Malawisaurus dixeyi
Malawisaurus dixeyi is one of the most frequently cited titanosaurs. It's regarded highly enough to be one of the anchors of Lithostrotia, which it has graciously repaid by hopping all over Titanosauria. Despite its renown, M. dixeyi has some problems: a questionably diagnostic holotype, a bunch of specimens assigned to it that can't be directly compared, and that classic of titanosaurs, a multi-taxic bone bed (Gorscak et al. 2015). Gorscak (2016) reported that M. dixeyi included "at least two distinct morphs". Both of these citations are SVP abstracts, so for the moment we are left in suspense as to what exactly constitutes M. dixeyi. M. dixeyi also has the questionable distinction of being entwined in one of the strangest taxonomic histories of any titanosaur. |
| Malawisaurus on display as part of a special exhibit at the Science Museum back in 2014. Unlike most titanosaurs, you can get a fairly complete mount out of the material assigned to M. dixeyi; the catch is how much of it actually is M. dixeyi. Note that there are phalanges on the hands; no phalanges have been recovered, but the metacarpals have articular surfaces for them (Gomani 2005). Osteoderms are not included, but they have been described for this species (Gomani 2005). |
Overviews of the complex history of the African sauropods assigned to the genus Gigantosaurus (no, not Giganotosaurus; that's a theropod and one of the contenders in the tedious, never-ending saga that is "World's Biggest Theropod") can be read in Jacobs et al. (1993) and Mannion et al. (2019). What makes it particularly irritating is that a significant part of the complexity was self-inflicted at the very start of the story, which means my sympathy for the perpetrators is so small it cannot be detected by modern science. Fraas (1908) described two sauropods from the Tendaguru Beds in Tanzania as species of "new" genus Gigantosaurus (G. africanus and G. robustus). Gigantosaurus wasn't exactly new, though; Harry Govier Seeley had used it almost forty years earlier for a different sauropod (Gigantosaurus megalonyx Seeley 1869). Fraas knew this but went ahead anyway because:
"Der Name Gigantosaurus wurde zwar früher von SEELEY (Index to aves etc. in Cambridge Museum 1869 p. 94) für die Hufphalange eines Dinosauriers angewendet, ist aber wieder eliminiert, nachdem LYDEKKER die Zugehörigkeit dieses Stückes zu Ornithopsis nachgewiesen hat. (LYDEKKER, Catalogue of the fossil reptilia and amphibia in the British Museum Part I p. 151.) Der Name Gigantosaurus ist besonders bezeichnend für die riesenhaften Dimensionen unserer afrikanischen Arten."
which is German for "Lydekker showed that Gigantosaurus Seeley is really Ornithopsis and Gigantosaurus would fit my sauropods better." Aside from being a touching gesture of faith in Ornithopsis (of course entirely misplaced), this is not how the rules work; sinking a genus does not make the name available, and there is no provision for commandeering a name on aesthetic or any other grounds. Sternfeld (1911) substituted Tornieria for the two African species, now T. africana and T. robusta. The siren song of Gigantosaurus was apparently too much to ignore, though. Janensch (1922) argued again that Seeley's name was vacated as a synonym of Ornithopsis, and that anyway the rules should be ignored for Gigantosaurus Fraas because it's less confusing and complicated that way. (Why exactly Gigantosaurus Fraas should be so special as to warrant this treatment was not stated.)
 |
| An atypical view of the mount, showing the wide stance of titanosaurs (although annoyingly enough the ilium is one of the few bones unrepresented in the M. dixeyi complex). |
Janensch then made the accurate observation that Fraas's two species represented different genera, and found that africanus likely belonged within the American diplodocid genus Barosaurus. Although he was mostly right (these days africanus is back to being Tornieria africana the diplodocid, but not within Barosaurus), he had further complicated the situation by removing africanus, usually interpreted as the type species of Gigantosaurus Fraas, from the genus he had just argued to resurrect. This left robustus on its own as second species of a preoccupied genus which the author argued should supersede the original usage because it's less confusing, and we haven't even gotten to dixeyi yet. (robustus later became Janenschia Wild 1991 and was briefly famous as the "Jurassic titanosaur", which is exactly half-right.) The stage was all set now for Haughton (1928) to name the subject of this entry, Gigantosaurus dixeyi. Janensch's goal of reducing confusion was so successful that Haughton placed the wrong species (robustus) in Barosaurus. Illustrating just how popular G. robustus and G. dixeyi were, along with dinosaurs as a whole, the two species were allowed to twist in the taxonomic wind until their redescriptions in the early 1990s.
As to the actual animal "G." dixeyi, Haughton had a shipment of bones collected by Dr. Frank Dixey from the "Mwakasyunguti area of Nyasaland" (Nyasaland being the British colonial name for what became known as Malawi in 1964 upon its independence). The bones, unfortunately, left something to be desired, most being fragmentary and weathered. Haughton took the best material, which he and Dixey interpreted as an associated skeleton, and named a new species of Gigantosaurus Fraas. The species name "dixeyi" was chosen to honor Dixey. The material chosen consisted of a right pubis, an anterior caudal, half a cervical, a partial scapula, and two bones interpreted as sternal plates, curated as 7405 in the South African Museum Collections. Haughton placed the new species in Gigantosaurus for, more or less, lack of anywhere better to place it. He noted that it was also similar to Titanosaurus, and betrayed a temptation to place it there instead. If you're curious, bones he reported but did not assign to G. dixeyi included more caudals, parts of two humeri, and parts of two femora. Thus matters stood for several decades, with dixeyi sometimes known as Tornieria dixeyi (see for example McIntosh 1990).
 |
| Another view of the left side of the mount. |
In the 1980s, a joint Malawi Department of Antiquities–Southern Methodist University group resumed study of the rocks that produced G. dixeyi, known now as the Dinosaur Beds and dated to the late Early Cretaceous. They had much better luck than Dixey, finding approximately 150 specimens from nine localities by 1993, including one site (the CD-9 quarry) with a great number of bones (Jacobs et al. 1993). With new material in hand, Jacobs et al. (1993) gave G. dixeyi its own genus, Malawisaurus, incorporating the country's name (so it becomes something like "Dixey's Malawi lizard"). They also refined the holotype to just the anterior caudal, reducing the other specimens described by Haughton to topotypes (specimens found at the same site as the holotype). Jacobs et al. focused on the material from CD-9 quarry, and from the quarry they focused on the cranial and vertebral material.
 |
| The CD-9 quarry map, from Gomani (2005) (figure 3). CC-BY-4.0, apparently. |
The most significant find described in Jacobs et al. (1993) is the snub-nosed premaxilla. This was an even bigger deal at the time, because basically the only other specimens described as titanosaur cranial bones were the bits assigned to Antarctosaurus wichmannianus and usually restored as a steep-faced Diplodocus-like skull. The M. dixeyi premaxilla is short and tall, with teeth intermediate in shape between the broad teeth of Brachiosaurus and Camarasaurus and the pencils of diplodocids. A dentary described in the same paper shows that unlike A. wichmannianus, the teeth in the lower jaw are not crowded into the front, nor is the jaw squared off. These factors helped to give A. wichmannianus an even worse reputation as a potential chimera of titanosaur postcrania and diplodocid skull material. Meanwhile, M. dixeyi briefly became the "face" of titanosaurs. Then we got Rapetosaurus (and eventually Sarmientosaurus and Tapuiasaurus), and it was demonstrated that Nemegtosaurus and Quaesitosaurus were titanosaurs, and squared dentaries like those of Bonitasaura were found. Now we know that titanosaurs had a variety of different skull configurations, and it was just kind of an accident of history that a skull that now seems to be an outlier temporarily became seen as typical. The question at this point is what was M. dixeyi doing to necessitate such a blunt face? (Or, I suppose, do the M. dixeyi skull bones from CD-9 belong to the same species of animal as Haughton's caudal?)
 |
| Figure 4 (click for caption) in Gomani (2005): the mythical maxilla (C and D), jugal (E and F), and parietal (G and H) of a titanosaur, plus that stubby premaxilla (A and B). CC-BY-4.0, apparently. |
Jacobs et al. (1993) thought there was only one titanosaur species in the Dinosaur Beds. Since we're doing this alphabetically, you already know that this is not true; Gomani (2005) described a second dentary type from CD-9 as Karongasaurus gittelmani, which we now can recognize as more conventionally titanosaurian. Gomani also provided descriptions of additional bones attributed to M. dixeyi, including additional skull bones from CD-9 (one of these, a braincase, has been given separate treatment in Andrzejewski et al. 2019, with endocast and inner ear), and also provided handy lists of specimens from various localities. By this time, bones attributed to M. dixeyi included everything except the ilium.
The story could have ended here, but as noted in the first paragraph, questions have crept in. Gorscak et al. (2015) noted that the caudal selected as the holotype lacks "specific diagnostic features and does not compare favorably with most of the more recently recovered anterior caudal vertebrae", and that material from some quarries does not overlap the type or the CD-9 material. Furthermore, some of the caudals appear to represent an Aeolosaurus-like titanosaur. With these and other considerations, making confident determinations of which material belongs to what species is difficult, to say the least.
Mansourasaurus shahinae
Mansourasaurus shahinae is among the most recently described titanosaurs, and the first to come from the late Late Cretaceous of Egypt. It is also a rarity as one of the relatively few titanosaurs known from an associated skeleton of more than a few bones, with cranial material to boot. M. shahinae was described in 2018 by Sallam et al. The genus name refers to Mansoura University in Mansoura, Egypt, honoring the "home institution of the research collaborative that undertook the field and laboratory work", while the species name recognizes Mona Shahin, "for her contributions to the foundation of the Mansoura University Vertebrate Paleontology Center (MUVP)" (Sallam et al. 2018). Therefore, this is "Mona Shahin's Mansoura University lizard".The type specimen of M. shahinae is MUVP 200, which includes "cranial fragments, dentaries, cervical and dorsal vertebrae and associated ribs, scapulocoracoid, sternal plate, humeri, radius, metacarpal III, metatarsals I, III and II or IV, probable partial osteoderms, and several unidentified fragments" (Sallam et al. 2018). Per the quarry map, this material came from an area of about 25 square m (270 square ft). It was found at the Dakhla Oasis, a little south and west of the center of Egypt in the large New Valley Governorate of the Western Desert. The stratigraphic unit is the Upper Member of the Campanian-aged Quseir Formation (Sallam et al. 2018).
The overall length of the type individual is estimated at 8 to 10 m long (26 to 33 ft) (Sallam et al. 2018), making this a smallish titanosaur, but it was not fully grown (the scapula and coracoid are not fused). There's no femur, so I can't include the length of that, but the humerus is 620 mm long (2 ft). In terms of proportions, the arms are on the short side, and the cervicals are not elongate, indicating M. shahinae was on the low-slung, stocky end of the titanosaur spectrum. Most of the cranial remains pertain to the lower jaw, which had a U-shaped joint rather than the squared-off front of some other titanosaurs. The mandible is also notable for the low number of tooth positions per side (only nine) and the proportionally deep "chin". No erupted teeth were preserved (Sallam et al. 2018).
In addition to these remains, an ulna (MUVP 201) was found about 20 m (66 ft) away at the same horizon. It may or may not also represent M. shahinae; to be on the safe side, Sallam et al. (2018) did not formally include it, and ran phylogenetic analyses with and without the ulna included in M. shahinae. In both cases M. shahinae nested with a clade of Eurasian titanosaurs (particularly small Late Cretaceous European taxa). Sallam et al. (2018) found this as part of a general pattern of division of many post-Cenomanian titanosaurs into clades restricted to the Americas or to Africa, Asia, and Europe. They interpreted this as divergence resulting from the "Middle" Cretaceous separation of Africa and South America. Gorscak and O'Connor (2019), the only other analysis to include M. shahinae to date, also found it to hang around European titanosaurs.
Sallam et al. (2018) also briefly mentioned two other titanosauriform specimens from the post-Cenomanian rocks of Egypt. One is a partial postcranium from the Quseir Formation at the Kharga Oasis, found in 1977 but to date only described in abstracts. The other is a femur from the Ammonite Hill Member of the Dakhla Formation, found at the Dakhla Oasis in 1980. It is several million years younger than M. shahinae and described as brachiosaur-like (Rauhut and Werner 1997), unlike the clearly titanosaurian M. shahinae.
Maxakalisaurus topai
Maxakalisaurus topai is perhaps most famous as the large mounted skeleton which had been displayed in the National Museum of Brazil, which as we all remember was severely damaged by fire in September 2018. Its gallery in the museum had actually just been reopened in July 2018 after the base of the mount had to be replaced (via crowd-sourced funding) following termite damage. Surprisingly, some parts of the mount have reportedly been recovered, but more details have not yet emerged. |
| This photo of the mount was found at Wikimedia Commons, taken by user Ednei.melo (CC BY-SA 4.0). I cropped the edges and tweaked the lighting slightly. Wikimedia Commons has a substantial gallery of photos of the mount; I chose this one because it was the most recent, taken in the brief period between the gallery reopening and the fire (you'll notice the different base style if you compare photos in the gallery). |
The story of M. topai begins in the 1990s. Reports of fossils in the Adamantina Formation at the Serra da Boa Vista in Minas Gerais, Brazil led the Paleovertebrate Sector of the museum to investigate, and over four field seasons (1998, 2000, 2001, and 2002) they recovered a partial skeleton of a titanosaur. It made the rounds of the abstract circuit before being formally named in Kellner et al. (2006). The genus name honors the indigenous Maxakali people, and the species name "topai" is a reference to the Maxakali creator god Topa, giving something like "Topa's Maxakali peoples' lizard."
The type specimen, MN 5013-V, included a partial maxilla with teeth, twelve partial cervicals, several cervical ribs, seven partial dorsals, dorsal ribs, a sacral neural spine, a sacral centrum, six caudals, several chevrons, parts of both scapulae and sternal plates, both humeri, two metacarpals, part of an ischium, part of a fibula, an osteoderm, and unidentified material. Part of a scapula and two sternal plates found at the site were interpreted as belonging to a second individual, and a caudal possibly pertaining to M. topai (but distinct from the known caudals) was also found. Most of the bones had some breakage, and probably were exposed to the elements (and trampled to some extent) before final burial. A few theropod and croc teeth indicate it was scavenged as well. The vertebrae and some of the ribs were partially articulated, with the limb bones found in association. Together the area occupied by the bones was 10 m by 4 m (33 ft by 13 ft). The depositional environment is interpreted as fluvial, with a seasonal climate (Kellner et al. 2006).
 |
| Some of the holotype of Maxakalisaurus topai, as figured in Brusatte et al. (2017:Figure 4). The identifications may be a bit confusing if you're thinking C=cervical, but C="in part C". I recommend going to the link to see the full caption, but the figure includes skull (C1), vertebral (C2–C12), chevron (C13), sternal (C14), humerus (C15), metacarpal (C16), ischium (C17), fibula (C18), and osteoderm (C19 and C20) specimens. CC BY-NC 4.0. |
The skull material is only fragmentary, but it does show the fairly typical pencil-like titanosaurian tooth form, combined with carinae (fine ridges that look like seams), which are uncommon in titanosaurs. The cervicals fall into the "elongate" category. The configuration of one of the metacarpals suggests there was a phalanx, unlike other titanosaurs which lack manual phalanges. The type individual was not fully grown, given the lack of fusion of some neural arches. It is interpreted as having been around 13 m long (44 ft) (Kellner et al. 2006). Further expeditions to the type locality found a partial dentary and a "ghost jaw" of associated loose teeth. The mandible is slender and slightly downcurved at the tip, but not notably exaggerated at the "chin". It falls in the "u-shape" group rather than the squared-off jaw group (França et al. 2016).
 |
| Figure 2 from França et al. (2016), showing the dentary fragment and free teeth. CC BY-SA 4.0. |
França et al. (2016) found M. topai in the aeolosaurine neighborhood, although the caudals aren't quite as exaggerated as the classic aeolosaurine form. Other recent analyses find it in the vast middle of Titanosauria (Bandeira et al. 2016; Gorscak et al. 2017; Sallam et al. 2018; Gorscak and O'Connor 2019; these last three are based on the same matrix).
References
Andrzejewski, K. A., M. J. Polcyn, D. A. Winkler, E. Gomani Chindebvu, and L. L. Jacobs. 2019. The braincase of Malawisaurus dixeyi (Sauropoda: Titanosauria): A 3D reconstruction of the brain endocast and inner ear. PLoS ONE 14(2):e0211423. doi:10.1371/journal.pone.0211423.Bandeira, K. L., F. M. Simbras, E. B. Machado, D. de Almeida Campos, G. R. Oliveira, and A. W. A. Kellner. 2016. A new giant Titanosauria (Dinosauria: Sauropoda) from the Late Cretaceous Bauru Group, Brazil. PLoS ONE 11(10):e0163373. doi:10.1371/journal.pone.0163373.
Brusatte, S. L., C. R. A. Candeiro, and F. M. Simbras. 2017. The last dinosaurs of Brazil: the Bauru Group and its implications for the end-Cretaceous mass extinction. Anais de Academia Brasileira de Ciências 89(3):1465–1485.
Fraas, E. 1908. Ostafrikanische Dinosaurier. Palaeontographica 55:105–144.
França, M. A. G., J. C. de A. Marsola, D. Riff, A. S. Hsiou, and M. C. Langer. 2016. New lower jaw and teeth referred to Maxakalisaurus topai (Titanosauria: Aeolosaurini) and their implications for the phylogeny of titanosaurid sauropods. PeerJ 4:e2054. doi:10.7717/peerj.2054.
Gomani, E. M. 2005. Sauropod dinosaurs from the Early Cretaceous of Malawi, Africa. Palaeontologia Electronica 8.1.27A.
Gorscak, E. 2016. Characterizing Africa Cretaceous continental faunas: paleobiogeographic patterns and new insights from sub-Saharan African titanosaurian sauropod dinosaurs. Journal of Vertebrate Paleontology, Program and Abstracts, 2016:146.
Gorscak, E., and P. M. O’Connor. 2019. A new African titanosaurian sauropod dinosaur from the middle Cretaceous Galula Formation (Mtuka Member), Rukwa Rift Basin, southwestern Tanzania. PLoS ONE 14(2):e0211412. doi:10.1371/journal.pone.0211412.
Gorscak, E., P. O'Connor, and E. Gomani Chindebvu. 2015. The re-evaluation of the sauropod dinosaur diversity from the Dinosaur Beds of Malawi reveal a hidden diversity for sub-equatorial African faunas. Journal of Vertebrate Paleontology, Program and Abstracts, 2015:133.
Gorscak, E., P. M. O'Connor, E. M. Roberts, and N. J. Stevens. 2017. The second titanosaurian (Dinosauria: Sauropoda) from the middle Cretaceous Galula Formation, southwestern Tanzania, with remarks on African titanosaurian diversity. Journal of Vertebrate Paleontology 37(4):e1343250.
Haughton, S. H. 1928. On some reptilian remains from the Dinosaur Beds of Nyasaland. Transactions of the Royal Society of South Africa 16:67–75.
Jacobs, L., D. A. Winkler, W. R. Downs, and E. M. Gomani. 1993. New material of an Early Cretaceous titanosaurid sauropod dinosaur from Malawi. Palaeontology 36:523–534.
Janensch, W. 1922. Das Handskelett von Gigantosaurus robustus u. Brachiosaurus brancai aus den Tendaguru-Schichten Deutsch-Ostafrikas. Centralblatt für Mineralogie, Geologie und Paläontologie 15:464–480.
Kellner, A. W. A., D. A. Campos, Z. A. K. Azevedo, M. N. F. Trota, D. D. R Enriques, M. M. T. Craik, and H. Paula Silva. 2006. On a new titanosaur sauropod from the Bauru Group, Late Cretaceous of Brazil. Boletim do Museu Nacional 74:1–31.
Mannion, P. D., P. Upchurch, D. Schwarz, and O. Wings. 2019. Taxonomic affinities of the putative titanosaurs from the Late Jurassic Tendaguru Formation of Tanzania: phylogenetic and biogeographic implications for eusauropod dinosaur evolution. Zoological Journal of the Linnean Society 185(3):784–909. doi:10.1093/zoolinnean/zly068.
McIntosh, J. S. 1990. Sauropoda. Pages 345–401 in D. B. Weishampel, P. Dodson, and H. Osmólska, editors. The Dinosauria. University of California Press, Berkeley, California.
Rauhut, O. W. M., and C. Werner. 1997. First record of a Maastrichtian sauropod dinosaur from Egypt. Palaeontologia Africana 34:63–67.
Sallam, H. M., E. Gorscak, P. M. O’Connor, I. A. El-Dawoudi, S. El-Sayed, S. Saber, M. A. Kora, J. J. W. Sertich, E. R. Seiffert, and M. C. Lamanna. 2018. New Egyptian sauropod reveals Late Cretaceous dinosaur dispersal between Europe and Africa. Nature Ecology & Evolution 2:445–451. doi:10.1038/s41559-017-0455-5. Supplementary information.
Seeley, H. G. 1869. Index to the fossil remains of Aves, Ornithosauria and Reptilia, from the secondary system of strata arranged in the Woodwardian Museum of the University of Cambridge. With a prefatory notice by the Rev. Adam Sedgwick. Cambridge: Deighton, Bell and Co.
Sternfeld, R. 1911. Zur Nomenklatur der Gattung Gigantosaurus Fraas. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin 1911:398.
Wild, R. 1991. Janenschia n. g. robusta (E. Fraas 1908) pro Tornieria robusta (E. Fraas 1908) (Reptilia, Saurischia, Sauropodomorpha). Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie) 173:1–4.
No comments:
Post a Comment