Training to Become a Fisher — The Spinosaurids
- 演化之聲
- Mar 10
- 8 min read
Dinosaurs were a group of animals with remarkable ecological diversity. Some were carnivores, others fed on plants and leaves; some specialized in insects, while others consumed fruits and seeds. Given such diversity, it is hardly surprising that certain dinosaurs relied primarily on fish. Among these fish-eating dinosaurs, the most famous is probably Spinosaurus.
Spinosaurus possessed an enormous body size and became widely known after appearing in the Jurassic Park film series, where it famously kills an adult Tyrannosaurus rex. Since then, it has often been imagined as an extremely ferocious dinosaur, the largest among predatory dinosaurs, dominating its environment as an unstoppable apex predator.
However, new research has gradually changed this perception. Evidence now suggests that spinosaurids were not terrestrial tyrants striding across the land. Instead, they seem to have spent much of their time near rivers and lakes, feeding primarily on fish. Even more striking, the fish-eating habits of spinosaurids appear to represent an evolutionary specialization that lasted tens of millions of years. This realization has dramatically altered the popular image of these dinosaurs.
With that in mind, let us take a closer look at the spinosaurid family.
Introduction to Spinosauridae
The spinosaurid family, Spinosauridae, belongs to the superfamily Megalosauroidea, making them relatives of Megalosaurus and other early large theropods.
According to the current fossil record, confirmed spinosaurid fossils range from roughly 130 million years ago in the Early Cretaceous to about 93 million years ago in the Late Cretaceous, spanning at least 37 million years. However, judging from the evolutionary development and geographic distribution of these fossils, the origin of Spinosauridae likely predates this interval.
The earliest possible spinosaurid fossil currently known comes from India and dates to the Middle Jurassic, around 170 million years ago. This material consists of a single claw, making its classification uncertain but intriguing.
Spinosaurids had a very wide geographic distribution. Confirmed fossils have been found on nearly every continent except North America and Antarctica—the latter largely because its fossil deposits remain difficult to access.
Known members of Spinosauridae include several basal forms as well as two major subfamilies: Baryonychinae and Spinosaurinae.
Apart from the poorly understood taxon Camarillasaurus cirugedae, whose classification remains debated, nearly all spinosaurids were large-bodied dinosaurs. One possible explanation is ecological: by specializing in fish, spinosaurids avoided direct competition with many other large carnivorous dinosaurs, allowing them to reach impressive body sizes in environments where aquatic prey was abundant.
Although the earliest potential spinosaurid fossil comes from India, the material is extremely fragmentary, and no additional spinosaurid fossils have yet been found there. As a result, the geographic origin and early evolutionary history of the group remain largely unknown. To understand their history, it is therefore useful to begin with the Cretaceous spinosaurids of Europe.
Basal Spinosaurids
At present, only one confirmed basal spinosaurid is known: Iberospinus natarioi.
This species was discovered in Portugal on the Iberian Peninsula. Its single known specimen is one of the most complete spinosaurid fossils ever found, yet even it remains highly fragmentary.
Although Iberospinus branched off early and lies outside both Baryonychinae and Spinosaurinae, researchers have noted that its fossils show certain anatomical similarities to baryonychines. This suggests that it may be more closely related to the baryonychine lineage.
Baryonychinae
Members of Baryonychinae are most commonly found in Europe. One of the best-known species is Baryonyx walkeri, discovered in the United Kingdom. This species represents one of the earliest confirmed spinosaurids known from the fossil record.
Spinosaurids were particularly diverse in Britain and the Iberian Peninsula. In recent years, paleontologists have even named two new baryonychine species from Britain and two more from Spain.
Among these discoveries, two British species—Ceratosuchops inferodios and Riparovenator milnerae—are especially significant. Together with the African species Suchomimus tenerensis, they form a clade known as Ceratosuchopsini.
This lineage represents a more derived group within Baryonychinae and shows that baryonychines successfully dispersed into Africa, where Suchomimus evolved.
This dispersal likely represents the first migration of spinosaurids into Africa. A second migration event later occurred with the lineage that led to Spinosaurus itself.
The two newly described Spanish species represent a different baryonychine evolutionary branch from the British lineage.
In addition, baryonychine teeth have been discovered in Brazil. Based on their characteristics, these teeth appear closely related to Suchomimus. This may suggest that baryonychines, particularly the Ceratosuchopsini lineage, were already capable of moving between Africa and South America before the continents fully separated.
Although baryonychines were also fish-eaters, they appear to have been somewhat less specialized for aquatic life than members of Spinosaurinae.
Spinosaurinae
The fossil record of Spinosaurinae is somewhat more problematic than that of baryonychines.
Some species, such as Siamosaurus suteethorni, were named solely on the basis of isolated teeth, making it difficult to compare them with other fossils from nearby regions.
Other taxa present different challenges. Oxalaia quilombensis, for example, was already considered uncertain as a distinct genus when disaster struck: its fossil material was destroyed in the catastrophic fire that devastated National Museum of Brazil. Of the museum's roughly twenty million specimens, less than ten percent were ultimately recovered after the fire.
Even the type specimen of Spinosaurus aegyptiacus suffered a similar fate. The original fossil, housed in the museum in Berlin, was destroyed during Allied bombing raids in World War II. These losses have significantly complicated research on Spinosaurus and Spinosaurinae.
Despite these setbacks, spinosaurines remain a fascinating group.
Their distribution appears to have been even broader than that of baryonychines, extending across Europe, Asia, Africa, and South America.
In Europe, spinosaurine fossils have been discovered on the Iberian Peninsula in Spain. The region has yielded numerous spinosaurid fossils from multiple evolutionary lineages, suggesting that the Iberian Peninsula may have been either the place of origin for spinosaurids or at least an important center of their early evolution. Some studies, however, propose that Britain might instead represent the group's point of origin, so the issue remains unresolved.
In Asia, besides Siamosaurus from Thailand, spinosaurine teeth have also been found in China and Japan. Laos has produced another remarkable species, Ichthyovenator laosensis.
Like Spinosaurus, Ichthyovenator possessed a dorsal sail. Interestingly, the sail of Ichthyovenator shows a distinctive gap in its middle section, making it one of the most recognizable spinosaurids.
South America preserves Irritator challengeri. Recent studies have shown that the lower jaw of Irritator could expand laterally, somewhat like the bill of a modern pelican. This ability would have increased the volume of the mouth, potentially allowing the animal to capture larger fish.
Africa, however, remains the primary homeland of Spinosaurus. Although the original type specimen was destroyed, several additional fossils have since been discovered. Some of these specimens remain controversial and may eventually be reassigned to new genera or recognized as additional species within Spinosaurus.
The Genus Spinosaurus
Finally, let us focus specifically on Spinosaurus.
This dinosaur could reach a length of about fourteen meters. Although its body was not as heavily built as that of Tyrannosaurus rex, it was still among the largest predatory dinosaurs known.
In recent years, our image of Spinosaurus has changed dramatically. A major study published in 2020 revealed that its tail possessed a fin-like structure. This discovery suggested that Spinosaurus may have been well adapted for swimming.
Even so, the lifestyle of Spinosaurus remains highly controversial, largely because of gaps in the fossil record.
Over the past several years, different research groups have published competing interpretations. A 2018 study argued that Spinosaurus would have struggled to swim efficiently, suggesting that it spent most of its time on land or in shallow water. The 2020 discovery of the tail fin, however, supported the idea that it was capable of powerful swimming.
Another study published in 2021 proposed that Spinosaurus may have behaved more like modern wading birds, remaining near shorelines. One argument was that the large dorsal sail might have disrupted balance in water.
In 2022, however, an analysis of bone density across spinosaurids revealed extremely dense bones in Spinosaurus, a trait typical of diving animals. This finding suggested that the dinosaur may have been well adapted for underwater swimming.
Yet another study that same year proposed that the dorsal sail may have prevented Spinosaurus from remaining stable in shallow water, meaning it might have swum mainly at the water surface and captured prey in a manner similar to wading birds.
This debate has continued for several years and will likely persist until more complete fossils of Spinosaurus are discovered.
Final Thoughts
Because spinosaurid fossils are often poorly preserved, our understanding of their evolutionary history remains incomplete. Many aspects of their biology and evolution are still uncertain.
Future discoveries of better-preserved spinosaurid fossils may eventually help resolve these mysteries and fill the many remaining gaps in our knowledge.
Author: Bai Leng
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