Important new Jurassic paper for those of you not subscribed to the VRTPALEO listserve...
RAUHUT, O.W.M., A.C. MILNER, and S. MOORE-FAY. 2009. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi(Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society Early View doi: 10.1111/j.1096-3642.2009.00591.x
ABSTRACT
The cranial osteology of the small theropod dinosaur Proceratosaurus from the Bathonian of Minchinhampton, England, is described in detail, based on new preparation and computed tomography (CT) scan images of the type, and only known, specimen. Proceratosaurus is an unusual theropod with markedly enlarged external nares and a cranial crest starting at the premaxillary-nasal junction. The skull is highly pneumatic, with pneumatized nasals, jugals, and maxillae, as well as a highly pneumatic braincase, featuring basisphenoid, anterior tympanic, basipterygoid, and carotid recesses. The dentition is unusual, with small premaxillary teeth and much larger lateral teeth, with a pronounced size difference of the serrations between the mesial and distal carina. The first dentary tooth is somewhat procumbent and flexed anteriorly. Phylogenetic analysis places Proceratosaurus in the Tyrannosauroidea, in a monophyletic clade Proceratosauridae, together with the Oxfordian Chinese taxon Guanlong. The Bathonian age of Proceratosaurus extends the origin of all clades of basal coelurosaurs back into the Middle Jurassic, and provides evidence for an early, Laurasia-wide, dispersal of the Tyrannosauroidea during the late Middle to Late Jurassic.
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I didn't think of this before, but of course this revised earlier date for the origin of Coelurosauria reduces the ghost lineage that is induced by a therizinosauroid identity for Eshanosaurus. Or at least it splits the ghost range between TWO tentatively-identified putative coelurosaurs.
ReplyDeleteActually, several of coelurosaur lineages are now known from the Middle Jurassic or earliest Late Jurassic:
ReplyDeleteTyrannosauroidea (Proceratosaurus, Guanlong); Alvarezsauridae (new form discussed at poster at SVP); Troodontidae (Anchiornis, maybe Jinfengopteryx); Avialae (Epidendrosaurus, Epidexipteryx). Also, the age date for Eshanosaurus is apparently extremely unbounded: it may be as old as the Early Jurassic or as young as the Early Cretaceous.
With recent taxonomic revisions the Middle Jurassic (or earliest Late Jurassic) contains the first appearance dates for a number of major dinosaur clades: Ornithopoda, Marginocephalia, Megalosauroidea, Carnosauria/Allosauroidea, etc.
This scenario points to an origin in nuclear Asia (isolated during Late Jurassic, full of endemisms) for Troodontidae, derived tyrannosauroids (specially proto-tyrannosaurids), proto-birds, marginocephalians, most of maniraptoan linneages. Gondwanan dromeosaurids and compsognathians/coelurosaurians (Mirischia, Santanaraptor)could be linneages split apart during Early Cretaceous (Asia-Europe-Africa- Northern S America route)
ReplyDelete"This scenario points to an origin in nuclear Asia (isolated during Late Jurassic, full of endemisms) for Troodontidae, derived tyrannosauroids (specially proto-tyrannosaurids), proto-birds, marginocephalians, most of maniraptoan linneages."
ReplyDeletePeople need to stop attempting all but the most basic Mesozoic dinosaur biogeography. In this case, it's obvious the reason for these records is because China is by far the place that preserves small Middle Jurassic dinosaurs best. Think of how many dinosaur taxa we have in the Morrison Formation, then reflect on the fact that other formations likely had similar numbers of spcies and that we keep on finding new ones in the Morrison too.
Even just looking at our current records for the theropod clades you listed, Morrison troodontids are known from several specimens (Koparion, Lori, possible unnamed teeth from Brett-Surman et al., 2005 and Chure, 1995) and teeth from Guimarota (Zinke, 1998). The Morrison also has dromaeosaurid teeth (Chure et al., 1993; Turner and Peterson, 1999), as does Late Jurassic Germany (van der Lubbe et al., 2009), Portugal (Zinke, 1998), possibly Ethiopia (Goodwin et al., 1999) and Middle Jurassic England (Metcalf and Walker, 1994). "Paleopteryx" from the Morrison may be microraptorian. Both the Guimarota and Morrison have preserved many other probably paravian teeth as well, in addition to a Morrison femur (Jensen, 1981). For oviraptorosaurs, we have Albian manual elements from Algeria (Lapparent, 1960), tha Santana sacrum (Frey and Martill, 1995), the Victorian material (Currie et al., 1996) and Microvenator of course. For therizinosaurs, we have Falcarius. Thecocoelurus from England may belong to one of the latter two clades. Nqwebasaurus and Rapator may be basal relatives of alvarezsaurids, even if the earliest known member of the latter family is Chinese. There are various possible Early Cretaceous North American ornithomimosaurs (Kirkland et al., 1998; Britt et al., 2004) and Pelecanimimus. There is a Tendaguru carpometacarpus which may be avialan or troodontid (Janensch, 1914) and Archaeopteryx from Germany. The closest relatives of tyrannosaurids are North American (Dryptosaurus, Stokesosaurus) and European (Aviatyrannis) as well as Asian.