Spinosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Spinosauridae

Genus: Spinosaurus

Species: Spinosaurus aegyptiacus

Introduction

Spinosaurus lived in what is now northern Africa during the Cenomanian stage of the Late Cretaceous period, specifically between 99 and 94 million years ago. The first discovered remains were found in Egypt in 1915, and although found more than a century ago, this species is still considered an enigmatic dinosaur. The destruction of the original specimens during World War II long limited the research possibilities as only a few incomplete remains were located in the decades after. A 2008 discovery led to more answers about its anatomy and habitat, though questions remain.

It is thought that Spinosaurus may have been the largest carnivore to have ever existed and is certainly the longest to date. Estimates indicate it may have topped the world's other two most famous and massive carnivores, Tyrannosaurus and Giganotosaurus . Spinosaurus's most distinctive feature, however, were its neural spines, up to 1.8 meters (6 ft) long, running along its back. These spines were likely interconnected with skin to form a fin-like sail structure.

Classification

Paleontologists use two major systems for classifying organisms. Linnaean taxonomy uses overall physical similarity to place organisms into different groups. By contrast, cladistics seeks to create groups of organisms based on evolutionary relationships; these groups are called “clades.” Cladistic analysis focuses on important key traits and attempts to trace the inheritance of a trait among descendants of a common ancestor.

Under the traditional Linnaean classification system, all spinosauroids belong to the Saurischia order, which is comprised of two major groups: the large herbivorous sauropods and the predominately carnivorous theropods. Nineteenth-century paleontologist Harry Seeley was the first to divide dinosaur species into one of two orders, Ornithischia, or bird-hipped dinosaurs, and Saurischia, or lizard-hipped dinosaurs. Spinosaurus is also part of the Theropoda suborder, a group of bipedal, generally carnivorous dinosaurs united by developments of the skull, teeth, and a few other skeletal features.

Using a cladistic analysis, Spinosaurus falls under the Theropoda (“beast-footed”) clade within the Saurischia clade. In 2017 Matthew Baron and his colleagues proposed that theropods such as Spinosaurus be reclassified from the Saurischia clade into the new clade Ornithoscelida based on their research into the development of carnivory. Theropods are an extremely diverse group of dinosaurs that first appeared during the Late Triassic period about 230 million years ago. The largest and most advanced theropod clade, Tetanurae (“stiff tailed”), includes the clade Spinosauroidae, which comprises the megalosaurs and the crocodile-skulled spinosaurids.

Spinosauroids lived during the Cretaceous period (145–66 million years ago) and are considered an unusual group of bipedal piscivorous (fish-eating) dinosaurs. These carnivores are basal among the tetanuran dinosaurs and include species such as Spinosaurus, Irritator, Baryonyx , and Suchomimus. Generalized characteristics include the elongated spines along their vertebrae, long crocodilian snout, muscular shoulders, and relatively long forearms compared to other theropod species such as Tyrannosaurus rex.

Anatomy

Weighing between 8,000 to 13,000 kilograms (17,600–28,700 lbs), measuring 14 to 18 meters (45–60 ft) in length, and standing at about 5 to 6 meters (16.5–20 ft) in height, Spinosaurus was an imposing dinosaur. Although considered to be the largest and longest predator species to have ever existed, Spinosaurus likely had a narrower build and shallower ribcage than either of its main rivals in terms of size—Tyrannosaurus and Giganotosaurus.

In addition to its impressive size, Spinosaurus also possessed a distinctive elongated snout and very long spines, up to 1.8 meters (6 ft) long, extending from its backbone. It is from these spines that Spinosaurus derives its name. These distinguishing bones extended from the vertebrae and were likely covered with skin to form a fin-like or sail structure along its back.

Paleontologists believe that the relatively long arms of Spinosaurus would have been highly functional in hunting, compared to other species such as Tyrannosaurus rex. Based on its skull anatomy, particularly its elongated jaws, conical teeth, and upward-facing nostrils, Spinosaurus was a carnivore species that subsisted primarily on fish and, similar to close relatives such as Baryonyx walkeri, possessed a long thumb claw to help it hunt its preferred food.

Although it exhibited relatively fast bipedal locomotion, some scientists believe it may also have occasionally displayed quadrupedalism, using its elongated forearms to walk on all four limbs.

Intelligence

Like many carnivore species, Spinosaurus ranks high compared with other dinosaurs. With an EQ falling somewhere between 1.0 and 1.9, Spinosaurus is considered one of the more intelligent species. Meat-eating behavior in dinosaurs usually indicates higher intelligence, and the majority of carnivores were more intelligent than their herbivorous relatives. This follows the belief that carnivorous species required greater cognitive capability and behavioral flexibility to efficiently hunt.

Reproduction and Population

Reproductive behavior and population numbers are difficult to estimate based solely on fossilized remains. This is particularly so when specimens are few, as is the case with Spinosaurus.

This species was originally thought to be the only African theropod to have existed. This Spinosaurus appears to have been restricted to northern Africa, suggesting a very limited population distribution. However, recent research has indicated that other theropod species were more common in Africa than paleontologists originally thought.

Like most dinosaur species, Spinosaurus was likely an oviparous (egg-laying) dinosaur, possibly laying several eggs at a time. Although no fossil evidence currently exists to highlight breeding behavior, it is possible that Spinosaurus exhibited some form of brooding behavior, such as seen in modern-day crocodiles that bury eggs underground to keep them warm.

Diet

The fossil record is too incomplete to provide any evidence of whether or not Spinosaurus displayed pack or solitary hunting and feeding habits. However, based on its skull anatomy and detention—particularly its elongated, tapered jaws, conical teeth in rosette arrangements, and high, upward-facing nostrils similar to that of a modern-day crocodile—it is thought that Spinosaurus was a carnivore species that subsisted primarily on fish and other aquatic vertebrates. Further evidence that Spinosaurus was piscivorous (fish-eating) comes from research on stable oxygen isotopes from theropod dinosaur tooth enamel, which indicated this species spent a considerable amount of time in the water, displaying a semi-aquatic existence, again similar to modern-day crocodile species. It is thought that by specializing as fish-eaters, Spinosaurus was able to avoid resource competition with other large predators, such as the allosauroids.

Information on feeding behavior and diet of Spinosaurus also comes from the fossils of similar or related species. Remains of Baryonyx walkeri, for example, have been found with fish scales in their stomachs. Given that this species is a close relative, this evidence supports the theory that Spinosaurus was also a fish-eater. ASpinosaurus tooth was also found in the fossilized remains of a pterosaur species. This has provided evidence that Spinosaurus also preyed upon these species for food and suggests it may have been a more generalized feeder than originally thought.

Behavior

As Spinosaurus was a very large and imposing carnivorous dinosaur, it is considered unlikely that this species had much to fear from other species in terms of predation. Spinosaurus appeared to be semi-aquatic and spent a significant portion of its life in the water. To date, no group or nest sites have been located, which makes it difficult to determine whether this species interacted socially (outside of obvious reproductive behavior), exhibited group or solitary living, or provided parental care.

One of the key debates among paleontologists involves the function of the sail-like back structure of Spinosaurus. . The most common views were that the sail was used either to regulate body temperature, much like the ears of a modern-day elephant, or to compete with rivals and attract mates. Some scientists believe that this type of thermoregulation would indicate dinosaurs were cold-blooded (an unsettled and highly controversial issue in paleontology), and therefore it is more likely that the structure was behavioral and used to attract mates or intimidate rivals. Yet another hypothesis is that the sail structure could have enhanced underwater movement, particularly while hunting for prey, as modern sailfish and some sharks do.

Debate continues regarding the function of the sail-like structure of Spinosaurus, and paleontologists have suggested that it may not be a fin at all, but more closely akin to a hump used to store fat, such as seen in bison.

Habitat and Other Life Forms

The shifting of the continents, known as continental drift, continued to occur during the Late Cretaceous period (99–66 million years ago). The world's major land masses became increasingly isolated, and dinosaur species experienced their last evolutionary radiation and abrupt geographical differentiation before their eventual extinction at the end of the Cretaceous period some 66 million years ago. This extinction event, one of only five such episodes throughout history, is called the K/T (or (P/T) extinction event and was responsible for wiping out the dinosaurs and 50 percent of all other life.

The Cretaceous was also characterized by the emergence and evolution of many new plant and animal species. Dinosaurs from this time have been found predominantly in Asia and western North America, consisting of coelurosaurian carnivores and ornithischian herbivores. Evidence of Late Cretaceous dinosaurs has been increasingly found on continental Africa, however, with fossils indicating the presence of at least three large carnivore species: Spinosaurus, Carcharodontosaurus, and Bahariasaurus. Fossils also indicate the presence of several sauropod herbivores such as Aegyptosaurus and Rebbachisaurus.

The majority of Spinosaurus remains have been located around northern Africa, including Egypt, Tunisia, Algeria, and Morocco. Although the Late Cretaceous experienced a general cooling trend, much of northern Africa exhibited a tropical climate. Little to no ice was found in the polar regions of the world, and there was little change in the thermal gradient from the equator to the poles. Gymnosperm and fern-dominated vegetation was still wide-spread, but the Late Cretaceous also witnessed the rapid radiation and diversification of angiosperms. Although evidence has provided only a partial view of their prehistoric habitat, much of the North African coastal area inhabited by Spinosaurus was thought to be covered with lakes, rivers, wetlands, tidal flats, and mangroves, which were ideal hunting grounds for this fish-eating predator.

Research

In 1912, fossil collector Richard Markgraf discovered the first specimen of a very strange carnivorous dinosaur from the Late Cretaceous in the Baharija Formation (Bahariya Formation) of Egypt. Ernst Stromer, a German paleontologist and financier of the African expedition, named the species Spinosaurus aegyptiacus in 1915. Although the remains were well-preserved, they were destroyed—along with Stromer's entire fossil collection—in a bombing raid on Munich, Germany, during World War II.

Additional fossils were found in Morocco, Tunisia, and Algeria in the late twentieth century, but specimens were relatively poor or partial, and general knowledge regarding this species remained limited. There is also some debate regarding the number of Spinosaurus species. It is commonly accepted that Spinosaurus aegyptiacus is a distinct species, and some believe a second species, Spinosaurus maroccanus, has also been unearthed in Morocco.

For many years, Spinosaurus was thought to be the only African theropod to have existed. However, continuing fieldwork in Africa, particularly by paleontologist Paul Sereno, has shown significant diversity in African theropods, many of which demonstrate relationships with species from other continents and provide new insight into the adaptive radiation and evolution of dinosaur species within Africa.

In 2008 paleontologist Nizar Ibrahim located Spinosaurus bones in eastern Morocco with the aid of an unnamed nomad. By 2014 Ibrahim reassembled the partial skeleton and displayed it along with bones created based on computer modeling. In a Science article, Ibrahim and his colleagues hypothesized S. aegyptiacus likely lived in water, given its flat, paddlelike feet; short hind limbs; dense leg bones suited to buoyancy in water; small hips; long, flexible tail suited to propulsion; high, sealable nares; and long neck. Some critics argued there was insufficient water in the region then, while others sought confirmation of the discovery site.

A 2018 PeerJ study countered S. aegyptiacus might have been a poor swimmer; using 3-D simulations based on Ibrahim's 2014 reconstruction, researcher Donald Henderson suggested the buoyancy of S. aegyptiacus would have impaired diving and a high center of mass caused tipping.

In another 2018 PeerJ study, Simone Maganuco​​ and Cristiano Dal Sasso's analysis of a juvenile Spinosaurus hind toe indicates the young creature was much like the adult and that it too spent a great deal of time in an aquatic environment.

Bibliography

Australian Museum, australianmuseum.net.au. Accessed Apr. 2010. .

Carpenter, Kenneth, editor. Carnivorous Dinosaurs. Indiana UP, 2005.

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

Department of Palebiology, Smithsonian National Museum of Natural History. Smithsonian Institution, www.paleobiology.si.edu. Accessed Apr. 2010.

Dinobase. University of Bristol, dinobase.gly.bris.ac.uk. Accessed Apr. 2010.

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.

Hopson, James A. “Relative Brain Size and Behavior in Archosaurian Reptiles.” Annual Review of Ecology and Systematics, vol. 8, 1977, pp. 429–48.

Ibrahim, Nizar, et al. “Semiaquatic Adaptations in a Giant Predatory Dinosaur.” Science, vol. 345, no. 6204, 11 Sept. 2014, pp. 1613–16, doi:10.1126/science.1258750. Accessed 24 Mar. 2020. ‌

Jerison, H. J. “Brain Evolution and Dinosaur Brains.” American Naturalist, vol. 103, no. 934, 1969, pp. 575–88.

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

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

Natural History Museum, www.nhm.ac.uk. Accessed Apr. 2010.

Norell, Mark, et al. Discovering Dinosaurs: Evolution, Extinction, and the Lessons of Prehistory. Updated and revised ed., U of California P, 2000.

Parker, Steve. Dinosaurus: The Complete Guide to Dinosaurs. 2nd ed., Firefly Books, 2016.

Poinar, George, and Roberta Poinar. What Bugged the Dinosaurs? Insects, Disease, and Death in the Cretaceous. Princeton UP, 2007.

UCMP. University of California Museum of Paleontology, www.ucmp.berkeley.edu. Accessed Apr. 2010.

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

Willis, K. J., and J. C. McElwain. Evolution of Plants. 2nd ed., Oxford UP, 2014.