A vida do Espinossauro

The true appearance of Spinosaurus. I have a big question! It troubled the minds of paleontologists, artists and admirers of life in the deep past throughout the 20th century. For the first time in the 110 years since its discovery, we have a good idea of ​​what it looked like in life, and now, we’re trying to understand its ecology more deeply. The big questions about Spinosaurus are no longer about what it was like, but how it lived. Did he swim? Or did it just sit at the water’s edge like a giant trap? There’s nothing obvious about a 50-foot-long, 10,000-pound dinosaur with a giant sail on its back and a host of adaptations for aquatic life. Today, you’ll get to know Spinosaurus like never before. How was he discovered? What are its relatives and where does it fit in dinosaur evolution? What was he like as a living, breathing animal? What are the hypotheses to explain the sail on the back? How did he eat and where did he live? And what can Spinosaurus teach us about paleontology itself? This is the story of a dinosaur that has gotten weirder and weirder with time, that has tested all the abilities of science and still challenges humanity’s ability to reconstruct one of the most magnificent creatures of the deep past. Let’s go? My name is Abner and welcome to ABC Land. Considerations Most Spinosaurus fossils are just teeth. There are thousands known. We have had a recent explosion of specimens being found, but still very incomplete ones. In addition, all African and South American Spinosaurids, which are the overwhelming majority, suffer from an evil: The clandestine market, private collecting and alterations. As regions of Egypt and Morocco where this animal is found have many poor people, this fuels a huge illegal trade in fossils. These fossils that are mined amateurly are often partially destroyed, heavily damaged and sometimes even altered to appear more valuable. The irritator’s skull, for example, was so modified that it was difficult to understand what was original, earning the name: irritator. The consequence of this underground market is that there is a lot of Spinosaurus material that is not known to science, decorating the living room of wealthy collectors. There are many fossils that scientists are simply unaware of or do not have access to because they belong to private collections. So if it weren’t for that, most likely Spinosaurus’s life would be much less enigmatic. It’s much easier to study Tyrannosaurus rex, an animal that we know of several complete skeletons, several similar animals from different parts of the world. Many of the discoveries about Spinosaurus tell the story of how we went, with each new body part being found, realizing that it was an increasingly aquatic animal. Starting with the skull and teeth, specialized for piscivory, which already suggested that they lived close to aquatic environments, at least. It was thought that they might behave like bears, being opportunistic predators and generalists on dry land, but with an ability to catch fish out of the water. But looking at the skeleton of a bear, there is no obvious adaptation for catching fish, as is the snout of Spinosaurids. In the same way that the skeleton of a hippopotamus does not make it clear that it is an animal that spends half the day submerged. Sometimes ecology is not explicit in anatomy, and the example of the hippopotamus will come in handy when we come to understand the lives of some of Spinosaurus’ relatives. We have to look deeper than what the skeletal structure alone suggests. Spinosaurus was a unique dinosaur in many ways. Many of the characteristics of this animal are exceptions, peculiarities. That’s why we got him so wrong. One of the most common and fundamental things for scientists in any field is being able to test their hypotheses directly. But paleontology is a difficult science. There is no way to directly study Spinosaurus because it is now extinct. No animal like this has lived in the last 70 million years, and never will again. All we have are shards of rock that borrowed their shape from the bones of these animals. This means that scientists who set out to study Spinosaurus have to be very methodologically creative. But all these methods, in one way or another, follow the principle of comparison. To get closer to reasonable hypotheses, we use comparisons between extinct and living beings. Sometimes it helps, sometimes it hinders. But with Spinosaurus, there is nothing comparable. Retro Spinosaurus was the best representation possible at the time, based on comparison with other giant theropods, or megatheropods. It was a conservative extrapolation, based on the scrap material that Spinosaurus has always been. Modern discoveries have allowed us to get a closer look at this animal’s anatomy, and for the first time, no major parts are missing. But that only brought more questions. Discovery Spinosaurus aegyptiacus was described in 1915 by the great paleontologist Ernst Strommer. It was found in Egypt, Barariya formation, and the first specimen was very fragmentary, although already indicative of an animal unlike anything known. The recovered material was a piece of the lower jaw, some neck vertebrae, some ribs and vertebrae with huge neural spines that formed a sail on the animal’s back. The first fossil of a species is called the holotype of that animal. Holotype, in taxonomy, the science that classifies living beings, is the individual that serves as a comparison and representation of an entire species. Each species that has already been named has a certain individual that serves to give concreteness to that name, which must be kept in a museum around the world. The only one that doesn’t is the human being, because that would be weird. If the original material or if the first example used in the description of the species is lost, a new holotype, or neotype, is determined. When some better and more complete example appears, it can be designated a neotype without necessarily losing the Holotype. A few years later, more material was found, the specimen became known as Spinosaurus B, even more fragmentary than the first, but composed of a piece of the femur, a tibia and some vertebrae. These two individuals were able to give some idea of ​​what the animal looked like, but some essential parts were missing, such as the skull, the tail, a fuller sail, whole legs and paws, and the arms and hands. Early depictions of Spinosaurus try to fit it into the carnivorous theropod stereotype carried by T rex and Allosaurus. They gave the animal a more rounded, generic head and giant theropod body . In addition, it had an extremely tall bipedal posture, dragging its tail on the ground, as we once imagined that dinosaurs did. From the shape of the teeth, it was extrapolated that it could feed on fish, and that ‘s pretty much what we’ve known about Spinosaurus for 100 years. Stromer also described other very important Egyptian dinosaurs, such as the sauropod Aegyptosaurus, Bahariasaurus, the super carnivore Carcharodontosaurus and the giant crocodile Stomatosuchus. He saw his life’s work destroyed by Allied bombing of the Munik museum in 1944, 29 years after its discovery. He was an anti-Nazi, and he pleaded with the authorities to have the specimens in the museum’s collection protected against the coming war. It has never been heard of, and the only existing traces of Spinosaurus and Aegyptosaurus have been lost. What was left were Stromer’s drawings and photos taken of the material. Its inaccessibility caused many scientists to begin to doubt the very existence of Spinosaurus. For some time, it was accused of being a chimera, a combination of different fossils used to forge a sensational creature and make it famous. This would explain the absurd appearance of this animal. Before new Spinosaurus skeletons themselves were found, we began to understand more about what he was like, from discoveries of closely related animals of the same family. We call this set of about 13 genera of dinosaurs related to Spinosaurus the Spinosaurids. The family Spinosauridae has two subfamilies: Baryonychinae and Spinosaurinae. In 1983, Baryonyx was discovered in England. Its name means heavy claw and it is one of the most complete theropods ever found in England and the most complete spinosaurid ever excavated. It was considerably smaller than Spinosaurus, but still a large dinosaur at 10 meters in length. It has a long, thin skull, with a curved maxilla that completes the angle of the jaw. Huge muscular arms with curved claws draw attention to this animal. This was interpreted as an adaptation for piscivory, the habit of eating fish. This hypothesis is supported by the shape of the animal’s teeth, very different from those of terrestrial carnivores and very similar to crocodile teeth, conical and adapted for slippery prey. With the discovery of Baryonyx, the skull of Spinosaurus was finally upgraded to a more scientifically plausible one. This interpretation of Spinosaurus as a Baryonyx with a sail on its back is the one that was most popularized, particularly in Jurassic Park 3. Among the most obvious differences between the skulls of Baryonyx and Spinosaurus is the position of the nostrils, much more in the middle of the snout in the in the case of Baryonix, and rather retracted and close to the top of the skull in the case of Spinosaurus. At this point, there was already plenty of reason to think that Spinosaurus, like all Spinosaurids at some level, lived near water and must have been able to swim. Which is also pretty obvious in Jurassic Park 3. But things were about to get weirder and weirder. A series of other discoveries in Asia and South America would broaden our view of the diversity of Spinosaurids, as well as their wide geographic distribution. Among these new discoveries are Irritator and Oxalaia. In 1996, a Spinosaurid named Irritator was unearthed in the Araripe plateau, in Ceará. Today, many consider it a synonym of another Brazilian species, called Angaturama. If this is true, Angaturama ceases to be a valid taxon and is considered another example of Irritator. I have this beautiful irritator from Yvy figures here at home! He’s my most beautiful dinosaur replica, and if you haven’t seen their work yet , I highly recommend it, because there’s a lot of new stuff coming too. All Brazilian dinosaurs, to popularize and value our paleofauna. I’ll leave the link to their store in the description. In 1997, Paul Sereno and team described Suchomimus, an African spinosaurid from the subfamily Baryonychinae. Suchomimus differed from Baryonyx in being larger and in having tall, flat neural spines, forming a small sail on the animal’s back that extended to the tail. Despite adaptations to the skull and hand claws for catching fish, it was clearly a terrestrial animal. It has been hypothesized that these lower “sails” could be analogous to humpbacks in animals that support a fatty structure. If that’s the case, maybe it served to store fat in times of abundance and burn it when necessary. This is unlikely in the case of larger sails. In 1999, in the Romualdo formation, in Maranhão, the tip of the snout and a fragment of the maxilla of a giant spinosaurid, named Oxalaia quilombensis, were discovered. The similarities between Oxalaia and Spinosaurus, based on the quality of the material, is great enough for some scientists to classify Oxalaia as a synonym of Spinosaurus, proposing that Oxalaia could be a subspecies of Brazilian Spinosaurus. This is amazing, because it means that regardless of taxonomic status, there was a giant Spinosaurid in Brazil, possibly as big as Spinosaurus itself. Unfortunately, history repeated itself, and the material that belonged to Oxalaia was lost in the fire that decimated the national museum in Rio de Janeiro in 2018. An incalculable tragedy. … In 2010, a new species was found in Laos, Southeast Asia, called Ichthyovenator. The specimen is missing the skull and limbs, but has very interesting parts of a complete hip sequence with well-preserved vertebrae. They reveal that it had a sail, larger than Suchomimus and smaller than Spinosaurus, with the detail of not being perfectly round, but having a break at the hip. This made us rethink Spinosaurus’ own sail shape, moving from the round sail to some more square shapes. This speculation is completely valid, since until today we do not know of an entire sequence of vertebrates with well-preserved neural spines to the point of determining the exact shape of Spinosaurus sail in life. Each new animal ended up influencing our image of Spinosaurus, until it finally did. Neotype 2014 In 2014, Dr. Nizar Ibrahim’s team announced the discovery of the most complete skeleton of Spinosaurus ever found, in the Kem Kem formation, in Morocco. The new skeleton, belonging to a subadult, preserves pieces of the skull, neck, spine, pelvis and limbs. He received the status of Neotype for Spinosaurus aegyptiacus, that is, he is now our example and reference of this species, since the original material was lost. Ibrahim searched the Sahara desert for years for new traces of the bizarre Spinosaurus, destroyed since 1944. He teamed up with local fossil hunters to find the treasure he was looking for. He found Spinosaurus bones being sold in the underground market, and asked to be taken to the place where they had found them. The Kem Kem formation was deposited in a river system, and a number of amazing animals have been found there. But Spinosaurus itself seemed to hide, and it took a while to be rediscovered. This dig changed our perception of Spinosaurus forever. He just got a little more bizarre. The paper describing this new material is called “Semi-aquatic adaptations in a giant predatory dinosaur” . , with broad feet and possibly connected by skin. It seemed evident that Spinosaurus was a specialist, unique even among its own evolutionary family, carrying a tendency to become increasingly adapted for life in fresh and brackish water. That publication spawned an explosion of artists depicting the new Spinosaurus swimming in open and even very deep water. In fact, let’s realize that with this animal, nothing is so simple and obvious. Update 2020 Ibrahim knew there was a lot more where this material came from, and in 2018, he went back to the dig to find even more bones from the same individual. The result of this expedition was the publication of the article “Aquatic Locomotion Propelled by the Tail in a Theropod Dinosaur” from 2020, where the first almost complete tail, with about 30 vertebrates and some additional pieces of the foot were described. Now with a laterally flattened tail, resembling an oar, which was interpreted as evidence of underwater locomotion by Ibrahim’s team. This subadult male is our strongest evidence for the existence of Spinosaurus, and it is based on him that we know almost everything about this animal. For the first time in history, we had at least one good example of each of the most important parts of Spinosaurus, and we are able to reconstruct this animal better than ever before. But it is unreasonable to think that the surprises coming from this dinosaur are over, because we are only beginning to understand its way of life. Color and general appearance Today, we know that Spinosaurus is a piscivorous megateropod with a series of adaptations for semi-aquatic life. It was the LONGEST theropod ever, estimated at 13-15 meters. Even the torso of this animal was longer than usual. In length, it was the largest carnivorous dinosaur that ever lived, on a par with the giant Tyrannosaurids and Carcharodontosaurids. There are few comparisons for it. Among non-avian dinosaurs there is no other case of readaptation to aquatic life. Apparently, this is a very terrestrial group, that even though they lived for hundreds of millions of years and reached an absurd diversity, they never fully transitioned to an aquatic life, and generally they are not even semi-aquatic. That’s weird, because it’s something that happens all the time in mammals! It is important to remember that other marine reptiles are not dinosaurs. The dinosaurs that most adapted to life near water are birds, and even among them, there was no case of complete transition. The most aquatic of all aquatic dinosaurs is the penguin, which is very skilled in its underwater flight, but since it lays eggs, they still need to get back to dry land to reproduce. Thing whales don’t need and couldn’t do. So something, or many things kept dinosaurs out of the water. And that makes Spinosaurus a rebel! Many compare Spinosaurus to a crocodile In addition to being a semi-aquatic archosaur, they have conical and intersecting teeth, much like Spinosaurus. Although large African crocodiles are often shown catching large prey such as gazelles and wildebeest, most crocodiles, caimans and gharials are very markedly piscivorous. They are opportunistic when the opportunity exists, but fish is the mainstay of their diet. They are capable of both chasing prey and ambushing underwater. Others say he was more like a heron. An animal that has clear adaptations for hunting in water but not actually living in it, or chasing prey in it. Spinosaurus was neither a crocodile nor a heron, it was its own thing and there simply is no completely reliable modern comparison to Spinosaurus. Did he have feathers? This is an interesting question: the plesiomorphic condition, that is, the one that is present in the direct ancestors of Spinosaurus is feathered. We’re going to talk about their evolution soon, but basically, if there wasn’t a selective pressure for the loss of feathers, the most scientifically parsimonious thing is to say that yes, Spinosaurus had feathers. However, there are two things that lead us to think that he either did not have them, or they were very vestigial and less prominent than in his ancestors. First, because he was a huge animal, so the more layers of thermal insulation, the harder it is to exchange heat with the environment. That’s why giant animals that live in the heat shed their fur. And second, because they spent a lot of time in the water, regardless of what they were doing there and how they hunted, which is what we’re going to discuss. Mammals that adapt to aquatic and semi-aquatic life generally lose their hair. This is because the smooth surface generates less friction, facilitates movement in the water, but also because it helps eliminate fungus that can thrive with constant humidity. So there are strong reasons to think that Spinosaurus lost its feathers evolutionarily, on its way to becoming a semi-aquatic megaheropod. Did he have lips? This is an easier question for Tyrannosaurus than Spinosaurus. Three main reasons lead us to believe that the rex, like most dinosaurs, had lips. 1- Teeth without protection would dry out and break very easily. 2- They are perfectly aligned, having a very certain space inside the animal’s mouth. 3- The ends of the skull closest to the teeth are punctuated by passages of nerves and blood vessels called foramina, which indicate that there was a lot of tissue to be supported in the region. Teeth in the mouth of an animal that spends a good deal of time in water does not have as many problems with dehydration. And in the case of Spinosaurus, the dental organization is a little more chaotic, similar to that of crocodiles. And this animal’s skull also has a good count of foramen, mostly concentrated at the tip of the snout. We will discuss these innervations more when we look more closely at the head. So there is support for both representations, with and without a lip. I prefer the one with lips, because that is the ancestral condition, and I believe that it has been conserved, even if in theory, it doesn’t necessarily need lips that much. But evolution does not work in the logic of use and disuse, and sometimes some detail in life that we are unaware of changes everything. Think of the hippopotamus, a large, aquatic animal with huge, completely covered teeth. What were your colors like? The coloring you are seeing is completely speculative, but far from impossible. It is the product of my friend Heitor’s imagination, and is part of the project “The last theropod”. His networks are in the description. There are reasons to think that Spinosaurus was any color. Maybe he had neutral colors that helped him camouflage in mud or sand, like hippos and large animals today. Or perhaps sexual selection was exerting strong selection pressure to produce outrageously colorful animals. Maybe that wasn’t, after all, the mystery of the candle? Some have proposed that the sail was the most colorful part of the animal, like a peacock’s tail. Maybe it changed color as the blood pooled on the candles. It could even be a form of visual communication. But there is no evidence that directly supports either hypothesis. We barely have the complete skeleton of the animal, let alone skin impressions or possible fossilized feathers. And even if it did, only the most perfectly preserved can give us color clues. This is done by looking at the different shapes of fossilized pigment cells, which are indicative of the animals’ color. This is how we know that Sinosauropteryx was red with a belly and white rings on its tail. That’s how we know Microraptor was black with metallic blue. And that Borealopelta was reddish. But they are exceptions. For Spinosaurus, color, skin pattern, and surface ornamentation remain completely speculative. Time and environment The family Spinosauridae was successful in much of the world in the early to mid -Cretaceous. From 139 to 93 million years ago, lasting more than 46 million years, a very long period for vertebrate families. We know that the first of them lived at the end of the Jurassic, but they only really met in the early to mid-Cretaceous. It is difficult to determine the time span of Spinosaurus itself with so few fossils, but we believe it lasted between 99–93 million years. That is, they went extinct 27 million years before Tyrannosaurus rex existed. Dr. Ibrahim estimates that the neotype was excavated from a deposit 95 million years old, between the Cenomanian and Turonian stages. Apparently, the mid-Cretaceous was its heyday. And they were history long ago when the age of dinosaurs ended. We don’t know exactly why they became extinct at the end of the Cretaceous, but it’s common, especially for lineages that become giants, to disappear without knowing why. The Cretaceous is a very long period, always remember that, it lasts 79 million years, which means that there is more time between the beginning and the end of the Cretaceous than from the extinction of the dinosaurs until today. So it’s not because two animals were from the Cretaceous that they lived together. Because, this also depends on the geographic distribution. At the time Spinosaurus lived, South America and Africa were separated only by a shallow and short sea, the young Atlantic Ocean, which was just beginning to form. South America was bathed by an immense continental sea that flooded a good part of the Amazon, and North Africa was divided in two by a continental sea of ​​similar proportions. The Trans-Saharan Sea Europe existed as a series of islands to the north of this region, rather than as a continuous continent. Cretaceous moisture and heat fueled seasonal storms and formed massive river systems in this region. They crossed the entire Sahara desert, making it a very different ecosystem. of a desert. This region was home to all the giant Spinosaurids that we know of. Smaller species lived in Europe and Asia, but there seemed to be something about North Africa and South America that made these animals gigant. This North African aquatic system, composed of rivers, lakes, lagoons, swamps and floodplains, became known as the river of the giants. Giant dinosaurs are known in their deposits, such as those already mentioned, and more: a series of giant fish, with really very stupid sizes. A larger-than-car coelacanth named Mawsonia, which may have been prey for Spinosaurus when younger, but certainly not as an adult. Onchopristis was a genus of giant sawfish that also lived in the rivers where Spinosaurus hunted, and is often depicted living with it. Other giant species of dipnoic fish are the size or larger than the largest freshwater fish in the world today: the arapaima. Perhaps the existence of giant fish was an opportunity that led to the existence of giant piscivores. Perhaps fish gigantism was an adaptive response to giant predators. Either way, Spinosaurus and its prey influenced each other in ways we still don’t understand. There were also, competing directly or indirectly with Spinosaurus, a series of giant crocodiles, such as Aegisuchus, Laganosuchus and many others, even terrestrial! Many of these animals are identified by their teeth, including Spinosaurus. River deposits were the best places in the region to form fossils. It means that eventually, we find land animals on the fossilized banks of these ancient rivers and lakes. But they are rare compared to the known remains of aquatic animals, as it takes a certain amount of coincidence for a corpse to end up washed away and eventually buried forever. But the amount of Spinosaurus teeth is a very strong indicator that it was constantly losing teeth in the river. They were replaced several times during their lifetime, and if they were being lost in the riverbed, it’s because that’s where it fed. Ecology and behavior The ecology of Spinosaurus is really impressive. Ecology is not conservation and environmentalism, as many associate, but the set of relationships between living beings and the many ways that energy is transferred between organisms. One of the principles of ecology is that of competitive exclusion. He assumes that: in a controlled environment, two species with homogeneous distribution cannot share exactly the same limited resource, because one tends to outcompete the other, and become extinct over generations. Lions, cheetahs and hyenas can only coexist because they have different prey preferences, however often they overlap, which we call niche sharing. It avoids competitive exclusion and allows many herbivores and many carnivores to coexist. The ecological pressure from carcharodontosaurs, deltadromeus, a series of carnivorous pterosaurs and crocodiles, must have greatly affected the Spinosaurids and forced them to this niche sharing scheme to avoid direct competition. The number of giant carnivores capable of living in the vicinity of the river of giants is almost comical . It has long been suggested that this would be the most dangerous place and time in Earth’s history. No other formation has as big a bias towards giant carnivores as Kem Kem. So this may have been a place where you either became an expert or went extinct. Spinosaurus descended from fully terrestrial animals. It is the largest and most adapted for aquatic life of all Spinosaurids. However, the pertinent adaptations for piscivory already existed in all Spinosaurids, being the ancestral condition under which Spinosaurus evolved influenced. Baryonyx, for example, already had many of the piscivorous characteristics that would become distinctive in Spinosaurus, while retaining many of the ancestral conditions that allowed it to he was a good generalist, opportunistic on land too. So we know that the Spinosaurids’ relationship with water is ancient, but the more derived and specialist forms were the ones that radicalized this trend. However, there is no single way to eat fish, and piscivory has many possible strategies. Two models have become dominant in an attempt to explain Spinosaurus’ method of predation, I will call the model here “active pursuit” and “patient ambush”. They are not mutually exclusive, but may need slightly different adaptations . In the patient ambush model, Spinosaurus hunted like a heron: standing still on the riverbank, with its snout partially in the water, waiting for prey to pass by to capture with as little effort as possible in a single movement. In the active pursuit model, it would enter the water and use its feet and tail to go to where the fish were, even if it was deep in the water. A closer look at each of the parts of this animal will help us understand which of these models scientists have preferred and why. Evolutionary context Spinosaurids are sister group to Megalosauridae, and both are within the larger Megalosauroid group. Megalosaurs were carnivores from the Jurassic, which were very successful in practically the entire planet. Megalosaurus, for example, already had a longer head, large, strong arms with a curved claw on the first digit, and taller neural spines on the tail vertebrae. Trends that would be accentuated by the only surviving lineage of megalosauroids in the Jurassic-Cretaceous extinction: the spinosaurids. So the closest dinosaur group evolutionarily to Spinosaurus are the megalosaurs, some of which may even be the direct ancestors of Spinosaurus. But going back a little further on the tree of life, let’s realize that the megalosauroids, which include Spinosaurus, are a sister group to Avetheropoda. Avetheropoda includes two important groups: Allosauroids and Coelurosaurs. The Allosauroids, as the name implies, are dinosaurs from the Allosaurus family, from the Jurassic, and in the Cretaceous they give rise to the Carcharodontosaurids, such as Carcharodontosaurus in Africa and Giganotosaurus in South America. And most importantly, Coelurosaurs give rise to the lineage that will lead to both the T rex, and the velociraptor, and all birds! So Avetheropoda has very important representatives in dinosaur history. Both Megalosauroidea and Avetheropoda are part of the Tetanuro dinosaurs. Tetanurs are the most important group of giant carnivorous dinosaurs, and among their shared characteristics are a stiff tail and 3 fingers on their hands, instead of 4 as Ceratosaurus and Abelisaurus have. That is, Spinosaurus is a theropod tetanuro and megalosauroid dinosaur. Skeletal Basics Now let’s look at each of Spinosaurus’ unique features more closely, to see what conclusion we come to about its enigmatic life habit. But first, we are going to locate ourselves in the skeleton of a slightly more normal dinosaur, to understand how strange Spino is. First we have the skull, which itself is made up of several bones: the snout is the premaxilla, the sides are the maxilla, and the top is the nasal bone. These three bones form the nasal fenestra. Fenestra is the scientific name for a hole in the skull. This is where the animal breathed. They meet the jugal and lacrimal bones and form the anteorbital fenestra, a feature shared by all dinosaurs. This slit, in addition to making the skull lighter, could help with the thermoregulation of the animal. Dimetrodon, which is a synapsid, for example, and not a dinosaur, does not have an anteorbital fenestra… as much as the one from Jurassic World does. Above the jugal is the posorbital, which together with the lacrimal form the orbital fenestra, where the eyes are housed at the top, with a supporting sclerotic ring. At the upper end of the skull are the parietal, squamosal, occipital, quadratojulgal and quadrate bones, forming the superior and inferior temporal fenestra. The mandible is made of three bones, the dentary, the surangular and the angular, and in the middle of them, the mandibular and surangular fenestra. In mammals, these bones are reduced, they are part of the inner ear and we only have the dentary in the maxilla. That is, dinosaurs have 3 bones in the jaw, mammals have only one. The spine can be divided into 4 parts: The cervical vertebrae, in the neck region, the dorsal vertebrae in the back region, with associated ribs and gastralia, the sacral vertebrae, usually with some degree of fusion, in the pelvis region, and the caudal ones , obviously on the tail, with the chevrons on the underside. Separating the cervical region from the dorsal region is the animal’s shoulder girdle, where the arms are supported. It is formed by the scapula, furcula, coracoid and sternum. The arms have the same bones as humans, humerus, radius, ulna, and in the hands carpals, metacarpals and phalanges. And associated with the sacral vertebrae is the animal’s hip, formed by the ilium, ischium and pubis. The legs, also like humans are composed of femur, tibia and fibula. The feet, also made of tarsi, metatarsals and phalanges. The last bone of the feet and hands, the ungal, is not the claw, the claw is even bigger, because it is a keratin covering that forms on top. Skull The skull of Spinosaurus was bizarre in many ways. It was compressed laterally, rather than ventrally as in crocodiles. Both adaptations to facilitate movement in the water, but one from side to side, the other from top to bottom. That is, if Spinosaurus wanted to move its head from side to side in the water, it would be much more difficult than vertical movement. And the most efficient way to penetrate the water would be to dip the nose directly. You can see that the premaxillary bone is highly modified, stretching a lot to cause this nostril retraction. The nostrils were much closer to the eyes, quite high on the muzzle, which made it easier for this animal to keep part of its head out and part in the water. But how? If we look at the position of Spinosaurus’ eyes, we’ll see that they’re also right on top of the head. On the surface, one might think that like crocodiles and hippos, this allowed them to be completely immersed in water as inconspicuously as possible. But we see that in this position, a good part of the animal’s head and the candle are exposed. This arrangement seems to make more sense in the garsa model, in which the animal hunts with a good part of its body out, with only the tip of its snout submerged. The nasal bone formed a crest, whose roughness indicates that there was attachment to a keratin structure. The exact shape of this crest in life, as well as its colors and function are much debated, and it is speculated that it has to do with sexual selection or visual communication. The teeth are conical and arranged so that they take turns in overlapping, which we call interlock. This is the same mechanism crocodiles use to form a mouth trap for slippery prey. In Spinosaurus, the tip of the snout was greatly curved, with a wave at the end of the jaw that fitted neatly into the shape of the skull. The tip of the snout is also richer than normal in foramens, small openings in the skull that serve as passages for nerves and blood vessels, making the tip of this animal’s snout very innervated, highly irrigated and probably very sensitive. This makes all the sense in the world, as this sensitivity helped him not to depend only on vision to catch fish. Depending on his sensitivity to vibration in the water, it’s possible he was able to hunt even in complete darkness. It’s reasonable to assume that it had some kind of crop, folds of skin on its neck that allow this region to stretch, as it was capable of swallowing huge prey whole. This complete vertebral sequence shows that this neck was very long, strong and articulated. The resting position would likely be in an S. Legs and Feet The legs were shorter compared to other megatheropods, particularly the femur. But being shorter doesn’t mean being weaker. The fourth trochanter, a muscle attachment region on the femur was proportional with the estimated size and weight of the animal. It is in this very distinctive small region in dinosaurs that the caudofemoralis longus muscle attaches ! This muscle joins the thigh with the tail And this tail muscle actively participated in the movement of any terrestrial dinosaur. But in the case of Spinosaurus, it was even more important, as we imagine it could use its tail to swim. He has a tail good enough to walk on land like any other giant carnivore, but nothing much bigger that would lead us to believe that this muscle was especially strong. The feet had some quirks! They were flat, even the nail was very flat, increasing the animal’s contact surface with the ground. The fourth little finger, which in most dinosaurs is tiny and retracted, reaches the ground and is quite expanded. Dr. Ibrahim argues that everything indicates that this animal had a skin connection between the toes, just like ducks. This would be an adaptation to increase swimming efficiency, or to stay on unstable terrain without sinking. So if that’s really the case, it could move very well in swampy and muddy environments. The arms were among the largest and most powerful of all dinosaurs. In a way he’s the T rex in reverse, with an arm and little legs. On each hand, three fingers: the first shorter and stronger, with an immense curved claw The second long and the third intermediate, both with claws much smaller than those of the first fingers. This must have given it a good ability to handle heavy and slippery prey. Sail The immense sail on its back was not exactly a revolutionary invention of this animal. Other Spinosaurids have this tendency and some more derived Allosauroids also had a thing for tall neural spines. An example is Acrocanthosaurus, which is the carcharodontosaurid with the most prominent sail. Hardly anything near Spino. Perhaps Spinosaurus’s sail was fulfilling the same function as its ancestors, or perhaps this structure was evolutionarily co-opted for another task. This is very common. The exact purpose of the candle’s existence is uncertain, but there are many theories, not necessarily mutually exclusive. Having a mainsail seems to be more of a disadvantage than an advantage from our perspective. Maybe it really was. Maybe they were extremely territorial and having a tall, big, colorful sail was a sign that you’re a healthy individual and best not to challenge. It has been suggested many times that this sail could be the result of sexual selection, being driven to evolve from the differential preference of females for males with larger sails. If this is the case, we expect to find a female Spinosaurus without or with a shortened sail. That’s the problem when the animal is so rare, fragmented and cracked. We don’t even know if he had sexual dimorphism, that is, if males and females were very different. This candle should also not be used to support any fat or muscle, the surface is very smooth and indicates that what was passing over it was really skin. And it is precisely this absence of many innervations that weakens the idea that it could be used to fill or empty with blood according to the animal’s need to exchange heat with the environment. But there is the possibility that Spinosaurus physiology surprises with something that is not necessarily in the bones, but that is beyond the capabilities of science for now. And finally, it was thought that it would provide some kind of stability for swimming, but it is not like the sail of a swordfish, for example. It would generate a lot of drag and make it difficult for the animal to swim underwater, in addition to causing a lot of imbalance. So this candle is still a complete mystery, we need more information to be more sure of how it worked and what purpose it served. Which sucks, because that’s the most striking and distinctive feature of this critter. Tail The tail issue is not as simple as it seems. Many hypothesized that she would not be muscular enough or even flexible. enough to motorize the animal’s swimming. In some models, the tail ends up breaking when it is bent too much, and apparently, the extremely thin and long bones would have to be flexible to some extent in life, to be able to allow a certain amount of movement. Perhaps the idea that they swim like crocodiles is misleading after all. In the 2020 paper describing Spinosaurus’s first nearly complete tail, a few things stood out. They found that the vertebrae had extremely long and thin neural spines, with an elongated chevron bone on the ventral part. Closer to the base of the tail, the transverse processes, which are these lateral structures of the vertebra, are greatly expanded, which indicates a very powerful musculature anchorage zone. The base of the tail was muscular and thick, but the last two thirds are different. The transverse process becomes successively smaller, until it disappears completely, making the final region of the tail thinner and more flexible. So the tail wouldn’t be all muscled, which definitely prevents them from swimming exactly like crocodiles. To the point that some even proposed that it was not used for swimming, but to attract females. Locomotion on Land and Water Would Spinosaurus have any kind of migration needs? Would it be seasonal or constant? This is something common for giant animals, mainly carnivores, that have to move to where their prey is. If Spinosaurus migrated, or if it moved around a lot every day, it was probably in the water. On Earth its movements would be very limited by its size, wide feet and short legs. This would make it impossible for this animal to run, for example. Quite different from what we saw in Jurassic Park. The center of mass was initially calculated at the midsection of the animal, which would make it an obligatory quadruped on Earth. But with the studies of the neck of Sigilmassasaurus, we understood that the posture of S would take the center of mass to the hip, allowing the bipedal posture. Despite the many adaptations for aquatic life, Spinosaurus does not appear to be an extremely fast, agile or powerful swimmer. Sailing would make it extremely difficult to make the quick turns in the water necessary to catch fish. A study by Ibrahim used bone sections from hundreds of extinct and living animals to create a mathematically plausible relationship between bone density and life habit. The big question is that animals associated with aquatic and semi-aquatic habits have denser bones, with less pneumatization than terrestrial animals. Land animals, and dinosaurs in particular, tend to float in water, which is very harmful if you have to hunt underwater. It means that the animal has to displace a lot of energy to sink. But Spinosaurus had fairly dense bones that made it sink more easily. This contradicts biomechanical studies that tested Spinosaurus’s buoyancy and stability in the water, which found that it would be very difficult for him to sink, and that he would need to keep tapping his feet all the time so that the sail wouldn’t fall to one side or the other. What might seem like a contradiction might actually make perfect sense if they moved through the water like hippos. They don’t sink too low or float too much, being in a perfect balance that allows them to practically “fly” slowly but very efficiently, maintaining direction and speed by making small touches, rather than actively swimming fast. If hippos, less hydrodynamic and with much less superficial adaptations for aquatic life, manage to move so gracefully in the water, I’m led to think that Spinosaurus was that for the better. Reproduction and Growth Why did they never become fully aquatic? Most likely because they were reproductively landlocked. Even assuming it could swim very well and actively, it would still need to nest on land, because as far as we know, no dinosaur has ever failed to lay an egg in order to give birth to a young. Perhaps this is why the transition to fully aquatic forms is more easier for mammals than for dinosaurs. Like all dinosaurs, Spinosaurus hatched from relatively small eggs, and they had to feed frantically to grow very fast during their first few years of life. Most did not survive. We don’t know what Spinosaurus’ childhood was like, unfortunately. We have no idea if they were born with the candle or if it developed as they matured. But they should bet on the quantity, not the quality of the puppies. It is possible that as a young man, he was prey to fish in the river of the giants, and only later did the situation reverse. The possibility of parental care exists, although completely speculative. And reproduction seems to be able to explain some of the strange characteristics of this animal. Whenever we are unable to understand a part of Spinosaurus, we blame sexual selection. A seemingly purposeless and harmful giant candle? She should be colorful and attract attention from females. A scandalous crest on the head? She should be colorful and attract attention from females. A flat tail and seemingly incapable of mobilizing swimming on its own? She should be colorful and attract attention from females. And so it goes. With dinosaurs this is actually very common, but we have to be careful not to put everything that apparently doesn’t make sense in the sexual selection box. My Conclusions Let’s recount the characteristics of Spinosaurus that suggest a piscivorous and semiaquatic way of life: 1-Conical teeth 2-An interlocked arch 3-Nostrils too far from the tip of the snout 4- Eyes high on top of the head 5- A long skull and thin 6-Short legs 7-An immense curved claw on the first finger 8-A fourth finger that touched the ground 9-Fingers spread out and possibly connected by skin 10-Flat and less pointed nails 11-The paddle-shaped tail 12- An extremely sensitive muzzle 13-Dense sinking bones And possibly even the sail, in some way we still don’t understand. Considering all the anatomical, environmental, ecological and evolutionary variables considered, my personal conclusion is that Spinosaurus was a semiaquatic giant capable of swimming, but not very fast. Its swimming was most likely used more for moving between regions of concentrated food resources, or for breeding, than for chasing animals at the bottom of the water while hunting. They might have used the immense African and South American rivers and coastlines as roads, but ineffectively as predators in pursuit. But on the shores, they reigned supreme, waiting patiently, like a heron, only thousands of times bigger. When its sensitive snout detected the presence of fish nearby, it would quickly shoot out with its long neck and catch the fish in its teeth to swallow it whole. In the case of larger prey, the huge and powerful claw could help kill and break it into swallowable pieces, as it was unable to chew. We realize that the reconstruction of Spinosaurus is a scientific task that takes more than a century to reach the current interpretations, and is considered one of the great works of paleontology. Some might say that the indirect and inferential methods of paleontology say nothing, and that the reconstructions rely so much on the imagination that they are little scientific. It is partly true that paleontology relies heavily on the imagination, and that it is impossible to test certain hypotheses directly without a time machine. But it is also true that with each new piece of information, the representation of this animal has radically changed and has come closer to reality. That’s the trend for any extinct animal. The more and better the material, the more information we have to base our reconstructions on, there’s nothing wrong with that. All of the earliest forms Spinosaurus ever had were at the time the most scientifically based and conservative extrapolation possible. This means that what we know today is not the true appearance of Spinosaurus, but the best interpretation based on known material and the good science of comparison, however incomparable that animal may be. I hope you came away from this video with more questions than answers, because that’s the spirit of paleontology. I look forward to hearing in the comments what you thought and what surprised you the most about Spinosaurus. Closing If you liked this video, know that you can help me to continue posting, funding the channel with a pix of any value to the email [email protected], it helps more than you can imagine! Also consider becoming a channel member, and we’ll build ABC Terra together! Thank you very much and have a great life!