The ocean rejected dinosaurs, one gland at a time
Nas margens entre a terra e o mar, o Spinosaurus ocupou um lugar que nenhum outro dinossauro jamais alcançou — e um novo estudo sobre seus fósseis começa a explicar por quê. Pesquisadores identificaram, nas cavidades do crânio do animal, vestígios de glândulas de excreção de sal posicionadas acima das órbitas oculares, estruturas análogas às encontradas em aves marinhas modernas e iguanas. A descoberta não apenas confirma a vocação aquática do Spinosaurus, mas lança uma pergunta mais profunda sobre os limites fisiológicos que impediram toda uma linhagem de criaturas de conquistar o oceano.
- O Spinosaurus passou décadas sendo reconstruído e desconstruído pela ciência — sua identidade como predador aquático era sugerida pelos ossos, mas nunca completamente explicada pela biologia.
- Viver no mar impõe um desafio invisível e letal: o excesso de sal destrói o equilíbrio interno dos organismos, e poucos animais evoluíram mecanismos para superá-lo.
- A análise de crânios fósseis revelou depressões ósseas que indicam a presença de glândulas filtradoras de sal — tecido mole que raramente fossiliza, mas que deixa marcas na estrutura do osso.
- A descoberta, celebrada pelo paleontólogo Andrea Cau como uma janela rara para a fisiologia de animais extintos, conecta anatomia, função e ecologia de forma inédita.
- O achado recoloca a questão central: se o Spinosaurus resolveu o problema do sal, por que nenhum outro dinossauro seguiu o mesmo caminho rumo ao oceano?
O Spinosaurus era uma criatura de proporções difíceis de imaginar — dezessete metros de comprimento, oito toneladas — e durante décadas a ciência não conseguiu decidir o que ele realmente era. Seus ossos eram densos demais para um animal puramente terrestre, sua cauda sugeria propulsão aquática, seus dentes lembravam os de um pescador. Mas uma questão persistia: ele poderia ter sobrevivido de verdade no ambiente marinho?
Viver no oceano exige mais do que nadar. O sal está em toda parte na água do mar, e em excesso é letal. Aves marinhas e certos répteis modernos resolveram esse problema evoluindo glândulas especializadas que filtram o sal do sangue e o excretam. Essas glândulas são tecido mole — quase nunca fossilizam. Mas deixam rastros: pequenos canais e depressões no osso onde um dia estiveram.
Foi exatamente isso que pesquisadores encontraram nos crânios do Spinosaurus. Acima de cada órbita ocular, havia marcas anatômicas de glândulas filtradoras de sal, posicionadas de forma quase idêntica às das aves marinhas vivas. O paleontólogo Andrea Cau, da Universidade de Bolonha, descreveu o achado como raro: pela primeira vez, era possível conectar fisiologia, ecologia e dieta em um animal extinto a partir da forma do próprio crânio.
As glândulas não alterariam a aparência do animal — diferente das iguanas marinhas, que desenvolvem crostas brancas de sal no rosto, o Spinosaurus carregava as suas sob a pele, em depressões acima do osso. Mas a anatomia conta uma história sobre adaptação e limite. O Spinosaurus havia evoluído a solução para o problema do sal. Conseguiu fazer o que nenhum outro dinossauro fez. E ainda assim, a linhagem terminou com ele.
A pergunta que emerge não é por que o Spinosaurus desenvolveu essas glândulas, mas por que nenhum outro dinossauro seguiu o mesmo caminho. A resposta sugerida pelo estudo é perturbadora em sua simplicidade: o custo fisiológico da vida marinha pode ter sido alto demais para a maioria das linhagens de dinossauros. O Spinosaurus foi um experimento bem-sucedido — mas solitário. Talvez tenha permanecido sozinho não por ser excepcionalmente capaz, mas porque o oceano era simplesmente exigente demais para o restante de sua espécie.
Spinosaurus was enormous—seventeen meters long, eight tons of muscle and bone—and for decades, scientists could not agree on what it actually was. Between 2014 and 2024, its reconstruction changed roughly six times, each version contradicting the last. Was it a heron-like hunter stalking shallow water? A fully aquatic predator with a paddle tail and teeth built for gripping fish? The bones themselves seemed to argue for the water: they were unusually dense, the kind of density that helps an animal stay submerged. But the deeper question—the one that kept paleontologists circling back—was whether Spinosaurus could have actually survived there.
Living in the ocean poses a problem that most land animals never face. Salt is everywhere in seawater, and while sodium is essential for regulating fluid balance and transmitting nerve signals, too much of it is lethal. Some modern marine birds and certain reptiles solved this problem by evolving specialized glands that filter salt directly from the bloodstream and excrete it. These glands are soft tissue, which means they almost never fossilize. But they leave traces—small channels and depressions in bone where they once sat.
When researchers examined Spinosaurus skulls, they found exactly those traces. Above each eye socket, they discovered anatomical evidence of salt-filtering glands positioned almost identically to those found in living marine birds. The discovery was striking not because it proved Spinosaurus lived in water—the dense bones and paddle tail already suggested that—but because it revealed something about the limits of dinosaur physiology. Here was a creature that had evolved the machinery to handle marine life, yet it remained an exception. No other dinosaurs followed this path. No lineage of fully aquatic dinosaurs ever emerged.
Andrea Cau, a paleontologist at the University of Bologna, called the finding rare because it connected physiology—the actual function of the gland and its role in salt regulation—to ecology and diet in an extinct animal. Reconstructing the internal workings of extinct biology is notoriously difficult. Most of what we know about dinosaurs comes from bone. Soft tissue, organs, glands—these vanish. Yet here, in the shape of the skull itself, was a window into how Spinosaurus managed a challenge that most dinosaurs never had to face.
The glands themselves would not have changed Spinosaurus's appearance much. Unlike marine iguanas, which have salt glands positioned inside the skull and develop visible white crusts of salt deposits on their faces after excreting the mineral, Spinosaurus carried its glands in depressions above the bone, covered by skin. The animal would have looked unremarkable. But the anatomy tells a story about constraint and adaptation. Spinosaurus could handle the salt. It could hunt in the water. It could do what no other dinosaur managed to do. And yet the lineage ended with it.
The question that emerges from this discovery is not why Spinosaurus evolved salt glands, but why nothing else did. Why did dinosaurs never fully commit to the ocean the way marine reptiles and, later, marine mammals did? The salt glands suggest one answer: the physiological burden of marine life may have been too steep for most dinosaur lineages to overcome. Spinosaurus was an experiment that worked, but only once. The glands that allowed it to survive in the water may have also been a sign of how difficult that survival actually was—a solution so specialized, so costly, that no other dinosaur ever bothered to evolve it. In the end, perhaps Spinosaurus remained alone not because it was uniquely successful, but because the ocean was simply too demanding for the rest of its kind.
Citas Notables
The discovery is a rare opportunity to connect physiology—the function of the gland and its role in salt regulation—and ecology in an extinct dinosaur— Andrea Cau, University of Bologna
La Conversación del Hearth Otra perspectiva de la historia
So we found salt glands in Spinosaurus. But why does that matter? Lots of animals have salt glands.
Because Spinosaurus is the only dinosaur we know of that had them. That's the puzzle. If living in water was such a good strategy, why didn't other dinosaurs evolve the same solution?
Maybe they didn't need to. Maybe they just stayed on land.
Right, but Spinosaurus clearly went into the water. Dense bones, a paddle tail, teeth for catching fish. It solved the salt problem. So the question becomes: what stopped every other dinosaur from doing the same thing?
You're saying the salt glands were hard to evolve?
Not hard exactly. Spinosaurus managed it. But maybe the cost was too high—the energy, the physiological strain. Spinosaurus could do it, but the trait never spread to other lineages. It was a dead end.
So the ocean rejected dinosaurs?
In a way. Not because dinosaurs couldn't adapt to water. Spinosaurus proves they could. But the adaptation was so demanding that only one lineage ever bothered. And that lineage didn't last.