2011
DOI: 10.1371/journal.pone.0023393
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Variation, Variability, and the Origin of the Avian Endocranium: Insights from the Anatomy of Alioramus altai (Theropoda: Tyrannosauroidea)

Abstract: The internal braincase anatomy of the holotype of Alioramus altai, a relatively small-bodied tyrannosauroid from the Late Cretaceous of Mongolia, was studied using high-resolution computed tomography. A number of derived characters strengthen the diagnosis of this taxon as both a tyrannosauroid and a unique, new species (e.g., endocranial position of the gasserian ganglion, internal ramification of the facial nerve). Also present are features intermediate between the basal theropod and avialan conditions that … Show more

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Cited by 47 publications
(72 citation statements)
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“…A small portion of the prootic is filled by what may be part of the anterior tympanic recess, but this sinus was probably mostly within the missing parabasisphenoid. The brain endocast is strikingly similar to those of tyrannosaurids, particularly Alioramus (20,26,34,35). There is only a slight midbrain flexure, resulting in a fairly shallow endocast that would have been tubular if complete.…”
Section: Description and Comparisonsmentioning
confidence: 75%
“…A small portion of the prootic is filled by what may be part of the anterior tympanic recess, but this sinus was probably mostly within the missing parabasisphenoid. The brain endocast is strikingly similar to those of tyrannosaurids, particularly Alioramus (20,26,34,35). There is only a slight midbrain flexure, resulting in a fairly shallow endocast that would have been tubular if complete.…”
Section: Description and Comparisonsmentioning
confidence: 75%
“…Rostral to this confluence and caudal to the position through which the cochlear branch of the vestibulocochlear (VIII) nerve enters the cochlear cavity, a short canal extends from the cranial cavity to the recessus scalae tympani. This penetration of what is presumably the opisthotic (the prootic-otoccipital suture is not clear) was interpreted by Bever et al (2011) to be an independent path of the glossopharyngeal (IX) nerve into the recessus scalae tympani. The nerve likely traverses the recessus scalae tympani in all tyrannosauroids (Witmer and Ridgely, 2009;contra Brochu, 2000, who interpreted IX as entering the vagal canal), presumably entering this space through the common medial aperture of the cavum metoticum.…”
Section: Dermal Roof Frontalmentioning
confidence: 99%
“…A cast of all major endocranial spaces was figured in Brusatte et al (2010a) but without an accompanying description. More recently, a short but detailed description was published that focused solely on endocranial features bearing directly on phylogenetic transformations within Tyrannosauroidea or that inform the early evolutionary history of avian neuroanatomy (Bever et al, 2011). Our purpose here is to narrow the descriptive gap currently separating the braincase of IGM 100/1844 from what is available for the remainder of its preserved skeleton.…”
Section: Introductionmentioning
confidence: 99%
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“…Studies of variation in extinct populations or species are more common when studying invertebrates, such as trilobites (Hughes and Labandeira, 1995;Labandeira and Hughes, 1994;Webster, 2007Webster, , 2014Hopkins, 2011), ammonoids (Hohenegger and Tatzreiter, 1992;Korn and Klug, 2007;Monnet et al, 2010;De Baets et al, 2013), and crinoids (Lane, 1963;Meyer and Ausich, 1997). Among fossil tetrapods, studies on intraspecific variation have been conducted for example for dinosaurs (Raath, 1990;Bever et al, 2011;Foth and Rauhut, 2013), ichthyosaurs (Maxwell, 2012), rodents (Renaud et al, 2006;Lazzari et al, 2010) and horses (MacFadden, 1997). Several studies on variation in extinct populations of fishes have been carried out during the last three decades, mostly concerning microstratigraphic changes in variation of meristic and morphometric characters of different body parts, or phenotypic variation as it relates to taxonomically informative characters (Bell and Haglund, 1982;Bell et al, 1985;Bell and Legendre, 1987;Cloutier, 1997;Smith, 1987;McCune, 1990McCune, , 1996Barton and Wilson, 1999;Micklich and Klappert, 2004;Grande, 2010; Table 1).…”
Section: Introductionmentioning
confidence: 99%