Allometric growth in the skull of Tylosaurus proriger  (Squamata: Mosasauridae) and its taxonomic implications

Stewart, Robert F.; Mallon, Jordan C.

doi:10.18435/vamp29339

Cited by 6 publications

(15 citation statements)

References 30 publications

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“…These results reject previous hypotheses that variation of mosasaur quadrates is ontogenetically uninformative ( Jiménez-Huidobro, Simões & Caldwell, 2016 ; Stewart & Mallon, 2018 ), where both species show unambiguous changes to the shape of the quadrate and its processes throughout growth ( Figs. 6 and 20 ).…”

Section: Discussionsupporting

confidence: 79%

“…8 ); ossification of the quadrate and basioccipital; enlargement of tooth crowns relative to skull size; and a progressive deepening and enlargement of the skull. The identification of RMM 5610 as a young individual in previous work is supported, but the identification ( Jiménez-Huidobro, Simões & Caldwell, 2016 ; Stewart & Mallon, 2018 ; Jiménez-Huidobro & Caldwell, 2019 ) of AMNH FARB 4909 as a relatively mature individual is not ( Fig. 5 ).…”

Section: Discussionmentioning

confidence: 55%

“…Hypothetical growth characters were identified by the author and in the literature, and include both diagnostic characters ( Bell, 1997 ; Jiménez-Huidobro & Caldwell, 2019 ) and characters explicitly proposed to be ontogenetically variable ( Harrell & Martin, 2015 ; Jiménez-Huidobro, Simões & Caldwell, 2016 ; Stewart & Mallon, 2018 ). Characters are described in detail in Data S3 , and measurements and tooth counts are listed in Tables 1 and 2 , respectively.…”

Section: Methodsmentioning

confidence: 99%

“… Stewart & Mallon (2018) described two purported subadult specimens of T. proriger (CMN 8162 and CMN 51258-51263) and hypothesized the growth pattern of various skull structures. The study revealed a significant correlation of all individual bone measurements with total skull length (TSL), as well as isometric growth for all characters except quadrate height (QH), which was found to be positively allometric, and premaxillary predental rostrum length, which was found to be negatively allometric.…”

Section: Introductionmentioning

confidence: 99%

“…Estimates made by the author using scale bars in the literature or due to incomplete material are indicated by a single asterisk, estimates from the literature are indicated by two asterisks, and missing measurements are indicated by question marks. TMP 1982.050.0010 is a cast of LACMNH 28964; CMN 51258 through 51263 are fragments from a single individual ( Stewart & Mallon, 2018 ); AMNH FARB 124 and 134 are a skull and jaws, respectively, from a single individual ( Jiménez-Huidobro & Caldwell, 2019 ); a measurement was published for CMN 8162 (B) ( Stewart & Mallon, 2018 ), but it is inaccurate due to restoration of the specimen (T. Konishi, 2019, personal communication).…”

Section: Introductionmentioning

confidence: 99%

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Craniofacial ontogeny in Tylosaurinae

Zietlow

2020

PeerJ

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Mosasaurs were large, globally distributed aquatic lizards that lived during the Late Cretaceous. Despite numerous specimens of varying maturity, a detailed growth series has not been proposed for any mosasaur taxon. Two taxa—Tylosaurus proriger and T. kansasensis/nepaeolicus—have robust fossil records with specimens spanning a wide range of sizes and are thus ideal for studying mosasaur ontogeny. Tylosaurus is a genus of particularly large mosasaurs with long, edentulous anterior extensions of the premaxilla and dentary that lived in Europe and North America during the Late Cretaceous. An analysis of growth in Tylosaurus provides an opportunity to test hypotheses of the synonymy of T. kansasensis with T. nepaeolicus, sexual dimorphism, anagenesis, and heterochrony. Fifty-nine hypothetical growth characters were identified, including size-dependent, size-independent, and phylogenetic characters, and quantitative cladistic analysis was used to recover growth series for the two taxa. The results supported the synonymy of T. kansasensis with T. nepaeolicus and that T. kansasensis represent juveniles of T. nepaeolicus. A Spearman rank-order correlation test resulted in a significant correlation between two measures of size (total skull length and quadrate height) and maturity. Eleven growth changes were shared across both species, neither of the ontogram topologies showed evidence of skeletal sexual dimorphism, and a previous hypothesis of paedomorphy in T. proriger was not rejected. Finally, a novel hypothesis of anagenesis in Western Interior Seaway Tylosaurus species, driven by peramorphy, is proposed here.

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Section: Discussionsupporting

confidence: 79%

Section: Discussionmentioning

confidence: 55%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Craniofacial ontogeny in Tylosaurinae

Zietlow

2020

PeerJ

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Assessing ontogenetic maturity in extinct saurian reptiles

et al. 2020

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Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.

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Climate, competition, and the rise of mosasauroid ecomorphological disparity

et al. 2022

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Mosasauroidea, prominent marine lizards (Squamata, Toxicofera) of the final 30 million years of the Cretaceous, have been extensively studied for their morphology, ecology and systematics in the past two centuries. However, the relative roles of biological and physical processes as drivers of their morphological diversification remain uncertain. Here we investigate the macroevolution of mosasauroid feeding and locomotory disparity using continuous characters measured from the mandible and forelimb as proxies. Patterns of morphospace occupation demonstrate important roles for innovation and niche partitioning in driving morphological disparity. The early evolution of Mosasauroidea is characterized by large shifts in morphology, especially elongation of the mandibular biting area and hydropedality. The later diversification of derived Mosasaurinae and Plioplatecarpinae is associated with a great expansion of morphospace, attributed to the acquisition of novel feeding and locomotory strategies. Temporally, disparity follows a top‐heavy profile, possibly reflecting opportunism in the wake of the Cenomanian–Turonian anoxic event. The highest levels of disparity are found in the latest Cretaceous, associated with the radiation of derived mosasaurids alongside the persistence of more basal forms. Major morphological innovations are not associated with evolutionary rate shifts, which differentiates them from earlier marine reptiles, and may reflect constant and greater niche occupation in Late Cretaceous oceans. Linear modelling of potential physical drivers indicates a minor role for these processes, suggesting that biological drivers were the primary sculptors of mosasauroid morphological disparity.

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Allometric growth in the skull of Tylosaurus proriger (Squamata: Mosasauridae) and its taxonomic implications

Cited by 6 publications

References 30 publications

Craniofacial ontogeny in Tylosaurinae

Craniofacial ontogeny in Tylosaurinae

Assessing ontogenetic maturity in extinct saurian reptiles

Climate, competition, and the rise of mosasauroid ecomorphological disparity

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