Wednesday, May 4, 2011

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Oxalaia quilombensis taxes. nov. - Spinosaurid giant Brazilian Cretaceous

Although the number of taxa described by us may not seem so, the fossil record of dinosaurs in Brazil relatively modest. This is especially true in the case of non-avialanních (neptačích) theropods. Aside from the Ichnofossils or be isolated impressions of feathers (Kellner et al. 1994), is known from the territory of Brazil, only 7 of these taxa: Spondylosoma and Staurikosaurus the Triassic theropod whose identity is doubtful, however, four positives from the Lower Cretaceous and one abelisaurid of Upper Cretaceous . Kellner et al. (2011) is now added to this list the other taxa, there are several interesting aspects. This is an extremely large predator originating from the period, from which there was no Brazilian theropods described. Taxon comes from site to Laje Coring, under the Alcântara Formation. The only known material was found on the beach of the island Cajual the northeastern coast of Brazil and consists of fused bones předčelistní (holotype), isolated left maxilla (assigned). So just do not impress completeness, Kellner et al. (2011), however, it can identify several autapomorfií under which erected a new name, Oxalaia quilombensis (Oxalá - revered deity of Africans deported to Brazil at the time of slavery; quilombo - settlements they founded).

Holotype taxon Oxalaia quilombensis (MN 6117-V) when viewed from the right (a) and left (b) side. Abbreviations: (ALV) tooth hole (NFO) otvůrek for nourishing blood vessels, (pm) předčelistní bone (TE) tooth. The scale corresponds to 5 cm. (Source: Kellner, et al. 2011: Figure 1)

Oxalaia is megalosauroidem - tetanur representative of the basal group, which is indeed more closely related ceratosauři than birds, but outside example Neotetanurae (consisting of bird, allosaurem, their most recent common ancestor and all its descendants). It is also the member of a specific group known as megalosauroidů spinosauridi, whose best-known representative is no doubt he Spinosaurus - piscivorous and semi-proven Aquatic (Amiot et al. 2010) gigantic theropod from the territory of North Africa, growing to lengths over 15 meters. The remains come from oxaláje svrchnokřídového degree Cenomanian and suggests that the animal, which belonged, reached the length of 12-14 mA weighing 5-7 tons (Kellner et al. 2011:100), making it quite comfortable settles among the largest known theropods - comparable size reached such famed patagonští karcharodontosauridi.
authors offer a welcome in the diagnosis of new taxa and a list autapomorfií: 1) the front end of the two conjoined předčelistních bone is widest between the 3rd and 4 Dental hole, 2) the bony palate the forward tip of the maxillary * closed předčelistními bones very thin (see the other images in this article), and 3) two additional teeth just below the 3rd functional tooth, 4) strongly ornamentovaný předčelistní lower surface of the bone. In addition to these features in the diagnosis of authors argue that without teeth indentations differ from oxaláju spinosaura and kristatusaura and that the gap between the fifth and sixth předčelistním (= premaxillárním) tooth is shorter than spinosaura.
preserved part of the premaxilla (cataloged as MN 6117-V), measured 20.1 cm in length and the width at the widest point apparently was about 12.6 cm. Comparison with other spinosauridy (whose size parameters published by Dal Sasso et al. [2005]), the authors came to the total skull length 135 cm, but beyond the realm of dental seventh hole, where he broke off part of the preserved bones of the cranium oxalájině do not know much. In addition, bones escaped further damage - spalling, abrasion. Nevertheless, we can identify strong and deep wells in the front edge of the bone, which the authors interpret as a neurovascular otvůrky, and openings for blood vessels nourishing the roots of teeth on the left side of the premaxilla. Number of dental holes - 7, while the last is incomplete on both sides - is consistent with suchomimem, kristatusaurem and "angaturamou (ie = irritatorem whereas Kellner angaturamu irritatora not a synonym certainly nothing to do with the fact that it alone in '96 described). In contrast, spinosaura skull, which, according to Dal Sasso et al. (2005) may be vided Spinosaurus aegyptiacus or egyptiakovi taxon very closely related, had only 6 premaxilla tooth holes. The first tooth was quite small, had the second highest average and 3 tooth socket. Gap (diastema) between 3 and 4 tooth is present, but less than suchomima; contrast diastema between 5 and 6 tooth is in a transition state between suchomimem or kristatusaurem (which is missing) and gave Sassovým spinosaura specimen (which is longer). Unlike Cr Sassovy skull and Algerian spinosaurida (MNHN SAM 124) lacks the muzzle oxaláje narrowing between 3 and 4 Dental hole; rostrum instead, gradually narrowing towards the rear. When

Bottom protrude forward předčelistní bone between two thin projections, one on each maxilla. The surface of the bones in these places harder than others spinosauridů.
no teeth (except for the replacement, which are still hidden in the jaw) are preserved, including the crown tip. In the right place, the dental crown preserved in the 3rd and 5 Dental hole in the left tooth row in the second and 3 hole. All of the lack of indentations, as well as other spinosauridů their cross-oval, not laterally flattened. Under the third teeth on both sides there are two replacement teeth (teeth replacement), which is the theropods highly unusual phenomenon. Another replacement teeth are the other dental holes, but only time one tooth per well. Interdental plates are significant between the 2nd and 3 and 3 and 4 Dental hole.
oxaláje second specimen is a fragment of the left jaw, cataloged as MN 6119-V, containing two complete (1 and 2) and one incomplete (3) tooth hole. Well preserved is only the inner (medial) side, the exterior is highly abrasion. A shallow depression on top of the bones apparently were part of the outer nostril holes.

image (a) and drawing (b) holotype oxalájina when viewed from below. Abbreviations: (IDPs), interdental plate, (m) of the maxilla, (pm) předčelistní bone (1-7) numbered tooth holes. The scale corresponds to 5 cm. Well you can notice the narrow processes maxilla, which are closed on both sides předčelistními bones. (Source: Kellner, et al. 2011: Figure 2)

The following authors of the study compared with other oxaláju spinosauridy. Material Taxon S. aegyptiacus direct comparison is not possible, because no part of the upper jaw did not. The specimen is described by Dal Sasso et al. (2005), has a different number of teeth premaxillárních (6 versus 7), and therefore is whether or not the egyptiaka not totožný s oxalájou. Kellner et al. (2011) nicméně připomínají, že v ontogenezi některých archosaurů (žijících krokodýlů nebo tyrannosaura) dochází se stárnutím ke ztrátě jednoho nebo dvou zubů. Bez dostatečně velkého vzorku (na jehož nutnost Kellner [2010] upozorňoval už dříve) ale nemůže být ontogenetická proměnlivost počtu premaxillárních zubů potvrzena. To je sice naprostá pravda, ale s Kellnerovým předpokladem (bohatě zužitkovaným právě ve výše citované revizi pteranodontidů, o níž jsem also wrote a blog ) that if the ontogenetic variability is demonstrated, we can return with ease to defaultnímu state (the differences are phylogenetically informative), it certainly could argue, and also disputed the with him. Different number of teeth is not however the only difference between oxalájí and gave Sassovou Skull fossil species has a dense distribution of dental holes and the aforementioned narrowing between 3 and 4 hole.
Other fossils with which the authors oxaláju compare the already mentioned Algerian skull MNHN SAM 124, which Taquet & Russell (1998) included the previously described taxon maroccanus Spinosaurus - a rather bold move, given that none of the material does not overlap with the original fossils marokana. Anyways, this incomplete rostrum under Kellner et al. lacks oxalájiny autapomorfie. From baryonychinů, sub spinosauridů described in 80 flights from Europe, oxaláju distinct teeth without indentations and the presence of diastema between 5 and 6 tooth. What
irritatora is concerned, the author rejects the first synonymity to "its" angaturamou, which causes him to find that while the irritatorem no comparison can be made from different angaturamy oxaláju missing sagittal (longitudinal and center), a comb and a wider nose.
authors subsequently revised spinosauridí fossil record from territory of Brazil. Spinosauridi is divided into two groups: baryonychiny and spinosauriny, both of which are the largest South American known state. Cristatusaurus Suchomimus and represent the first group and Kellner et al. (2011) point out that it may be synonymous. Spinosaurini nevroubkovanými teeth are united, a symbol which is the (neptačích) theropods unique. Premaxillárních first pair of teeth are less and the gap between dental holes wider. Brazilian representative is Irritator (and, if you Kellner and Angaturama ), whose morphology is, however, according to the authors so different that it could represent a third, previously unknown spinosauridů group. Oxalaia would not belong to her - she is far more similar to African taxa, namely Sassově spinosaurovi Dal (Dal Sasso et al. 2005) and Morocco's skull, allegedly belonging P. maroccanus (Taquet & Russell 1998). Kellner et al. mention that Medeiros reported on the whereabouts of two types oxaláje spinosauridích teeth. One of them (morphotypes 2) corresponds well to oxaláje, the other is either worn by the first type, or - which was the preferred explanation Medeiros - represents another example spinosaurinních theropods.
In conclusion, the authors note that Oxalaia showing obvious signs spinosauridů with high probability this is a spinosaurina closely related to African taxa mentioned above. This entails quite interesting biogeographical implications, which, however, Kellner et al. (2011) leave entirely untouched. If I yet known in the Cenomanian has been Africa and South America completely separate, so that these relationships deserve some explanation. (You may know but some continental bridge, whose existence is so well founded, that no one is worth it faunálními exchanges between the two continents to deal with.) Given that Oxalaia has several unique derived characters, and its stratigraphic and geographic occurrence of which overlap with other spinosauridy, meets the main criteria for recognition as a new taxon. (At this point again quoted Kellner [2010], in the case oxaláje but the argument for the distinction is rather stronger than the geosternbergie and dawndraka .) Oxalaia substantially increases size and diversity of Brazilian theropods shows that spinosauridi were represented in early-Cenomanian coastal regions of South America.


* loath to use for the maxilla, a Czech name - the "upper jaw" - I planned to explain several times, but so far has not happened. Here's why: while the flat face of the skull, which is characteristic of people, it makes sense to limit the "upper jaw" on this one bone, the elongated skulls of most other vertebrates Sun In herpetologických texts can often encounter statements such as "bones of the upper jaw - the premaxilla, maxilla, Jugal ...", so consistently Czech 'maxilla bone - mezičelist, upper jaw bone zygomaticum ...". Obviously inappropriate and confusing. (And not to mention the "mezičelisti" to me has always conjured up an exotic structure between the upper and lower jaw. While I understand that the term comes from the fact that this bone when viewed from above the closed both the maxilla, but "předčelistní bone "is far less confusing name, though used less frequently.) truth is that not always is included in the upper jaw bone and as far back as Jugal bone or even square. But neither the resources to do it (for example, dinosaurs Holtz & Brett-Surman 1997), can not avoid the fact that many Amniota upper jaw consists of at least two paired bones (maxilla and premaxilla), and even if If it does not complicate such rostrál horned dinosaurs.

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