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Abstract Crocodylomorpha, which includes living crocodylians and their extinct relatives, has a rich fossil record, extending back for more than 200 million years. Unlike modern semi‐aquatic crocodylians, extinct crocodylomorphs exhibited more varied lifestyles, ranging from marine to fully terrestrial forms. This ecological diversity was mirrored by a remarkable morphological disparity, particularly in terms of cranial morphology, which seems to be closely associated with ecological roles in the group. Here, I use geometric morphometrics to comprehensively investigate cranial shape variation and disparity in Crocodylomorpha. I quantitatively assess the relationship between cranial shape and ecology (i.e. terrestrial, aquatic, and semi‐aquatic lifestyles), as well as possible allometric shape changes. I also characterize patterns of cranial shape evolution and identify regime shifts. I found a strong link between shape and size, and a significant influence of ecology on the observed shape variation. Terrestrial taxa, particularly notosuchians, have significantly higher disparity, and shifts to more longirostrine regimes are associated with large‐bodied aquatic or semi‐aquatic species. This demonstrates an intricate relationship between cranial shape, body size and lifestyle in crocodylomorph evolutionary history. Additionally, disparity‐through‐time analyses were highly sensitive to different phylogenetic hypotheses, suggesting the description of overall patterns among distinct trees. For crocodylomorphs, most results agree in an early peak during the Early Jurassic and another in the middle of the Cretaceous, followed by nearly continuous decline until today. Since only crown‐group members survived through the Cenozoic, this decrease in disparity was likely the result of habitat loss, which narrowed down the range of crocodylomorph lifestyles.
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Late Cretaceous Notosuchians of the Maevarano Formation, Mahajanga Basin: An Ecomorphological Perspective
ABSTRACT The Maastrichtian Maevarano Formation of northwestern Madagascar represents deposition in a seasonal dry-wet system and hosts a rich assemblage of well-preserved fossil vertebrates. Notosuchian crocodyliforms, a diverse group of mesoeucrocodylians frequently found in Upper Cretaceous rocks of Gondwana, are well represented in this assemblage. The current study focuses on the four recognized notosuchians (Simosuchus clarki, Araripesuchus tsangatsangana, Miadanasuchus oblita and Mahajangasuchus insignis), examining their morphologic diversity to provide insight into the ecology of these sympatric taxa. Here, several complete and incomplete skulls were examined, with measurements of each cranial opening acquired for quantitative analysis. Digital photographs and high-resolution renderings based on CT/µCT reconstructions were utilized. The size, position, and orientation of the external nares, orbits, and choanae were characterized, with the relative position and size of temporal, suborbital, and external mandibular fenestrae noted for comparisons. The dentitions (size, shape, number of teeth) of the four notosuchians were also included in this study, allowing direct insight into feeding ecology of the four taxa. From the data and approaches used herein, morphologic differences were utilized to interpret potential roles of the different species in the Maevarano ecosystem. The four notosuchians can be divided between terrestrial and semi-aquatic habits, and within these ecologies, size and tooth shape assist in determining possible feeding ecology. Of the three primarily carnivorous taxa (Mahajangasuchus, Miadanasuchus, Araripesuchus), only Miadanasuchus and Araripesuchus overlapped ecologically as terrestrial predators. Maximum adult size differences between these two forms likely contributed to differences in prey choice, thereby permitting coexistence in the terrestrial environment. Simosuchus, the other terrestrial notosuchian, clearly differs from the others based on both skull and dental morphology and occupied a primarily herbivorous niche. Finally, Mahajangasuchus is the sole semi-aquatic notosuchian in the assemblage, sharing this habitat with representative and smaller-bodied neosuchians and other aquatic vertebrates and potentially competing with the other carnivorous forms for prey. In sum, the Maevarano Formation vertebrate assemblage can be used as a case-study for comparison with other Mesozoic assemblages with multiple crocodyliforms.
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- Award ID(s):
- 2242717
- PAR ID:
- 10567347
- Publisher / Repository:
- ISSN 2220-0681)
- Date Published:
- Journal Name:
- Madamines
- ISSN:
- 2220-0681
- Subject(s) / Keyword(s):
- Ecomorphology crocodyliforms Maastrichtian Maevarano Formation Mahajanga Basin Madagascar
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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