552


THOMAS L. STUBBS AND MICHAEL J. BENTON Stratigraphic assignments were based on the


primary literature, previous compendia of marine reptile diversity, and the Paleobiology Database (paleodb.org) (Benson et al. 2010; Young et al. 2010; Benton et al. 2013; Kelley et al. 2014). Species-level stratigraphic assignments were used in most cases, but in the disparity analyses there were a number of instances in which species could not be sampled in a time bin due to inadequately preserved material. In these cases, the stratigraphic range of a representative taxon belonging to the same genus was extended to account for that taxon’s absence (Supplemen- tary Data). There were two instances in which taxa could not have their absence accounted for by amember of the same genus, both of them in the Norian time bin. Because it is important to represent all forms at a given time, we decided to represent their ecomorphological characteristics with a closely related species; we used Psephochelys polyosteoderma to represent the placodont species Psephoderma alpinum (and placodonts in general), and we used Guanlingsaurus liangae to represent the large edentulous ichthyosaur Shonisaurus sikanniensis. Disparity Sensitivity Analyses.—To scrutinize


temporal trends of marine reptile disparity we performed sensitivity tests using alternative protocols and data subsets. First, disparity was recalculated based onwithin-binmean pairwise dissimilarity fromthe originalGower intertaxon distance matrix for all 206 taxa (without PCOa ordination; e.g., Close et al. 2015). Second, disparity analyses were undertaken based solely on the nine continuous functional metrics (C1–C9) measured across all taxa, to ensure that the calculated trajectory of marine reptile disparity through time was not simply the result of overwhelming dominance from binary characters. The ichthyosaur Thalattoarchon was removed, because it could not be scored for enough continuous characters. Because size can dominate data sets based on linear measurements and ratios, additional tests were run on eight continuous variables minus the character total mandibular length (C9). For both cases, the z-transformed continuous characters were converted into a variance-covariance matrix and subjected to principal components analysis (PCA) to derive multivariate ordination axes and the


corresponding PC scores for all 205 taxa. Missing values were accounted for using iterative imputation with 10,000 bootstrap replicates (Ilin and Raiko 2010). Seven ordination axes were retained from the nine- character analysis (accounting for 98.9% of variance), and six axes were retained from the analysis with size removed (accounting for 98.7% variance). Following the protocol discussed above, disparity based on the sum of variances and sum of ranges was calculated in the 16Mesozoic time intervals. Skull-Size Trends.—To complement the


disparity analyses, we also examined patterns of skull-size evolution in all Mesozoic marine reptiles. Skull size represents an ecomorpho- logical characteristic that can be compared broadly across all marine reptile clades and used to identify patterns of phenotypic diversity. In 354 marine reptile species, maximum skull length (MSL) was measured from the anterior tip of the premaxilla to the posterior margin of the squamosal. Data were collected during museum visits and from published tables and figures (Supplementary Data). For incomplete specimens, MSL was estimated based on cranial proportions of closely related species or total mandible length (required for <5% of taxa). Juvenile specimens, identified based on discussions in the literature, were not included in the data set. Temporal trends of skull-size evolution were explored by plotting log10-transformed MSL against geological time based on the stratigraphic range midpoints of all species. Univariate disparity, based on the range and interquartile range, was examined in the same time bins as the multivariate disparity analyses. Comparative Disparity and Diversity


Analyses.—To test whether all marine reptile clades have similar trajectories of disparity through time, we compared the temporal disparity profiles of sauropterygians, eosauro- pterygians, ichthyosauromorphs, thalatto- suchians, and mosasauroids. These analyses were based on subsets of the primary data set (both continuous and binary characters). Some characters became redundant in the individual analyses and were removed, and the data subsets were then separately z-transformed


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192