Few fossils

Before 2014, paleontologists had only a handful of fossils from the tail of Spinosaurus. They theorized that its tail, like that of other theropods, was primarily used to balance the forward-leaning center of gravity and was most likely rigid. They thought the tail was also a secondary means of aquatic propulsion, adding thrust to the movement of the limbs as it crawled and waded in the shallows. (Read about how the bizarre Spinosaurus makes history as first known swimming dinosaur.)

Pre-2015 Spinosaurus tail fossils Pre-2015 Spinosaurus tail fossils Pre-2015 Spinosaurus tail fossils

A bone bonanza

Excavations in 2018 in Morocco found 131 additional bone fragments, including 36 vertebrae, fundamentally changing our understanding of the Spinosaurus tail.

Spinosaurus tail fossils from 2018 excavations Spinosaurus tail fossils from 2018 excavation Spinosaurus tail fossils from 2018 excavations

Longer and more flexible

The latest find paints a much clearer picture of the tail. It is far more elongated vertically and less rigid than once thought, indicating that the tail was a powerful source of thrust in the water.

Muscle Cross section Vertebra 4 The anterior tail is stiffer and more muscular, providing propulsion. Elongation The tail vertebrae get longer as they extend down the tail, giving it length and flexibility for propulsion. Lateral flexibility Bony spinal overhangs on the vertebrae are small and don’t overlap much, allowing the tail to flex laterally. Neural spines Chevrons A long, skinny sail Elongated extensions above and below the tail, called neural spines and chevrons, give the tail abundant surface area. Cross section Vertebra 31 The posterior tail is thinner and more flexibile, acting like a rudder. Elongation The tail vertebrae get longer as they extend down the tail, giving it length and flexibility for propulsion. Lateral flexibility Bony spinal overhangs on the vertebrae are small and don’t overlap much, allowing the tail to flex laterally. A long, skinny sail Elongated extensions above and below the tail, called neural spines and chevrons, give the tail abundant surface area. Neural spines Chevrons Cross section Vertebra 4 Cross section Vertebra 31 The anterior tail is stiffer and more muscular, providing propulsion. The posterior tail is thinner and more flexibile, acting like a rudder. Muscle Elongation The tail vertebrae get longer as they extend down the tail, giving it length and flexibility for propulsion. Lateral flexibility Bony spinal overhangs on the vertebrae are small and don’t overlap much, allowing the tail to flex laterally. A long, skinny sail Elongated extensions above and below the tail, called neural spines and chevrons, give the tail abundant surface area. Neural spines Chevrons Muscle Cross section Vertebra 4 Cross section Vertebra 31 The anterior tail is stiffer and more muscular, providing propulsion. The posterior tail is thinner and more flexible, acting like a rudder.

3D Spinosaurus Animation An animation video of a 360 model of a Spinosaurus.

MODELING: DAVIDE BONADONNA AND FABIO MANUCCI; ANIMATION AND TEXTURING: FABIO MANUCCI; COLOR DESIGN: DAVIDE BONADONNA, DI.MA. DINO MAKERS SCIENTIFIC SUPERVISION; SIMONE MAGANUCO AND MARCO AUDITORE; RECONSTRUCTION BASED ON: NIZAR IBRAHIM AND OTHERS, NATURE, 2020.

Studies of the tail show that it had up to eight times as much thrust as other theropod tails, allowing it to swim against currents and accelerate to capture prey.

MODELING: DAVIDE BONADONNA AND FABIO MANUCCI; ANIMATION AND TEXTURING: FABIO MANUCCI; COLOR DESIGN: DAVIDE BONADONNA, DI.MA. DINO MAKERS SCIENTIFIC SUPERVISION; SIMONE MAGANUCO AND MARCO AUDITORE; RECONSTRUCTION BASED ON: NIZAR IBRAHIM AND OTHERS, NATURE, 2020.

Ancient wetlands

North Africa 95 million years ago had rich river systems. Ernst Stromer found the first Spinosaurus specimen in Egypt in 1912; the latest finds have been located in Morocco.

2008 and 2018 finds (Kem Kem beds) Stromer’s 1912 find TUnISIA Rabat MOROCCO libya libya Algeria EGYPT sahara Western Sahara niger AFRICA Africa’s coastline 95 million years ago Spinosaurus fossil discovery site 1000 mi 1000 km 2008 and 2018 finds (Kem Kem beds) Stromer’s 1912 find Tunis Algiers TUnISIA Rabat Tripoli MOROCCO Cairo libya libya Algeria EGYPT sahara Western Sahara niger Niamey AFRICA Africa’s coastline 95 million years ago Spinosaurus fossil discovery site 1,000 mi 1,000 km 2008 and 2018 finds (Kem Kem beds) Stromer’s 1912 find Tunis Algiers TUnISIA Rabat Tripoli MOROCCO Cairo libya libya Algeria EGYPT sahara Western Sahara niger Niamey AFRICA Africa’s coastline 95 million years ago Spinosaurus fossil discovery site 1,000 mi 1,000 km

Putting the pieces together

The first ideas of how Spinosaurus looked were informed by a limited fossil record and a narrow understanding of dinosaurs in general. Further finds have added to our concept of what Spinosaurus looked like, leading us to the aquatic predator we now see.

1936 A bipedal theropod Ernst Stromer found the first partial skeleton of Spinosaurus in 1912. Limited by the specimen, reconstructions of Spinosaurus relied on other fossil records of theropods from that time, giving Spinosaurus a bipedal stance and a short snout, like other theropods. 2014 The world’s biggest predator A major find by Nizar Ibrahim added new pieces to the skeleton, cementing theories that Spinosaurus was primarily quadrupedal and had a large dorsal sail and a more crocodilian skull, with teeth suggesting a diet heavy on fish. The tail was still largely a mystery, however, and it was thought to provide balance and a secondary (to the hind legs) method of swimming. 2020 An aquatic predator The vertebra discovery provided evidence for the tail as the primary mode of aquatic locomotion—and also provided possible explanations for other oddities: The Spinosaur's center of gravity leans forward, which aids swimming, and its curved claws are more suited for catching prey in water than for walking on land. 1936 A bipedal theropod Ernst Stromer found the first partial skeleton of Spinosaurus in 1912. Limited by the specimen, reconstructions of Spinosaurus relied on other fossil records of theropods from that time, giving Spinosaurus a bipedal stance and a short snout, like other theropods. 2014 The world’s biggest predator A major find by Nizar Ibrahim added new pieces to the skeleton, cementing theories that Spinosaurus was primarily quadrupedal and had a large dorsal sail and a more crocodilian skull, with teeth suggesting a diet heavy on fish. The tail was still largely a mystery, however, and it was thought to provide balance and a secondary (to the hind legs) method of swimming. 2020 An aquatic predator The vertebra discovery provided evidence for the tail as the primary mode of aquatic locomotion—and also provided possible explanations for other oddities: The Spinosaur's center of gravity leans forward, which aids swimming, and its curved claws are more suited for catching prey in water than for walking on land. 1936 A bipedal theropod Ernst Stromer found the first partial skeleton of Spinosaurus in 1912. Limited by the specimen, reconstructions of Spinosaurus relied on other fossil records of theropods from that time, giving Spinosaurus a bipedal stance and a short snout, like other theropods. 2014 The world’s biggest predator A major find by Nizar Ibrahim added new pieces to the skeleton, cementing theories that Spinosaurus was primarily quadrupedal and had a large dorsal sail and a more crocodilian skull, with teeth suggesting a diet heavy on fish. The tail was still largely a mystery, however, and it was thought to provide balance and a secondary (to the hind legs) method of swimming. 2020 An aquatic predator The vertebra discovery provided evidence for the tail as the primary mode of aquatic locomotion—and also provided possible explanations for other oddities: The Spinosaur's center of gravity leans forward, which aids swimming, and its curved claws are more suited for catching prey in water than for walking on land.