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Spinosaurids were large [[Bipedalism|bipedal]] [[carnivore]]s. Their [[crocodilia]]n-like skulls were long, low and narrow, bearing conical teeth with reduced or absent [[Glossary of dinosaur anatomy#serrations|serrations]]. The tips of their upper and [[Glossary of dinosaur anatomy#mandible|lower jaws]] fanned out into a spoon-shaped structure similar to a [[Rosette (design)|rosette]], behind which there was a [[Glossary of dinosaur anatomy#subnarial gap|notch]] in the upper jaw that the expanded tip of the lower jaw fit into. The [[Glossary of dinosaur anatomy#bony nostrils|nostrils]] of spinosaurids were retracted to a position further back on the head than in most other theropods, and they had bony crests on their heads along the midline of their skulls. Their robust shoulders wielded stocky forelimbs, with three-fingered hands that bore an enlarged [[Glossary of dinosaur anatomy#unguals|claw]] on the first [[Glossary of dinosaur anatomy#digit|digit]]. In many [[species]], the upwards-projecting [[Glossary of dinosaur anatomy#neural spine|neural spines]] of the [[Glossary of dinosaur anatomy#vertebrae|vertebrae]] (backbones) were significantly elongated and formed a [[Neural spine sail|sail]] on the animal's back (hence the family's etymology), which supported either a layer of skin or a fatty hump.
The genus ''[[Spinosaurus]]'', from which the family, one of its [[subfamily|subfamilies]] (Spinosaurinae) and [[Tribe (biology)|tribes]] (Spinosaurini) borrow their names, is the longest known terrestrial [[Predation|predator]] from the fossil record, with an estimated length of up to {{Convert|14|m|sp=us}} and body mass of up to {{convert|7.4|MT|ST}} (similar to the weight of an [[African elephant]]). The closely related genus ''[[Sigilmassasaurus]]'' may have reached a similar or greater size, though its [[Taxonomy (biology)|taxonomy]] is disputed. Direct fossil evidence and anatomical [[adaptation]]s indicate that spinosaurids were at least partially [[piscivorous]] (fish-eating), with additional fossil finds indicating they also fed on other dinosaurs and [[pterosaur]]s. The [[Osteological|osteology]] of spinosaurid teeth and bones has suggested a [[semiaquatic]] lifestyle for some members of this [[clade]]. This is further indicated by various anatomical adaptations, such as retracted eyes and nostrils; and the deepening of the tail in some taxa, which has been suggested to have aided in underwater propulsion akin to that of modern [[crocodilia]]ns. Spinosaurs are proposed to be closely related to the [[megalosaurid]] theropods of the Jurassic. This is due to both groups sharing many features such an enlarged claw on their first manual ungual and an elongated skull.<ref>{{cite journal |last1=Benson |first1=Rodger |title=A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods |journal=Zoological Journal of the Linnean Society |date=2010 |volume=158 |issue=4 |pages=882–935 |doi=10.1111/j.1096-3642.2009.00569.x |s2cid=84266680 |doi-access=free }}</ref> However, some propose that this group (which is known as the Megalosauroidea) is paraphyletic and that spinosaurs represent either the most basal [[tetanurans]]<ref>{{cite journal |title=A NEW PHYLOGENY OF THE CARNIVOROUS DINOSAURS |journal=GAIA |pages=5–61 |url=https://www.geol.umd.edu/~tholtz/gaiaphyl.pdf}}</ref> or as basal [[carnosaurs]] which are less derived than the megalosaurids.<ref>{{cite journal |last1=Rauhut |first1=Oliver |title=Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs |journal=Scientific Reports |date=2019 |volume=9 |issue=18826 |page=18826 |doi=10.1038/s41598-019-53672-7 |pmid=31827108 |pmc=6906444 |bibcode=2019NatSR...918826R }}</ref> Some have proposed a combination of the two ideas with spinosaurs being in a monophyletic Megalosauroidea inside a more inclusive Carnosauria that is made up of both allosauroids and megalosauroids.<ref>{{cite journal |last1=Rauhut |first1=Oliver |title=Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany |journal=PNAS |date=2012 |volume=109 |issue=29 |pages=11746–11751 |doi=10.1073/pnas.1203238109 |pmid=22753486 |pmc=3406838 |bibcode=2012PNAS..10911746R |doi-access=free }}</ref>
== History of discovery ==
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