| Oxalaia | |
|---|---|
 | |
| Holotype snout in multiple views | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Spinosauridae |
| Genus: | †Oxalaia Kellneret al.,2011 |
| Species: | †O. quilombensis |
| Binomial name | |
| †Oxalaia quilombensis Kellneret al., 2011 | |
| Synonyms | |
| |
Oxalaia (in reference to the African deityOxalá) is a controversialgenus ofspinosauriddinosaur that lived in what is now theNortheast Region ofBrazil during theCenomanianstage of theLate Cretaceousperiod, sometime between 100.5 and 93.9 million years ago. Its only knownfossils were found in 1999 onCajual Island in the rocks of theAlcântara Formation, which is known for its abundance of fragmentary, isolated fossil specimens. The remains ofOxalaia were described in2011 by BrazilianpalaeontologistAlexander Kellner and colleagues, who assigned the specimens to a new genus containing onespecies,Oxalaia quilombensis. The species name refers to the Brazilianquilombo settlements.Oxalaia quilombensis is the eighth officially namedtheropod species from Brazil and the largestcarnivorous dinosaur discovered there. One study suggested that this taxon is ajunior synonym of the closely related African genusSpinosaurus, but this was disputed by subsequent studies which consider the genus to be diagnostic.
AlthoughOxalaia is known only from two partial skull bones, Kellner and colleagues found that its teeth andcranium had a few distinct features not seen in other spinosaurids or theropods, including two replacement teeth in each socket and a very sculpturedsecondary palate.Oxalaia's habitat was tropical, heavily forested, and surrounded by an arid landscape. This environment had a large variety of lifeforms also present inMiddle-Cretaceous North Africa, due to the connection of South America and Africa as parts of thesupercontinentGondwana. As a spinosaurid, the traits ofOxalaia's skull and dentition indicate a partlypiscivorous (fish-eating) lifestyle similar to that of moderncrocodilians. Fossil evidence suggests spinosaurids also preyed on other animals such as small dinosaurs andpterosaurs.
Oxalaia stems from theAlcântara Formation, a succession ofsedimentary rocks that is part of theItapecuru Group of theSão Luís-Grajaú Basin, in northeastern Brazil. These rocks have been dated by scientists to theCenomanianstage of theLate Cretaceousperiod, 100.5 to 93.9 million years ago.[1][2] Outcropping at the northern coast of the formation, the Laje do Coringa locality is made up mostly ofsandstones andmudstones, along withconglomerate rock layers containing fossil plant andvertebrate fragments.[3] These sediments were deposited under marine andfluvial conditions similar to those of theBahariya Formation in Egypt, whereSpinosaurus remains have been found.[1][4] In 1999,fossils ofOxalaia were recovered from the Laje do Coringa.[5]Palaeontologist Elaine Machado, of theNational Museum of Rio de Janeiro, was surprised to find such a well-preserved fossil at the site and stated in a press release that "this is how most scientific discoveries happen, it was by accident".[6] The finding was a rare occurrence due to the erosive nature of the tides at the deposit, which are responsible for the fragmented state of most fossils in thebone bed; remains not found on site are often removed from the formation by wave action.[5] Generally, the majority of fossil remains found at the Alcântara Formation consist of teeth and isolated skeletal elements, of which the Laje do Coringa site has yielded hundreds.[1][5][7]
Oxalaia is one of threespinosauriddinosaurs discovered in Brazil, the other two beingIrritator and its possiblesynonymAngaturama, both of which were also initially known from partial skulls. They were discovered in theRomualdo Formation of theSantana Group, part of theAraripe Basin.Microfossils date this formation to theAlbian, around nine to six million years beforeOxalaia.[5][8][9] The fossil record of spinosaurids is poor compared to those of othertheropod groups; very few body fossils are known and mostgenera have been erected from isolated elements such as vertebra or teeth.[10][11] Theholotype specimen ofOxalaia quilombensis, designatedMN 6117-V, was foundin situ (at its original place of deposition) with part of the left side embedded in the rockmatrix; it consists of the fusedpremaxillae (frontmost snout bones) from a large individual. An isolated and incomplete leftmaxilla (main upper jaw bone) fragment (MN 6119-V) was referred toOxalaia because it showed the same general traits occurring in spinosaurids, the maxilla was discovered on the rock surface, having possibly moved from its original location after erosion. Both bone fragments were found onCajual Island,Maranhão, in theNortheast Region of Brazil, and were housed at the National Museum ofRio de Janeiro.[5] In 2018,a fire engulfed the palace housing the museum,[12] possibly destroyingOxalaia's specimens, along with various other fossils found in Brazil.[13] It was noted by paleontologist Rodrigo Vargas Pêgas in 2025 that the badly damaged remains ofOxalaia were recovered, and the publication for the recovered items is in preparation.[14] Besides the partial skull bones, numerous spinosaurid teeth had earlier been reported from the Laje do Coringa site.[5] Additionally, two distal caudal vertebra (specimens UFMA 1.10.229 and UFMA 1.10.240) discovered in theAlcantara Formation ofBrazil were assigned toSigilmassasaurus in 2002.[15] However, other researchers noted that these specimens are indeterminate spinosaurids, most likely belonging toOxalaia considering the geographical and geological context.[16][17]
The discoveries ofOxalaia and of the Late Cretaceous reptilesPepesuchus andBrasiliguana were announced in a presentation by theBrazilian Academy of Sciences in March 2011.[18][19] Machado describedOxalaia as "the dominant reptile of [what is now] Cajual Island". She stated that there is interest in spinosaurids in Brazil and abroad because of their debut in theJurassic Park franchise and their distinctiveness among othercarnivorous dinosaurs.[18] Thespecies description ofOxalaia was written by Brazilian palaeontologistsAlexander Kellner, Elaine Machado, Sergio Azevedo, Deise Henriques, and Luciana Carvalho. This paper, among many others, were composed into a volume of 20 works on prehistoric biodiversity that was published by the academy in March2011.[6] Thetype speciesOxalaia quilombensis is the eighth officially named species of theropod from Brazil. Thegeneric nameOxalaia is derived from the name of the African deityOxalá, which was introduced into Brazil during the slavery period. Thespecific namequilombensis refers to thequilombo settlements like those on Cajual Island, which were founded by escaped slaves.[5]
The holotype premaxillae are together approximately 201 millimetres (7.9 inches) long, with a preserved width of 115 mm (4.5 in) (maximal estimated original width is 126 mm (5.0 in)), and a height of 103 mm (4.1 in). Based on skeletal material from related spinosaurids, the skull ofOxalaia would have been an estimated 1.35 metres (4.4 feet) long;[5] this is smaller thanSpinosaurus's skull, which was approximated at 1.75 m (5 ft 9 in) long by Italian palaeontologistCristiano Dal Sasso and colleagues in 2005.[20] Kellner and his team compared the Dal Sasso specimen (MSNM V4047) toOxalaia's original snout in 2011; from this they estimatedOxalaia at 12 to 14 m (39 to 46 ft) in length and 5 to 7tonnes (5.5 to 7.7short tons; 4.9 to 6.9long tons) in weight, making it the largest known theropod from Brazil,[5] the second largest beingPycnonemosaurus, which was estimated at 8.9 m (29 ft) by one study.[18][21]
The tip of therostrum (snout) is enlarged and the rear-end constricted, forming the terminalrosette shape that distinguishes spinosaurids;[5] this form would have interlocked with the also-expanded front of thedentary (tooth-bearing bone of themandible).[22] The rostrum ofOxalaia features broad, deepforamina (holes) that are possiblynutrient canals for blood vessels and nerves; it is also rounder in side view than that ofSpinosaurus, whose upper jaw ends in a more acute downward angle as shown by specimens MSNM V4047 andMNHN SAM 124. The maxillae show a pair of elongated and thin processes extending forwards along the midline of the roof of the mouth; they are encased between the premaxillae and border an elaborate, triangle-shaped pit at their front end. Similar processes are present inSuchomimus,Cristatusaurus, and MNHN SAM 124, although not as exposed.[5] These structures compose the animal'ssecondary palate.[5][23] The undersides of the premaxillae are greatly ornamented inOxalaia, in contrast to the smoother condition it has in other spinosaurids.[5]
The premaxillae have sevenalveoli (tooth sockets) on each side, the same number found inAngaturama,Cristatusaurus,Suchomimus, and MNHN SAM 124 (referred toSpinosaurus); MSNM V4047, another upper jaw specimen fromSpinosaurus, had only six. It cannot be confirmed whether this lower number of teeth is due toontogeny; for that, a largersample size is necessary. A largediastema (gap in tooth row) separates the third tooth socket from the fourth; this is observed in all other spinosaurids, being smaller inSuchomimus. Another diastema of nearly equal length is found between the fifth and sixth alveolus; this diastema is seen in MNHN SAM 124 and is much longer in MSNM V4047 but is absent fromSuchomimus andCristatusaurus. The maxilla fragment referred toOxalaia (MN 6119-V) has two alveoli and a broken third one that includes a partial tooth. Like the premaxilla, it had preserved nutrient canals. It also features a shallow dent in the middle, suggesting it was located near theexternal nares (bony nostrils). Small fragments inside some of the remaining alveoli show that unlike itsEarly Cretaceous relativesSuchomimus andCristatusaurus,Oxalaia lackedserrations on its teeth. Apart from the single, functional tooth in each socket, there were tworeplacement teeth,[5] which according to Kellner are "a common feature insharks or in some reptiles, but not in theropods".[19] A cross-section of the teeth showed the typical oval shape exhibited by spinosaurs rather than the lateral compression of other theropod teeth.[5]
The spinosaurid teeth reported from Laje do Coringa were classified into two primarymorphotypes by Brazilian palaeontologist Manuel Medeiros in 2006. Both show typical spinosaurine dentition, though morphotype II has smoother tooth enamel than the first.[24]Oxalaia's teeth display a closer morphology to morphotype I while the second grouping of teeth represent either worn down morphotype I teeth or an undescribed spinosaurine from the Alcântara Formation.[5]
The type elements ofOxalaia closely resemble those of specimens MSNM V4047 and MNHN SAM 124, both referred toSpinosaurus aegyptiacus. Kellner and colleagues differentiatedOxalaia from it and other spinosaurids by itsautapomorphic (distinguishing) craniodental features, like its sculptured palatal part of the premaxillae, and the possession of two replacement teeth in each position.[5][23] More fragmentary spinosaurids such asSiamosaurus and "Sinopliosaurus"fusuiensis are based only on teeth, making them difficult to separate from othertaxa. The habit of naming theropods from isolated teeth or tooth fragments has resulted in many invalid and synonymous genera; it has also occurred with spinosaurids and is compounded by the common lack of overlapping skeletal remains—a precondition of validly distinguishing taxa.[23][25]
In 2017, aphylogenetic analysis by the Brazilian palaeontologists Marcos Sales and Cesar Schultz concluded thatOxalaia was more closely related to African spinosaurines than to Brazilian spinosaurines likeAngaturama, as indicated by a wider snout and the lack of a dorsalsagittal crest on the premaxillae. The Brazilian generaOxalaia andAngaturama were recovered as the two closest relatives ofSpinosaurus,Oxalaia forming itssister taxon. Though fragmentary, the Brazilian material indicates that spinosaurines were more diverse than previously recognized.Spinosaurus differs fromOxalaia by its significantly more widely spaced tooth sockets, the presence of a slight narrowing between its third and fourth sockets, and the sharper slope of its snout.Oxalaia is currently assigned to thesubfamilySpinosaurinae due to the morphology of its upper jaw and the absence of fine serrations on its teeth that typifybaryonychines.[5][23] Below is acladogram by Sales and Schultz, in whichOxalaia is grouped in the Spinosaurinae, as a closer relative toSpinosaurus thanAngaturama.[23]
In contrast, Arden et al. (2018) recoveredOxalaia closer toIrritator thanSpinosaurus based on their phylogenetic analysis, the cladogram of which is reproduced below:[26]
| Spinosauridae |
| |||||||||||||||||||||||||||||||||||||||||||||
In 2020, a paper by Robert Smyth and colleagues assessing spinosaurines from theKem Kem Group did not find the autapomorphies ofOxalaia quilombensis sufficient to warrant a separate taxon, but instead considered them a result ofindividual variation. The authors thus considered the species a junior synonym ofSpinosaurus aegyptiacus. If supported by future studies, this would implySpinosaurus aegyptiacus had a wider distribution and support a faunal exchange scenario between South America and Africa during the Cenomanian when there was little separation of South America and Africa by water, which allowedSpinosaurus aegyptiacus to traverse the short distance of the sea into South America.[28]
However, subsequent studies have rejected its synonymy withSpinosaurus aegyptiacus based on diagnostic features of the holotype (MN 6117-V) and the referred specimen (MN 6119-V). In 2021, Lacerda, Grillo and Romano noted that the anteromedial processes of the holotype maxillae (MN 6117-V) contact medially, a condition not observed in MSNM V4047 which has been referred to as a specimen ofSpinosaurus, and thus adding a new possible diagnostic feature ofOxalaia. They also suggested that the premaxilla ofOxalaia is wider in the posterior portion than that of MSNM V4047, and that the lateral morphology of its rostrum was distinguished from other spinosaurines based on their morphometric analysis.[29] In 2023, Isasmendi and colleagues consideredOxalaia as a valid taxon based on the examination of its referred maxilla (MN 6119-V) which suggests that the position of its external naris would have been more anteriorly located, a condition similar to that ofIrritator andbaryonychines, differing fromSpinosaurus aegyptiacus.[30]
The Late Cretaceous deposits of the Alcântara Formation have been interpreted as a humid habitat of tropical forests dominated byconifers,ferns, andhorsetails. These forests were surrounded by an arid-to-semi-arid landscape that was probably subjected to brief periods of heavy rainfall followed by lengthy dry periods.[1][31] A great abundance and variety of animal taxa, such as dinosaurs,pterosaurs, snakes,molluscs,crocodilians,notosuchids, and fish have been discovered in the formation. Aquatic taxa known from the deposits include the largecoelacanthMawsonia gigas; the rayMyliobatis sp. (of uncertain species); twosclerorhynchidsawfishes; as well as severalbony fish,ray-finned fish, andlungfish species.[1][32] Dinosaur fossil remains suggest the presence ofdiplodocoids likeItapeuasaurus cajapioensis, basaltitanosaurs, a giant Carcharodontosaurid sp., anoasaurid closely related toMasiakasaurus, and adromaeosaurid. Also, characteristic teeth and a vertebralcentra were referred toSpinosaurus sp.[1][33]
Most of the flora and fauna discovered in the Alcântara Formation was also present in North Africa in theKem Kem Beds of Morocco during the Cenomanian; with a few exceptions includingOxalaia quilombensis,Atlanticopristis equatorialis,Equinoxiodus alcantariensis, andCoringasuchus anisodontis. According to Medeiros and colleagues, the Laje do Coringa assemblage may also be linked to the contemporaneous Bahariya Formation in Egypt, which holds a distinct combination of key taxa constitutingSpinosaurus aegyptiacus,Carcharodontosaurus saharicus, andOnchopristis numidus. This extreme similarity between the Cretaceousbiota of Brazil with that of Africa is a result of their connection as parts of thesupercontinentGondwana (which comprised most landmasses of the modern southern hemisphere). This connection was broken by rifting and sea-floor spreading 130–110 million years ago. Afterwards, the transoceanic assemblages would have continued to evolve separately, contributing to small differences between taxa.[1][34] Machado stated that Cajual Island was still attached to the African continent during the Cenomanian.[6] Similarly, Medeiros and colleagues noted that the presence of an island chain or other lasting land connection during that time could explain the faunal similarities.[1]
.jpg)
As a spinosaur,Oxalaia would have had large, robust forelimbs; relatively short hindlimbs; elongatedneural spines (upwards projections of the vertebrae) forming a ridge orsail on its back; and tall neural spines on its caudal vertebrae which—similar to the tails of modern crocodilians—may have aided in swimming.[10][35] Spinosaurids likely spent most of their time near or in water and fed mostly on aquatic animals, avoiding direct competition with other large predators but being able to sustain themselves on terrestrial animals if necessary. Such behavior is observed in cases such as juvenileIguanodontid bones found in the stomach cavity of aBaryonyx fossil and anIrritator tooth embedded in pterosaur remains.[10][36] The conical, transversely oval-shaped teeth ofOxalaia and its nasal openings, that were retracted further back on the skull than in most theropods (likely to avoid water entering its nostrils while fishing) are characteristic of spinosaurids. Both features are useful adaptations for catching and feeding on fish.[5][10][22] The expanded, interlocking front jaws and piercing teeth of spinosaurs worked as an efficient fish trap, a trait also exhibited by theIndian gharial—the mostpiscivorous extant crocodilian.[22] Kellner compared the general appearance of spinosaurid skulls to those ofalligators.[19]
{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link){{cite news}}: CS1 maint: multiple names: authors list (link)
Data related toOxalaia at Wikispecies.jpg)
.jpg)
.png)
.jpg)
