Theropoda: Spinosauridae

Taxa on this Page

1. Baryonychinae X
2. Baryonyx tenerensis (=Suchomimus) X
3. Baryonyx walkeri X
4. Irritator X
5. Spinosauridae X
6. Spinosaurinae X
7. Spinosaurus X

Spinosaurs - semiaquatic theropods

Spinosauridae.  Among the more unusual of the theropod dinosaurs, spinosaurids were lightly built predators with elongated vertebral spines and crocodile-like jaws with specialized teeth. Fish probably formed most of their diet. Two main groups exist: the baryonychids, who are most famous for their elongated, many-toothed skulls and large hand claws; and the spinosaurids, which had more cranial ornamentation and generally a larger sail (reminiscent of Dimetrodon). Spinosaurids, like Baryonyx tenerensis (also known as Suchomimus), have very short and stocky arms, thumb claws which are dramatically larger than the other unguals, unguals with greater angles of curvature, a tapering shaft, and more oval slender cross-section (like that of a carnosaur or Torvosaurus claw). Spinosaurid teeth are much more oval in cross-section than in typical theropods. There are a number of crocodilian like features in the skulls of spinosaurids: including the elongate snout, conical teeth, secondary palate (so it could breath through it's nostrils, even while the mouth is closed, a mamamlian feature not shared by most reptiles), and more. These features have been associated with the adoption of a piscivorous diet in crocodylomorph evolution. As with modern crocodiles, spinosaurs were not obliged to only eat fish. They could eat land animals as well. Remnants of Iguanodon bones as well as Lepidotes fish scales are found among the fossil stomach contents of Baryonyx walkeri. The paleoenvironments from which known spinosaurids come all support diverse communities of fish, some of which were very large. There is currently no evidence that these were seasonal communities, and would seem likely to be permanent residents. Thus, we have very large packages of fish meat not otherwise easily exploitable by theropods, although they would have been in competition with contemporary giant crocodiles. The relationship of the spinosaurids is not completely clear, although the most likely option is that the spinosaurs are cousins to the megalosaurids. Greg Paul in his Predatory Dinosaurs of the World however suggests that they might actually be late surviving (and giant) coelophysoids (podokesaurs). An interesting piece of evidence here is the presence of a "subnarial gap" or kink in the jaw, under the nostrils, that is found only in the Podokesauridae (Coelophysoidea) and Spinosauridae. There is no evidence of a ' subnarial gap ' in any other theropods groups outside of those two. It is however a feature that is common in archosaurs in general. Eoraptor apparently has a subnarial gap, but Herrerasaurus does not. There are differing views over whether either is a true theropod. However in an scientific paper Paul Sereno et al. affirm Megalosaur (Torvosaur) relationships. There may be only a superficial resemblence between spinosaurids and coelophysids in respects to the premaxillary/maxillary portion of the skull in profile. In addition, the anatomical arrangement in coelophysoids differs from the condition in spinosaurids (although the latter could be derived from the former). But now that the postcranial anatomy of spinosaurids are a lot better known than back in the mid-1980s, it seems that there is not much in the rest of the skeleton to link spinosaurids and coelophysoids. Some restorations of spinosaurians made recently show them as quadrupedal, a mistake based on early descriptions of the arms of Baryonyx walkeri. MAK120304

Habits

The following is taken verbatum from Wikipedia:

A 2010 publication by Romain Amiot and colleagues found that oxygen isotope ratios of spinosaurid bones indicates semiaquatic lifestyles. Isotope ratios from teeth from the spinosaurids Baryonyx, Irritator, Siamosaurus, and Spinosaurus were compared with isotopic compositions from contemporaneous theropods, turtles, and crocodilians. The study found that, among theropods, spinosaurid isotope ratios were closer to those of turtles and crocodilians. Siamosaurus specimens tended to have the largest difference from the ratios of other theropods, and Spinosaurus tended to be have the least difference. The authors concluded that spinosaurids, like modern crocodilians and hippopotamuses, spent much of their daily lives in water. The authors also suggested that semiaquatic habits and piscivory in spinosaurids can explain how spinosaurids coexisted with other large theropods: by feeding on different prey items and living in different habitats, the different types of theropods would have been out of direct competition. (Amiot et al 2010)

Descriptions

Spinosauridae

Range: Barremian to Cenomanian of Eur., Afr, SAm, & ?Aus

Phylogeny: Tetanurae/Megalosauroidea/Megalosauridae : Xuanhanosaurus + (Megalosaurinae + ((Piatnitzkysaurus + Marshosaurus) + (Afrovenator + Dubreuillosaurus) + Avetheropoda) + (Eustreptospondylus + * : Baryonychinae + Spinosaurinae))

Comments: MAK010506

Links Thescelosaurus! (short but useful description of each species); Wikipedia; Mikko's phylogeny (dendrogram only); Origin and evolution of Spinosauridae in French, argues for Eustreptospondylus as a basal spinosaur

Baryonychinae

Range:

Phylogeny: Spinosauridae : + Spinosaurinae + *

Comments: Baryonychines are characterized by (among other traits) the increased number and decreased size of dentary (jawbone) teeth (about 30) and a blade-shaped ventral keel to the anterior dorsal centra of the vertebrae. MAK010506

Baryonyx walkeri Charig and Milner, 1986

Synonyms: Suchosaurus cultridens, Suchosaurus girardi

Horizon: Wealden formation of Surrey, England and Spain (Barremian)

Phylogeny: Spinosauridae :

Size: Length 9.5 meters estimated, weight about 1.7 tonnes (Paul 1988)

Comments: Known from most of a skull and skeleton, this is the most complete theropod dinosaur unearthed to date in Britian. Originally referred to as the "Surrey dinosaur", and nicknamed "Claws" on account of its huge claws, which conjured images of a gigantic dromaeosaurid, this animal is now known to be a close relative of Spinosaurus. It was probably a fish-eater. Suchomimus is a close relative, and probably belongs in the same genus. MAK010506

Baryonyx tenerensis (Sereno, Beck, Dutheil, Gado, Larsson, Lyon, Marcot, Rauhut, Sadleir, Sider, Varricchio, G. Wilson, and J. Wilson, 1998)

Synonym: Suchomimus tenerensis

Horizon: Elrhaz Formation, Tenere Desert region, Niger (Late Aptian)

Phylogeny: Spinosauridae :

Size: length over 11 meters, weight several tonnes

Comments: First a boring but (un)necessary nomenclatural preamble before discussing this animal's paleoecology.

As there is little to distinguish Suchomimus from Baryonyx, or for that matter from the more poorly known Cristatusaurus lapparenti Taquet and Russell, 1998, it is likely that the three are congeneric. This is a rare instance where sufficient material shows how similar two species can be, invalidating the usual need for monotypal fossil genera. Baryonyx having taxonomic priority (being named in the 1980s) would be the default genus name, so Suchomimus tenerensis becomes Baryonyx tenerensis. It is possible also that C. lapparenti is a senior synonym of S. tenerensis and so has priority over the latter, see comments by Mickey Mortimer, which would give Baryonyx lapparenti as the correct name for Suchomimus tenerensis. Of course these could also be different but closely related species, so at least "tenerensis" is probably safe. In any case, the name Suchomimus is so familar among dinophiles, and this is such a distinctive animal, that it will doubtless be known as Suchomimus for a very long time MAK120304

Baryonyx tenerensis ("Suchomimus") had an elongate snout and piscivorous adaptations that make the skull resemble a fish-eating crocodilian such as the gavial. It differs from Baryonyx in that the snout is even more crocodilian like. The skull is estimated at about 1.2 m (4 ft) in length, the overall creature was 11 meters or more. The robust forelimbs armed with very large curving claws, including a sickle-like thumb, that could be used like gaffing hooks on fish or other prey. Tall blade-like neural spines ran along its back, rising into a low (60cm tall) "sail" over the hip region (sacral vertebrae) and base of the tail.

Nearly 3.5 m (12 ft) high at the hips, B. tenerensis may have waded into rivers and lakes like to catch fish, but probably could swim in deeper water as well, using its back legs and possibly its tail for propulsion. Suchomimus may have swept its mouth back and forth through the water, much like a pelican, and snapped when it encountered prey. This would allow it to keeps its eyes above the waterline and still reach down into the muddy waters for large lungfish.

Fish-eating habits are indicated by structural parallels with modern crocodiles. Crocodiles species such as the Nile, Salt-Water, Muggers have jaws on par with Baryonyx walker. Although thinner than most animals but still wide enough and strong enough to take down large animals like water buffalo. The piscivorous crocodylians like the gharial and false gharial and the African slender snouted croc all have jaws suitable for fishing and small animal catching. If they were to attempt to tackle a large animal their jaws would snap under the stress. B. tenerensis had jaws like the latter, so the same rules seem to apply.

Unlike conventional fish-eaters B. tenerensis had relatively high skull. Piscivores need a long low skull so they can swip the skull through the water to catch fish. Onviously Suchomimus 's methods of catching food were different to crocodiles.

B. tenerensis is likely to have eaten land animals as well as fish. It had a relatively long, thin neck, plus very strong forearms and massive (by theropod standards) shoulders. It shared the local environment with a massive (10-15 meter) crocodile, built on a rather modern design, which occupied the lurk-in-the-water carnivore niche. The long jaw was better able to withstand twisting than the wider skull of Carcharodontosaurus, so it would have attacked different, probably smaller, prey on land. The thin jaws could not have tackled animals like iguanodonts. MAK010506

Spinosaurinae

Range: Albian to Cenomanian of Afr & S Am

Phylogeny: Spinosauridae : Baryonychinae + *

Size: (Paul 1988)

Comments: Spinosaurines are characterized by very straight teeth lacking serrations, and lack the derived increase in dentary tooth number. The difference between baryonychine and spinosaurine teeth is that spinosaurine teeth seem to be less curved, whereas baryonychines retain something closer to the original theropod curvature in lateral view. They remain, however, much rounder in cross-section than allosaur or ceratosaur teeth of the same height. MAK010506

Irritator challengeri Martill, Cruickshank, Frey, Small, and Clarke, 1996

Synonym: possibly Angaturama limai Kellner and Campos, 1996

Horizon: Romualdo Member of the Santana formation, Albian of Brazil

Phylogeny: Spinosaurinae :

Size: Length about 5.5 to 6 meters, weight about 500 or 600 kg

Comments: This animal's name comes from the fact that the skull was both damaged and artificially lengthened by amateur fossil hunters before it was described. Angaturama limai Kellner & Campos, 1996, another unusual theropod from the same formation, consisting of the front part of the jaws, is probably from the same species. MAK010506

Spinosaurus aegyptiacus

Horizon: Baharija Beds of Egypt, also Morocco (Albian-Cenomanian)

Phylogeny: Spinosaurinae :

Size: about 15 meters estimated, weight about 4.5 tonnes (Paul 1988)

Comments: A huge but lightly built animal, with vertebral spines taller than a man (the tallest part of the large bony sail is over the thorax - the mid-dorsal vertebrae), Spinosaurus did not seem to compete with the contemporary Cacharodontosaurs. Perhaps, like the Baryonchines, it was semi-aquatic; probably a fish-eater. Early illustrations wrongly showed Spinosaurus to resemble a conventional carnosaur (like Allosaurus) with a Dimetrodon-style sail or fin on the back (there are still some illustrations that show Spinosaurus as a chunky animal with long thick forearms, sometimes in a quadrapedal pose). The remains were lost in WWII. Spinosaurus marrocanus Russell, 1996, from the ? Albian of Morocco may or may not be the same species. Material referred to as "Spinosaurus B" seems to belong to two theropods: the vertebrae to Sigilmassasaurus (a large theropod of uncertain relationships - Wikipedia), and the limb material to the allosaur Carcharodontosaurus (Thescelosaurus). MAK010506

Image: Skeletal reconstruction of Spinosaurus aegyptiacus, photo by Kabacchi, via Wikipedia, Creative Commons Attribution