions. You can’t predict what fossils will be found, and while most species seem to cluster geographically and chronologically, they can surprise us with their extended survival. Just this month, another extinct mammal with big teeth extended it’s timeline, but by five million years. Fanged kangaroos like Balbaroo fangaroo weren’t exactly impressive predators, as they were browsing herbivores that scurried around ancient Australia, but they apparently did better than we’d previously given them credit for. Like the European saber-toothed cats, the pressures that drove them to their (final!) extinction is now be rethought, since in their case they seem to have outlived their regions major climate crisis known to have taken place 15 million years ago.

Source: This Saber-Toothed Cat Mingled With Modern Humans by Michelle Z. Donahue, National Geographic

On October 4th, 2017 we learned about

Pinning down the causes and effects of overly picky eaters

“Do I have eat all of it?”

My daughter looked at me, trying her best to look sad and tortured over the possibility of eating three more forkfuls of salad. The effect was slightly diminished though by her hand, which was still pinching her nose to stop herself from actually tasting her food.

“Yes, eat all of it.”

For all the groaning and whining, she did finish the serving of vegetables. Like most kids her age, she’d greatly prefer a diet strictly composed of starches and sugars, and so this melodrama wasn’t that surprising. However, it also wasn’t that bad- she’s been slowly expanding her range of palatable foods. I can’t really say that she’s a picky eater, because she will try new foods, occasionally even admitting to like them. What may seem “picky” one night might not on another, or to another parent. Because having a limited diet can have an impact on one’s health, scientists are trying to figure out what metrics can be used to classify a truly picky eater.

Figuring out what makes kids finicky

There are a lot of factors involved in a kid’s attitude towards food. Environmental feedback from parents and caregivers counts for a lot, but there’s evidence that kids all have an underlying predisposition for certain foods over others. One distinction that’s being made is cases where kids object to a meal because they don’t like the food, or if they’re objecting as a way to gain control over a situation. That’s sometimes easier said than done, as some kids seem to swing back and forth in their reactions to anything that’s not their favorite macaroni and cheese.

One truly measurable criteria may turn out to be genetics. Kids identified as “picky” by the adults in their lives had their DNA tested, with particular attention given to five genes related to taste. Out of those five, two genes were more likely to have variations in kids that turned their noses up to everything. Kids with very limited palates were most likely to have an unusual nucleotide on the TAS2R38 gene, and kids that turned meals into power struggles showed differences on their CA6 gene. Incidentally, both genes are associated with bitter taste perception, and so these kids’ objects may be tied to feeling extra sensitive to bitter flavors. Since evolution has used bitterness as a toxic defense mechanism in many species of plants, it’s not surprising that it would be an issue kids would fight about.

Minimal menu leads to damaged eyes

This doesn’t mean that picky eaters aren’t worth working with. Most veggies aren’t going to give them a dangerous dose of toxins, but it may just save them from serious vitamin deficiencies. A boy in Canada was recently brought to a hospital because his vision was deteriorating at an alarming rate, and could only make out a blur of movement if objects were dangled a foot in front of his face. Dry patches were found around the edge of his iris, and his cornea was somewhat disfigured.

Doctors eventually realized that he was severely vitamin A deficient, thanks to an extremely limited diet of lamb, pork, potatoes, apples, cucumbers and Cheerios. Without a trace of carrots, sweet potatoes, spinach or fish in his diet, the boy had essentially starved himself of a nutrient most of us don’t need to worry much about. Instead of eating his vitamin A, he was left to receive multiple doses of it intravenously, which restored much of his vision, but not all of it. At least the apples and Cheerios are helping the poor kid get some fiber.

Source: Got a picky eater? How 'nature and nurture' may be influencing eating behavior in young children, MedicalXpress.com

On September 12th, 2017 we learned about

DNA test defies long-held assumptions by revealing that a decorated Viking warrior was, in fact, female

It’s weird when a fantasy series for kids ends up beating actual archaeologists to a historical fact. As it turns out though, thanks to characters like Astrid in the How to Train Your Dragon series, my kids are apparently more comfortable with the notion of a female Viking warrior than most scholars have been for the past 137 years. A grave in Birka, Sweden was discovered with a considerable amount of equipment suitable for a high-ranking warrior, but nobody even really considered the idea that this warrior was a woman until this year, when genetic testing firmly established her XX chromosomes.

The grave in question is known as BJ581, and is somewhat famous as an example of a successful warrior’s grave. In addition to the human skeleton, the grave also contained the bodies of a male and female horse, a sword, an axe, a spear, armor-piercing arrows, a battle knife, two shields and a board game. Many of these items have since been found to be representative of warrior burial practices in the Middle Ages, but the board game stands out. The chess-like game is thought to be a sign that this particular warrior was able, and probably expected, to have a mastery of strategy and tactics, quite likely as a commander on the battlefield. The conclusion is therefore that the occupant of grave BJ581 wasn’t not only a fighter, but a skilled and accomplished one at that.

Weapons aren’t for women?

This same collection of grave goods has long been used as evidence that this warrior was male, because people were used to that idea, more or less. Researchers from the 1880s onward have essentially assumed that anyone able to wield a weapon must be male, most likely because of researchers’ own cultural standards. In most of the studies of this grave, there was little investigation into the skeleton’s sex because it was considered a foregone conclusion. Only recently did Anna Kjellström actually investigate the sex of the body, a task made easier with modern DNA analysis. In addition to the discovery of two X chromosomes, isotope samples from the skeleton’s tooth root and upper arm also revealed that this woman had probably moved to Birka from elsewhere somewhere between ages four and nine.

As definitive as the chromosomes are in this case, there’s still push-back in the academic community to accept this correction. In some cases, people point to the idea that women may have been buried with weapons that were heirlooms, or for ceremonial purposes. Women may have been buried alongside male warriors and their weapons. People have even wanted to rewrite the meaning of the game pieces, suggesting that maybe this longstanding sign of tactical prowess was actually, after 100 years of agreement, included because the deceased might have enjoyed playing games. This is all despite other historical records pointing women’s martial abilities in Viking societies, even beyond kids’ movies and cartoons.

Accepting female fighters

The warrior from grave BJ581 isn’t the first woman to face this kind of resistance. The most famous example is probably the Scythian women more commonly known as Amazons. Famous even in their own time, myths and exaggerations created some doubt about if these warriors really did fight bows and arrows, spears and swords from horseback as written and depicted in contemporaneous artwork. Today we have the physical evidence, including genetic testing, to confirm many of these legends, and it seems that the reputation of female Viking warriors may be on a similar track. With this new knowledge from Birka, people are now wondering how many other Viking women have been misidentified in other graves, and further tests should help settle some doubts about who exactly was fighting in Viking armies.

My third grader asked: Women have smaller bones than men?

Part of what sparked the interest in testing this warrior’s skeleton’s DNA was that the bones were proportionally a bit slighter than one might expect for a male. Hips and shoulders are usually more obvious hints at a skeleton’s sex, but studies have also found that males are more likely to have slightly thicker bones, such as around the tibia.

Source: First Female Viking Warrior Proved Through DNA by Kristina Killgrove, Forbes

On August 21st, 2017 we learned about

External stimuli sets off a slate of unexpected gene expression in stickleback fish brains

In a tense situation, your body can spring into action, altering various physiological processes to help you respond to potential danger. Your heart rate may spike, you might breath faster, and the release of hormones like adrenaline can help sharpen you vision and dull pain. It’s a pretty amazing biological tool kit, and scientists have recently found that it may be more complicated than previously understood. Studies of bees, mice and now stickleback fish have found that a fleeting encounter with an intruder may trigger a flurry of activity based around the animal’s DNA, a bit of anatomy not normally associated with temporary responses to daily stimuli.

The primary function of DNA is to act as an archive or schematic of your body. Each cell has an incredibly tightly coiled series of nucleotides that are usually only unpacked when a cell is dividing and needs to help build a new cell, or when specific proteins are needed to help the body function. The complexity of the molecules involved reinforced the assumption that this was always a slow process, but researchers tracking gene expression in stickleback brains found that DNA may be more accessible than we understood. Even interactions external to the body, such as encountering an intruder in one’s territory, were enough to trigger specific genes to start producing new proteins in the fish’s brains.

Specific sequence on a schedule

There seemed to be a reliable formula to the observed gene expression. Within 30 minutes of an encounter with a potential threat, genes relating to hormone production were accessed and activated. 60 minutes after the encounter, genes that helped control metabolism were active, followed by genes related to immune function and homeostasis at 120 minutes. The fact that these genes were observed in the telencephalon and diencephalon brain centers, which are related to learning, memory and social information, may suggest that all this activity is meant to help the fish learn or at least remember their run-ins with trouble.

There’s likely more to this than simply being a reinforcement of more obvious activity between neurons. Sticklebacks are very territorial, and seem to claim any space they can control as their own. However, that means that they’re starting this chain of genetic activity many times a day, which seems energetically costly if each encounter requires unpacking sections of DNA on top of other responses. It may be that the DNA is not as immediately tied to the events themselves, but is actually priming the brain to help it learn more easily. More research is needed into how this all affects the fish’s memory, but it seems that DNA is relied upon more frequently than anyone expected.

Source: Brief Interactions Spur Lasting Waves Of Gene Activity In The Brain, Scienmag

On May 4th, 2017 we learned about

Age and “sweet tooth” genes can make eating sugar less satiating

Apologies if this makes me a bad parent, but I’m not actually sure how much sugar my kids eat each day. I do know that it makes them very excited to do so, and so every possible spike in sucrose and fructose in their daily routine is something to be negotiated, connived or at least celebrated. In the case of my four- and eight-year-old, a lot of this love for sweets is probably tied to their ages— kids taste receptors don’t work the same way adults’ do, and their growth seems to help them use those calories too. If these preferences last past their 16th birthdays though, their mom and I may be to blame, not because of parenting, but because of genetics.

Dessert-oriented DNA

Danish researchers recently isolated what they believe to be a “sweet tooth” gene, FGF21. Two variations in this gene was associated with significantly higher amounts of sugar consumption on a daily basis among the 6,500 people who participated in the study. The more common variations of the gene help produce hormones that calm neurological reward responses, making sugar less exciting to our brains after a certain amount has been eaten. People with this genetic sweet tooth don’t seem to have that same cap, and happily consume more sugar without feeling sated by it. More troubling, there may this reward connection may mean these people are also more likely to consume more alcohol and cigarettes, although that hasn’t been explicitly proven yet.

Before you start blaming FGF21 for the last candy bar you ate, don’t forget the other sweet tooth gene, SLCa2. Identified in 2008, this gene produces a protein called GLUT2, which helps move glucose around the body and help us feel full after our blood sugar levels are normalized. In lab experiments, mice with a mutation on the FGF21 gene were prone to eating more food than other mice, and there may be a correlation with Type 2 Diabetes. Overall, a change in a single amino acid correlated with as much as 25 more grams of sugar than people without the sweet tooth mutation.

Caloric counterbalance

Importantly, neither sweet tooth gene mutation really synced up with serious health problems (although these test participants’ dentists may have a different opinion on that.) People with FGF21 mutations actually had lower body mass indexes on average, so if they were somehow eating more calories due to extra sugar, they were also making up for it elsewhere in their diets. People with SLCa2 mutations were similar— while they may have eaten anywhere from 3 to 15 additional grams of sugar than other people, they weren’t consuming extra calories as a result. They were just making sugar a bigger proportion of their diet. This may be problematic if the remaining calories aren’t providing enough vitamins, antioxidants and fiber, but by itself a sweet tooth isn’t necessarily a bad thing.

Source: Crave Sugar? Maybe It's in Your Genes by Dina Fine Maron, Scientific American

On April 10th, 2017 we learned about

Squid, cuttlefish and octopuses found to aggressively alter their genes without updating their DNA

Cephalopods are part of an ancient lineage, with some of the family tree predating the dinosaurs. A subset of these animals known as coleoids, which includes octopuses, squid and cuttlefish, stand out from the group, which is hard to do in a family of boneless, tentacled, color-changing weirdos. What makes these particular sea creatures so unusual is their unusually-developed brains, the biggest of any invertebrate. It hasn’t been definitively linked, but new analysis of coleoid genomes suggests that big brains are the result of some very unusual genetic activity taking place on an unprecedented scale.

To get what big-brained coleoids are doing to build up their gray matter, we need to first take a look at how most animals grow their bodies. Most organisms on Earth are get by with their DNA acting as a sort of archive for the whole body’s blueprints. When new tissue is to be grown, separate but similar molecules transcribe the information from your DNA into a sort of working copy, usually pared down to whatever information is relevant for that part of the body. Proteins are then built off of the chains of RNA, and those proteins are then incorporated into new cells. As my second-grader put it, the DNA is the “instructions, and the RNA is the kit and tools you use to make something.”

Octopuses, squid and cuttlefish somehow didn’t find this system sufficient, and have shifted a lot of weight onto the “working copy” of their body plans. Instead of the small edit or transcription error here or there, usually not accounting for more than one percent of the overall genome, brainy coleoids change at lot as their RNA transcribes information from their DNA. Researchers found as many as 130,000 edited RNA sites, most of which concerned the construction of the animals’ nervous systems and brains. Instead of having the DNA carry the plans for advanced neurological functions, those instructions seem to only exist temporarily when the RNA goes to work. The one big exception to this coleoid editing process is the shelled nautilus, although just as they skip these RNA-upgrades, they’re also considered to be the dimmest bulb of the bunch, so the correlation holds.

RNA transcription trade-offs

It would seem like keeping some of these neat upgrades outside of your permanent DNA archive would have some drawbacks. Most animals do fine without these last-minute edits to their genome, so the extra complication might come with a price. As far as researchers can tell, the trade-off is that these species’ DNA has had to dedicate a lot of space to preserve the sections of data that need special RNA editing. As a result of this packaging, the amount of genetically-inheritable adaptations has been slightly diminished, which means that evolutionary change has been very slow-going.

The upside of this system is that even if each possibly beneficial mutation can’t easily be passed on to the next generation in more inert DNA, the last-second edits to RNA can be very responsive to the needs of each individual octopus or squid. It may allow for more flexibility with environmental changes, or even be a way to encode experiences and memory without a big cerebellum to put them in.

Source: Octopuses Do Something Really Strange to Their Genes by Ed Yong, The Atlantic

On March 7th, 2017 we learned about

Isolating the mechanisms that let rays, skates and sharks sense electricity

Rays, skates and sharks have a sense that our ancestors gave up (mostly). These cartilaginous fish generally don’t have great eyesight, but they can make up for it by sensing electric activity in their prey. This ability, known as electrosensory, allows something like a little skate (Leucoraja erinacea) to detect prey buried under a layer of sand, picking up the electrical activity of the animal’s heart beat. The basics of this ability have been known for some time, but researchers now say they’ve figured out the underlying biology that makes it all possible.

To try to trace each step of some skates’ electrosensitivity, researchers modified skate’s genomes to isolate different genes that were thought to play a role in the electrosensory organs. Bit by bit, they put together how electrical activity in prey can somehow be detected and transmitted to the skate’s brain. The process starts with voltage-sensitive calcium in specialized cells, which draws in calcium ions when activated. To boost that signal, the calcium ions also trigger potassium in the cell, which causes an oscillation in the surrounding electrical field. This helps get even a faint amount of electricity up to a threshold that will trigger a nerve signal to the skate’s brain.

Electrosensitivity in our ears?

This bit of biochemistry may seem quite esoteric, but it has connections to our own anatomy. The genes involved in detecting electric perturbations were found to be connected to the genes that our bodies use to build our ears’ sensitivity to sound. Long ago, many organisms probably relied on electrosensitivity to find prey, particularly considering the how well electricity conducts in water. Sharks, rays and skates held onto this ability, but other fish repurposed some of these sensors into a structure called a lateral line, which lets them detect movement in the water around them. Eventually, those genes were modified further, and now play a role in how we detect sound.

In the lab, researchers were able to make similar modifications to ion channels on rat cells (not rats) that they carried out on the skates. This similarity helps support the idea of a common point of origin, and may allow for new avenues for research. It’s possible that insight gained from skates’ and sharks’ electrosensitivity will help inform us about how our inner ears send signals to our brains.

Source: Study shows how skates, rays and sharks sense electrical fields, Phys.org

On February 26th, 2017 we learned about

New investigations into long-accepted attributes of monarch butterflies

This is a story about chromosomes, misidentified butterflies, and conflicting evidence, complete with a missing person. It’s also a story where the details simultaneously count, but kind of don’t, at least from the larger perspective of illustrating how science works. The whole thing lacks a romantic interest, but that might get worked out soon if there’s enough sexual dimorphism between the butterflies.

Specifying species

For 40 years, scientific literature has been in agreement that monarch butterflies (Danaus plexippus) have 30 chromosomes— the packets of DNA that are shared and resorted during fertilization, but are also used when a cell divides itself. Counting the number of chromosomes has been a fairly stable concept, and so if a study from 1975 reported that these butterflies have 30 chromosomes, there hasn’t been a lot of reason for doubt. As such, other studies have relied on that figure, citing it as a reference point over and over.

However, one of the strengths of the scientific method is that ideas can be challenged, if you have evidence to do so. In the case of the monarchs, a postdoc noted that his own observations didn’t match up with the established chromosome count, and so he started investigating why that might be true. One of the immediate questions that came up was that the 1975 paper was conducted in India, a country that is not on any of the standard migration routes for monarch butterflies native to the Americas.

This bit of geography was especially reverent when considering taxonomic confusion already surrounding monarchs. Many other species benefit from mimicking the bright orange markings of monarchs, because they signal to birds that they may be poisonous and not worth eating. These similarities have apparently been good enough to also confuse humans, with many scientists struggling to definitively classify monarchs and their relatives for over 100 years. In this case, monarchs and tiger butterflies (Danaus genutia) were only officially designated separate species in 1954. Without today’s instantaneous exchanges of information (#monarchsplit?#butterflygate?), it’s easy to see how the 1975 chromosome count may have accidentally been conducted on tiger butterflies, which do live in India.

The best answers beget new questions

Unfortunately, the original authors of that study aren’t available to answer these questions. Fortunately, science can dig into the question anyway by looking for more evidence in the form of butterfly DNA. Six young, verified monarchs have since been found to have 28 chromosomes, which seems like it should settle the debate, but things get better. A second paper has recently been published asserting 30 chromosomes again, which is where scientific investigation may really have a chance to shine. While the confusing history of monarch identification might have created a bit of intrigue, new, conflicting results might point to new, larger scientific questions about these butterflies’ genetics. Butterflies in the same genus as monarchs have been known to have some unusual variability in their chromosomes, so all this investigation may lead to a more profound understanding of these insects, well beyond a single figure in an old publication.

My second grader said: They do look similar, but tiger butterflies have more white

My four-year-old then said: Maybe that’s because one is a boy and one is a girl?

Tiger butterflies do generally have more white on their wings, but that wouldn’t really be confused with the differences between male and female monarchs. Male monarchs can be identified by claspers on their abdomens, to small black spots along the dark veins of their hind-wings, and thinner black veins in their wing markings overall. Both males and female do have some white spots, but not the in the concentration you find on a tiger butterfly’s wings.

Source: Monarch miscalculation: Has a scientific error about the butterflies persisted for more than 40 years? by Michael Price, Science

On February 6th, 2017 we learned about

Yeasts may let us cut cows out of the process of making milk

Milk is a substance that has, for millions of years, been made exclusively by mammals. Most species use the mix of water, proteins, minerals and sugar to feed their babies exclusively, but humans have have decided that it’s worth consuming dairy throughout our lives, even if we get it from other animals like cows and goats. With demand growing for dairy, but livestock requiring a lot of resources and space to raise, new sources of milk are being developed, even from well outside the animal kingdom.

Protein production

The newest form of milk should look a lot like what we’re used to getting from cows, but it will largely be sourced from yeasts. This isn’t to say that we’ll be directly milking yeasts, but that the yeasts will grow many of the crucial proteins, like casein, normally produced by cows. Researchers were able to isolate which genes are responsible for these proteins in the cows, and then inserted those genes into the yeast’s relatively simple genome.

With yeast producing these proteins, many of the other ingredients in bovine milk can also be sourced without actual cows. There are some things beyond the reach of yeast though, such as sugars like lactose (or some equivalent) and immunoglobins that help protect against bacteria like E. coli and Helicobacter pylori.

Alternatives to animals

Yeast-sourced milk isn’t the first cowless milk option, but it’s the closest you’ll find to the real thing. Soy and rice milks have been fairly decent analogs to bovine milk for a while, but yeast will offer something much closer to a mammalian food-source without involving too many large, resource-heavy mammals (unless you count the humans involved…) It will be a while before it can compete with the price of milk from cows, but as people become more sensitive to how much it costs the world to raise even a single cow, this might seem like a very efficient option.

Source: Your Breakfast Is About to Take a Weird Turn by Marta Zaraska, Mother Jones

On October 27th, 2016 we learned about

Sorting out when exactly snake fangs evolved to be so scary

Not to undersell the gravitas of a 500-pound anaconda, but most people’s initial image of a ‘scary snake’ involves a view of some very specialized fangs. We’re not wrong to be concerned with the fangs of cobras and vipers, since these highly evolved teeth can pierce and deliver potentially fatal venom with an impressive degree of efficiency. Of course, any threat severe enough to have possibly influenced the evolution of other animals didn’t happen easily, and in the case of venomous snakes seems to have involved two major milestones: moving venom-delivering teeth to the front of the mouth, then transforming those teeth into tubes.

Fangs up front

It’s forgivable if you’ve never noticed how many teeth the average snake has, especially if you’re distracted by bigger fangs right up front. Those fangs, as venom-delivery devices, were once located in the back of the a snake’s mouth, closer to where the venom producing glands are located. Some snakes, like the boomslang (Dispholidus typus), still carry their relatively inefficient fangs at the back of their mouth, meaning they have to open their jaws as wide as possible before gnashing on their prey to deliver otherwise potent venom. It can work, but around 60 million years ago, the shared ancestor of vipers and cobras made a pretty big improvement on this arrangement.

Looking at developing snake embryos, researchers noticed that fangs first develop at the back of the mouth in every species. However, cobras and vipers then have a second key stage thanks to mutations on the Sonic hedgehog gene, where the fangs basically become uncoupled from the other teeth, migrating to the front of the mouth. This is partially thanks to that section of the jaw growing faster in these snakes, “moving” anatomy around relative to other parts of the mouth. It was apparently a successful enough shift to warrant dropping other structures, mainly the front row of teeth that used to occupy that part of the mouth.

When teeth became tubes

This was only one part of snakes’ predatory prowess though, since the original, primitive fangs weren’t the venom syringe we see in modern animals. Fossils have proven that snakes had modern, tube-shaped fangs by the Miocene period, between five to twenty million years ago, but things are a little murkier before that. There isn’t a lot of evidence about the development of enclosed teeth, but we do know that snakes and other reptiles were toting venom in their mouths as far back as the Triassic period, around 200 million years ago.

Uatchitodon was a genus of carnivorous reptiles known only from their teeth, but their teeth tell us a lot. An older species, Uatchitodon kroehleri, likely delivered venom with grooved teeth, like a modern gila monster (Heloderma suspectum). Rather than piercing and injecting venom, these teeth require a bit more mashing to deliver the toxin to its target. A later species, Uatchitodon schneideri, known only from one tooth, seems to have made the leap to tubular teeth though, possibly providing this evolutionary upgrade to snakes before they moved their fangs to the front of their mouth.

Without more fossilized snake fangs, it’s hard to say for sure, but looking at the growth of replacement fangs, there is a developmental stage where fangs grow first with grooves, then cover seal those grooves up to make venom-delivering tubes. This developmental sequence makes sense, because a groove could still carry toxins well enough. The evolutionary progression of these teeth makes it clear that snakes haven’t been willing to settle for good enough though, pushing these two teeth as dangerous as possible.

Source: Snakes were originally rear-fanged, Leiden University News & Events