Systematic Biology Advance Access published April 2, 2015

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Running head: OUTGROUP CHOICE AND THE ORIGIN OF CROCODYLIFORMES

What‘s in an Outgroup? The Impact of Outgroup Choice on the Phylogenetic Position of Thalattosuchia (Crocodylomorpha) and the Origin of Crocodyliformes

Eric W. Wilberg1, 2 1. Department of Geoscience, University of Iowa, Iowa City, IA, USA 2. Current Address – Department of Geology and Geography, Georgia Southern University, Statesboro, GA, USA Correspondence: Department of Geology and Geography, Georgia Southern University, P.O. Box 8149, Statesboro, GA 30460, USA Phone: 517-944-9100 Email: [email protected]

© The Author(s) 2015. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For Permissions, please email: [email protected]

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Abstract.— Outgroup sampling is a central issue in phylogenetic analysis. However, good justification is rarely given for outgroup selection in published analyses. Recent advances in our understanding of archosaur phylogeny suggest that many previous studies of crocodylomorph and crocodyliform relationships have rooted trees on outgroup taxa that are only very distantly related to the ingroup (e.g., Gracilisuchus stipanicicorum), or might actually belong within the ingroup. Thalattosuchia, a group of Mesozoic marine crocodylomorphs, has a controversial phylogenetic position – they are recovered as either the sister group to Crocodyliformes, in a basal position within Crocodyliformes, or nested high in the crocodyliform tree. Thalattosuchians lack several crocodyliform apomorphies, but share several character states with derived long-snouted forms with a similar ecological habit, suggesting their derived position may be a result of convergent evolution. Several of these ―shared‖ characters may result from ambiguously worded character state definitions – structures that are superficially similar but anatomically different in detail are identically coded. A new analysis of crocodylomorphs with increased outgroup sampling recovers Thalattosuchia as the sister group to Crocodyliformes, distantly related to long-snouted crocodyliforms. I also demonstrate that expanding the outgroup sampling of previously published matrices results in the recovery of thalattosuchians as sister to Crocodyliformes. The exclusion of thalattosuchians from Crocodyliformes has numerous implications for large-scale evolutionary trends within the group, including extensive convergence in the evolution of the secondary palate characteristic of the group. These results demonstrate the importance of careful outgroup sampling and character construction, and their profound effect on the position of labile clades.

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Keywords: Outgroup sampling, Thalattosuchia, Crocodylomorpha, Crocodyliformes, convergence

―As parsimony analysis attributes character states to the hypothetical stem species of the tree, fixing the position of the root determines the direction of character transformations, and so the relative plesiomorphy of features.‖ – J.S. Farris, 1982 (p. 329)

Since tetrapods first transitioned onto land, many groups have returned to the water. Secondarily aquatic lineages have arisen in nearly every major tetrapod group. Crocodylians and their relatives (Crocodylomorpha) are no exception to this pattern. Numerous crocodylomorph lineages have produced marine or estuarine predators possessing elongate tubular snouts; a putative adaptation for piscivory (Langston 1973). This repeated evolution of similar skull shapes is not limited to slender snouted marine forms. Several snout shapes have recurred throughout crocodylomorph evolution (Brochu 2001), and studies have shown that within crowngroup crocodylians snout shape is more highly correlated with functional parameters than with phylogeny (e.g., Pierce et al. 2008; Sadlier and Makovicky 2008). The pattern within modern and fossil crocodylians suggests that Mesozoic crocodylomorphs possessing similar rostral morphology may not be closely related. The evolution of long slender snouts in marine crocodylomorphs may have occurred a single time or multiple times convergently. Historically, longirostry (possession of a long snout) was thought to have arisen multiple times within crocodylomorphs (Kälin 1955; Langston 1973; Buffetaut 1982). Morphological phylogenetic analyses of the crown-group consistently support at least three independent

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derivations of the long-snouted condition (e.g., Norell 1989; Brochu 1997a) while molecular analyses suggest only two (e.g., Gatesy et al. 2003; McAliley et al. 2006; Meredith et al. 2011; see Brochu 2001 for a detailed discussion of this issue). Three groups of non-crown crocodylomorphs were traditionally thought to have independently evolved longirostry: thalattosuchians, dyrosaurids, and pholidosaurs (Kälin 1955; Langston 1973; Buffetaut 1982). The thalattosuchians are a unique clade of crocodylomorphs demonstrating the most extreme archosaurian adaptation to the marine environment (Hua and Buffetaut 1997; Young and Andrade 2009). The group is known from marine deposits of the Lower Jurassic through the Lower Cretaceous, and includes two groups: Metriorhynchidae and Teleosauridae. Though longirostry is prevalent among thalattosuchians, not all possess an elongate snout. Some taxa (e.g., Dakosaurus) possess relatively short, robust snouts. This has been used as evidence against functionally correlated characters uniting thalattosuchians with pholidosaurs/dyrosaurids (Pol and Gasparini 2009). Dyrosauridae and Pholidosauridae make up the other two clades of non-crown group longirostrine crocodylomorphs. The dyrosaursids are found primarily in coastal marine environments from the Cretaceous through the Eocene, while Pholidosauridae (latest Jurassic through the Cretaceous) contains both marine and freshwater forms (Hua and Buffetaut 1997). Traditionally the pholidosaurs and dyrosaurids were not thought to be closely related (Buffetaut 1982), however, all phylogenetic analyses including both groups have recovered them as a clade (e.g., Benton and Clark 1988; Clark 1994; Buckley and Brochu 1999; Wu et al. 1997; Ortega et al. 2000; Sereno et al. 2001, 2003; Brochu et al. 2002; Pol and Norell 2004a, b; Jouve et al.

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2006; Larsson and Sues 2007; Jouve 2009; Young and Andrade 2009; Turner and Sertich 2010; Bronzati et al. 2012). Historically, thalattosuchians were interpreted as basal ―mesosuchians‖ distantly related to crown-group Crocodylia (Kälin 1955; Buffetaut 1982). Parsimony analyses support thalattosuchian monophyly but have not clarified their phylogenetic position. This issue has been termed the ―longirostrine problem‖ (Clark 1994). Three mutually exclusive topologies can be found in published analyses (Fig. 1). Some analyses recover thalattosuchians as sister to Crocodyiformes (Fig. 1 - position a; Jouve 2009; Pol and Gasparini 2009; Wilberg 2015). Some place them in a basal position among mesoeucrocodylians (Fig. 1 - position b; e.g., Sereno et al. 2001, 2003; Larsson and Sues 2007; Sereno and Larsson 2009; Young and Andrade 2009; Young et al. 2012), and others as derived mesoeucrocodylians more closely related to the crown (Fig. 1- position c; e.g., Clark 1994; Wu et al. 1997, 2001; Pol and Norell 2004a, b; Jouve et al. 2006; Jouve 2009; Pol and Gasparini 2009; Turner and Sertich 2010; Andrade et al. 2011; Pritchard et al. 2013). Analyses drawing thalattosuchians crownward link them with other longsnouted clades, suggesting that convergence related to snout shape may be confounding efforts to recover a phylogenetic signal. A point directly related to the phylogenetic position of thalattosuchians that has yet to be investigated involves outgroup sampling in published analyses. Outgroup sampling is of primary importance in phylogenetic analyses, affecting ingroup relationships and, in placing the root, polarizing characters (Lyons-Weiler et al. 1998). However, justification is rarely given for outgroup selection. There are essentially three different outgroup sampling schemes in published crocodyliform phylogenetic analyses. Data sets based directly on the original analyses of Clark

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(Clark 1994) modified primarily by the addition of ingroup taxa and characters (e.g., Pol and Norell 2004a, b; Pol et al. 2004; Gasparini et al. 2006; Turner and Buckley 2008; Pol and Gasparini 2009; Pol et al. 2009; Turner and Sertich 2010; Pritchard et al. 2013) generally root their topologies on Gracilisuchus stipanicicorum and include two ―sphenosuchian‖ crocodylomorphs: Terrestrisuchus gracilis, and Dibothrosuchus elaphros (it should be noted that these analyses greatly reduced the number of sampled outgroups originally present in Clark 1994). Analyses based on the data set of Jouve (e.g., Jouve et al. 2006; Jouve 2009) root the tree on the rauisuchid (sensu Nesbit 2011) Postosuchus kirkpatricki, and include the ―sphenosuchian‖ crocodylomorphs Sphenosuchus acutus, Dibothrosuchus elaphros, and Kayentasuchus walkeri. Other analyses root their trees on a protosuchian (e.g., Buckley and Brochu 1999; Sereno et al. 2001; Brochu et al. 2002; Sereno et al. 2003; Larsson and Sues 2007; Sereno and Larsson 2009). Though some published analyses have utilized different outgroup sampling schemes (e.g., Young and Andrade 2009; Andrade et al. 2011; Young et al. 2012), most include fewer than four taxa. Some analyses recovering thalattosuchians basally within Mesoeucrocodylia (e.g., Sereno et al. 2001, 2003; Larsson and Sues 2007; Sereno and Larsson 2009) utilize a protosuchian outgroup. This outgroup sampling scheme a priori excludes the possibility that thalattosuchians are the sister group to Crocodyliformes (Fig. 1– position a). These analyses assumed ingroup monophyly, presumably based on the results of early cladistic analyses (Benton and Clark 1988; Clark 1994). When sampling only a single outgroup, it is not possible to test the monophyly of the ingroup (Nixon and Carpenter 1993; Barriel and Tassy 1998; Sanderson and Shaffer 2002; Puslednik and Serb 2008). Addition of more distant outgroups (without constraining their topology as in Maddison et al. 1984) allows for a more severe test of phylogenetic relationships

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by removing this assumption (Meacham 1986; Nixon and Carpenter 1993) and should render a more stable ingroup topology (Puslednik and Serb 2008). A separate problem involves the selection of individual outgroup taxa. Smith (1994) suggested that sampling the two closest successive sister groups is the ideal scheme for choosing outgroups. However, sampling beyond the two closest sister groups allows a further test that the presumed sister group is, in fact, the sister group (Graham et al. 2002). A similar suggestion is made by Brusatte (2010) for determining the minimum number of species necessary to represent a supraspecific taxon in an analysis of higher level relationships. Yet caution should be exercised to avoid sampling a very distantly related taxon (without sampling other outgroup taxa to break up the resulting long phylogenetic branch). Very distantly related taxa are expected to share fewer relevant character states with the ingroup and have had greater time to accumulate homoplasy. Published analyses rooting on Gracilisuchus and sampling few other outgroup taxa recover thalattosuchians as sister to the other longirostrine crocodyliforms (Fig. 1 – position c). The phylogenetic position of Gracilisuchus is contentious. While some analyses of archosaur relationships have recovered Gracilisuchus as a close relative of Crocodylomorpha (e.g., Brusatte et al. 2010), many have recovered it as somewhat more distantly related (e.g., Benton and Clark 1988; Parrish 1993). Recent work on archosaur phylogenetics suggests that Gracilisuchus is actually a basal suchian, very distantly related to Crocodylomorpha (Nesbitt 2011). Thus, Gracilisuchus might not represent an ideal outgroup choice in the absence of additional, more proximal outgroups. Previous work has demonstrated that outgroup sampling can have a great effect on ingroup relationships, particularly for labile clades (e.g., Spaulding et al. 2009). Spaulding et al.

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(2009) showed that Mesonychia, an archaic group of carnivorous ungulates sometimes linked with the origin of whales (e.g., Luo and Gingrich 1999), is highly labile within the ungulate tree. When few outgroups were sampled, Mesonychia was recovered in a derived position (close to Cetacea), but when the full suite of outgroups was sampled, Mesonychia was recovered in a basal position (Spaulding et al. 2009). This conflict, at least superficially, mirrors that seen with Thalattosuchia and the longirostrine crocodyliforms – an instance of strong, but conflicting, character support for multiple highly divergent topologies. The three contentious longirostrine groups are all found in marine environments suggesting they share similar ecological/functional pressures. Early phylogenetic analyses recovered all three long-snouted groups as a clade (e.g., Benton and Clark 1988; Clark 1994; Wu et al. 1997; Pol and Norell 2004a, b; Pol et al. 2004). This grouping was treated skeptically from the beginning and was originally dismissed as the result of convergence (Clark 1986; Benton and Clark 1988). Later works no longer dismissed the longirostrine clade but it has remained suspect for three primary reasons (Pol and Gasparini 2009). First, thalattosuchians possess the plesiomorphic condition for many characters (which must be optimized as reversals when sister to other longirostrine groups; Benton and Clark 1988). Second, because crocodyliforms have demonstrably evolved similar skull shapes numerous times (Langston 1973; Busbey 1995; Brochu 2001), it was assumed that snout shape is not a reliable phylogenetic character. Finally, the sister group relationship between thalattosuchians and pholidosaurs/dyrosaurids requires a long ghost lineage because thalattosuchians first appear in the Early Jurassic, while pholidosaurs/dyrosaurids first appear in the Cretaceous. Additionally, analyses have demonstrated that when characters suspected of correlation with a slender snout shape (as

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suggested by Clark; 1994) are removed, thalattosuchians are recovered as either basal mesoeucrocodylians (e.g., Buckley and Brochu 1999; Jouve et al. 2006) or as the sister group to Crocodyliformes (e.g., Pol and Gasparini 2009). Brochu (2001) proposed that the inclusion of dyrosaurids and pholidosaurs in an analysis draws the thalattosuchians up the tree. When dyrosaurids and pholidosaurs are excluded from analyses, thalattosuchians move back towards the base of the tree (e.g., Buckley et al. 2000; Tykoski et al. 2002; Turner and Calvo 2005 – though removal of dyrosaurids while retaining pholidosaurs does not change the position of Thalattosuchia; Jouve et al. 2006). There are three potential non-mutually exclusive hypotheses to explain these results. 1. The three groups of marine crocodylomorphs are indeed monophyletic and thalattosuchians are characterized by multiple character state reversals that, in the absence of evidence from dyrosaurids or pholidosaurs, are mistaken for plesiomorphies. 2. They are not monophyletic, but characters related to convergence on the longsnouted morphotype are pulling them together. 3. Character information supporting the non-crocodyliform affinities of thalattosuchians is present, but the lack of proper outgroup sampling forces the reconstruction of plesiomorphic character states as synapomorphies for Thalattosuchia. This is a difficult question to address by analyzing the current literature. Early attempts at reconstructing the crocodyliform tree sampled thalattosuchians mostly as composite taxa (Metriorhynchidae, Teleosauridae; e.g., Clark 1994). More recent analyses based on species-

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level data generally include only the most derived forms (e.g., Cricosaurus and Dakosaurus), and sample only one or two teleosaurids (e.g., Pol and Gasparini 2009; Turner and Sertich 2010), or include several teleosaurids, but weakly sample metriorhynchids (e.g., Jouve 2009). These sampling schemes may obscure important character information that could be obtained by more comprehensive sampling of thalattosuchian taxa. Additionally, as most teleosaurid species have yet to be included in a phylogenetic analysis, much data from the early history of the clade has not been sampled. Some of these taxa may retain plesiomorphic character states that will impact the relationship of thalattosuchians among other crocodylomorphs. The only published analyses sampling a wide range of thalattosuchians are based on the matrix of Young (e.g., Young and Andrade 2009; Young et al. 2012; Parrilla-Bel et al. 2013). However, this data set samples only a single protosuchian taxon and relatively few outgroup taxa. Thus a large amount of character and taxon information has not yet been included in previous efforts to address the longirostrine problem. Its addition will be an important test of the competing scenarios. This study will address these issues by expanding character information and ingroup and outgroup sampling. I will also test the effects of outgroup sampling on the phylogenetic relationships of crocodylomorphs in general, and the position of Thalattosuchia in particular, through modification to the outgroup sampling scheme of this and previously published data sets.

Institutional Abbreviations CNRST-SUNY, Centre National de Recherche Scientifique et Technologique du Mali–Stony Brook University, Stony Brook, New York, U.S.A.; HMN, Museum für Naturkunde Humboldt-

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Universtät, Berlin, Germany; NHMUK, Natural History Museum, London, United Kingdom; SMC, Sedgwick Museum, Cambridge, United Kindgom; UOMNCH, University of Oregon Museum of Natural and Cultural History, Eugene, Oregon, U.S.A.

MATERIALS AND METHODS

Taxon and Character Sampling To test the relationships of the thalattosuchian crocodylomorphs I performed a phylogenetic analysis of 394 morphological characters scored for eight outgroup and 78 ingroup taxa including 24 thalattosuchian species (online Appendix 1). This new data set is a modified version of that presented in Wilberg (2015) with the addition of ten new characters and the modification of many others (online appendix 2). To minimize errors in character coding, I focused ingroup sampling on specimens I could observe firsthand or those with detailed published descriptions. I made an effort to sample widely from all major crocodylomorph groups. Taxon sampling within Thalattosuchia focused on capturing the broad range of morphologies present in the group across their entire temporal duration. Outgroup sampling was increased from previous analyses with the intent of better characterizing the distribution of character states in non-crocodyliforms. The basal suchian Gracilisuchus was used to root the tree based on its position in the broad scale analysis of Archosauria by Nesbitt (2011). The rauisuchid (sensu Nesbitt 2011) Postosuchus kirkpatricki was included for two primary reasons. First, Rauisuchidae has frequently been recovered as the sister group to Crocodylomorpha, just outside the phylogenetically unstable ―Sphenosuchia‖ (e.g., Benton and Clark 1988; Parrish 1993; Juul

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1994; Nesbitt 2011). Second, Postosuchus kirkpatricki is well known from multiple specimens representing nearly the complete skeleton allowing the scoring of most characters. Six ―sphenosuchian‖ taxa were also sampled. Three of these have been recovered as the sister taxon to Crocodyliformes in previous analyses (Junggarsuchus sloani, Clark et al. 2004; Kayentasuchus walkeri, Nesbitt 2011; Almadasuchus figarii, Pol et al. 2013). The inclusion of these taxa will provide a more stringent test of the potential placement of Thalattosuchia as the sister group to Crocodyliformes. To assess the sensitivity of the topology to outgroup sampling, the analysis was also run in three permutations: excluding the basal suchian Gracilisuchus (rooting on Postosuchus); excluding the non-crocodylomorph taxa Gracilisuchus and Postosuchus (rooting on Hesperosuchus agilis); and excluding all non-crocodyliforms and rooting on the protosuchian Orthosuchus stormbergi as in some published analyses (e.g., Sereno and Larsson 2009). As with any paleontological phylogenetic analysis, the study data set contains relatively high amounts of missing data (40.75% missing or inapplicable). Much of the missing data is concentrated in the postcranial characters as numerous crocodylomorph taxa are known primarily from cranial material. Three taxa (Zaraasuchus shepardi, Eoneustes gaudryi, and Steneosaurus brevidens) are highly incomplete (80-82%), while median incompleteness per taxon is approximately 36%. However, while missing data has been shown to reduce phylogenetic accuracy (e.g. Wiens 2003; Prevosti and Chemisquy 2010 and references therein), the quantity of missing data does not directly correlate with the information content of a taxon. A highly incomplete taxon may still increase resolution if it contains informative synapomorphic information (Kearney and Clark 2003; Wiens 2003).

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Parsimony Analysis The phylogenetic data set was analyzed in TNT v1.1 (Goloboff et al. 2008) using equally weighted parsimony. Minimal length trees were found using a heuristic search with 1000 replicates of Wagner trees using random addition sequences followed by TBR branch swapping. The shortest trees obtained from these replicates were subjected to a final round of TBR branch swapping to ensure all minimum length trees were discovered. Zero-length branches were collapsed if they lacked support under any of the minimal length trees (Rule 1 of Coddington and Scharff 1994). Two separate analyses were run. In the first, to test the effect of potentially nested sets of homologies present in some multistate characters, 36 characters were treated as ordered (online Appendix 2). In the second, multistate characters were treated as unordered to avoid making a priori assumptions about the process of evolution (though whether treating such characters as unordered involves better justified assumptions has been questioned; e.g., Lipscomb 1992; Slowinski 1993).

Nodal Support Nodal support was assessed using jackknife resampling as applied to character data (Farris et al., 1996). Jackknife support was calculated in TNT using 1000 replicates with the probability of independent character removal set at 0.37 (~e -1; as recommended in Farris et al., 1996). A heuristic search was employed with each replicate consisting of 10 random addition sequences, saving 10 trees per replicate. The resulting topologies were summarized using GC frequencies (difference between the frequency of recovering a given group and the most frequent

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contradictory group; Goloboff et al., 2003). GC frequencies are preferred over absolute frequencies (the standard method of counting frequencies in bootstrap and jackknife analyses) because they account for the evidence in support of a clade as well as the amount of evidence falsifying that clade.

Comparative matrices To assess the effect of outgroup sampling on tree topology, two previously published crocodylomorph taxon-character matrices (Turner and Buckley, 2008; Sereno and Larsson, 2009) were investigated. The analysis of Turner and Buckley (2008) consists of 75 taxa and 290 characters and includes Gracilisuchus stipanicicorum, Terrestrisuchus gracilis, and Dibothrosuchus elaphros as outgroup taxa (rooted on Gracilisuchus). The analysis of Sereno and Larsson (2009) includes 43 taxa and 252 characters (rooted on the protosuchian Orthosuchus stormbergi). Both matrices were unaltered with the exception of the addition of new outgroup taxa. In the case of Turner and Buckley (2008) the single terminal taxon Postosuchus kirkpatricki was added. For comparative purposes both Postosuchus and Gracilisuchus were added to the data set of Sereno and Larsson (2009). These data sets were analyzed using unweighted parsimony in TNT v. 1.1 and the same search parameters described above. Both analyses incorporated additive characters, and these were retained as such. Gracilisuchus was set as the root for both matrices. All phylogenetic data sets are available as supplementary online material (http://dx.doi.org/10.5061/dryad.00ss6).

RESULTS

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Parsimony analysis of the ordered study data set resulted in 42 most parsimonious trees (MPTs) of length 1691 (Fig. 2); CI = 0.306, RI = 0.710). The unordered analysis yielded 566 MPTs (length = 1648; CI = 0.312; RI = 0.703). The strict consensus of the unordered analysis is highly congruent with that of the ordered analysis, but much resolution is lost within Notosuchia and Neosuchia (Supplementary Fig. S1). Details of the results discussed below pertain to the ordered analysis unless otherwise noted. In all MPTs thalattosuchians are sister to Crocodyliformes, rather than within. This result occurs in spite of the inclusion of numerous non-thalattosuchian long-snouted taxa (dyrosaurids and pholidosaurs). Twenty unambiguous and nine ambiguous synapomorphies support the exclusion of Thalattosuchia from Crocodyliformes (Table 1). An additional six steps are required for Thalattosuchia to rejoin Crocodyliformes, where they are recovered as basal mesoeucrocodylianas (Supplementary Fig. S2), while inclusion of Thalattosuchia in the longrostrine clade demands twelve additional steps (Suppmentary Fig. S3). Monophyly of Thalattosuchia is robustly supported by a GC jackknife index of 99. Within Thalattosuchia, the genus Steneosaurus is paraphyletic, and in need of taxonomic revision (as suggested also by the analysis of Mueller-Töwe, 2006). Pelagosaurus typus, a thalattosuchian of controversial affinity, is here found as the basal-most metriorhynchoid, a relationship recovered in some recent analyses (e.g., Pol et al. 2009; Young et al. 2012, 2013; Adams 2013; Parrilla-Bel et al. 2013) and is fairly well supported (GC jackknife: 69). Relationships within Metriorhynchoidea differ slightly from those of Young and Andrade (2009; and subsequent analyses based on the same data set; e.g., Young et al. 2012). However, the few incongruent nodes are not particularly

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strongly supported here, and the analysis by Young and Andrade (2009) includes a more comprehensive sampling of metriorhynchids. Kayentasuchus is here recovered as the sister taxon to Crocodyliformes + Thalattosuchia (consistent with the topology of Nesbitt 2011). This differs from the analyses of Clark et al. (2004) and Pol et al. (2013) which recovered Junggarsuchus and Almadasuchus respectively as the sister taxon to Crocodyliformes. However, the position of Kayentasuchus is not strongly supported and only two additional steps are required to make the clade of Junggarsuchus+Almadasuchus sister to Crocodyliformes + Thalattosuchia. Many of the features of the braincase linking Junggarsuchus and Almadasuchus with crocodyliforms are not preserved in Kayentasuchus, thus additional fossil material may be required to resolve this portion of the tree with any confidence. This analysis recovers a monophyletic Protosuchia, an uncommon result found in some previous analyses (e.g., Wu et al., 1994, 1997, 2001; Jouve et al. 2006). The analysis also recovers a monophyletic Notosuchia (including a monophyletic Peirosauridae in some MPTs), Atoposauridae, Goniopholididae, Dyrosauridae, and Pholidosauridae – clades commonly recovered in other published analyses. Elosuchus, a longirostrine taxon once proposed to be closely related to Stolokrosuchus (Lapparent de Broin 2002), is recovered as sister to a clade formed by Dyrosauridae and Pholidosauridae, distant from Stolokrosuchus. Analysis of the ordered data set excluding Gracilisuchus and rooting on Postosuchus resulted in 42 MPTs (length 1676). Analysis of the ordered data set excluding the noncrocodylomorph outgroups (Gracilisuchus, and Postosuchus) and rooting on Hesperosuchus resulted in the same 42 MPTs (length 1632). The strict consensus for each of these reduced

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analyses is identical to that of the full data set (Supplementary Fig. S4). Permutations of the unordered analysis with restricted outgroup sampling yielded results congruent with the ordered analyses and will not be discussed here. Analysis of the ordered data set excluding the eight ―outgroup‖ taxa and rooted instead on the protosuchian Orthosuchus resulted in 32 MPTs (Fig. 3; length 1493). Importantly, thalattosuchians join a clade with other longirostrine crocodyliforms (dyrosaurids, pholidosaurs and Elosuchus). Protosuchia is no longer monophyletic (which it cannot be if the tree is rooted on a single protosuchian taxon), and much resolution is lost among notosuchians. Most other clades are retained. Internal relationships of Thalattosuchia are drastically different from the original analysis. Teleosaurids form a paraphyletic grade leading to Metriorhynchoidea. Steneosaurus remains paraphyletic, but Teleosaurus becomes the basal-most member of Thalattosuchia. Metriorhynchoid relationships are unchanged. Two additional steps are required to recover the thalattosuchian topology present in the full analysis (with teleosaurid monophyly and S. brevior + S. brevidens as the basal-most teleosaurids). The recovery of Thalattosuchia as part of the longirostrine clade reverses the polarity of two characters (41 and 304). Character 41 describes the orientation of the orbit. In all outgroup taxa (as well as basal crocodyliforms), the orbits are laterally oriented. The same is true of metriorhynchoids and of the basal-most teleosaurids (e.g., S. brevior). More derived teleosaurids (e.g., Teleosaurus), however, possess more dorsally directed orbits. When Thalattosuchia is a part of the longirostrine clade, dorsally directed orbits are optimized as the primitive state, with laterally directed orbits arising secondarily in metriorhynchoids and S. brevior. Character 304 describes the number of premaxillary teeth. When thalattosuchians are sister to Crocodyliformes,

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four premaxillary teeth are optimized as primitive for the clade, with an increase to five in Teleosaurus, and a decrease to three in some teleosaurids and in metriorhynchoids more derived than Pelagosaurus. However, when thalattosuchians join the longirostrine clade, five premaxillary teeth are optimized as primitive, drawing Teleosaurus to the base of the Thalattosuchia.

Comparative Matrices Reanalysis of the data matrix of Turner and Buckley (2008) resulted in 120 MPTs of length 1122 (Fig. 4a; CI = 0.320, RI = 0.706). Addition of Postosuchus to the matrix drastically alters the resulting topology (Fig. 4b). This analysis resulted in 16 trees of length 1157 (CI = 0.310, RI = 0.692). Thalattosuchians are recovered as the sister group to Crocodyliformes (an additional two steps are required to place them within Crocodyliformes). The exclusion of Thalattosuchia from Crocodyliformes is supported by thirteen unambiguous and five ambiguous synapomorphies (Table 1). Protosuchia becomes monophyletic including Fruitachampsa and Hsisosuchus. Notosuchian relationships remain largely unchanged, but the peirosaurids (including Mahajangasuchus) join Notosuchia. This result is very similar to the topology recovered by Turner and Sertich (2010). Relationships in the rest of the tree are largely identical. Analysis of the data set of Sereno and Larsson (2009) resulted in two MPTs of length 984 (Fig. 5a; CI = 0.34, RI = 0.66). This result differs slightly from that reported by Sereno and Larsson (2009). The difference in the number of MPTs is merely a result of the stricter collapsing rule employed here. However, the tree length is two steps shorter than in Sereno and Larsson (2009), and the relationships between Sphagesaurus, Notosuchus, and Malawisuchus are

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fully resolved. The cause of this discrepancy is unknown; however, the difference is minor and should not affect interpretations drawn from this study. Addition of Gracilisuchus and Postosuchus causes major topological changes (Fig. 5b). This analysis resulted in 12 MPTs (length = 1029; CI = 0.323, RI = 0.641). Thalattosuchia is again sister to Crocodyliformes, rather than within. One ambiguous and nineteen unambiguous synapomorphies support the exclusion of Thalattosuchia from Crocodyliformes (Table 1). An additional ten steps are required to place Thalattosuchia within Crocodyliformes. Another major change involves taxa normally allied with Notosuchia. Araripesuchus becomes polyphyletic and, with the clade formed by Uruguaysuchus, Simosuchus, and Anatosuchus, forms a paraphyletic grade leading to neosuchians.

DISCUSSION The analysis presented here (Fig. 2) recovers thalattosuchians as the sister group to Crocodyliformes. This result occurs in spite of relatively dense sampling of other longirostrine taxa (four pholidosaurs, three dyrosaurs, Elosuchus, Stolokrosuchus, and Gavialis). The effect of excluding other longirostrine taxa on the phylogenetic position of Thalattosuchia has been discussed by several authors (e.g., Buckley and Brochu 1999; Jouve et al. 2006; Jouve 2009; Pol and Gasparini 2009). When pholidosaurs and dyrosaurs were excluded from these analyses, thalattosuchians were recovered either as basal mesoeucrocodylians (when rooting on a protosuchian; Buckley and Brochu 1999), or sister to Crocodyliformes (when rooting on Gracilisuchus; Pol and Gasparini 2009). Thus, the results presented here are novel in recovering a basal position for thalattosuchians in spite of extensive longirostrine taxon sampling. The

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analysis of Young and Andrade (2009) also sampled numerous longirostrine taxa, including pholidosaurs, dyrosaurs, and thalattosuchians, but recovered thalattosuchians as basal mesoeucrocodylians rather than outside of Crocodyliformes. However, this analysis sampled only a single protosuchian, potentially obscuring character state optimizations at the base of the tree. The addition of Postosuchus to the outgroup acts to change the polarity of several character transformations in the phylogenetic matrices. Many of these character state changes are synapomorphies for Crocodyliformes that were previously optimized as reversals in thalattosuchians. Inclusion of Postosuchus also increased the number of character states that were scored for the root. For example, character 206 of Turner and Buckley (2008; cranial table width with respect to ventral portion of skull: as wide as ventral portion - 0); or narrower than ventral portion of skull - 1) was scored as unknown for all non-crocodyliform outgroups, leading to state 1 being reconstructed at the root. Addition of Postosuchus (scored for state 0), reconstructs state 0 as plesiomorphic. This state is shared with thalattosuchians, and makes a narrow skull table a synapomorphy of crocodyliforms (though the state is reversed in some protosuchians and Baurusuchus). Clark (in Benton and Clark, 1988) noted that thalattosuchians lack several crocodyliform synapomorphies, and suggested that thalattosuchians might be the sister group to crocodyliforms (though this topology was not among the most parsimonious). The plesiomorphic character states retained by thalattosuchians were reconstructed as secondary losses in topologies in which Thalattosuchia fell within Crocodyliformes. Resolving thalattosuchians as the sister group to crocodyliforms instead reconstructs the lack of these features as plesiomorphic, making several

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characters perfectly congruent (CI = 1). I shall discuss several of these characters that exclude thalattosuchians from Crocodyliformes. All crocodyliforms, exclusive of thalattosuchians, possess a relatively flat skull table (char. 24 of Turner and Buckley 2008), while no non-crocodyliform crocodylomorphs possess this morphology (though Almadasuchus comes close). Perhaps more importantly, characters relating to the relationship of the quadrate with the braincase and the presence of a prearticular bone are more congruently optimized when thalattosuchians are not members of Crocodyliformes. One major morphological feature distinguishing crocodyliforms from other crocodile-line archosaurs is the extensive reinforcement of the skull, with the jaw joint tightly articulated with the braincase (Clark 1994). This allows for expanded jaw musculature and the ability to resist torsion caused by struggling prey (Busbey 1995). This transformation appears to have occurred in mosaic fashion, with the quadrate gradually increasing in articulation with the braincase, beginning in derived ―sphenosuchian‖ crocodylomorphs (Pol et al. 2013). In all crocodyliforms, the quadrate is tightly sutured to the braincase, contacting the laterosphenoid (covering most of the prootic externally; char. 47 of Turner and Buckley 2008; char. 161 of Sereno and Larsson 2009). Such is not the case in thalattosuchians, where the quadrate is expanded onto the braincase, but is not directly sutured to the laterosphenoid, basisphenoid, or pterygoid (Holliday and Witmer 2009; Jouve 2009; Fernández et al. 2011). This leaves a broadly exposed prootic that forms much of the lateral surface of the braincase. When thalattosuchians form a clade with pholidosaurs and dyrosaurs, they are optimized as secondarily losing the tight articulation of the quadrate with the braincase; a scenario which seems unlikely from a functional

22

standpoint given that numerous members have been interpreted as large macrophagous predators (Young et al. 2012). Presence of the prearticular bone in the mandible predates Tetrapoda (present in Osteichthyes; Friedman and Brazeau 2010). Absence of a prearticular is an apomorphic feature of mesoeucrocodylians, but a prearticular is present in non-crocodyliform crocodylomorphs, protosuchians, and thalattosuchians. In topologies in which thalattosuchians are allied with longirostrine crocodyliforms, thalattosuchians are inferred to have re-evolved this feature. Loss of the feature is a synapomorphy for Mesoeucrocodylia in topologies where thalattosuchians are sister to crocodyliforms, or Metasuchia if thalattosuchians are basal mesoeucrocodyilans. Another potentially important feature involves the groove on the lateral surface of the squamosal for external ear valve musculature attachment (char. 56 of Sereno and Larsson). This feature is absent in non-crocodyliform crocodylomorphs (and thalattosuchians) with the possible exception of Kayentasuchus, but is present in all crocodyliforms. The ear valve acts to close the otic aperture while submerged and the absence of this feature in highly aquatic thalattosuchians seems counterintuitive (unless they evolved a different solution, or closed off the aperture completely as in cetaceans). However, other highly aquatic crocodyliforms such a dyrosaurids retain the insertion for this musculature. The presence of a squamosal groove in Kayentasuchus (the sister taxon to Thalattosuchia + Crocodyliformes), if truly homologous with that of crocodyliforms, renders ancestral state reconstruction ambiguous in this part of the tree. In spite of the numerous plesiomorphic features retained in thalattosuchians, they possess some features uniting them with other long-snouted crocodyliforms. Many of these characters have been hypothesized to be correlated with longirostry (Benton and Clark, 1988; Clark, 1994;

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Jouve et al., 2006; Pol and Gasparini, 2009). This issue was extensively discussed by Pol and Gasparini (2009), and they presented evidence demonstrating that many of these putative ―longirostrine characters‖ are incompatible with biological dependence (eight of the 12 investigated). Only the extensive participation of the splenial in the mandibular symphysis was optimized as an unambiguous synapomorphy for the longirostrine clade. However, exclusion of the four potentially non-independent characters in their data set did not change their topology and thalattosuchians and pholidosaurs/dyrosaurids remained a clade. Some of the other characters uniting thalattosuchians and pholidosaurs/dyrosaurids in the analysis of Pol and Gasparini (2009) may be misleading due to vagueness of character state descriptions failing to accurately reflect anatomy. The first step in character construction often involves the search for similarity in structures between taxa. However, in looking for this similarity, one should not resort to gross similarity in shape or size. When possible the systematist should refer to topological similarity, connectivity, and structural correspondence (Rieppel and Kearney 2002). As noted by Nesbitt (2011), characters describing the shape of complex structures formed by multiple bones can be problematic. Modifications to different bones could produce the same general shape. These character states would be scored the same, even though the architecture of the structure is anatomically different. For example, dyrosaurids and thalattosuchians share greatly enlarged supratemporal fenestrae (optimized as an ambiguous synapomorphy of the longirostrine clade in Pol and Gasparini 2009). But, in thalattosuchians the elongation of these fenestrae is caused primarily by posterior elongation of the postorbital bone, while in dyrosaurids, it is caused by anterior elongation of the squamosal (Fig. 6).

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An elongate ―tubular‖ rostrum is another such feature (char. 3 of Turner and Buckley, 2008; similar to char. 4 of Sereno and Larsson, 2009). The snout is a complex structure composed of several bones. While most thalattosuchians share a tube-shaped snout with pholidosaurs/dyrosaurids, the bones forming the snout are quite different. In thalattosuchians, the snout is composed of the maxillae and premaxillae, while in pholidosaurs and dyrosaurids, the nasals extend the length of the snout, forming the dorsal portion (Fig. 6). This major anatomical difference suggests these taxa should not be scored the same for this character, and that characters such as this might best be elaborated to include references to the individual bones forming the structure. Interpretation of the rostral form character is further clouded because this character is often treated as additive (e.g., Turner and Buckley 2008). However, it is unclear to this author how these character states (narrow oreinirostral [0], broad oreinirostral [1], nearly tubular [2], or platyrostral [3]) form a logical transformation series. Is ―platyrostral‖ really more similar to ―tubular‖ than to ―broad oreinirostral‖? Reanalysis of the Turner and Buckley matrix with character 3 set as unordered greatly reduces resolution in the strict consensus, but has no effect on the longirostrine clade. Another synapomorphy of the longirostrine clade is the transversely-flattened postorbital bar (char. 26 of Turner and Buckley 2008). However, construction of the postorbital bar differs radically between thalattosuchians and pholidosaurs/dyrosaurids. Thalattosuchians are unique among crocodylomorphs in that the postorbital is positioned lateral to the jugal along the postorbital bar. Ancestrally, the postorbital lies anterior to the jugal, but in all crocodyliforms, the postorbital lies medial to the jugal (with the exception of the phylogenetically enigmatic

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Hsisosuchus, where the ancestral state is retained). Thus, thalattosuchians and pholidosaurs/dyrosaurids should not be scored identically for this character. This character should only be scored for taxa in which the postorbital lies medial to the jugal. Thalattosuchians and taxa possessing a postorbital that lies anterior to the jugal should be coded as inapplicable. A further synapomorphy uniting longirostrine taxa could result from insufficient fossil material. Thalattosuchians and pholidosaurs/dyrosaurids were united in lacking a mastoid antrum that extends through the supraoccipital (char. 63 of Turner and Buckley 2008; char. 170 of Sereno and Larsson 2009). This character state has no obvious functional relation to the possession of a long snout and thus seems good evidence of shared ancestry. However, observation of this character in fossil taxa is often difficult, due to infilling by sediment or poor preservation. Its visibility relies on the availability of CT data, hemisected specimens, or specimens that are serendipitously broken to expose this passage. The lack of a continuous mastoid antrum is visible in exquisitely preserved acid prepared specimens of Pelagosaurus typus (pers. obs; NHMUK PV 32600; Clark 1986), as well as hemisected teleosauroid braincases (Fig. 7a; SMC J35177a; SMC J35177b; Seeley 1880). Recent CT scans of Metriorhynchus cf. westermani (Fernández et al. 2011), and the fractured braincase of the metriorhynchoid Zoneait nargorum (UOMNCH F39539; Wilberg 2015) also demonstrate a solid supraoccipital. Non-crocodyliform crocodylomorphs for which this character can be scored all possess a solid supraoccipital (Sphenosuchus acutus - Walker 1990; Kayentasuchus walkeri – Clark and Sues 2002; Junggarsuchus sloani – Clark et al. 2004). Wu and Chatterjee (1993) state that Dibothrosuchus elaphros possesses a mastoid antrum extending through the supraoccipital, but whether the pneumatic recesses actually connect is unobservable in the

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holotype (J. Clark, pers. com.). Thus, based on the phylogenetic hypothesis presented here, the presence of a continuous mastoid antrum is a synapomorphy of Crocodyliformes. If it is present in Dibothrosuchus this is the result of convergence. The state of this character in pholidosaurs/dyrosaurids has been somewhat uncertain. In the first cladistic matrices of Clark (Benton and Clark 1988; Clark 1994), Dyrosaurus and Pholidosaurus are coded as lacking a mastoid antrum that extends through the supraoccipital. These codings have persisted in most matrices based directly on the original work of Clark (e.g., Turner and Buckley 2008; Pol et al. 2009), and Sarcosuchus imperator and Terminonaris robusta have also been coded as lacking this feature. However, natural endocasts of the middle ear region and associated structures of Pholidosaurus meyeri (HMN R. 2066; Koken 1887) clearly demonstrate a fully connected and well-expanded mastoid antrum above the brain cavity (Fig. 7b, c). Unfortunately, these endocasts were attributed to Pholidosaurus on the sole basis that Pholidosaurus was the only known crocodylomorph from that stratigraphic level of the Hastings sandstone (D. Schwarz-Wings pers. comm.). Evidence for a continuous mastoid antrum in pholidosaurs would be greatly strengthened by CT scanning of pholidosaur braincase material, but this is beyond the scope of this study. The state in dyrosaurids is slightly more difficult to interpret. Dyrosaurids possess greatly expanded otic capsules, often so large that they actually meet at the midline, separating a dorsal and ventral portion of the brain cavity (Fig. 7d). This inflation forces the roof of the brain cavity to expand dorsally, narrowing the supraoccipital. Thus, it could be interpreted that the expanded otic capsules of dyrosaurids caused the closure of the transverse canal connecting the mastoid antra. However, a specimen of Rhabdognathus keinensis (CNRST-

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SUNY 277) shows a narrow tube extending through the supraoccipital in the dorsal roof of the braincase (Fig. 7d). This is interpreted as a narrowed, but continuous mastoid antrum connecting the middle ear regions. This interpretation is supported by the report of a similar diverticulum present in CT scans of Rhabdognathus aslerensis (CNRST-SUNY 190; Dufeau 2011). While I have no evidence to contradict previous codings for Sarcosuchus, Dyrosaurus, or Terminonaris, given the presence of a fully connected mastoid antrum in both Pholidosaurus and Rhabdognathus, two relatively distantly related taxa, it seems likely that pholidosaurs and dyrosaurs do possess a continuous mastoid antrum as in all other crocodyliform taxa for which this character can be scored. The character modifications suggested above may have a profound effect on the phylogenetic placement of Thalattosuchia, even in the absence of expanded outgroup sampling. To test this proposition, I recoded three characters in the matrix of Turner and Buckley (2008): characters 3 (rostrum proportions), 26 (postorbital bar shape), and 63 (mastoid antrum connectivity). The rostrum proportions character was rephrased based on the shape of the maxilla and topological relationships between the maxilla and adjacent bones as follows: 0: maxilla much taller than wide, lateral surface nearly vertical (―narrow oreinirostral‖); 1: maxilla much taller than broad, dorsal surface inclined towards midline (―broad oreinirostral‖); 2: maxilla width and height approximately equal, more than three times as long as tall, bordered medially by nasals (―nearly tubular‖ with maxillae not meeting at midline); 3: maxillae wider than tall, dorsomedial surface near horizontal (―platyrostral‖); 4: maxilla width and height approximately equal, more than three times as long as tall, maxillae meeting at midline (―nearly tubular‖ w/ abbreviated nasal contribution). In essence, this modification splits the original state 3 ―nearly

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tubular‖ to take into account the contribution of the nasals to the rostrum. All thalattosuchians (except the two species of Dakosaurus) were recoded as state 4, as was Gavialis.This character is here treated as unordered. Modification of character 26 (postorbital bar shape) involved the recoding of thalattosuchian taxa, Gracilisuchus, Terrestrisuchus, Dibothrosuchus, and Hsisosuchus as inapplicable (though, of course, current computer algorithms treat inapplicable data in the same fashion as missing data). Character 63 (continuity of mastoid antrum) was recoded as present in Rhabdognathus and Pholidosaurus based on evidence presented above. This feature was originally coded as absent for Sarcosuchus, Terminonaris, and Dyrosaurus and these codings were retained in the absence of contradictory evidence. The data set of Turner and Buckley (2008) was reanalyzed using the original matrix and search parameters, but with modification to the scoring of the three characters mentioned above (the modified taxon-characer matrix is available in the supplementary online materials). This search resulted in 2038 MPTs of length 1121. The strict consensus is largely unresolved (Fig. S5), but in some of the MPTs Thalattosuchia is recovered as the sister group to Crocodyliformes. These results demonstrate the importance of character formulation and scoring.

Secondary Palate Evolution Understanding of the evolutionary history of Crocodyliformes was traditionally based on development of the bony secondary palate through three evolutionary grades: ―Protosuchia‖, ―Mesosuchia‖, and Eusuchia (e.g., Langston 1973). Protosuchians have a modest secondary palate, with the internal choana bordered anteriorly by the maxillae. ―Mesosuchians‖ have a

29

more extensive palate, with the choana bordered anteriorly by the palatines, and eusuchians have an elaborate secondary palate with the internal choana enclosed entirely within the pterygoids. However, if thalattosuchians are the sister group to Crocodyliformes, this scenario is more complicated than it once seemed. Thalattosuchians possess a well-developed secondary palate of the ―mesosuchian‖ grade. Optimization of the palatal development character (char. 163) suggests that the ―mesosuchian‖ palate is primitive for Crocodyliformes, and an extensive secondary palate has been lost at least twice (Fig. 8). Other non-thalattosuchian taxa further complicate the evolution of this character. Zossuchus davidsoni and Fruitachampsa callisoni (protosuchians) possesses a palate with two choanal openings; the posterior (and presumably functional) opening is enclosed anteriorly by the palatines, as in ―mesosuchian‖-grade crocodyliforms, while the anterior is bordered anteriorly by the maxillae as in the ―protosuchian condition‖ (Pol and Norell 2004a; Clark 2011). North American goniopholidids (derived neosuchians) such as Eutretauranosuchus delfsi and Calsoyasuchus valliceps, share an internal choana that is anteroposteriorly elongate and bordered anteriorly by the maxillae (the ―protosuchian‖ condition; Pritchard et al. 2013). Evolution of the ―eusuchian condition‖ is also homoplastic. Mahajangasuchus insignis possesses an internal choana entirely enclosed by the pterygoids, but in a manner unlike that of eusuchians (Turner and Buckley 2008). Thus, the evolution of the secondary palate is much more complicated than once thought, likely involving multiple gains and/or losses.

CONCLUSIONS

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Previous studies have demonstrated the importance of taxon and character sampling to the issue of thalattosuchian relationships (e.g., Clark 1994; Buckley and Brochu 1999; Jouve et al. 2006; Jouve 2009; Pol and Gasparini 2009). This study is the first to demonstrate the great effect of outgroup sampling on the phylogenetic structure of Crocodylomorpha. The goal of phylogenetic analysis may be to recover structure within the ingroup (Maddison et al. 1984), but broad outgroup sampling acts as a test of ingroup monophyly. While there are no guarantees that a particular outgroup taxon or number of outgroups will yield the ―correct‖ ingroup topology (Nixon and Carpenter 1993) it seems prudent to sample numerous outgroup taxa, especially where large-scale relationships between clades remain an active question. Analyses of crocodyliform relationships should include outgroups sampled from closely related noncrocodyliform clades. If the relationships between these groups are not well known, the effects of outgroup sampling should be assessed by investigating changes to ingroup topology under different outgroup sampling schemes. This study also highlights issues related to character construction and state description. Existing crocodyliform character sets include only brief state descriptions and are rarely figured. Some of the included characters may treat homology at too superficial of a level (e.g. general shapes of complex, multipartite structures). These characters need to be reassessed and their states should be described in a higher level of detail. Future work should aim for more clarity in character descriptions as interpretations of these characters are central to the repeatability of phylogenetic analyses. Legitimate differences in interpretation of morphology exist, but many differences in character state coding in current published literature are likely due to ambiguity in character state descriptions.

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Overall, the phylogenetic results presented here are consistent with numerous previously published phylogenetic hypotheses (with the exception of the position of thalattosuchians). However, while support for several individual clades is high, the backbone of the tree demonstrating the relationships between these groups is only weakly supported. It is these nodes that are of the greatest interest when investigating large-scale patterns and timing of evolution in crocodylomorphs. Future efforts at resolving these issues should carefully consider both outgroup sampling and character construction.

SUPPLEMENTARY MATERIAL Data available from the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.00ss6

FUNDING Funding for this project was provided by the National Science Foundation (Doctoral Dissertation Improvement Grant DEB-1011097 to C. Brochu) and the University of Iowa Department of Geoscience.

ACKNOWLEGMENTS I thank C. Brochu, M. Spencer, J. Adrain and the University of Iowa Paleo. Group for discussion and thank J. Clark, M. Benton, A. Busbey, and an anonymous reviewer for helpful comments on an earlier draft of this manuscript. I also thank editors F. Anderson and N. MacLeod for constructive comments. I thank D. Schwarz-Wings for background concerning the pholidosaur endocasts. The phylogenetic analysis was performed in TNT v. 1.1, a program

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provided free of charge thanks to a subsidy from the Willi Hennig Society. I thank the following people for access to specimens: M. Carrano and D. Bohaska (USNM), B. Simpson (FMNH), C. Mehling and M. Norell (AMNH), L. Steel and S. Chapman (NHMUK), A. Henrici (CM), M. O‘Leary (SUNY Stony Brook), J. Cundiff and M. Lyons (MCZ), R. Allain (MNHN), P. Jeffery and D. Siveter (OUM), T. Tokaryk and M. Vovchuk (SMNH), X. Xu and F. Zheng (IVPP), O. Rauhut and M. Moser (BSPG), R. Schoch, R. Boettcher, and M. Rasser (SMNS), P. Havlik (GPIT), R. Hauff (UH), D. Schwarz-Wings (MNHB), A. Folie and A. Dréze (IRSNB).

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TABLE 1. Synapomorphies supporting the exclusion of Thalattosuchia from Crocodyliformes. Characters indicated in bold have a CI = 1.0. Character state transformations indicated with an asterisk support this topology only under ACCTRAN optimization; transformations indicated with a ―^‖ support this topology only under DELTRAN optimization. All other synapomorphies are unambiguous. Analysis

Synapomorphies 1 (01), 53 (01), 56 (01); 61 (10), 62 (02), 77 (01), 83 (10), 88^ (10); 123 (10), 131 (01),

This analysis:

132* (10); 195* (01); 199 (01), 204 (01), 205 (21), 218* (01); 219 (01), 220 (01), 222*

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(01); 230* (01); 256 (01), 258 (01), 260* (20); 287* (10); 290 (01), 311 (01), 355 (10), 363^ (01); 364 (01) 24 (01), 30 (01), 33 (10), 36 (02), 47 (01), 49 (12), 63^ (01); 68 (01), 79^ (01); 84* (01); Turner and Buckley 2008:

94* (01); 99 (01), 117 (01), 145 (01), 150 (01); 165* (10); 206 (01), 252 (01) 18* (01), 37 (01), 39 (01), 48 (01), 54 (01), 55 (01), 56 (01), 69 (01), 73 (01), 78 (01),

Sereno and Larsson 2009:

100 (01), 138 (10), 154 (01), 160 (01), 161 (01), 170 (01), 207 (01), 230 (02 or 12), 244 (01), 252 (12)

FIGURE CAPTIONS FIGURE 1. Generalized phylogeny of Crocodylomorpha showing the three potential positions of Thalattosuchia. a) Sister group to Crocodyliformes; b) basal mesoeucrocodyilans; c) Derived neosuchians, allied with pholidosaurs/dyrosaurids to form a ―longirostrine clade‖. FIGURE 2. Strict consensus of 42 MPTs of length 1691 (CI = 0.306, RI = 0.710). Values above nodes represent GC jackknife support scores. Thalattosuchia is highlighted in gray.

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FIGURE 3. Strict consensus of 32 MPTs of length 1493 when outgroup taxa are excluded and the tree is rooted on Orthosuchus stormbergi (ordered analysis). Thalattosuchians are highlighted in gray. FIGURE 4. Trees resulting from the reanalysis of the matrix of Turner and Buckley (2008). a) Original analysis: strict consensus of 120 MPTs of length 1222 (CI = 0.320, RI = 0.706); b) Modified analysis including Postosuchus: Strict consensus of 16 MPTs of length 1157 (CI = 0.310, RI = 0.692). Thalattosuchians are highlighted in gray. FIGURE 5. Trees resulting from the reanalysis of the matrix of Sereno and Larsson (2009). a) Original analysis: strict consensus of two MPTs of length 984 (CI = 0.340, RI = 0.660); b) Modified analysis including Gracilisuchus and Postosuchus: strict consensus of 12 MPTs of length 1029 (CI = 0.323, RI = 0.641). Thalattosuchian taxa are highlighted in gray. FIGURE 6. Dorsal surface of two crocodylomorph skulls illustrating anatomical differences of similarly shaped and identically coded character states. a) A thalattosuchian Peipehsuchus teleorhinus; b) A dyrosaurid - Dyrosaurus maghribensis (redrawn from Jouve et al. 2006). Nasal bones demonstrating their different contribution to the ―tubular‖ snout; Squamosals showing their differential contribution to the elongation of the supratemporal fenestra. Anatomical abbreviations: na, nasal; sq, squamosal.

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FIGURE 7. Specimen photographs demonstrating continuity or discontinuity of the mastoid antra. a) A hemisected teleosaurid braincase (―Teleosaurus macrocephalus‖; SMC J35177a) with a solid supraoccipital. b, c) natural endocast of the ear canal region from Pholidosaurus meyeri (HMN R. 2066) in anterior (b) and dorsal (c) views showing a large and fully connected mastoid antrum. d) partial braincase of Rhabdognathus keinensis (CNRST-SUNY 277) showing the greatly enlarged otic capsules and a narrow, but continuous tube through the supraoccipital here interpreted as the transverse passage of the mastoid antra. Anatomical abbreviations: dvs, dorsal venous sinus; fm, foramen magnum; icc, internal carotid canal; ma, mastoid antrum; mec, middle ear canal; oc, occipital condyle; otc, otic capsules; pf, pituitary fossa; scc, semicircular canals; so, supraoccipital. FIGURE 8. Strict consensus tree showing ACCTRAN optimization of the secondary palate character. Taxa highlighted in gray possess a secondary palate constructed differently from other taxa possessing the same bones forming the anterior border of the choana. It should be noted that while both ―sphenosuchians‖ and protosuchians possess an internal choana bordered anteriorly by the maxillae, the secondary palate is more extensive among protosuchians.

Generalized phylogeny of Crocodylomorpha showing the three potential positions of Thalattosuchia. a) Sister group to Crocodyliformes; b) basal mesoeucrocodyilans; c) Derived neosuchians, allied with pholidosaurs/dyrosaurids to form a “longirostrine clade”. 196x152mm (300 x 300 DPI)

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Strict consensus of 42 MPTs of length 1691 (CI = 0.306, RI = 0.710). Values above nodes represent GC jackknife support scores. Thalattosuchia is highlighted in gray. 274x467mm (300 x 300 DPI)

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Strict consensus of 32 MPTs of length 1493 when outgroup taxa are excluded and the tree is rooted on Orthosuchus stormbergi (ordered analysis). Thalattosuchians are highlighted in gray. 258x353mm (300 x 300 DPI)

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Trees resulting from the reanalysis of the matrix of Turner and Buckley (2008). a) Original analysis: strict consensus of 120 MPTs of length 1222 (CI = 0.320, RI = 0.706); b) Modified analysis including Postosuchus: Strict consensus of 16 MPTs of length 1157 (CI = 0.310, RI = 0.692). Thalattosuchians are highlighted in gray. 182x154mm (300 x 300 DPI)

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Trees resulting from the reanalysis of the matrix of Sereno and Larsson (2009). A) Original analysis: strict consensus of two MPTs of length 984 (CI = 0.340, RI = 0.660); B.) Modified analysis including Gracilisuchus and Postosuchus: strict consensus of 12 MPTs of length 1029 (CI = 0.323, RI = 0.641). Thalattosuchian taxa are highlighted in gray. 161x95mm (300 x 300 DPI)

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Dorsal surface of two crocodylomorph skulls illustrating anatomical differences of similarly shaped and identically coded character states. a) A thalattosuchian - Peipehsuchus teleorhinus; b) A dyrosaurid Dyrosaurus maghribensis (redrawn from Jouve et al. 2006). Nasal bones demonstrating their different contribution to the “tubular” snout; Squamosals showing their differential contribution to the elongation of the supratemporal fenestra. Anatomical abbreviations: na, nasal; sq, squamosal. 211x315mm (300 x 300 DPI)

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Specimen photographs demonstrating continuity or discontinuity of the mastoid antra. a) A hemisected teleosaurid braincase (“Teleosaurus macrocephalus”; SMC J35177a) with a solid supraoccipital. b, c) natural endocast of the ear canal region from Pholidosaurus meyeri (MNHB MB.R. 2066) in anterior (b) and dorsal (c) views showing a large and fully connected mastoid antrum. d) partial braincase of Rhabdognathus keinensis (CNRST-SUNY 277) showing the greatly enlarged otic capsules and a narrow, but continuous tube through the supraoccipital here interpreted as the transverse passage of the mastoid antra. Anatomical abbreviations: dvs, dorsal venous sinus; fm, foramen magnum; icc, internal carotid canal; ma, mastoid antrum; mec, middle ear canal; oc, occipital condyle; otc, otic capsules; pf, pituitary fossa; scc, semicircular canals; so, supraoccipital. 393x841mm (300 x 300 DPI)

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Strict consensus tree showing ACCTRAN optimization of the secondary palate character. Taxa highlighted in gray possess a secondary palate constructed differently from other taxa possessing the same bones forming the anterior border of the choana. It should be noted that while both “sphenosuchians” and protosuchians possess an internal choana bordered anteriorly by the maxillae, the secondary palate is more extensive among protosuchians. 212x312mm (300 x 300 DPI)

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