| Suchomimus | |
|---|---|
 | |
| Reconstructed skeleton at theChicago Children's Museum | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Spinosauridae |
| Clade: | †Ceratosuchopsini |
| Genus: | †Suchomimus Serenoet al., 1998 |
| Type species | |
| †Suchomimus tenerensis Serenoet al., 1998 | |
| Synonyms | |
Suchomimus is agenus of largetheropoddinosaur that lived in what is nowNiger during theAlbian toAptianstages of theEarly Cretaceousperiod, 112 million years ago. The only knownspecies isS. tenerensis, originally described in 1998 bypaleontologistPaul Sereno and colleagues from severalfossils discovered one year earlier in theElrhaz Formation. Although these fossils come from multiple specimens, they represent one of the most anatomically well-documentedspinosaurids. The animal'sgeneric name, which means "crocodile mimic", alludes to its elongated skull andpiscivorous adaptations, while thespecific name refers to theTénéré Desert, where the fossils were discovered.
With an estimated length of 9.5–11 metres (31–36 ft) and abody mass ranging from 2.5–3.8 metric tons (2.8–4.2 short tons),Suchomimus was a particularly large theropod. As its generic name suggests, the animal’s skull was elongated, low, and narrow, resembling that ofcrocodilians. The tip of thesnout flared laterally to form arosette, and the jaws bore numerous finely serrated conical teeth, with the largest ones positioned near the front. The neck ofSuchomimus was relatively short, while its powerfully built forelimbs bore a large, curvedclaw on each thumb. Along the midline of the animal's back ran a lowdorsal sail, built from the longneural spines of itsvertebrae. Its cranial and limb features indicate that it was a primarily piscivorous predator adapted for hunting inshallow waters.
Many paleontologists considerSuchomimus to be a probablejunior synonym of the contemporaneous spinosauridCristatusaurus, although the lattertaxon is based on much more fragmentary remains. Some researchers have also suggested thatSuchomimus might represent an African species of the European spinosauridBaryonyx, and it has occasionally been referred to in thescientific literature asB. tenerensis. However, more recent studies continue to regard the two genera as distinct. According to the fossil record of the Elrhaz Formation,Suchomimus lived and hunted in afluvial environment of vastfloodplains alongside many other dinosaurs, in addition topterosaurs,crocodylomorphs,bony fishes,turtles, andbivalves.
In late 1997, AmericanpaleontologistPaul Sereno and his team conducted an expedition at the Gadoufaoua site in theTénéré Desert ofNiger, where they uncovered variousfossils. On 4 December, team member David Varricchio discovered a largethumbclaw belonging to a massivetheropoddinosaur, remarkably well exposed on the surface. According to Sereno, the sand and wind had gradually revealed this claw, which had remained visible in this state for at least two centuries. Subsequent excavations at the site recovered several fossils from different individuals of this enigmatic theropod, which proved to belong to thespinosauridfamily. On 13 November 1998, theScience Magazine published a study led by Sereno, formally naming and describing the newgenus andspeciesSuchomimus tenerensis based on the fossils discovered during the expedition. The generic nameSuchomimus derives from theAncient Greekσοῦχος (souchos, "crocodile"), andμῖμος (mimos, "mimic") literally meaning "crocodile mimic", in reference to its elongatedsnout andpiscivorous adaptations. Thespecific nametenerensis refers to the desert where the animal’s fossils were found.[1][2]
All known fossil specimens were recovered from the Tegama Beds of theElrhaz Formation and are now housed in the paleontological collections of theMusée National Boubou Hama inNiamey. Theholotype, catalogued as MNN GDF500, consists of a partial skeleton lacking the skull. It contains threeneck ribs, parts of fourteendorsal (back)vertebrae, tendorsal ribs,gastralia (or "belly ribs"), pieces of threesacral vertebrae, parts of twelvecaudal (tail) vertebrae,chevrons (bones that form the underside of the tail), ascapula (shoulder blade), acoracoid, a partial forelimb, most of thepelvis (hip bone), and parts of a hindlimb. Other notable specimens are also mentioned in the paper describing thetaxon. Specimens MNN GDF 501 to 508 include asnout, aquadrate from the back of the skull, threedentaries (tooth-bearing bones of the lower jaw), anaxis (second neck vertebra), a rear cervical vertebra, and a rear dorsal vertebra. Specimens MNN GDF510 and 511 consist of two caudal vertebrae. In the same article, Sereno and colleagues also reported additional bones and teeth attributed to this dinosaur, though their catalogue numbers were not specified.[2] AlthoughSuchomimus is among the best-known spinosaurids anatomically, its original description remains relatively brief.[3]
More than two months beforeS. tenerensis was formally described in thescientific literature,[2] French paleontologistPhilippe Taquet and his Canadian colleagueDale A. Russell named another spinosaurid from the Elrhaz Formation,Cristatusaurus lapparenti, based on fragments of jaws and vertebrae.[4] The fossils of this taxon were first discovered in 1973 by Taquet at Gadoufaoua, who later reported the find and described the fossilpremaxillae in a paper published in 1984. Although he did not assign them ascientific name at the time, the author recognized the fossils as belonging to a large theropod of the Spinosauridae family based on anatomical features shared with the now-destroyed holotype ofSpinosaurus aegyptiacus.[5] In a 1986 publication, British paleontologistsAlan Charig andAngela Milner noted that the jaw elements described by Taquet were nearly indistinguishable from those of the spinosauridBaryonyx walkeri, which they had just described from a partial skeleton dating to theBarremian stage of theWeald Clay Formation inEngland.[6] In a 1997 follow-up to their preliminary paper, the same authors referred Taquet’s fossils to an indeterminate species ofBaryonyx, despite their younger geological age.[7] In their 1998 paper, Sereno and colleagues agreed with Charig and Milner that there were no significant differences between the fossil skulls ofBaryonyx andCristatusaurus, concluding that the latter should be regarded as anomen dubium.[2]
In 2002, French paleontologistÉric Buffetaut and his Tunisian colleague Mohamed Ouaja expressed support for the proposedsynonymy betweenCristatusaurus andBaryonyx, noting that Milner had acknowledged the possibility thatSuchomimus might also becongeneric withBaryonyx with later anatomical comparisons.[8] The same year, American paleontologistHans-Dieter Sues and colleagues concluded thatS. tenerensis was sufficiently similar toB. walkeri to be placed within the same genus,renamed asBaryonyx tenerensis, and that it was likely identical toCristatusaurus.[9] These interpretations were also concurred by Milner in 2003.[10] In aconference abstract released the following year, American paleontologist Stephen Hutt and British researcher Penny Newbery also supported the synonymy based on a large theropod vertebra discovered on theIsle of Wight, England, which they attributed to an animal closely related to these two taxa.[11] Nevertheless, subsequent studies have continued to treatSuchomimus andBaryonyx as separate genera.[12][13][14][15][16] A 2017review paper by the Brazilian palaeontologist Carlos Roberto A. Candeiro and colleagues stated that this debate was more in the realm of semantics than science, as it is generally agreed thatSuchomimus andBaryonyx are distinct, related genera.[17] As for thevalidity ofCristatusaurus, it continues to be disputed in recent studies. This taxon is generally regarded as a likely senior synonym ofSuchomimus, as both originate from the samestratigraphic units and show no sufficiently distinct anatomical differences to justify a clear separation between them. Thus,Cristatusaurus is currently considered as anomen dubium,[18][19][20] pending further analyses that could clarify its taxonomic position.[15][16] However, in the event that the synonymy between the two genera is confirmed,nomenclatural priority would normally be given toC. lapparenti, as it was described earlier thanS. tenerensis.[3]
Suchomimus would have reached 9.5–11 metres (31–36 ft) in length and weighed 2.5–3.8 metric tons (2.8–4.2 short tons).[2][21][22][23] Canadian paleontologists François Therrien and Donald M. Henderson proposed that a 10.3 metres (34 ft) longSuchomimus would have weighed more than 5.2 metric tons (5.7 short tons) based on their ratio between skull length and body length; however, they noted that they might have overestimated the size of spinosaurids (i.e.,Suchomimus andBaryonyx).[24] The holotype specimen ofSuchomimus is considerably larger than that ofBaryonyx,[2] although this may be explained by the possibly immature status of the latter.[7]
Unlike most giant theropod dinosaurs,Suchomimus had a verycrocodilian-like skull, with a long, low snout and narrow jaws formed by a forward expansion of thepremaxillae (frontmost snout bones) and the hind branch of themaxillae (main upper jaw bone). The premaxillae had an upward branch, excluding the maxillae from theexternal nares (bony nostrils). The jaws had about 122 conical teeth, pointed but not very sharp and curving slightly backwards, with fineserrations and wrinkledenamel. The tip of the snout was enlarged sideways and carried a "terminalrosette" of longer teeth, seven per side in the premaxillae and about the same number in the corresponding part of the lower jaw. Further back, there were at least 22 teeth per upper jaw side in the maxilla, while the entire lower jaw side carried 32 teeth in the dentary bone.[2]
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The upper jaw had a prominent kink just behind the rosette, protruding downwards; this convexly curved part of the maxilla had the longest teeth of the entire skull. The internal bone shelves of the maxillae met each other in the midline of the skull over a long distance, forming a closedsecondary palate that stiffened the snout and setting off the internal nostrils and palatal complex (including thepterygoid,palatine, andectopterygoid) towards the back of the skull. The nostrils, unlike in most theropods, were retracted further back on the skull and behind the premaxillary teeth. The external nares were long, narrow, and horizontally positioned; the same was true of the largerantorbital fenestrae, a pair of bony openings in front of the eyes. The rear of the skull is poorly known but for a short quadrate bone, which had broad condyles (round protrusions) away from the centre of attachment and—like in the spinosauridBaryonyx—had a largeforamen (opening) separating it from thequadratojugal bone. The lower jaws were greatly elongated and narrow, forming a rigid structure as their dentaries touched each other at the midline, reinforcing themandible againsttorsional (bending and twisting) forces.[2]
The neck was relatively short but well-muscled as shown by strongepipophyses (processes to which neck muscles attached). There were about sixteen dorsal vertebrae.Suchomimus had significantly extended neural spines—blade-shaped upward extensions on the vertebrae—which were elongated at the rear back. Those of the five sacral vertebrae were the longest. The elongation of these structures continued until the middle of the tail. The spines may have held up some kind of low crest orsail of skin that was highest over its hips, lower and extending further to the back than that ofSpinosaurus, in which the sail reached its highest peak over the dorsal vertebrae. This condition was more reduced inBaryonyx.[2] The furcula was V-shaped and indicates a high and narrow trunk.[25]
The scapula had a rectangularacromion, or attachment site forclavicle (collarbone). Thehumerus (upper arm bone) was very strongly built, only equaled in size among non-spinosaurid theropods by that ofMegalosaurus andTorvosaurus, with robust upper corners. The humerus had a boss (bone overgrowth) above thecondyle that contacted its hook-shapedradius (forearm bone). Accordingly, theulna of the lower arm was well-developed with an enormousolecranon (upper process set-off from the shaft), an exceptional trait shared withBaryonyx. The heavy arm musculature powered sizable hand claws, that of the firstdigit (or "thumb") being the largest with a length of 19 centimetres (7.5 inches). Only the thirdmetacarpal (long bone of the hand) is known, showing a robustmorphology (form). In thepelvis, theilium (main hip bone) was high. Thepubis (pubic bone) had a front surface that was wider than the side surface, and its forward-facing lower end was flattened and rectangular, with a brief flange along the midline, in contrast to the expanded boot shape it had in other theropods. Theischium (lower and rearmost hip bone) bore a lowobturator flange. Thefemur (thighbone) was straight and robust, with a length of 107 cm (42 in) in the holotype. Itslesser trochanter is markedly plate-like. In the ankle, theastragalus had an ascendingprocess taller than that ofAllosaurus.[2]
In their original 1998 description ofSuchomimus, Sereno and colleagues identified severalautapomorphies (unique derived traits) distinguishing it from other theropods: its expanded rear dorsal, sacral, and front caudal neural spines, the robust upper corners of the humerus, and the boss above thehumerus' condyle that contacted its hook-shaped radius. The authors placedSuchomimus within Spinosauridae and named twosubfamilies within thisclade,Baryonychinae (all spinosaurids more closely related toBaryonyx) and Spinosaurinae (all spinosaurids closer toSpinosaurus), withSuchomimus assigned to the former. Apart from its apparently taller sail,Suchomimus was very similar to the spinosauridBaryonyx from theBarremian of England, and shared traits with it such as the reduced size and increased amount of teeth behind the snout tip in the mandible than spinosaurines, strong forelimbs, a huge sickle-curved claw on its "thumb", and strongly keeled front dorsal vertebrae. Spinosaurines are characterized by straight, unserrated, and more widely spaced teeth and the small size of their first premaxillary teeth. Sereno and colleagues pointed out that the more retracted nostrils inIrritator and the tall sail ofSpinosaurus could also be unique traits of spinosaurines, though material from other taxa is needed to know for sure.[2] They also united the spinosaurids and their closest relatives in the superfamily Spinosauroidea, but in 2010, the British palaeontologist Roger Benson considered this a junior synonym ofMegalosauroidea (an older name).[26]
In their original 1998 paper, Sereno and colleagues analyzed the distribution of forty-five traits to produce acladogram that showedSuchomimus andBaryonyx to be distinct but closely related genera.[2] Based on the classification previously proposed between 1986 and 1997 by Charig and Milner, German paleontologistOliver Rauhut reinstated the family Baryonychidae in 2003, noting the fragmentary and now-destroyed nature of theSpinosaurus holotype, while including this taxon within the group alongsideBaryonyx,Suchomimus,Irritator, and its possible junior synonym,Angaturama.[18] The following year, however, American palaeontologistThomas R. Holtz Jr. and his colleagues regarded Baryonychidae as a synonym of Spinosauridae and reassigned these genera to the latter family,[3] a classification that was subsequently supported by most later revisions.[27][20] In 2017, Brazilian paleontologists Marcos Sales and Cesar Schultz have questioned themonophyly of Baryonychinae (meaning it might be anunnatural group), stating that the South American spinosauridsAngaturama andIrritator represent intermediate forms between Baryonychinae and Spinosaurinae, based on their craniodental (skull and tooth) features.[16] Although not ruling out this possibility, American paleontologist Chris T. Barker and his colleagues established in 2021 a newtribe within the Baryonychinae, named Ceratosuchopsini, a clade that includesCeratosuchops,Riparovenator, andSuchomimus. Theircladogram can be seen below.[28]
| Spinosauridae |
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Spinosaurids appear to have been widespread from theBarremian to theCenomanianstages of theCretaceousperiod, about 130 to 95 million years ago, while the oldest known spinosaurid remains date to theMiddle Jurassic.[29] They shared features such as long, narrow, crocodile-like skulls; sub-circular teeth, with fine to no serrations; the terminal rosette of the snout; and a secondary palate that made them more resistant to torsion. In contrast, the primitive and typical condition for theropods was a tall, narrow snout with blade-like (ziphodont) teeth with serrated carinae.[30] The skull adaptations of spinosauridsconverged with those of crocodilians; early members of the latter group had skulls similar to typical theropods, later developing elongated snouts, conical teeth, and secondary palates. These adaptations may have been the result of a dietary change from terrestrial prey to fish. Unlike crocodiles, the post-cranial skeletons of baryonychine spinosaurids do not appear to have aquatic adaptations.[30][31] Sereno and colleagues proposed in 1998 that the large thumb-claw and robust forelimbs of spinosaurids evolved in the Middle Jurassic, before the elongation of the skull and other adaptations related to fish-eating, since the former features are shared with theirmegalosaurid relatives. They also suggested that the spinosaurines and baryonychines diverged before the Barremian age of the Early Cretaceous.[2]
Several hypotheses have been proposed about thebiogeography of the spinosaurids. SinceSuchomimus was more closely related toBaryonyx (from Europe) than toSpinosaurus—although that genus also lived in Africa—the distribution of spinosaurids cannot be explained asvicariance resulting fromcontinental rifting. Sereno and colleagues proposed that spinosaurids were initially distributed across thesupercontinentPangea but split with the opening of theTethys Sea. Spinosaurines would then have evolved in the south (Africa and South America: inGondwana) and baryonychines in the north (Europe: inLaurasia), withSuchomimus the result of a single north-to-southdispersal event.[2] In 2002, Buffetaut and Ouaja also suggested that baryonychines could be the ancestors of spinosaurines, which appear to have replaced the former in Africa.[8] Milner suggested in 2003 that spinosaurids originated in Laurasia during the Jurassic and dispersed via the Iberianland bridge into Gondwana, where theyradiated.[10] In 2007, Buffetaut pointed out thatpalaeogeographical studies had demonstrated that Iberia was near northern Africa during the Early Cretaceous, which he found to confirm Milner's idea that the Iberian region was astepping stone between Europe and Africa, which is supported by the presence of baryonychines in Iberia. The direction of the dispersal between Europe and Africa is still unknown,[32] and subsequent discoveries of spinosaurid remains in Asia and possibly Australia indicate that it may have been complex.[14]
Candeiro and colleagues suggested in 2017 that spinosaurids of northern Gondwana were replaced by other predators, such asabelisauroids, since no definite spinosaurid fossils are known from after the Cenomanian anywhere in the world. They attributed the disappearance of spinosaurids and other shifts in the fauna of Gondwana to changes in the environment, perhaps caused bytransgressions in sea level.[17] Barker and colleagues found support for a European origin for spinosaurids in 2021, with an expansion to Asia and Gondwana during the first half of the Early Cretaceous. In contrast to Sereno, these authors suggested there had been at least two dispersal events from Europe to Africa, leading toSuchomimus and the African part of Spinosaurinae.[28]
Charig and Milner had proposed apiscivorous (fish-eating) diet for the closely relatedBaryonyx in 1986.[6] This was later confirmed in 1997 with the discovery of partially digested fish scales found in theBaryonyx holotype.[7] In 1998, Sereno and colleagues suggested the same dietary preference forSuchomimus, based on its elongated jaws, spoon-shaped terminal rosette, and long teeth reminiscent of those of piscivorous crocodilians.[2] Holtz Jr. noted that spinosaurid teeth were adapted for grasping rather than slicing, hence their reduced serrations, which in most other theropods were more prominent.Suchomimus's extensive secondary palate, which would have made the roof of the mouth more solid, allowed it to better resist twisting forces exerted by prey. The rest ofSuchomimus's body was not particularly adapted to the water.[30] The discovery ofSuchomimus revealed that spinosaurid skulls were significantly shallower, more elongated, and narrower than previously thought.[2]
The use of the robust forelimbs and giant claws of spinosaurs remains a debated topic. Charig and Milner speculated in 1986 thatBaryonyx may have crouched by the riverbank and used its claws togaff fish out of the water, similarly toGrizzly bears.[6] In 1987, British biologist Andrew Kitchener hypothesized a use inscavenging carcasses,[33] though this has been critiqued by other researchers who pointed out that in most cases, a carcass would have already been largely emptied out by its initial predators.[27][7] A 2005 study by Therrien and colleagues posited that spinosaur forelimbs were probably used for hunting larger prey items, given that their snouts could not resist the bending stress.[34] In a 2017 review of the family, American paleontologist David Hone and Holtz Jr. also considered possible functions in digging for water sources or hard-to-reach prey, as well as burrowing into soil to construct nests.[27] A 2022 study comparing the bone densities ofSuchomimus,Baryonyx, andSpinosaurus reveals that spinosaurids had ecologically disparate lifestyles.Suchomimus itself was more adapted to a life hunting inshallow water due to its hollow bones, whileBaryonyx andSpinosaurus were capable of fully submerging underwater and diving after prey. Courtesy of denser bones, the latter two spinosaurids could hunt underwater for prey and occupy a more derived lifestyle thanSuchomimus could.[35]Isotopic geochemical lines of evidence also support a semi-aquatic foraging habit forSuchomimus; its δ44/42Ca values are highly negative, in contrast to contemporaryabelisaurids andcarcharodontosaurids, indicating a greater reliance on aquatic resources.[36]
The Elrhaz Formation, part of theTegama Group, consists mainly offluvial sandstones with low relief, much of which is obscured by sand dunes.[37][38] Thesediments are coarse- to medium-grained, with almost no fine-grainedhorizons.[39]Suchomimus lived in what is now Niger, during the lateAptian to earlyAlbian stages of theEarly Cretaceous, 112 million years ago.[39][40] The sediment layers of the formation have been interpreted as an inland habitat of extensive freshwaterfloodplains and fast-moving rivers, with a tropical climate that likely experienced seasonal dry periods.[39]
This environment was home to a variety of fauna, including dinosaurs,pterosaurs, turtles, fish,hybodont sharks, and freshwaterbivalves.[40][38] BesidesCristatusaurus,Suchomimus coexisted with other theropods like the abelisauridKryptops palaios, the carcharodontosauridEocarcharia dinops (likely achimaera including spinosaurid bones[41]), and an undescribednoasaurid. Herbivorous dinosaurs of the region includediguanodontians likeOuranosaurus nigeriensis,Elrhazosaurus nigeriensis,Lurdusaurus arenatus, and twosauropods:Nigersaurus taqueti and an unnamedtitanosaur.Crocodylomorphs were abundant, represented by the giantpholidosaur speciesSarcosuchus imperator, as well as smallnotosuchians likeAnatosuchus minor,Araripesuchus wegeneri, andStolokrosuchus lapparenti.[38] The local flora probably consisted mainly offerns,horsetails, andangiosperms, based on the dietary adaptations of the largediplodocoids that lived there.[39]
Dean, J. D. (1998).Colossal Claw (Television documentary).National Geographic Television.
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