The ecological diversification and evolution of Teleosauroidea (Crocodylomorpha, Thalattosuchia), with insights into their mandibular biomechanics

Abstract

Throughout the Jurassic, a plethora of marine reptiles dominated ocean waters, including ichthyosaurs, plesiosaurs and thalattosuchian crocodylomorphs. These Jurassic ecosystems were characterized by high niche partitioning and spatial variation in dietary ecology. However, while the ecological diversity of many marine reptile lineages is well known, the overall ecological diversification of Teleosauroidea (one of the two major groups within thalattosuchian crocodylomorphs) has never been explored. Teleosauroids were previously deemed to have a morphologically conservative body plan; however, they were in actuality morphofunctionally more diverse than previously thought. Here we investigate the ecology and feeding specializations of teleosauroids, using morphological and functional cranio‐dental characteristics. We assembled the most comprehensive dataset to date of teleosauroid taxa (approximately 20 species) and ran a series of principal component analyses (PC) to categorize them into various feeding ecomorphotypes based on 17 dental characteristics (38 specimens) and 16 functionally significant mandibular characters (18 specimens). The results were examined in conjunction with a comprehensive thalattosuchian phylogeny (153 taxa and 502 characters) to evaluate macroevolutionary patterns and significant ecological shifts. Machimosaurids display a well‐developed ecological shift from: (1) slender, pointed tooth apices and an elongate gracile mandible; to (2) more robust, pointed teeth with a slightly deeper mandible; and finally, (3) rounded teeth and a deep‐set, shortened mandible with enlarged musculature. Overall, there is limited mandibular functional variability in teleosaurids and machimosaurids, despite differing cranial morphologies and habitat preferences in certain taxa. This suggests a narrow feeding ecological divide between teleosaurids and machimosaurids. Resource partitioning was primarily related to snout and skull length as well as habitat; only twice did teleosauroids manage to make a major evolutionary leap to feed distinctly differently, with only the derived machimosaurines successfully radiating into new feeding ecologies.

Shark mandible evolution reveals patterns of trophic and habitat-mediated diversification

“…S13 ). This pattern is consistent with other studies of jaw shape variation in vertebrates, in which MA appears consistently as one of the most important functional variables 30 , 56 , 57 , 59 . This reflects a trade-off between jaws with high bite force but slow closing versus jaws with low bite force but rapid closing.…”

“…Mandible shape variation in sharks can be explained in terms of functional interpretations of the major shape differences. This helps validate assumptions that studies of shape variation in jaw structure can provide reasonable proxies for primary feeding ecology, as is commonly done in palaeobiological and macroecological studies 30 , 56 – 59 . The jaw-closing mechanical advantage (in-lever length/out-lever length) (hereafter “MA”) correlates strongly with PC1 scores ( R = 0.89, p < 0.001; Supplementary Fig.…”

Comparative functional morphology indicates niche partitioning among sympatric marine reptiles

“…-Proexochokefalos heberti, the only large-bodied teleosauroid in the Pierce II Guild, clusters together with Machimosaurini of the Crunch Guild (see §4). This result was extensively discussed by Foffa et al [5] and in detail by Johnson et al [27], who showed that tooth specialization in Machimsaurini lagged behind mandibular adaptations linked to consuming large-bodied prey items. Similarly, we notice that geosaurines of the GDP-clade evolved their morphofunctional complex in advance of the dental adaptations that place them in the Cut guild.…”

“…In other words, it may be possible to derive ecologically informative patterns from analysing the size, shape and mechanical performance of marine reptile lower jaws through time. The macroevolutionary trajectories of plesiosaurs, ichthyosaurs and thalattosuchians have all been individually investigated [18,19,[22][23][24][25][26][27][28][29], but rarely are there comparisons across sympatric clades and within the same assemblage. This unexplored gap prevents us from understanding whether different groups converged upon analogous solutions under similar ecological/selection pressures and from investigating broad ecological phenomena (i.e.…”

Limited convergence in the postcranium of aquatic Crocodylomorpha

“…2019a), to semiaquatic and semiterrestrial (Johnson et al . 2022) respectively. Although relatively more elongated, the humerus of Platysuchus multiscrobiculatus resembles that of extant crocodylians, namely in the shape and orientation of the proximal head, distal condyles, and position of the deltopectoral crest.…”