Dino of the Week: Dilophosaurus

Type Species: Dilophosaurus wetherilli

Classification: Dinosauria – Saurischia – Theropoda – Dilophosauridae 

Time Period: Early Jurassic

Location: North America

Diet: Carnivore

Dilophosaurus was the apex predator of its time in the Sinemurian and Pliensbachian stages of Early Jurassic North America some 196 to 183 million years ago. Its name means ‘two-crested lizards’ due to the twin sweeping crests atop its skull. Skeletal remains have been found in Arizona, and trackways have been uncovered in Connecticut (thus it’s no surprise that Dilophosaurus is Connecticut’s state dinosaur). The holotype specimen is remarkable in that it showed healed injuries and even signs of a developmental disability. The injuries on the specimen are consistent with those sustained from crushing forces, and there were two pits on the right humerus that may have been from pus-filled abscesses. The holotype specimen had a smaller and more delicate left humerus than the right, but the condition was reverse in its forearms; this may be due to a developmental anomaly called fluctuating asymmetry, often caused by traumatic stressors in the early years of development. Scientists have studied further specimens and have found fractures, tumors, and other anatomical deformities. What they have absolutely not found is a cowl on its neck and the ability to spit venom, as is portrayed Michael Crichton’s novel Jurassic Park and Stephen Spielberg’s cinematic adaptation. So, no, for the umpteenth time, we have no reason to believe that Dilophosaurus was venomous. 

a reconstruction of a 'furry' Dilophosaurus

Dilophosaurus was a medium-sized carnivore analogous to the size of a brown bear. It’s known from plentiful remains and may have been a pack hunter, as several specimens were fossilized together (this is rare for animals that didn’t ‘run together,’ unless they died in a catastrophic event – such as a flood – and were entombed together at the feet of the floodwaters). Dilophosaurus could reach up to twenty-three feet in length and clock in at 880 pounds. It had dual, sweeping crests atop its head, and it was slender and lightly built with a narrow snout. The upper jaw had a gap or kink below the nostril, and the jawbone was slender and delicate at the front but deep at the back. Its teeth were long, curved, thin, and compressed sideways; the teeth in the lower jaw were significantly smaller than those of the upper jaw, and most of the teeth had serrations at their front and back edges. Dilophosaurus had a long neck, and its vertebrae were hollow and light. Its arms were long and slender and powerful. Each hand had four fingers: the first was short but strong with a sickening claw, the second two fingers were longer and slenderer with smaller claws, and the fourth was vestigial. Its thigh bone was robust, its feet were stout, and the toes bore large claws. Trackways in Connecticut show that Dilophosaurus had a six and a half feet stride and that its claws alone made impressions. 

was Dilophosaurus pescetarian? It's a cool idea!

Dilophosaurus’ predatory lifestyle has been the subject of debate over the years. American paleontologist Robert Weems argued that Dilophosaurus had a weak bite and used its teeth for plucking and tearing rather than biting. He theorized that Dilophosaurus was a scavenger rather than a predator, and that if it did kill large prey, it would’ve done so with its clawed hands and feet rather than with its jaws. Later, paleontologist Robert Bakker argued that Dilophosaurus’ massive neck and skull and large upper teeth were expertly designed for killing large prey and robust enough to attack the largest sauropodomorphs in its environment. The paleontologist Paul Sereno also rejected Weems’ arguments for Dilophosaurus as a scavenger, claiming that strictly-scavenging terrestrial animals are a myth. He insisted that Dilophosaurus’ snout was better braced than had been thought and that the large, slender teeth were more lethal than the claws. He argued that Dilophosaurus was fully capable of hunting large herbivores, but that didn’t mean it wouldn’t snap up smaller prey when the opportunity arose. More recently in 2007, it was theorized that Dilophosaurus may have been primarily pescetarian (a fish-eater). Scientists highlighted how the ends of the jaws were expanded to the sides, forming a ‘rosette’ of interlocking teeth. This arrangement is similar to those of the later spinosaurids, which are known to have eaten fish; it’s also similar to modern gharials, which subsists largely on a pescetarian diet. Furthermore, Dilophosaurus’ nostrils were retracted back on the jaws, similar to spinosaurids (though the latter’s nostrils are more retracted). Such retraction of the nostrils may have limited water splashing into the sinus cavities while fishing. Both Dilophosaurus and spinosaurids had long arms with well-developed claws, perfect for catching fish. The Early Jurassic ‘Lake Dixie,’ which extended from Utah to Arizona and Nevada, would’ve provided abundant fish in the post-apocalyptic, biologically-impoverished world following the Triassic-Jurassic Extinction Event. Perhaps Dilophosaurus is a theropod that specialized in tapping into this abundant niche?

gnarly crests bruh

Proponents of the pescetarian Dilophosaurus also point to the head crests. While these wouldn’t necessarily help with a fishing lifestyle – no one is suggesting they were used as lures! – they wouldn’t risk damage in combat. Dilophosaurus’ head crests – similar to a cassowary with two crests – were each made of a curved bony ridge, like a third of a dinner plate, and barely as thick. These thin, fragile crests projecting at an angle above the eyes. The fragility of the crests is a major concern for those who argue for a brutal predatory lifestyle of taking down large prey; they could easily be broken in a scuffle. If Dilophosaurus was a fisher, however, there’s much less chance of them being damaged in the pursuit of food. The purpose of the crests has been debated, and different roles have been assigned to them: were they used for thermoregulation (the regulation of body temperature)? were they used to indimidate rivals or attract mates? were they used to identify one’s own species or even to distinguish between male and female (if the crests were to be smaller, perhaps, on females than males, in a form of sexual dimorphism)? The theory of thermoregulation has been cast aside, since it’s become apparent that dinosaurs were warm-blooded to begin with. Current hypotheses tend towards sexual display or species recognition with an acknowledgement of the distinct possibility of crest differences between genders. 

did Dilophosaurus travel or hunt in family groups? It seems likely!

Dilophosaurus’ fossils were found in the Kayenta Formation of Arizona, which – during the Early Jurassic – was the confluence of several rivers and close to Lake Dixie. By the Middle Jurassic, this area was being encroached upon from the north by a sandy dune field. The animals of the Early Jurassic were adapted to a seasonal climate, and abundant water could be found in streams, ponds, and lakes. The climate experienced rainy summers and dry winters. Dilophosaurus lived alongside large prosauropods such as Sarahsaurus, heterodontosaurs, primitive thyreophorans such as the lightly-armored Scutellosaurus and Scelidosaurus, and smaller theropods such as Coelophysis. The Kayenta Formation has also coughed up microbial or ‘algal’ limestone, petrified wood, plant impressions, freshwater bivalves and snails, various crustaceans, and invertebrae trace fossils. Representatives of the plentiful marine environments – lakes, rivers, and ponds – are common, from hybodont sharks, bony fish, lungfish, salamanders, caecilians, the early frog Prosalirus, and the Early Jurassic turtle Kayentachelys. There are also lizards, numerous crocodylomorphs such as Protosuchus, a panoply of early mammals, and the pterosaur Rhamphinion. It’s safe to say, then, that Dilophosaurus lived in a happening place!