692


ANTOINE VERRIÈRE ET AL.


the contemporary procolophonoids (Fig. 6), which are small, lizard-like animals. Body-size effects on preservation have previously been observed in other groups (Brocklehurst et al. 2012), but here the context is different. First, and as mentioned above, the fossil record of parareptiles does not include any apparent Lagerstätten, which would have increased the number of well-preserved small animals.While it might seem intuitive that large and robust skeletons are less likely to be destroyed than smaller ones, this study and others (e.g., Fara and Benton 2000; Brocklehurst et al. 2012; Cleary et al. 2015) indicate the relationship may not be so simple. Methodological Implementations.—Anumberof


different implementations of the CCM have been used in the various studies on diverse clades.Here,weexamine the impact of using the different CCM methods on our interpretations of the fossil record. The comparison of the different completeness metrics highlights some general issues.First,itappears thatthe CCMa results can be distorted by the fact that this method does not take into account the state of preservation of the individual bones. With the CCMa, each bone receives a percentage completeness score corresponding to the number of characters that refer to it. But it is assumed that, if a bone is present, every character can be scored on this bone. As the characters generally refer to detailed anatomical structures, and not to the entire element, a particular aspect of morphology may not necessarily have been preserved even if the bonewas. The CCMa does not take into account the fact that a bone may be preserved, but not in such a way that allows all characters to be scored. Because of this, it could be argued that the CCMa tends to overestimate specimen completeness. There is another consequence resulting


from the way the combined character list is constructed. Some of the characters in the list may refer to bones that are present in some clades but not others. For such a group, the completeness is biased toward lower values: highly complete specimens may receive a lower score, since a bone they never possessed will be marked as missing. The importance of this effect obviously depends on the


percentage of completeness attributed to the absent bone. In this study, osteoderms are a good example of this phenomenon. Among parareptiles, only pareiasaurs have osteo- derms, but these structures represent 2.8% of the CCMa score. The groups that do not have osteoderms will therefore have a maximum completeness of 97.2%. The more characters are referring to such elements and the more complete the specimen, the greater the under- estimation of completeness. This effect is insignificant in this study due to the small percentage of characters relating to osteoderms. But in other groups or in the case of sexual dimorphism, it may be an issue and should be considered in future studies where this is applicable. The CCMb, meanwhile, is more prone to


underestimate completeness. In the phyloge- netic matrices, especially in those including a great variety of taxa, some characters refer to structures that may not be naturally present in every clade and will be scored as question marks, as if that portion of the anatomy were missing. This therefore increases the number of unscored characters and decreases the completeness. However, the results of the correlation tests (Table 2) and of the agreement coefficient (Fig. 4) indicate that the two CCM methods are measuring the same signal. Moreover, despite the fact that CCMa should overestimate completeness while CCMb underestimates it, CCMa is not consistently higher thanCCMb(Figs. 3, 5).Wecan therefore conclude that the different issues highlighted above are not significantly affecting the results. Ultimately, the most accurate method, the


one that has the least biases, is the SCM. Indeed, the only source of imprecision is the resolution of the geometric models. But although reliable, this method suffers from being relatively time-consuming to implement. Particularly, the construction of the individual skeletal models requires access to multiple specimens or accurate descriptions for relevant measurements to be made. The choice is therefore to be precise by using thosemodels or to be fast by employing subjective values, as initially proposed by Mannion and Upchurch (2010). Interestingly, Cleary et al. (2015) showed in their study on ichthyosaurs that


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