Murusraptor barrosaensis is unique in having anterodorsal process of lacrimal longer than height of preorbital process, and a thick, shelf-like thickening on the lateral surface of surangular ventral to the groove between the anterior surangular foramen and the insert for the uppermost intramandibular process of the dentary. Two other characters are only known in Murusraptor; sacral ribs hollow and tubelike; short ischia distally flattened and slightly expanded dorsoventrally. These characters are equivocal because they are unknown in other members of the clade. Also, the following combination of diagnostic characters was obtained after running the phylogenetic analysis using TNT [ 42 ]: Character 95, basipterygoid processes of the basisphenoid located anteroventrally, with basisphenoid recess opening posterodorsally (also present in coelophysids); Character 98, basisphenoid with a shallow embayment indentation between basal tubera and basipterygoid processes (also present in Cryolophosaurus and basal theropods); Character 216, rather straight chevrons (reversal to the plesiomorphic condition).

Description

The holotype specimen of Murusraptor barrosaensis (MCF-PVPH-411) was found preserved in a sand-filled channel deposit (Fig 3).

It was mostly disarticulated, although the bones had remained closely associated with each other, and included both large and small elements. Most collected ribs were in natural sequence parallel to each other, suggesting the specimen was partially articulated when buried. Clay nodules were mixed amongst the bones. The orientations of the ribs and pubes, and the distribution of bones suggest that the animal was lying on its right side. Bones were stacked in as many as four layers. The right ilium was standing vertically upside down. The complete left ilium is the only element that was predepositionally broken; the preacetabular blade had snapped across the top of a large dorsal vertebra, and was separated slightly from the rest of the ilium. Incompleteness of the other bones is erosional. Several bones appear to have been bored by dermistids [43–44], which left characteristic trails of osseous fragments in the sediments. Parts of the skeleton showed pathologic damage.

Dentition. Thirty-one teeth were recovered amongst the bones of the skeleton, although twenty-six are complete enough to provide measurable data (Table 1). Comparison of the teeth recovered suggests that there are many gaps in the sequence, and that there would have been many more functional teeth in the jaws of the animal when it was alive. Four premaxillary teeth were reported and as many as 17 maxillary teeth in the juvenile Megaraptor specimen (MUCPv 595) [36], which would give a total tooth count of about 80 teeth. Similarly, the dentary of the holotype of Austalovenator wintonensis has 18 alveoli [29,36], which suggests that the total number of teeth would have been at least 76. PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Table 1. Tooth measurements of Murusraptor barrosaensis. https://doi.org/10.1371/journal.pone.0157973.t001 For the estimated size of the animal (See S3 and S4 Files), these are all relatively small, the tallest one (MCF-PVPH-411.50) having a crown height of 29 mm (Fig 16A–16C). PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 16. Maxillary teeth of Murusraptor barrosaensis, holotype, MCF-PVPH-411. Left? maxillary tooth MCF-PVPH-411-50 in mesial (A), posterior (B) and labial (C) views. Maxillary tooth MCF-PVPH-411-79 in mesial view (D) and close-up of posterior denticles. Scalebar: 1 cm. https://doi.org/10.1371/journal.pone.0157973.g016 The first teeth of megaraptorids that were unquestionably associated with skeletal material were from Orkoraptor [28], and these are comparable in size and morphology with those of Murusraptor. Teeth associated with the juvenile specimen of Megaraptor are also relatively small, with the maximum crown height of a maxillary tooth reported as 17 mm [35]. Australovenator teeth [29,36] are also similar in size (the largest crown height is 25 mm) and outline, although there are some differences in the denticulation. The relatively small ratio of the tooth to animal size can also be found in some spinosaurids and troodontids. The largest tooth collected (MCF-PVPH-411.50) has a crown height 2.5 times the height of the smallest crown recovered (MCF-PVPH-411.54). Most collected teeth have roots, show the same morphology, and are preserved in the same way. Therefore it is assumed that all of them belong to the holotype specimen of Murusraptor barrosaensis. The serrations are relatively small, and on first glance it appears that most of the teeth lack denticles on the anterior carina. This is also the case for Megaraptor [35] and Orkoraptor [28]. However, wherever the tip is preserved (MCF-PVPH-411.50/64/66/78/79/88), there are 6–10 serrations, usually completely worn down. The exceptions include MCF-PVPH-411.87 (which is probably a premaxillary tooth with a flat lingual surface, convex labial surface and large serrations on both sides of the tooth). The carinae are generally on the midline of the tooth, which makes it difficult to distinguish labial from lingual sides. There are exceptions, like MCF-PVPH-411.50 and MCF-PVPH-411.66, where the carinae extend far down the anterolingual margins of the teeth, although even in these teeth the denticles were restricted to the distal tips. This is even true for MCF-PVPH-411.77, which appears to be either a premaxillary or anterior dentary tooth (J-shaped in cross section). However, another premaxillary tooth with an almost identical crown (MCF-PVPH-411.52) has small serrations that extend far down the carina towards the root. Sereno et al. [26] identified one tooth as Aerosteon because of its proximity to the rest of the associated skeleton. Although it falls within the size range of the cheek teeth of Murusraptor, this shed tooth is clearly from an abelisaurid [37].