A new Late Cretaceous snake from Patagonia: Phylogeny and trends in body size evolution of madtsoiid snakes

A new madtsoiid snake from the Paleogene of South America (northwestern Argentina), based on an articulated postcranial skeleton

“…In order to assess the position of the new taxon among snakes and its affinities with Madtsoiidae, it was included in the data matrix from Gómez et al (2019), with the addition of a few scoring changes and a new character: the absence/presence of distinct fossae on the dorsolateral surface of the neural arch (Supplemental Data). The character scorings of the new taxon were based only on anatomical information observed on the available blocks.…”

“…The character scorings of the new taxon were based only on anatomical information observed on the available blocks. The resulting matrix of 265 characters and 55 taxa was analyzed by maximum parsimony in TNT v.1.5-beta (Goloboff and Catalano, 2016), following the same procedures as in Gómez et al (2019) for tree search. The analysis was performed under equal weight and consisted of 500 tree replicates obtained by random addition sequence (RAS), searching for new tree topologies with tree bisection and reconnection (TBR), saving 100 trees per replication and collapsing branches of zero length after tree search.…”

“…A final round of TBR branch swapping was performed to the trees obtained, and the outgroup Varanus was used for rooting the optimal topologies. Most characters were treated as unordered during tree search, except a few multi-state characters based on continuous data (Supplemental Data), which were treated as ordered following Gómez et al (2019). Node support was calculated by the Bremer index and under absolute frequencies by jackknifing (p = 0.36, 1000 pseudo-replicates).…”

“…Madtsoiidae are an extinct group of snakes known from the Late Cretaceous to the Late Pleistocene (LaDuke et al, 2010;Rage et al, 2014). Their monophyly and placement among snakes are highly debated, but many recent phylogenetic analyses have retrieved madtsoiids as an early diverging lineage of snakes outside crown group Serpentes, indicating their importance for understanding the early evolution of the group (e.g., Caldwell et al, 2015;Garberoglio et al, 2019aGarberoglio et al, , 2019bGómez et al, 2019;Fachini et al, 2020). Alternatively, other recent hypotheses have placed madtsoiids inside crown group Serpentes, either as an early radiation of non-alethinophidian snakes (e.g., Longrich et al, 2012;Hsiang et al, 2015;Harrington and Reeder, 2017;Zaher et al, 2022) or more deeply nested within Alethinophidia (e.g., Wilson et al, 2010;Zaher and Scanferla, 2012).…”

“…Taxa considered to be small-sized, i.e., less than 2 meters in estimated length, include Alamitophis argentinus, Alamitophis elongatus, and Patagoniophis parvus (Albino, 1986(Albino, , 1994(Albino, , 2000(Albino, , 2007. Rionegrophis madtsoioides (Albino, 1986(Albino, , 2007, with an estimated length between 2 and 4 meters, represents a mid-sized form, and Eomadtsoia ragei, with an estimated length surpassing 4 meters is considered a large-sized form (Gómez et al, 2019). In contrast, South American Cenozoic records are less diverse and only represented by the mid-to-large form Madtsoia (Simpson, 1933;Albino, 1993;Albino and Brizuela, 2014;Rage, 1998).…”