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

  • ️Sat Jan 01 2022

. 2022 Nov 18;12(11):e9484.

doi: 10.1002/ece3.9484. eCollection 2022 Nov.

Affiliations

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

Michela M Johnson et al. Ecol Evol. 2022.

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.

Keywords: Crocodylomorpha; Teleosauroidea; Thalattosuchia; ecology; functional morphology; mandibular biomechanics.

© 2022 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

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Conflict of interest statement

The authors declare no competing interests.

Figures

FIGURE 1
FIGURE 1

Simplified evolutionary tree and time‐calibrated geological timescale of Teleosauroidea, with the inclusion of Pelagosaurus typus (Metriorhynchoidea) as the outgroup. Major clades within Teleosauroidea (Teleosauridae, Machimosauridae, Machimosaurinae and Machimosaurini) are highlighted. Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 2
FIGURE 2

Principal component analysis (PC) of teleosauroid dentition along the PC1 (37.02%) and PC2 (23.82%). The blue star represents the most basal teleosauroid, Plagiophthalmosuchus gracilirostris, purple circles represent Teleosauridae, gray triangles indicate Machimosauridae, and red hexagons represent Machimosaurini (a distinctive tribe within Machimosauridae). See Data S2 for abbreviated names. Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 3
FIGURE 3

Principal coordinates analysis (PCo) of teleosauroid dentition along the PCo1 (38.05%) and PCo2 (12.88%). The blue star represents the most basal teleosauroid, Plagiophthalmosuchus gracilirostris, purple circles represent Teleosauridae, gray triangles indicate Machimosauridae, and red hexagons represent Machimosaurini (a distinctive tribe within Machimosauridae). See Data S2 for abbreviated names. Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 4
FIGURE 4

Principal component analysis (PCA) of teleosauroid mandibles along the PCA1 (44.51%) and PCA2 (14.13%). The blue stars represent specimens of the most basal teleosauroid, Plagiophthalmosuchus gracilirostris, purple circles represent Teleosauridae, gray triangles indicate Machimosauridae, and red hexagons represent Machimosaurini (a distinctive tribe within Machimosauridae). See Data S2 for abbreviated names. Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 5
FIGURE 5

Simplified teleosauroid evolutionary tree with time‐calibrated scale and heatmap displaying length of the mandibular symphysis relative to the mandibular ramus length (MSL/ML). Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 6
FIGURE 6

Simplified teleosauroid evolutionary tree with time‐calibrated scale and heatmap displaying length of the adductor muscle attachment sites relative to the mandibular ramus length (maL/ML). Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 7
FIGURE 7

Simplified teleosauroid evolutionary tree with time‐calibrated scale and heatmap displaying (a) anterior mechanical advantage (aMA) and (b) posterior mechanical advantage (pMA). Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 8
FIGURE 8

Simplified teleosauroid evolutionary tree with time‐calibrated scale and heatmap displaying opening mechanical advantage (oMA). Silhouettes provided by PhyloPic© by S. Hartman, G. Monger and N. Tamura.

FIGURE 9
FIGURE 9

Simplified teleosauroid evolutionary tree with time‐calibrated geological scale displaying six different ecomorphotypes within Teleosauroidea and different ecotype divergences within Machimosauridae. For ecomorphotypes: green represents longirostrine specialist; light blue represents pelagic form; yellow represents macrophage/durophage form; brown represents semi‐terrestrial form; purple represents longirostrine generalist; orange represents mesorostrine generalist; and black represents unknown. For machimosaurid ecotypes: circle represents ecotype 1; triangle represents ecotype 2; star represents ecotype 3 (with [left] corresponding tooth and [right] mandible silhouettes, in which a question mark represents unknown). The box shows hypothesized prey items. Silhouettes provided by PhyloPic© by Spotila, K. Sorgan, I. Braasch, E. Schumacher, C. Cevrim, and H. Filhol.

FIGURE 10
FIGURE 10

Visualization of the two different jaw types within teleosauroids: (a) the “gracile jaw type” and (b) the “‘robust jaw type”. Specimen and silhouette for the gracile type is Charitomenosuchus leedsi (NHMUK PV R 3806), and specimen and silhouette for the robust type is Proexochokefalos heberti (MNHN.F 1890‐13). Scale bars: 5 cm (a) and 10 cm (b).

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