Palaeobiodiversity of crocodylomorphs from the Lourinhã Formation based on the tooth record: insights into the palaeoecology of the Late Jurassic of Portugal

Abstract

Crocodylomorphs were a diverse clade in the Late Jurassic of Portugal, with six taxa reported to date. Here we describe 126 isolated teeth recovered by screen-washing of sediments from Valmitão (Lourinhã, Portugal, late Kimmeridgian–Tithonian), a vertebrate microfossil assemblage in which at least five distinct crocodylomorph taxa are represented. Ten morphotypes are described and attributed to five clades (Lusitanisuchus, Atoposauridae, Goniopholididae, Bernissartiidae and an undetermined mesoeucrocodylian). Four different ecomorphotypes are here proposed according to ecological niches and feeding behaviours: these correspond to a diet based on arthropods and small vertebrates (Lusitanisuchus and Atoposauridae), a generalist diet (Goniopholididae), a durophagous diet (Bernissartiidae) and a carnivorous diet. Lusitanisuchus mitracostatus material from Guimarota is here redescribed to achieve a better illustration and comparison with the new material. This assemblage shares similar ecomorphotypes with other Mesozoic west-central European localities, where a diversity of crocodylomorphs lived together, avoiding direct ecological competition through niche partitioning. The absence of large marine crocodylomorphs, present in other contemporaneous assemblages, is here interpreted as evidence that the Valmitão assemblage was deposited in a freshwater environment, although sample bias cannot be completely ruled out. These affinities are further supported by the presence of lanceolate and leaf-shaped teeth associated with continental clades.

New dinosaur, crocodylomorph and swim tracks from the Late Jurassic of the Lusitanian Basin: implications for ichnodiversity

“…Analysis of the osteological record reveals that crocodylomorphs were diverse in the Late Jurassic ecosystems of the Lusitanian Basin, with six different taxa reported so far (Krebs & Schwarz 2000; Puértolas‐Pascual & Mateus 2020; Guillaume et al 2020). The latter authors recently reported five different clades ( Lusitanisuchus , Atoposauridae, Goniopholididae, Bernissartiidae and an undetermined mesoeucrocodylian) in the same formation (Praia da Amoreira‐Porto Novo Fm.)…”

“…Finally, the palaeoecology of both groups should be analysed. Many of the crocodylomorphs identified in the formation are freshwater crocodylomorphs that would have been well adapted to an aquatic lifestyle (Guillaume et al 2020; Wilberg et al 2020). By contrast, although pterosaurs lived close to marine and freshwater habitats, there are doubts about how they could have produced the traces since they would have been partially constrained to remain at the surface of the water (Hone & Henderson 2014).…”

“…Dinosaurs from different groups have been identified throughout the basin, including theropods (Malafaia et al 2017a), ornithopods (Rotatori et al 2020), sauropods (Mocho et al 2017) and thyreophorans (Costa and Mateus 2019). The crocodylomorph record has recently been shown to be remarkably rich, with at least six taxa reported (Guillaume et al 2020). This high diversity is particularly notable in comparison with the rather low ichnodiversity identified so far.…”

Testing the Usefulness of the Surface Collecting Method in a Vertebrate Microfossil Site from the Barremian of Spain (Los Menires, Mirambel Formation)

“…Teeth attributed to atoposaurids had crowns with mesial and distal carinae and were ornamented with apicobasal ridges. These also showed a wide morphological variability comprising conical, lanceolate, and broad leaf-shaped crowns in relation to the position in the dental arcade (e.g., [35,36]). Osteichthyans are scarce, but remains have been identified in addition to scales, such as some lanceolated teeth with smooth carinae belonging to Amiiformes indet.…”

Introducing the First European Symposium on the Evolution of Crocodylomorpha

“…This study not only addresses the palaeobiodiversity of the Lourinhã crocodylomorph fauna, but also explores their ecological relationships. Based on the different dental morphologies, four distinct feeding behaviours (durophagous, "insectivorous", hypercarnivorous and generalist) are hypothesized (Guillaume et al, 2020).…”