Redescription and phylogenetic affinities of the caimanine Eocaiman cavernensis (Crocodylia, Alligatoroidea) from the Eocene of Argentina

Abstract

A T present, six extant species of Caimaninae are distributed within the genera Caiman, Melanosuchus and Paleosuchus. These are found mostly in South and Central America (the only exception is Caiman crocodilus, the distribution of which extends as far north as southern Mexico; Thorbjarnarson 1992; Brochu 1999, Grigg & Kirshner 2015. Phylogenetically, Caimaninae is defined as the group that includes C. crocodilus and all crocodylians closer to it than to Alligator mississippiensis (Brochu 1999(Brochu , 2003. It belongs to Alligatoroidea, one of the three main lineages of the crown-group Crocodylia, together with Crocodyloidea and Gavialoidea (Brochu 1999(Brochu , 2003.Within Alligatoroidea, the sister group of Caimanine is Alligatorinae, which is currently represented by only two extant species: A. mississippiensis of North America and A. sinensis from China (Grigg & Kirshner 2015). Nevertheless, compared with Caimaninae, the fossil record of Alligatorinae has been historically regarded as much richer (Brochu 2010), with a more widespread geographic distribution and several species documented for the Cenozoic (Brochu 1999(Brochu , 2003 Whiting et al. 2016).In the twenty-first century, however, new discoveries have revealed a higher diversity of Caimanine during the Cenozoic, especially in South America, but also with

Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem

“…Notably, the clade consisting of Caiman crocodilus + (Tsoabichi greenriverensis + (Paleosuchus trigonatus + Paleosuchus palpebrosus)) is deeply nested within Jacarea, and sister to a polytomous clade of stratigraphically early caimanines, comprising Protocaiman peligrensis, Necrosuchus ionensis, and Bottosaurus harlani. The placement of this latter trio of taxa within Caimaninae is consistent with recent analyses, including evidence for a deeply nested position for both Bottosaurus and Necrouchus (Brochu, 2011;Bona et al, 2018;Cossette & Brochu, 2018;Cidade, Fortier & Hsiou, 2020;Cossette, 2021;Godoy et al, 2020).…”

“…Several studies have also turned to combined morphological and molecular analyses to resolve the gharial problem, and these typically recover the molecular topology (Poe, 1997;Gatesy et al, 2003;Gold, Brochu & Norell, 2014;Lee & Yates, 2018;Iijima & Kobayashi, 2019;Hekkala et al, 2021). However, the results of combined analyses depend strongly on the proportions of different data types (e.g.…”

“…Poe, 1997;Brochu, 1997b), and might simply reflect the data with the strongest signal (Brochu, 2003). Furthermore, combined analyses including fossil taxa continue to face the issue of temporal incongruence, given that the earliest appearing, latest Cretaceous gavialoids are still recovered within the crown gharial clade (Gatesy et al, 2003;Gold, Brochu & Norell, 2014;Iijima & Kobayashi, 2019). Lee & Yates (2018) introduced stratigraphic data (Bayesian tipdating) into combined analyses, which resolved both the topological and temporal incongruence.…”

“…reductive coding) and the use of different character weighting strategies (Groh et al, 2020;Nicholl et al, 2020;Rio et al, 2020;Ristevski et al, 2020Ristevski et al, , 2021; see also Johnson, Young & Brusatte, 2020). Furthermore, there have been relatively few attempts to introduce novel sources of data into phylogenetic analyses of Crocodylia, such as morphometric data (Gold, Brochu & Norell, 2014;Bona et al, 2018) and continuous characters (Groh et al, 2020).…”

“…Whereas most previous analyses have recovered Borealosuchus in the stem of Brevirostres (Alligatoroidea + Crocodyloidea) (Brochu, 1997a(Brochu, , 2004aHua & Jouve, 2004;Brochu, 2006;Jouve et al, 2015;Narváez et al, 2015Narváez et al, , 2016Salas-Gismondi et al, 2016;Groh et al, 2020), others recover Borealosuchus as either the sister taxon to Gavialoidea (Salisbury et al, 2006;Pol, Turner & Norell, 2009;Martin, 2010a;Puértolas-Pascual, Canudo & Cruzado-Caballero, 2011), or in a polytomy with Gavialoidea and Brevirostres (Brochu, 2012;Hastings, Reisser & Scheyer, 2016). In Analysis 1.3 (and indeed all analyses except 2.1 and 3.1), Borealosuchus is the sister taxon to Crocodylia, similar to the results of Gatesy et al (2003) and Gold, Brochu & Norell (2014). This result is weakly supported in Jackknife (50) and Bootstrap (36) replicates, with Bremer support of 4.7.…”