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Spinosaurids
Fossil range: Late JurassicLate Cretaceous, 155–93.5 Ma
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Illustration of Spinosaurus.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Superfamily: Spinosauroidea
Family: Spinosauridae
Stromer, 1915
Subfamilies
  • Baryonychinae
  • Spinosaurinae (type)
Synonyms
  • Baryonychidae Charig & Milner, 1986
  • Irritatoridae Martill et al., 1996

Spinosauridae is a family of specialised theropod dinosaurs. Members of this family were large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth with no or only very tiny serrations. The front dentary teeth fanned out, giving the animal a characteristic look. The name of this family alludes to the typically conspicuous sail-like structure protruding from the back of species in the type genus, Spinosaurus. The purpose of the sail is disputed, whereas popular explanations are that it may have served as a thermoregulator, a threat display, or as a sexual display during courtship, some palaeontologists rather interpret the neural spine elongation in Spinosaurus as a support of a muscular/fatty hump.[1]

First spinosaurids appeared during the Late Jurassic and became abundant in the Early Cretaceous. So far, the Late Jurassic record of spinosaurids consists only of referred teeth.[2] They seem to disappear in the Cenomanian though teeth from the Turonian of Argentina have been attributed to spinosaurid dinosaurs.[3] Spinosaurid fossils have been recovered in Africa, Europe, South America, and Asia.

Contents

Paleobiology

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Predatory behavior

Studies of spinosaurids (specifically of Irritator) have shown that they had a very different skull shape and construction compared to other large predatory dinosaurs like Allosaurus and Tyrannosaurus. In most predatory dinosaurs, the jaws were broad either in width, height, or both, while spinosaurid jaws were thin and narrow. This lead paleontologists like Sues, Frey and Martill to conclude that spinosaurids, unlike other theropods, were not specialized in attacking large, struggling prey.[4]

Sues and colleagues studied the construction of the spinosaurid skull, and concluded that their mode of feeding was to use extremely quick, powerful strikes to seize small prey items with the jaws, employing the powerful neck muscles in rapid up and down motion. Due to the narrow snout, powerful side to side motion of the skull in prey capture is unlikely.[4]

Diet

Spinosaurids have in the past often been considered mainly fish-eaters (piscivores), based on comparisons of their jaws with the jaws of modern crocodilians. Rayfield and colleagues, in 2007, were the first to conduct actual biomechanical studies on a spinosaurid skull (using the European spinosaurid Baryonyx). They found that the structure and bite force of baryonychine jaws was almost identical to modern gharials, supporting the idea that at least baryonychines were mainly fish-eaters, though the jaws spinosaurines appeared to have been more generalized.[5]

Direct fossil evidence shows that spinosaurids fed on fish as well as a variety of other small to medium-sized animals, including small dinosaurs. Baryonyx was found with fish scales and the digested bones of a young Iguanodon in its stomach cavity, and there is one documented example of a spinosaurid having eaten a pterosaur.[6] It is likely that spinosaurids were generalists specializing in small prey of any kind, fish included.[4]

Taxonomy

The family Spinosauridae was named by Ernst Stromer in 1915 to include the single genus Spinosaurus. The family was expanded as more close relatives of Spinosaurus were uncovered. The first cladistic definition of Spinosauridae was provided by Paul Sereno in 1998 (as "All spinosaurids closer to Spinosaurus than to Torvosaurus).

Spinosauridae contains two subfamilies--Spinosaurinae and Baryonychinae. The subfamily Spinosaurinae was named by Sereno in 1998, and defined by Holtz et al. (2004) as all taxa closer to Spinosaurus aegyptiacus than to Baryonyx walkeri. The subfamily Baryonychinae was named by Charig & Milner in 1986. They erected both the subfamily and the family Baryonychidae for the newly discovered Baryonyx, before it was referred to the Spinosauridae. Their subfamily was defined by Holtz et al. in 2004, as the complementary clade of all taxa closer to Baryonyx walkeri than to Spinosaurus aegyptiacus.

Classification

External links

References

  1. ^ Bailey, J. B. (1997). "Neural spine elongation in dinosaurs: Sailbacks or buffalo-backs?" Journal of Paleontology 71 (6) : 1124-1146.
  2. ^ Buffetaut, E. (2008). "Spinosaurid teeth from the Late Jurassic of Tengaduru, Tanzania, with remarks on the evolutionary and biogeographical history of the Spinosauridae." In J.-M. Mazin, J. Pouech, P. Hantzpergue, V. Lacombe., Mid-Mesozoic Life and Environments. Cognac (France), June 24th-28th 2008, pp. 26-28.
  3. ^ Salgado, L., Canudo, J.I., Garrido, A.C., Ruiz-Omeñaca, J.I., Garcia, R.A., de la Fuente, M.S., Barco, J.L., and Bollati, R. (2009). "Upper Cretaceous vertebrates from El Anfiteatro area, Río Negro, Patagonia, Argentina." Cretaceous Research in press.
  4. ^ a b c Sues, H.D., Frey, E. and Martill, D.M. (2002). "Irritator challengeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil." Journal of Vertebrate Paleontology, 22(3): 535-547.
  5. ^ Rayfield, E.J., Milner, A.C., Xuan, V.B. and Young, P.G. (2007). "Functional morphology of spinosaur 'crocodile-mimic' dinosaurs." Journal of Vertebrate Paleontology, 27(4): 892-901.
  6. ^ Buffetaut, E., Martill, D. and Escuillié, F. (2004). "Pterosaurs as part of a spinosaur diet." Nature, 429: 33.
  7. ^ Buffetaut, Eric; Suteethorn, Varavudh; Tong, Haiyan; and Amiot, Romain (2008). "An Early Cretaceous spinosaurid theropod from southern China". Geological Magazine 145 (5): 745–748. doi:10.1017/S0016756808005360.  

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