An Ultimate Guide to Leedsichthys: The Fish of Leeds

Leave a comment / / Updated on: 24th September 2023

Name MeaningFish of LeedsHeightN/A
PronunciationLeed-sich-thisLength9–30 meters (29.5–98.4 feet) 
EraMesozoicMiddle-Late JurassicWeight45 metric tons (49.6 short tons)
ClassificationActinopterygii, Pachycormiformes and PachycormidaeLocationEurope and South America

Leedsichthys Pictures

Leedsichthys is a giant member of an extinct group of Mesozoic bony fish that lived during the Jurassic Period. | CoreyFord via Getty Images

The Leedsichthys

Gage Beasley Prehistoric's Leedsichthys Concept
Gage Beasley Prehistoric’s Leedsichthys Concept

Most ray-finned fish are quite small.

The largest member of this group is the oarfish, which grows up to 11 meters (36 feet) long but has a very thin body.

Now imagine a ray-finned fish larger and heavier than the oarfish!

That’s the Leedsichthys, often regarded as the largest ray-finned fish and one of the world’s largest fish!

Although Leedsichthys fossils were difficult to interpret, scientists are sure they measured at least nine meters (29.5 feet), but they may have reached a maximum size of more than 30 meters (98.4 feet) long!

Leedsichthys | estt via Getty Images

That’s quite impressive, isn’t it?

These giant fish roamed our planet’s prehistoric seas between 165 and 152 million years ago.

Supposedly, they were suspension feeders with distinctive, specialized gill rankers that served as aids in feeding.

Do you want to learn more fascinating details about the Leedsichthys?

Keep reading, as we’ve got plenty!

Gage Beasley's Prehistoric Shirt Collection
Gage Beasley’s Prehistoric Shirt Collection
Gage Beasley's Prehistoric Plush Collection
Gage Beasley’s Prehistoric Plush Collection

Physical Characteristics

Leedsichthys was a carnivorous fish that inhabited Jurassic Seas that could grow to be 53 feet long. | CoreyFord via Getty Images

Before discussing some possible characteristics of the Leedsichthys, it’s important to note that many details haven’t been confirmed because interpreting and analyzing the fossils belonging to this genus has been quite challenging.

The reason behind this is that large parts of the discovered skeleton consisted of unfossilized cartilage, and no vertebrae have been preserved.

This made size estimations almost impossible.

Although scientists could outline a plausible appearance, they advise that the details are only speculation.

Those details even pertain more to the scientific field and will be useless to wildlife enthusiasts who are merely interested in discovering how this large ray-finned fish looked.

We’ll start with the size, as it is probably the most distinctive characteristic of the genus.

Gage Beasley Prehistoric's Leedsichthys Size Comparison Chart
Gage Beasley Prehistoric’s Leedsichthys Size Comparison Chart

Although scientists aren’t sure yet how large the Leedsichthys was exactly, they confirmed it is the largest known bony fish in the Osteichthyes group.

In 1889, when the type specimen was described, the Leedsichthys was estimated to have had a length of nine meters (29.5 feet) and a tail height of 2.74 meters (9 feet).

Almost a century later, upon discovering a different pachycormid called Asthenocormus, scientists compared its bones to those of the newly discovered genus and proposed a completely different size.

They argued that the Leedsichthys may have been as long as 27.6 meters (90.5 feet). Later, size estimations went up to 35 meters (114.8 feet).

Other scientists supported the first version that the Leedsichthys could not have been so large and that a length of 9–10 meters (29.4–32.8 feet) was more plausible.

Leedsichthys prehistoric fish | Elenarts108 via Getty Images

Some weight estimations suggest that the Leedsichthys may have weighed roughly 45 metric tons (49.6 short tons), but this number still needs to be officially confirmed.

It has been proposed that the Leedsichthys had a large, wide, and elongated head.

It had five gill arches with rows of parallel gill rakers (bony or cartilaginous structures projecting from the branchial arch) that measured between 3 and 12 centimeters (1.2 and 4.7 inches) long.

Each gill raker was equipped with a series of teeth.

The Leedsichthys probably had two large, elongated pectoral fins, a dorsal fin, and possibly a triangular anal fin. It is unknown whether it had pelvic fins.  

Habitat and Distribution

The holotype specimen for the Leedsichthys genus was recovered from southeast England.

More precisely, it was found in the Oxford Clay Formation and consisted of more than a thousand skeleton elements attributed to one individual.

Other important fragmentary remains were discovered in the following locations:

  • Normandy
  • Wallücke, Germany
  • Chile
  • Vaca Muerta Formation, Argentina

As you’ve probably noticed, the Leedsichthys was quite widespread.

We cannot rule out the possibility that its distribution went further than this, and future findings may confirm this theory.

Oxford Clay (Jurassic) exposed near Weymouth, England. | Wilson44691 via Wikipedia

It has been suggested that the lifestyle and behavior of the Leedsichthys can be compared to those of the whale shark and the basking shark.

These two shark species are pelagic suspension feeders, found at depths of up to 200 meters (656 feet) below sea level.

Since the Oxford Clay Seas had approximately the same depths, scientists argue that the Leedsichthys lived in the same habitat as whales and basking sharks.

Mentioning the precise climate that dominated the world at the time would result in quite an extensive discussion.

The discovered fossils belonged to different periods, so the temporal range of the Leedsichthys extends for millions of years, during which the world registered numerous climatic changes.

Behavior and Diet

Leedsichthys is about to swallow an marine reptile. | CoreyFord via Getty Images

As mentioned, the Leedsichthys was likely swimming at depths up to 200 meters (656 feet) below sea level.

Since it lacked any teeth, it was likely a suspension feeder.

This means that it fed on food particles suspended in water, which may have included phytoplankton, bacteria, zooplankton, and detritus.

Leedsichthys used their gill rakers to extract these food particles from the water.

However, it remains unknown what exactly it selected to eat.

Restoration based on modern interpretation of the fossils | Dmitry Bogdanov via Wikipedia (CC BY 3.0)

For example, while it has been confirmed that it ate zooplankton and small aquatic animals, scientists aren’t sure whether it enjoyed phytoplankton and algae.

Some fossilized furrows discovered in Switzerland have been associated with the Leedsichthys.

Apparently, it may have used its mouth to spout water to disturb and eat the so-called benthos, organisms living on or near the bottom of the sea.

Apart from these details, little else is known about the behavior and diet of the Leedsichthys.

One more thing to mention is that the fish could move at speeds of approximately 17.8 km/h (11 mph).

Life Cycle

Leedsichthys | Elenarts108 via Getty Images

The reproductive behavior and life cycle of the Leedsichthys are poorly known.

Only some studies focus on Leedischthys’ growth rate, metabolic rate, and lifespan.

Scientists estimate that, at one year old, juveniles were already 1.6 meters (5.2 feet) long, and they continued growing throughout their lives, although the growth rates were likely relatively slow.

At 3–4 years of age, they reached five meters (16.4 feet) in length, and by the time they were 8–15 years old, Leedsichthys grew to 10 meters (feet) long.

Sexual maturity likely occurred when they were between six and nine meters (19.7 and 29.5 feet) long.

Considering that most teleosts live only up to 15 years, we can assume that the lifespan of the Leedsichthys was similar.

Leedsichthys is a giant member of an extinct group of Mesozoic bony fish that lived during the Jurassic Period. | CoreyFord via Getty Images

However, some teleosts, like rockfish, have a remarkably long lifespan of over 100 years.

So how long did the Leedsichthys live? It will remain a mystery until future findings!

If they were indeed teleosts, as many scientists presume, they were likely oviparous, meaning that males and females released the sperm and the eggs in the water, where external fertilization occurred.

However, some teleost species reproduce via internal fertilization, so we cannot be 100% sure which was true for the Leedsichthys.

Some teleosts are also known to exhibit sexual dimorphism.

Since the physical characteristics are poorly known, it remains unknown whether they had any special sexually dimorphic features.

Evolution and History

Leedsichthys lived in the middle to late Jurassic Period and fed on plankton. | SciePro via

The classification of Leedsichthys is still highly debatable, which is why outlining an evolutionary history for this genus is problematic.

These fish are often considered very basal teleosts.

On the other hand, the evolutionary history of teleosts says that the most basal members of this group are the Elopomorpha and the Osteoglossomorpha fish, dating to the Early Triassic.

Since the Leedsichthys lived millions of years later, can it be considered a basal member of the teleost group?

Other scientists consider Leedsichthys  basal members of the Amiiformes order, in which case they would be closely related to the living bowfin.

Although this classification is still questioned, the Leedsichthys is a member of the Teleosteomorpha clade and the Pachycormiformes order, which includes all the fish more closely related to extant teleosts than to the members of the Holostei group.

Tail fin of Leedsichthys problematicus on display at the Field Museum of Natural History’s Jurassic Oceans exhibit. | Jonathan Chen via Wikipedia (CC BY-SA 4.0)

If we turn to the discovery history of the Leedsichthys, we arrive in the 1880s in Peterborough, England, when Alfred Nicholson Leeds, a gentleman farmer, found some large fish fossils that were later attributed to the Omosaurus stegosaurian.

Othniel Charles Marsh later concluded that the bones, in fact, belonged to a giant fish.

The species was named Leedsichthys problematicus.

The generic name was coined in honor of Alfred Nicholson Leed, who discovered it, while the specific name pointed to how fragmentary the remains were and how challenging it was to analyze them.

After scientists named the genus, paleontologists discovered that another Leedsichthys specimen had been unearthed years before in Normandy.

In 1901, some remains were again mistakenly identified as dinosaur tail spikes, further indicating how much mystery revolves around this genus.

Dogsthorpe Star Pit nature reserve | Bogbumper via English Wikipedia (CC BY-SA 3.0)

An important specimen was discovered at the Dogsthorpe Star Pit.

This particular specimen was the one to attract people’s attention and led to the Leedsichthys appearance in several documentaries.

The skeleton discovered in Wallücke, Germany, was again attributed to a different creature, this time a stegosaurian called Lexovisaurus.

Leedsichthys discoveries from Chile led to the description of another species in the genus, Leedsichthys notocetes.

However, it is not fully recognized, as scientists aren’t sure there are any specific differences between the two.

Interactions with Other Species

eedsichthys being attacked by Pliosaurus rossicus. | Dmitry Bogdanov via Wikipedia (CC BY 2.5)

During the Middle and Late Jurassic, when the Leedsichthys were alive, the world was full of bizarre prehistoric creatures.

Obviously, the most renowned are the dinosaurs, as they’re now featured in any movie, video game, or documentary about our world’s evolutionary history.

However, the dinosaurs and other famous terrestrial creatures you may have heard about had nothing in common with the Leedsichthys.

Instead, this large fish lived among the numerous fish species and other aquatic creatures.

Leedsichthys was an enormous marine fish that was a carnivore in the seas of the Jurassic Period. | CoreyFord via Getty Images

In the Oxford Clay Sea, for example, the Leedsichthys shared its habitat with other pachycormiformes, including the Martillichthys and the Hypsocormus.

Its fossils were also associated with the Metriorhynchus, a marine crocodile measuring three meters (feet) long.

Its tooth was found in a Leedsichthys bone, suggesting it may have been a predator of this large fish.

Another predator may have been the Liopleurodon, a carnivorous marine reptile, a powerful swimmer, and likely an apex predator in its habitat.

Cultural Significance

Fossil fish Leedsichthys lewis, Cretacic, Cenomaniense (Cenomanian), Lebanon | Paola Iamunno via Getty Images

The Leedsichthys aroused the interest of scientists around the world, first for the mystery revolving around its identification and appearance, and secondly due to its enormous size, which further raised questions regarding its growth rate.

Although its scientific classification isn’t set in stone yet, it is undoubtedly a pivotal member of the ray-finned fish class.

Hopefully, future discoveries will lead to breakthrough studies revealing more details about this mysterious aquatic creature.

Considering how difficult it was for scientists to describe this genus, you would expect it to be poorly known in popular culture.

Leedsichthys in ARK: Survival Evolved | Photo via ARK: Survival Evolved Fandom

However, thanks to the giant specimen discovered at the Dogsthorpe Star Pit, the Leedsichthys is now renowned among wildlife enthusiasts as well.

After this discovery, it appeared in the Sea Monsters series and in a documentary called The Big Monster Dig.

The Leedsichthys is also a creature in the ARK: Survival Mode video game.


The Leedsichthys inhabited our world’s prehistoric waters from the Middle Jurassic to the Late Jurassic.

It is considered the largest ray-finned fish and, if that isn’t enough, one of the largest fish ever discovered!

No wonder the genus is now of such interest to scientists!

However, despite its popularity and importance, the genus is quite problematic, as fossils have been difficult to identify and interpret, which is why the physical characteristics, including the size, of the Leedsichthys are poorly known.

It may have been as large as nine meters (29.5 feet) long, or it may have reached lengths of over 30 meters (98.4 feet). No one truly knows!

Instead, scientists are somewhat more convinced of its lifestyle, arguing that it lived in waters up to 200 meters (656 feet) deep, was a suspension feeder, and moved quite fast, considering its size. 


Was the Leedsichthys bigger than a blue whale?

If we consider the maximum size estimate of the Leedsichthys, which is 35 meters (114.8 feet) long, we may say it was larger than the blue whale, which has a maximum length of 29.9 meters (98 feet).

However, blue whales are probably much heavier than Leedsichthys.

Nevertheless, the length of 35 meters (114.8 feet) for the Leedsichthys is widely considered an overestimation, so it remains unknown whether it was indeed larger than a blue whale.

Why did Leedsichthys go extinct?

It is unknown why the Leedsichthys went extinct, although some scientists suggest it happened primarily because of climate change.


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