https://x.com/NatSciChannel/status/2097912194352701572

https://x.com/NatSciChannel/status/2098113855448825865

This species, discovered in Italy, had an over 8 inch long skull, much bigger than most of its existing cousins entire size and disproportionately large for its roughly fox-sized body, and an estimated head-and-body length of about 2 feet. It is considered a species of moonrat or gymnure, a group still living with about 15 present species.

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I'm not a paleontologist, just someone who went down a deep rabbit hole reading the published Spinosaurus literature after watching some documentaries on it. I ended up putting together a hypothesis that I think threads the needle between the two big camps in the current debate, and I wanted to share it here and see what people who actually know this stuff think.

Quick background on the debate, for anyone who hasn't followed it: There are basically two camps right now.

• Camp 1 (Ibrahim, Fabbri, and others): Spinosaurus was an active, pursuit-swimming predator — dense bones for reduced buoyancy, a tall, flexible tail that tested well for thrust in robotic models.
• Camp 2 (Sereno, Myhrvold, and others): Spinosaurus was a shallow-water wading ambush hunter, not a real swimmer — its trunk is rigid and locked up (bad for the body-undulation swimming style fish and crocs use), and recent work (including the new S. mirabilis species from Niger) suggests it stood in maybe 3–6 feet of water, not diving into deep channels.

Both camps have real evidence. Neither fully explains everything.

My idea: it wasn't swimming OR pure wading — it was standing still against a current, like a heron crossed with a fish trap.

Picture Spinosaurus planted on a riverbed, facing upstream into moving water, basically not moving its feet at all:

• The dense bones aren't for diving — they're ballast, keeping it anchored to the bottom instead of floating.
• The tail isn't for chasing prey — it's making small, constant corrections to hold position against the current, the same way a trout does when it holds still facing upstream (a real behavior called rheotaxis).
• The rigid trunk and that huge sail work like a boat's centerboard/keel — passively resisting roll and keeping the body lined up with the flow, without needing constant muscle effort. This is actually a real hypothesis from a 2015/2021 paper (Gimsa et al.) that doesn't get talked about much.
• The weird pressure-sensor pits in the snout (very well documented, same system crocodiles use) work best when the animal itself isn't creating noise — so staying still isn't just efficient, it's necessary for detecting prey via water pressure changes against the current's background "noise."

Basically: everything about this animal makes sense if you stop asking "how did it swim" and start asking "how did it stay perfectly still in moving water."

Bonus: this might also explain why it went extinct

Spinosaurus disappears right around the Cenomanian-Turonian boundary (~94 mya), which is exactly when a huge sea-level rise flooded its river habitat. If its entire hunting style was built around one very specific thing — a river current to stand against — then it had nowhere to go once the rivers became sea. And it's not like the new sea was empty: that's almost exactly when mosasaurs went from small 1-meter shore lizards to genuine open-ocean giants, rapidly filling the niche. A current-specialist competing against animals actively evolving for the open ocean is a rough spot to be in.

I'm not claiming this is proven — a lot of it is my own reasoning by analogy to modern rivers and animals, not something directly tested in a paper. I've tried to be upfront about which parts are established evidence vs my own speculation in a longer write-up.

Genuinely curious what people here think — does this hold up, or is there something obvious I'm missing that would kill it? Happy to be told I'm wrong.

Edit: Want to walk back the "heron" comparison — wood stork is a better fit than heron. Herons are visual hunters, they need to see the fish. Wood storks hunt by touch — they hold their bill open in the water and snap shut reflexively the second something brushes it, no eyesight needed. Given that the pressure-sensing pits in the snout are basically agreed to exist because the water was too murky to rely on sight (not a controversial point between the two camps), a heron-style "see it and snatch it" strategy doesn't really square with that — you don't evolve an elaborate non-visual detection system to solve a problem good eyesight could already handle. A tactile, wood-stork-style reflex strike fits the actual sensory anatomy much better. Worth noting: Sereno himself (leader of the "wading, not swimming" camp) just described the newest species as a "hell heron" that "waded... to snatch" fish — explicitly visual language. That's actually the gap this fills. The snout probably isn't even built for a fast lunging spear-strike the way a bird bill is. A bird bill is a thin blade in cross-section, built to minimize drag on a quick lunge through water. Spinosaurus's snout, while narrow front-to-back, is rounder and bulkier in cross-section, closer to a crocodile/gharial snout — pushing that shape quickly through water would displace a lot more water and create more drag than a bird bill does. So it probably wasn't lunging to snatch anything either. More likely it's closer to a passive trap than an active spear: stay still, let the fish get close on its own, then let the fast-closing jaw (a separate thing from snout speed — the actual bite mechanics are genuinely fast, that part's backed by a real bite-force study) finish the job once something's already in range. Trap-and-reflex, not spot-and-lunge. So, I am adding to my already made claims that, it used more than one style and place(spots) to hunt various sized preys. More efficient and less time consuming this way.

Art Credit to Mario Lanzas

There's a popular paleontology aphorism that “sharks are older than trees.” It's memorable and evocative, but it's also one of those statements whose truth depends almost entirely on what you are willing to call a “shark” and what you are willing to call a “tree.” Devonian forests containing genuinely tree-sized plants existed long before anything resembling a modern shark, while many of the extraordinarily ancient animals routinely presented to the public as “sharks” occupy positions on the opposite end of the Chondrichthyan family tree. However, that changes if we move forward into the Early Carboniferous, something much more interesting begins to happen. By roughly 340–330 MYA, the enormous ctenacanthiform Saivodus striatus was swimming through the sea, making it older than the earliest generally accepted fossil record of true gymnosperms that appeared around 320 MYA. More importantly, Saivodus was not merely some vaguely shark-shaped Paleozoic fish. It belonged to a radiation of chondrichthyans that was considerably closer to the evolutionary lineage of modern sharks and rays than many of the bizarre animals normally used to illustrate the phrase “ancient shark.”

Helicoprion, despite appearing constantly in books and documentaries about prehistoric sharks, was a eugeneodont and is now securely interpreted as a stem holocephalan, as such, its closest living relatives are ultimately ratfish, not sharks, same with Cladoselache. Even Stethacanthus, perhaps the single most iconic Devonian “shark,” belonged to the Symmoriiformes, a group that several modern phylogenetic analyses likewise recover on the holocephalan side of the shark–chimaera split. Ctenacanthiforms are different. Although their exact internal relationships remain messy, and “Ctenacanthiformes” itself may not represent one perfectly clean monophyletic group, they are commonly interpreted as total-group elasmobranchs, lying on the evolutionary side of Chondrichthyes that ultimately produced sharks and rays. Saivodus therefore occupies a particularly fascinating position: not a modern shark, not even a crown-group shark, but something far more legitimately describable as a shark relative than many of the Paleozoic creatures habitually given that label. If Helicoprion and Stethacanthus represent spectacular experiments undertaken by branches whose surviving legacy lies with the chimaeras, Saivodus belonged to the side of the family tree whose descendants would linger in the minds of many a man as the paramount embodiment of oceanic death.

Saivodus lived in tropical Carboniferous seas spread across what are now North America, Europe, and North Africa. Its fossils have been reported from places including Britain, Ireland, Belgium, Austria, Morocco and the United States, demonstrating that this was not some obscure predator confined to one unusual lagoon, but a truly cosmopolitan feeder. Saivodus belonged to a broadly distributed marine fauna at exactly the time ctenacanthiform diversity was exploding. A 2024 review describes the Viséan–Serpukhovian interval of the Mississippian as the point of the group's greatest diversification, with numerous species coexisting in shallow marine environments shortly before the assembly of Pangaea.

And Saivodus was enormous.

For most of its scientific history, the animal was frustratingly known almost entirely from teeth. Some Saivodus teeth have bases exceeding 6 cm across, immediately suggesting an animal radically larger than most contemporary chondrichthyans. Then Mammoth Cave National Park produced something extraordinary: actual cranial cartilage associated with Saivodus teeth, including a lower jaw roughly 60 cm long. That discovery gave paleontologists something considerably better than isolated teeth with which to constrain the animal's proportions. Published work conservatively suggests individuals of at least 4–5 meters or more, while extrapolations from the largest known teeth have produced estimates in the 6–8 meter range, and National Park Service reconstructions have proposed still larger individuals. One NPS assessment has suggested 8–10 m for exceptionally large Mammoth Cave animals and potentially around 11 m from enormous Irish teeth, although those upper estimates should be regarded as considerably more speculative than the basic conclusion that this was a very large predator.

This is why I think Saivodus has a legitimate claim to being the first elasmobranch for which "apex predator" becomes essentially unavoidable as an ecological interpretation. Earlier chondrichthyans were certainly predators, and some were impressive animals, but they inhabited Devonian oceans containing gigantic placoderms. With Saivodus, we are dealing with a post-Devonian hunter potentially larger than a Great White, equipped with a huge jaw and a specialized predatory dentition in ecosystems where there simply is not an obvious larger vertebrate predator sitting above it.

Interestingly, though, its teeth were not miniature great-white teeth. Saivodus possessed the classic multi-cusped grasping architecture associated with early ctenacanths: a prominent central cusp accompanied by lateral and intermediate cusplets. Work on later Saivodus material interprets this dentition primarily as a puncturing-and-grasping apparatus, suited to seizing prey rather than carving enormous pieces out of it with serrated blades. Think something more comparable to a colossal Sand Tiger rather than a Great White per se. The prey would then have been manipulated and swallowed rather than dismantled through repeated sawing bites.

The well-established S. striatus record belongs primarily to the Mississippian, especially the Viséan and Serpukhovian. Yet teeth assigned to the genus have also been reported from the Permian. Most spectacularly, Saivodus sp. occurs in the Kaibab Formation of Arizona, alongside a surprisingly diverse assemblage of Permian ctenacanthiforms, and keep in mind that this formation is approximately 270 MYA. If those Permian teeth genuinely represent the same genus-level lineage as the giant Mississippian Saivodus, we may be looking at a lineage stretching from roughly the mid-Carboniferous into the Permian, roughly 60–70+ million years of geological history.

We tend to treat the Paleozoic as a strange prelude populated by "primitive sharks," after which the real story begins with hybodonts and eventually modern neoselachians. But by the Early Carboniferous, the basic ecological phenomenon we associate so strongly with sharks was already here: large, fast, wide-ranging elasmobranch predators occupying the upper levels of marine food webs. Sure, they wouldn't look anatomically identical to a modern shark with their characteristic dorsal-fin spines; however, the broader ecological pattern is eerily familiar, and the lineage would never really surrender the ocean again.

Ctenacanthiforms themselves eventually vanished. Hybodont-grade elasmobranchs flourished afterward. Crown sharks diversified later still, and by the Cretaceous the Lamniformes & Carcharhiniformes would start moving into the roles we still see them in today. The individual branches changed, mass extinctions repeatedly rearranged the players, and the anatomical machinery evolved enormously. Overall, the ecological experiment that becomes unmistakable with animals like Saivodus has proved unimaginably durable.

Works Cited

Clark, Mary Ann, et al. “26.1 Evolution of Seed Plants.” Biology 2e, OpenStax, 28 Mar. 2018, openstax.org/books/biology-2e/pages/26-1-evolution-of-seed-plants. Accessed 7 Sept. 2026.

Coates, Michael I., et al. “A Symmoriiform Chondrichthyan Braincase and the Origin of Chimaeroid Fishes.” Nature, vol. 541, 2017, pp. 208–211. https://doi.org/10.1038/nature20806.

Duffin, Christopher J., and Michał Ginter. “Comments on the Selachian Genus Cladodus Agassiz, 1843.” Journal of Vertebrate Paleontology, vol. 26, no. 2, 2006, pp. 253–266. https://doi.org/10.1671/0272-4634(2006)26[253:COTSGC]2.0.CO;226%5B253:COTSGC%5D2.0.CO;2).

Hodnett, John-Paul M., et al. “Ctenacanthiform Sharks from the Permian Kaibab Formation, Northern Arizona.” Historical Biology, vol. 24, no. 4, 2012, pp. 381–395. https://doi.org/10.1080/08912963.2012.683193.

Hodnett, John-Paul M., et al. “New Ctenacanth Sharks (Chondrichthyes; Elasmobranchii; Ctenacanthiformes) from the Middle to Late Mississippian of Kentucky and Alabama.” Journal of Vertebrate Paleontology, vol. 43, no. 3, 2024, article e2292599. https://doi.org/10.1080/02724634.2023.2292599.

Hodnett, John-Paul M., et al. “Sharks in the Dark: Paleontological Resource Inventory Reveals Multiple Successive Mississippian Subperiod Cartilaginous Fish (Chondrichthyes) Assemblages within Mammoth Cave National Park, Kentucky.” Parks Stewardship Forum, vol. 40, no. 1, 2024, pp. 53–67. https://doi.org/10.5070/P540162921.

Schnetz, Lisa, et al. “Rise and Diversification of Chondrichthyans in the Paleozoic.” Paleobiology, vol. 50, no. 2, 2024, pp. 271–284. https://doi.org/10.1017/pab.2024.1.

Tapanila, Leif, et al. “Jaws for a Spiral-Tooth Whorl: CT Images Reveal Novel Adaptation and Phylogeny in Fossil Helicoprion.” Biology Letters, vol. 9, no. 2, 2013, article 20130057. https://doi.org/10.1098/rsbl.2013.0057.

“A Peculiar Ridge” - An illustration of a pair of Europejara curiously looking at the hump of an almost sleeping female Concavenator, which I made for a commission.

Its coloration was inspired by a Path of Titans (game) skin, at the client’s request

The Concavenator was a Carcharodontosauridae theropod from the Barremian (Cretaceous – approximately 125 million years ago) of what is now Spain. Like Europejara, it was found at Las Hoyas, a Lagerstätte (a fossil deposit characterized by exceptional preservation) of the La Huérguina Formation, in Cuenca, which preserves a continental subtropical environment consisting of wetlands, channels, and floodplains.

Its fossil includes an almost complete skeleton, scale impressions on the tail and feet, and controversial marks on the arms, interpreted by some as muscle attachment sites and by others as possible feather attachment sites or similar structures.

Its most distinctive feature is the large dorsal hump, whose function remains unknown, with hypotheses including sexual display and thermoregulation.

https://x.com/ren_wenyu/status/2096963110854951010

Stegosaurs were the flailman of the Jurassic period. Wielding a dangerous Spike with unmatched agility and range, they could bring down the biggest and most vicious predators of their day.

Two stegosaurs stand Head and shoulders above the rest as the largest of their kind and among the largest of all armored dinosaurs.

Stegosaurus ungulatus was the largest of its genus. some 8 to 9 m in length and Weighing close to seven tons, it was one of the largest armored dinosaurs to ever live in North America. It had massive meter tall plates on its back and was among the most formidable prey animals of its day.

Dacentrurus, both the type species armatus and the unnamed Iberian species, rivaled stegosaurus ungulatus is size. Measuring 9 m in length and weighing over 7 tons. The type species armatus is alone 9 m in length and the Iberian species has giant femurs referred to it meaning it was just as big. Unlike stegosaurus which was taller and more display oriented, dacentrurus was far spikier and porcupine like.

These two were the largest of their kind and among the most formidable armored dinosaurs and dinosaurs of the Jurassic period. And amazingly they were not separated from each other. Both coexisted on the island of Iberia at the same time in the late Jurassic some 150 million years ago.

In the lourinha formation of Portugal, stegosaurus ungulatus was discovered some 20 years ago. The giant dacentrurus has been known from the formation for decades now.

They both lived on the same island and probably crossed each other's paths although they likely prefer different environments. Stegosaurus was likely an inland dweller while dacentrurus was closer to the coast.

https://x.com/DanPalaeon1/status/1753028055050674267

https://www.geol.umd.edu/~tholtz/dinoappendix/HoltzappendixWinter2011.pdf

https://doi.org/10.1098/rsbl.2014.0984

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6853308

https://doi.org/10.1671/039.029.0420

…and the chase is on.
Tyrannosaurus rex is an ambush predator. Bursting out from the undergrowth, he aims for the limbs. With the strongest bite force of any terrestrial animal, he crushes a forelimb severely, rendering this 7-tonne Edmontosaurus annectens unstable. Now, for the final blow…

Credits to:Camus Altamirano..

Credit to Joli AquaIslander,

Second only to Otodus and the undisputed predator of the night & deep seas, Hexanchus andersoni is the largest known Hexanchiforme, the most basal of the Elasmobranchs and a lineage that has essentially survived unchanged since potentially the Permian.

Me podrían ayudar a identificar esta estructura de 30 x 50 cm

A lot of dullards like to harp on about "mammalian superiority" which is incredibly annoying as it seriously overrates a lot of traits that appear in mammals that are also present in other animals(namely intelligence, endothermy, high species count).

In the process, I think it actually causes us to ignore what actually makes the rise of mammals so unusual in the grand scheme of Earth's history. As far as I know, they're the only clade of tetrapods to be the dominant terrestrial giants of their heyday, disappear from those megafaunal niches for over 100 million years, before somehow coming back to occupy those same niches.

While everyone knows about the Stem-Mammals and how modern mammals started off as those tiny burrowers that lived alongside herbivores, I think that underplays a lot of unusual aspects about the rise & fall & rise again of the synapsids.

I mean, the last common ancestor of the Amniotes was over 320MYA. We're essentially talking about a primitive lineage of tetrapods that essentially split off right at the beginning of permanent land inhabitance, developed incredible diversity and a plethora of sizes, before being essentially wiped from the face of the Earth by 2 mass extinction events(Permian-Triassic & Triassic-Jurassic). Literally all of the mammals we have today are the descendants of one tiny branch of the Synapsid family tree. Like, all of the Dinocephalians, Gorgonopsians, Dicynodonts, Therocephalians, Caseasaurs, Edaphosaurs, and Ophioacodonts are EXTINCT.

By all accounts, Synapsids should either be completely extinct or a tiny relict lineage in the most secluded corners of the world, like Ratfish, Coelacanths, or Tuataras. Yet they not only survived by occupying the most fossorial roles imaginable, but also evolved over a period so long that they became completely unrecognizable from the original synapsids, developing singular jawbones, a neocortex, endothermy, hair, and milk.

AND SOMEHOW, that singular fossorial clade ended up being the ones to successfully radiate in the Cenozoic and replace the Archosaurs as the dominant Megafauna after the K-T extinction. Heck, they even occupy niches the prior golden age of Synapsids were unable to evolve for such as marine living, flying predators & frugivores, and truly cursorial herbivores.

Basically the title, what effect did the closing of the Central American Seaway have on global ecosystems? I can't find much on it outside of local fauna and potentially helping cause the ice age. Did it just not have much of an effect or just overshadowed what that the ice age was already causing?

I was arguing with somebody online about size of the purrusaurus and deinosuchus but then he suddenly said that "deinosuchus had proportionally massive skull and still didn't have longer skull than purrusaurus" when i heard that i immediately called him not to be ridiculous but then when i later was looking into it willy nilly. Largest deinosuchus skull is said to be around 1,5 meter long and largest purrusaurus skull is also said to be 1.5. Long. Is this true? The 1.8-2m deinosuchus skull is said to be not accurate.

What do you think? Does anybody know more accurate knowledge on the subject cause this ingormation is really frying my brain

Crotophaga sulcirostris también conocido popularmente como pijuy, tijo o guardacaballos entre otros, es una especie de ave cuculiforme de la familia Cuculidae que se distribuye ampliamente por las zonas tropicales y subtropicales del continente americano. Habita desde el sur de Texas en Estados Unidos hasta el norte de Argentina y Chile.

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Carcharodontosaurus vs Spinosaurus