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Downloaded from http://sp.lyellcollection.org/ at CAPES on May 3, 2013S. J. NESBITT ET AL.tomography (micro-CT) data for, cervical vertebraeof Bromsgroveia walkeri, Effigia okeeffeae, Hypselorhachismirabilis and Batrachotomus kupferzellensisand reconsidered archosaur PSP morebroadly, concluding that no rauisuchians displayunambiguous evidence of PSP. However, rauisuchiansdo have features (well-developed vertebrallaminae and fossae) that are absent in extant diapsidsthat lack PSP, and which do accompany instances ofunambiguous evidence for PSP in extinct archosaurs.Thus, rauisuchians (and some other nonornithodirans)may have had a non-invasive systemof pulmonary air sacs. Extant birds and crocodilianshave unidirectional lung ventilation (Farmer &Sanders 2010; Sanders & Farmer 2012), and phylogeneticcharacter optimization suggests that this mayhave evolved in their common ancestor (i.e. at thebase of Archosauria) and therefore may also havebeen present in rauisuchians (Perry et al. 2011;Butler et al. 2012). The relationship betweenvarious inferred extinct lung morphologies andmetabolism has yet to be worked out.Future directionsInterest in Triassic vertebrates has skyrocketed overthe past 15 years and there is little to suggest that itwill slow down soon. Rauisuchians or some of theirmore probably monophyletic subgroups (e.g. Shuvosauridae)lie at the heart of this Triassic renaissance,not least because some of them have beenconfused with many other groups of Triassic archosaurs,and knowledge of them clearly impacts whatwe know of pseudosuchians and of early archosaursmore broadly. This current volume attests tothe recent and ongoing research on rauisuchiansbecause more than half of the volume is devotedto these organisms. Even though there is renewedinterest and a number of important finds, there are,however, a number of challenges that lie ahead.Rauisuchian palaeontology has changed enormouslysince Gower’s (2000) overview of thegroup. To a large degree, the optimism expressedby Gower (2000, pp. 476–478) has proven wellfounded. Since 2000, the levels of interest andresearch effort focused on these organisms havegrown dramatically, and the number and geographicaldistribution of rauisuchian researchers hasexpanded healthily (especially as many early-careerresearchers have begun to work on the group). Technologicaladvances have played their part, from theuse of digital photography to greatly enhance thespeed and accuracy of recording information onspecimens that are too numerous and large to beloaned between collections, to the application ofcomputed tomography to examine internal structuresof bones non-destructively. Gower (2000)wrote only in vague terms about advances in rauisuchianpalaeobiology (beyond systematics) thatcould come from focused, careful research, and hedid not clearly foresee the speed and scope of discoverythat, since then, has included many spectacularnew fossils, detailed descriptions, newphylogenetic hypotheses, muscle reconstructions,histological studies and considerations of possiblepneumaticity.Gower (2000) highlighted a number of points ofcaution that lay at the heart of establishing a foundationfor rauisuchian studies, emphasizing detailedosteological documentation of both newly discoveredand previously described material as vital toall other vertebrate palaeontological contributions,including studies of function, ecology and evolutionbuilt on such morphological data. Improvement inthis basic documentation has undoubtedly contributedto the great increase in knowledge of rauisuchianssince 2000, and the field would do well tocontinue to pay attention to this aspect. Other potentialpitfalls noted by Gower (2000) also seem tohave been largely avoided, including restrictingthe use of suprageneric taxa as terminals in phylogeneticanalyses, assessing the support of phylogenetichypotheses, and restraint in naming newsuprageneric taxa on the basis of each new phylogenetichypothesis. We now additionally recommendthat continued effort is expended to avoidchimeric holotypes (a problem in previous taxonomicstudies of rauisuchians), and that morphologicalstudies bear in mind the ongoing need toresolve and find additional homologies for use insystematic analyses.Very few researchers currently argue for themonophyly of rauisuchians based on explicit phylogeneticanalyses, so does the term ‘Rauisuchia’ forthis unnatural ‘group’ still have any use? The mostrecent, large-scale archosaur phylogenies (e.g. Brusatteet al. 2010; Butler et al. 2011; Nesbitt 2011)suggest that we are closer to being able to applysome suprageneric names to particular groups ofrauisuchians (Poposauroidea, Shuvosauridae) withmore confidence that these are monophyletic.However, several taxa are still far from completelyknown; many have not been included in all of thelargest recent phylogenetic analyses (e.g. ‘Mandasuchus’,Heptasuchus, Luperosuchus), and manyrauisuchian nodes in published trees have not beencompellingly resolved. Thus, an umbrella term(rauisuchians) for most of the non-ornithosuchid,non-aetosaurian and non-crocodylomorphan (andpossibly non-phytosaurian) pseudosuchians probablystill has some use – if only to serve as anongoing reminder that a robust, comprehensive phylogenyhas yet to be achieved, and to prevent misunderstandingwhen trying to find ways to preciselyand accurately refer to particular groups without