Afrovenator

Afrovenator
Skeletal reconstruction of Afrovenator
Temporal occurrence
Middle Jurassic ( Bathonium ) to? Upper Jurassic ( Oxfordium )
168 to? 157 million years
Locations
Niger
Systematics
Lizard dinosaur (Saurischia) Theropoda Tetanurae Spinosauroidea Megalosauridae Afrovenator
Scientific name
Afrovenator
Sereno et al., 1994

Afrovenator is a genus of large, relatively basal theropods that lived in the late Middle or possibly early Upper Jurassic in northern Africa. The only species described so far is Afrovenator abakensis .

etymology

The generic name is made up of the prefix afro- (meaning 'relating to Africa, belonging to Africa, African') and the Latin word venator , which means 'hunter'. The epithet of the type species abakensis is derived from the name 'In Abaka', the Tuareg name for the area in which the fossils of the holotype of the species were discovered (see material and locality ).

Material and find location

The known fossil material from Afrovenator has so far been limited to the holotype of the type species (collection number: MNN  TIG1 formerly UC  OBA 1), a relatively complete skeleton, which includes a partial upper skull (cranium) without premaxillary, frontal, parietal and square jugals as well as a pre-articular (non-tooth bearing lower jaw bone), both humerus bones, both almost complete hands, almost complete pelvis, legs and parts of the cervical, trunk and tail spine.

These remains were discovered in the Tamerát fossil locale, about 100 km west-southwest of Agadez in the Tiouarén Formation of the Iullemmeden Basin in Niger and were first scientifically described in 1994 by Paul Sereno , Jeffrey Wilson, Hans Larsson, Didier Dutheil and Hans-Dieter Sues .

The sediments of the find layer represent an alluvial plain in a semi-humid or humid climate. Traditionally regarded as Early Cretaceous , which made Afrovenator abakensis the first relatively complete theropod from the Cretaceous Africa at the time of the first description, the Tiouarén Formation was based on the dinosaur fauna it contained in 2009 to a late Middle to early Upper Jurassic age ( Bathon - Callov ,?  Oxford ) newly dated.

features

Skull reconstruction with darkening of the unknown bones. The well-known pre-articular structure, which is located on the inside of the lower jaw, is not shown, nor is the relatively small promaxillary window.

In the first description (Sereno et al., 1994) the following features are considered diagnostic for the type abakensis Afrovenator and typed by them genus Afrovenator indicated: praise shaped front edge of the Antorbitalfossa ; third cervical vertebra with low, rectangular spinous process; " Almost crescent-shaped" carpal bone ( "semilunate" carpal ; result of the fusion of the two distal carpalia and characteristic of the less basal theropods ) very flat; Metacarpale I with broad "wing" for the joint with metacarpale II.

The (reconstructed) skull is low and elongated compared to other large-headed theropods such as Allosaurus . Bone ridges and ridges are also weak. The low, rounded lacrimal ridge is pneumatized . The "maxillary window" ^* is relatively far back and the promaxillary window is slit-shaped. The maxillary has 14 alveoli for dagger-like teeth, the rearmost tooth position being closer to the tip of the snout than the front end of the eye opening. The quadratum is relatively high with a dorsoventral length of more than half the height of the skull in the area of ​​the eye socket.

With an estimated total length of 7 to 9 meters, Afrovenator was one of the large (but not largest) theropods. The proportions of the long bones suggest a rather slender and lightly built animal. According to the first description, the centers of the cervical vertebrae have deep, lateral pneumatic recesses ( pleurocoel cavities ). The cervical vertebrae, articulated with one another, form an upward curve, which lifted the head above the back line during life. The pelvis is similar to that of Allosaurus : In the ilium, both the transverse ridge above the socket for the joint head of the femur (English supraacetabular crest ) and the hollow on the underside of the rear part of the bone (English brevis fossa ) are moderately developed; in the ilium, the oburator process (more or less noticeable process on the lower edge of the front / upper part of the bone) is trapezoidal and the rear / lower ( distal ) end is thickened ("distal foot"); the pubis has a slender shaft and a comparatively weakly thickened front / lower (distal) end (i.e. it did not form a so-called “pubic boot”, such as the pubis of Allosaurus ). The thigh bone (femur) is only slightly longer than the "shin" (tibia) and has a wide, wing-shaped anterior trochanter ("small trochanter"; prominent attachment point for muscles located on the outside-front at the upper end of the femoral shaft). The astragalus (one of the two large tarsal bones) shows the remains of a low ascending process, and the (reconstructed) foot skeleton is generally slender and elongated.

^* The use of the term “maxillary fenestra” in Sereno et al. (1994) is a bit misleading, because the authors apparently use it to denote no breakthrough in the bone, i.e. no window i. e. S., but only a rounded indentation (fossa) in the anterior part of the antorbital fossa.

Way of life and habitat

Live reconstruction

Its habitat consisted of lush wooded areas near lakes or rivers. He coexisted with the original Macronarian Jobaria , whose young he may have hunted.

Nothing is known about his social behavior due to the small amount of fossil material available. By analogy with similar, better-known theropods ( Allosaurus , Mapusaurus ), one can speculate, however, that it may have lived in packs and then even hunted adult sauropods.

Systematics

The result of the cladistic analysis carried out in the context of the first description (Sereno et al., 1994) shows Afrovenator as a representative of the extensive theropod clade Tetanurae . Within this clade, it appears as the most basal representative of the most basal Tetanurae clade "Torvosauroidea" (Spinosauroidea, Megalosauroidea) , which, in addition to Afrovenator, also includes the Spinosauridae and Torvosauridae (Megalosauridae) , the two last-named taxa being differentiated from Afrovenator by the presence of a characteristic sickle-shaped distinguish the last (distal) phalanx of the first finger of the hand. Tetanurae synapomorphies of the Afrovenator skull include in this analysis the presence of a maxillary fossa and the position of the rearmost tooth position in front of the front edge of the eye socket, Tetanurae synapomorphies of the postcranial skeleton are the "semilunate" carpale, the (presumably) atrophied third finger, the Wing-like or blade-like anterior trochanter of the femur and the lower ascending process of the astragalus (see characteristics ).

The results of the following analyzes mostly confirm the position of Afrovenator as a basal tetanur or spinosauroid / megalosauroid, albeit with variable relationships to the Spinosauridae and Megalosauridae. In addition, due to the modification and increasing size of the data sets (both with regard to the number of characteristics and with regard to the number of included taxa) and also due to the revision of the characteristic ^{codes **} partly different synapomorphies for the tetanurae and their subclades ^*** than those in mentioned in the first description.

^** For example, Benson (2010) and Carrano et al. (2012) the Jugale of Afrovenator in their data matrices contrary to the information in Sereno et al. (1994) as unpneumatized (features 34 and 52 respectively with feature status 0) and also for the wing-shaped anterior trochanter the coding (Benson, 2010: feature 191, condition 0; Carrano et al. (2012: feature 308, condition 0)) does not correspond the information in Sereno et al. (1994), although Benson (2010) explicitly states that he obtained the data on Afrovenator from its first description. In addition, Benson (2010) explicitly states that Megalosaurus is the only genus within the Megalosauridae, who have a pneumatized Jugale. A pneumatized Jugale is therefore not listed here as a feature of Afrovenator .

^*** For example, the presence of a large maxillary fossa in Benson (2010: characteristic 15, state 1) is a synapomorphism of the common clade of Ceratosauria and Tetanurae (=  Neotheropoda ; 0 → 1) and the presence of a "real" maxillary window (characteristic 15, state 2) a synapomorphism of the Neotetanurae (1 → 2; in each case only under the ACCTRAN premise) or the somewhat less inclusive common clade of Allosauroidea  + Coelurosauria (0 → 2; only under the DELTRAN premise). In Carrano et al. (2012) is, however, a "real" Maxillarfenster a synapomorphy the Tetanurae while at the Megalosauroidea (incl. Afrovenator (Engl.) As a relatively basal clade of Tetanurae a reversal reversal of this state) is carried through to Maxillarfossa. The presence of an enlarged terminal phalanx of the first finger of the hand is in Benson (2010: characteristic 159, state 1) a synapomorphism of his "New clade B" (mainly Spinosauridae + Megalosauridae), but in this hypothesis Afrovenator is within this clade (and although within the Megalosauridae) in a sister group relationship with Dubreuillosaurus , which is characterized by a reversal with regard to this feature (i.e., unlike in Sereno et al., 1994, secondary loss within the Megalosauridae instead of a plesiomorphic state within the Megalosauroidea, although only under ACCTRAN- Premise). In Carrano et al. (2012) it is similar. In his case, the ingroup within the Megalosauridae, identified by the reversal (characteristic 259, state 0, only under ACCTRAN premise), to which Afrovenator belongs and which he calls Afrovenatorinae, comprises more than just two terminal taxa.

literature

• Roger BJ Benson: A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society. Vol. 158, No. 4, 2010, pp. 882-935, doi: 10.1111 / j.1096-3642.2009.00569.x .
• Matthew T. Carrano, Roger BJ Benson, Scott D. Sampson: The phylogeny of Tetanurae (Dinosauria: Theropoda). In: Journal of Systematic Palaeontology. Vol. 10, No. 2, 2012, pp. 211-300, doi: 10.1080 / 14772019.2011.630927 .
• Paul C. Sereno, Jeffrey A. Wilson, Hans CE Larsson, Didier B. Dutheil, Hans-Dieter Sues: Early Cretaceous Dinosaurs from the Sahara. In: Science. Vol. 266, No. 5183, 1994, pp. 267-271, doi: 10.1126 / science.266.5183.267 (alternative full text access: University of Michigan PDF 1.4 MB).

Individual evidence

1. ↑ ^{a b} M. T. Carrano et al .: The phylogeny of Tetanurae (Dinosauria: Theropoda). 2012 (see literature ), p. 222 f.
2. ↑ cf. Fig. 1A in Paul C. Sereno, Allison L. Beck, Didier B. Dutheil, Hans CE Larsson, Gabrielle H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson , Jeffrey A. Wilson: Cretaceous sauropods from the Sahara and the uneven rate of skeletal evolution among dinosaurs. In: Science. Vol. 286, No. 5443, 1999, pp. 1342–1347, doi: 10.1126 / science.286.5443.1342 (alternative full text access: University of Washington PDF 320 kB).
3. ↑ ^{a b} P. C. Sereno et al .: Early Cretaceous Dinosaurs from the Sahara. 1994 (see literature ).
4. ↑ Oliver WM Rauhut, Adriana López-Arbarello: Considerations on the age of the Tiouaren Formation (Iullemmeden Basin, Niger, Africa): Implications for Gondwanan Mesozoic terrestrial vertebrate faunas. In: Palaeogeography, Palaeoclimatology, Palaeoecology. Vol. 271, No. 3–4, 2009, pp. 259–267, doi: 10.1016 / j.palaeo.2008.10.019
5. ↑ cf. Brief discussion in Jerald D. Harris: A reanalysis of Acrocanthosaurus atokensis , its phylogenetic status, and paleobiogeographic implications, based on a new specimen from Texas. New Mexico Museum of Natural History and Science Bulletin. Vol. 13, 1998 ( online ), p. 69 (Appendix 2)
6. ↑ Thomas R. Holtz Jr .: Dinosaur Genus List. (PDF; 704 kB) (Version from January 12, 2012). In: Supplementary Information to "Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages". Retrieved October 3, 2013 . 
7. ^ ^{A b} Gregory S. Paul: The Princeton Field Guide to Dinosaurs. Princeton University Press, Princeton NJ 2010, ISBN 978-0-691-13720-9 .
8. ↑ cf. Cladograms in MT Carrano et al .: The phylogeny of Tetanurae (Dinosauria: Theropoda). 2012 (see literature ), pp. 216 ff., 247 ff.
9. ↑ RBJ Benson: A description of Megalosaurus bucklandii. 2010 (see literature ), supplementary material (Appendix S3: Feature coding)
10. ↑ MT Carrano et al .: The phylogeny of Tetanurae (Dinosauria: Theropoda). 2012 (see literature ), supplementary file no. 3 (source code of the Nexus file, which contains, among other things, the feature matrix).
11. ↑ RBJ Benson: A description of Megalosaurus bucklandii. 2010 (see literature ), supplementary material (Appendix S1: Taxon list and sources for the attribute states)
12. ^ ^{A b} R. BJ Benson: A description of Megalosaurus bucklandii. 2010 (see literature ), Table 6 and supplementary material (Appendix S2: Description of characteristics)
13. ↑ ^{a b} M. T. Carrano et al .: The phylogeny of Tetanurae (Dinosauria: Theropoda). 2012 (see literature ), supplementary file No. 2 (descriptions of characteristics).

Web links

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