Data from: Morphology, fossils, divergence timing, and the phylogenetic relationships of Gavialis

Although morphological data have historically favored a basal position for the Indian gharial (Gavialis gangeticus) within Crocodylia and a Mesozoic divergence between Gavialis and all other crocodylians, several recent molecular data sets have argued for a sister-group relationship between Gavialis and the Indonesian false gharial (Tomistoma schlegelii) and a divergence between them no earlier than the Late Tertiary. Fossils were added to a matrix of 164 discrete morphological characters and subjected to parsimony analysis. When morphology was analyzed alone, Gavialis was the sister taxon of all other extant crocodylians whether or not fossil ingroup taxa were included, and a sister-group relationship between Gavialis and Tomistoma was significantly less parsimonious. In combination with published sequence and restriction site fragment data, Gavialis was the sister taxon of all other living crocodylians, but the position of Tomistoma depended on the inclusion of fossil ingroup taxa; with or without fossils, preferred morphological and molecular topologies were not significantly different. Fossils closer to Gavialis than to Tomistoma can be recognized in the Late Cretaceous, and fossil relatives of Tomistoma are known from the basal Eocene, strongly indicating a divergence long before the Late Tertiary. Comparison of minimum divergence time from the fossil record with different measures of molecular distance indicates evolutionary rate heterogeneity within Crocodylia. Fossils strongly contradict a post-Oligocene divergence between Gavialis and any other living crocodylian, but the phylogenetic placement of Gavialis is best viewed as unresolved.

尽管形态学数据历来支持印度食鱼鳄（Gavialis gangeticus）在鳄目（Crocodylia）中处于基部分支的位置，且认为食鱼鳄属（Gavialis）与其他所有鳄类的分化发生在中生代，但近期多项分子数据集却提出，食鱼鳄属与印尼假食鱼鳄（Tomistoma schlegelii）构成姐妹群关系，二者的分化时间不早于晚第三纪。研究将化石加入包含164个离散形态性状的性状矩阵，并进行简约性分析。当仅单独分析形态学数据时，无论是否纳入内群化石类群，食鱼鳄均为其他所有现生鳄类的姐妹群；而食鱼鳄与印尼假食鱼鳄构成姐妹群的假说，其简约性得分显著更低。当结合已发表的序列数据与限制性酶切位点片段数据进行分析时，食鱼鳄仍是其他所有现生鳄类的姐妹群，但印尼假食鱼鳄的系统发育位置则取决于内群化石类群是否被纳入；无论是否纳入化石，最优形态学拓扑结构与分子拓扑结构均无显著差异。晚白垩世地层中已发现亲缘关系更接近食鱼鳄而非印尼假食鱼鳄的化石，而印尼假食鱼鳄的化石近亲则见于始新世早期地层，这强烈表明二者的分化远早于晚第三纪。将化石记录给出的最小分化时间与不同分子距离测度进行对比，结果显示鳄目类群存在进化速率异质性。化石证据强烈驳斥了“食鱼鳄与其他任何现生鳄类的分化发生在渐新世之后”的假说，但食鱼鳄的系统发育位置目前仍未被明确解析。