Lexovisaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Stegosauridae

Genus:Lexovisaurus

Species:Lexovisaurus durobrivensis

Introduction

Lexovisaurus was a mid-sized herbivorous dinosaur that lived in Late Jurassic Europe. A member of a diverse group of herbivores that thrived during the Jurassic period, Lexovisaurus occupied the island chains of what would become England and France. The species is a representative of the stegosaurids, armored herbivores that appeared only in parts of the northern hemisphere.

In the Triassic period, the continents of the earth were united in a single land mass known as Pangaea. Dinosaurs first appear in the fossil record from this period and appear to have spread widely across the world. Pangaea split apart during the Jurassic and Cretaceous periods, leading to isolated populations of dinosaurs that eventually evolved into unique southern and northern varieties.

Lexovisaurus and the other stegosaurs are known from fossils uncovered in North America, Europe, and Asia, suggesting that the species only thrived in part of the northern hemisphere. This may indicate that the earliest representative of the group evolved after North America, Europe, and Asia split apart from the southern continents.

Classification

Paleontologists use two primary methods to classify organisms into different groups. Linnaean taxonomy, or systematics, organizes organisms according to overall physical similarity, while cladistics creates groups called “clades” that are intended to represent the evolutionary relationships between species.

According to the traditional Linnaean system, Lexovisaurus belongs to the order Ornithischia, based on the “bird-like” orientation of the animal's pelvis. (Though in the twenty-first century some researchers began to question the longstanding division of dinosaurs into the ornithischian and saurischian orders, it remained in wide use.) From there, Lexovisaurus is placed into the infraorder Stegosauria and the family Stegosauridae, which were ornithischians with small heads, unique armor, and tail spikes.

Cladistic analysis uses the clade Thyreophora, made up of ornithischian dinosaurs armored with osteoderms, or bony skin deposits. The clade eurypoda contains thyreophorans with spiked tails, informally called thagomizers, and pairs of plates lining the back. Cladistic analysis has made further classification of the genus Lexovisaurus uncertain; some paleontologists suggest it should be abandoned for an alternate genus, combining it with other related stegosaurs.

Anatomy

Lexovisaurus was a mid-sized dinosaur, reaching lengths of between 5 and 6 meters (16.4–19.6 ft) and weighing between 900 and 1,200 kilograms (1,984–2,645.5 lbs). It was quadrupedal, with longer hind legs than forelegs, and short feet ending in blunt claws. The animal had a thick build, with a tall midsection and large stomach.

Stegosaurs had small heads, one of the diagnostic characteristics of the group, with beaked snouts and small eyes set on the sides of the head. Lexovisaurus's short beak was covered in a layer of keratin, similar to those of turtles and some other beaked reptiles.

Lexovisaurus had rows of osteoderms along its back, in the form of both flattened plates and sharp, conical spikes along its back. There were also segments intermediate between plate and spike form, often called “splates.” The species had a long, flexible tail with between four and six tail spikes.

Intelligence

Scientists have used encephalization quotient (EQ), based on brain and body size, to estimate animal intelligence. With reduced skull size, the stegosaurs had among the lowest EQ levels of any dinosaur group. Some stegosaurs are estimated to have had EQ ratings in the range of 0.1 to 0.5, placing them at the lower end of the dinosaur intelligence spectrum. Dinosaurs, in general, were likely less intelligent than modern mammals and birds living similar lifestyles.

Reproduction and Population

Paleontologists believe that dinosaurs were generally oviparous, or egg-laying animals. No eggs or nests have been discovered for stegosaurs like Lexovisaurus, but most paleontologists believe that the species laid eggs in shallow nests dug into the ground. The species may have covered its nests in soil and vegetation, in order to protect the developing eggs from climatic conditions and to speed the incubation process. Paleontologists are uncertain whether species like Lexovisaurus provided any parental care to their hatchlings, or whether young stegosaurs foraged on their own after hatching.

Lexovisaurus is known only from isolated fossils and paleontologists have been unable to estimate the animal's frequency within its environment. In addition, paleontologists do not currently know whether male and female Lexovisaurus were identical in appearance or whether they differed in size or other physical characteristics.

Diet

Lexovisaurus is believed to have been herbivorous, like other stegosaur species. The animal's short beak would likely have been used to strip vegetation, which the animal probably swallowed whole, allowing large quantities of plant matter to ruminate in its large stomach.

There were a wide variety of plants in its environment, most belonging to the gymnosperm group. A variety of conifer species were present in Late Jurassic Europe, as well as cycads and a wide variety of pteridophytes, which included both ferns and tree ferns. Lexovisaurus probably browsed on low lying vegetation, as the animal was quadrupedal and too large to rear onto its back legs when feeding.

Behavior

Paleontologists are uncertain about the purpose of the plates and spines on the backs of Lexovisaurus and other stegosaurids. Some paleontologists have suggested that the plates and spines were used for defense, discouraging predators from attacking the animal's spine. Some paleontologists believe that the spines and plates had a sexual function, helping animals to attract mates. Some have suggested that stegosaur plates might have been brightly-colored, helping to communicate information about the animal's breeding status or health.

The tail spines of Lexovisaurus may have been a defensive weapon, helping to discourage predators. Alternatively, the tail spikes might have been used in contests between members of the species competing for mates. Many mammalian herbivores with horns use their ornaments for both defense and mate competition, and the spiked tails of Lexovisaurus and other stegosaurs may have served multiple functions.

Habitat and Other Life Forms

In the Late Jurassic, most of Europe was divided into an island chain now referred to as central Laurasia. The islands contained semi-tropical forest habitats. There were a variety of reptiles and amphibians living in central Laurasia, including crocodiles and a variety of turtles. Sea turtles and other ocean reptiles, such as plesiosaurs, may have occasionally come ashore on these islands.

In addition to stegosaurs like Lexivosaurus, central Laurasia was also home to a variety of sauropods, quadrupedal herbivores known for their large size and long necks. Cetiosaurus was one of the sauropod species known from the Late Jurassic fossil beds of Europe. Additionally, there were several species of ankylosaurs in the area, armored relatives of the stegosaurs known for the evolution of clubbed tails and extensive dorsal armor.

There were also a variety of predatory dinosaurs in central Laurasia, such as the mid-sized theropod Eustreptospondylus, which might have hunted small dinosaurs and scavenged along the island shores. Piveteausaurus was a larger theropod that also lived in central Laurasia and may have encountered Lexivosaurus.

Research

The remains of Lexovisaurus were first discovered in the 1880s, and were initially classified in the genus Omosaurus. In 1957 paleontologist R. B. Hofstetter separated it into its own genus, with the type species Lexovisaurus durobrivensis. With relatively few fossils known, further research has largely focused on classification, a field prone to frequent shifts and disagreements among researchers. Paleontologists continue to search for additional specimens of Lexovisaurus and related species in an effort to better understand the relationships within the stegosaurid group.

Bibliography

Bowman Bailey, Jack. “Neural Spine Elongation in Dinosaurs; Sailbacks or Buffalo-Backs?” Journal of Paleontology, vol. 71, no. 6, 1997, pp. 1124–46.

Briggs, Derek E. G., and Peter R. Crowther. Paleobiology II. Wiley-Blackwell, 2001.

Carpenter, Kenneth. Eggs, Nests and Baby Dinosaurs: A Look at Dinosaur Reproduction. Indiana UP, 1999.

Carrier, David R., and Colleen G. Farmer. “The Evolution of Pelvic Aspiration in Archosaurs.” Paleobiology, vol. 26, no. 2, 2000, 271–93.

Chinsamay-Turan, Anusuya. Microstructure of Dinosaur Bone: Deciphering Biology with Fine-Scale Techniques. Johns Hopkins UP, 2005.

“Dino Fins More Like Humps?” Science, vol. 279, 1998, p. 1139.

Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. 3rd ed., Cambridge UP, 2016.

Fastovsky, David E., and David B. Weishampel. Evolution and Extinction of the Dinosaurs. 2nd ed., Cambridge UP, 2007.

Horner, Jack, and James Gorman. How to Build a Dinosaur: Extinction Doesn’t Have to Be Forever. Dutton, 2009.

Horner, John R., and Edwin Dobb. Dinosaur Lives: Unearthing an Evolutionary Saga. Mariner Books, 1998.

Lucas, Spencer G. Dinosaurs: The Textbook. 6th ed., Columbia UP, 2016.

Martin, Anthony J. Introduction to the Study of Dinosaurs. 2nd ed., Blackwell, 2006.

"Ornithischia: Stegosauridae." Palaeos, palaeos.com/vertebrates/ornithischia/stegosauridae.html. Accessed 24 Apr. 2020.

"The Ornithischian Dinosaurs." UC Museum of Paleontology, ucmp.berkeley.edu/diapsids/ornithischia/ornithischia.html. Accessed 24 Apr. 2020.

Paul, Gregory S. The Princeton Field Guide to Dinosaurs. 2nd. ed., Princeton UP, 2016.

Sereno, Paul C., et al. “Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs.” Science, vol. 286, 1999, p. 1342.

Weishampel, David B., et al., editors. The Dinosauria. 3rd. ed., U of California P, 2007