An official website of the United States government
Abstract Enamel is the hardest tissue in the vertebrate body. Although variation in enamel microstructure is often linked with diet, the gross proportions of the tissues that compose vertebrate teeth remain relatively unexplored in reptiles. To investigate the patterns of enamel thickness in crocodyliforms, we used micro‐computed tomography scanning to evaluate enamel thickness in teeth ofAlligator mississippiensisfrom rostral, intermediate and caudal locations in the tooth row from an ontogenetic range of animals. We also evaluated enamel thickness in the derived teeth of several extinct crocodyliforms with disparate craniodental morphologies. Our data show that enamel thickness scales isometrically with skull length. We also show that enamel is relatively thicker in caudal teeth than teeth in more rostral positions, concordant with the higher bite forces they experience during feeding. We compared our data with existing enamel thickness data reported from dinosaurs and mammalian taxa to find that archosaurs have markedly thinner enamel than most mammals. These findings serve as a basis for future investigations into the diversity and function of the proportions of dental tissues.
more »
« less
Exceptionally rapid tooth development and ontogenetic changes in the feeding apparatus of the Komodo dragon
Dental developmental and replacement patterns in extinct amniotes have attracted a lot of attention. Notable among these are Paleozoic predatory synapsids, but also Mesozoic theropod dinosaurs, well known for having true ziphodonty, strongly serrated carinae with dentine cores within an enamel cap. The Komodo dragon,Varanus komodoensis, is the only extant terrestrial vertebrate to exhibit true ziphodonty, making it an ideal model organism for gaining new insights into the life history and feeding behaviours of theropod dinosaurs and early synapsids. We undertook a comparative dental histological analysis of this extant apex predator in combination with computed tomography of intact skulls. This study allowed us to reconstruct the dental morphology, ontogeny, and replacement patterns in the largest living lizard with known feeding behaviour, and apply our findings to extinct taxa where the behaviour is largely unknown. We discovered through computed tomography thatV.komodoensismaintains up to five replacement teeth per tooth position, while histological analysis showed an exceptionally rapid formation of new teeth, every 40 days. Additionally, a dramatic ontogenetic shift in the dental morphology ofV.komodoensiswas also discovered, likely related to changes in feeding preferences and habitat. The juveniles have fewer dental specializations, lack true ziphodonty, are arboreal and feed mostly on insects, whereas the adults have strongly developed ziphodonty and are terrestrial apex predators with defleshing feeding behaviour. In addition, we found evidence that the ziphodont teeth ofV.komodoensishave true ampullae (interdental folds for strengthening the serrations), similar to those found only in theropod dinosaurs. Comparisons with other species ofVaranusand successive outgroup taxa reveal a complex pattern of dental features and adaptations, including the evolution of snake-like tongue flicking used for foraging for prey. However, only the Komodo dragon exhibits this remarkable set of dental innovations and specializations among squamates.
more »
« less
- Award ID(s):
- 1902242
- PAR ID:
- 10555494
- Editor(s):
- Joger, Ulrich
- Publisher / Repository:
- PLOS One
- Date Published:
- Journal Name:
- PLOS ONE
- Volume:
- 19
- Issue:
- 2
- ISSN:
- 1932-6203
- Page Range / eLocation ID:
- e0295002
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Tooth replacement rates of polyphyodont cartilaginous and bony fishes are hard to determine because of a lack of obvious patterning and maintaining specimens long enough to observe replacement. Pulse-chase is a fluorescent technique that differentially colours developing mineralized tissue. We present in situ tooth replacement rate and position data for the oral and pharyngeal detentions of Ophiodon elongatus (Pacific lingcod). We assessed over 10 000 teeth, in 20 fish, and found a daily replacement rate of about two teeth (3.6% of the dentition). The average tooth is in the dental battery for 27 days. The replacement was higher in the lower pharyngeal jaw (LPJ). We found no difference between replacement rates of feeding and non-feeding fish, suggesting feeding was not a driver of tooth replacement. Lingcod teeth have both a size and location fate; smaller teeth at one spot will not grow into larger teeth, even if a large tooth nearby is lost. We also found increased rates of replacement at the posterior of the LPJ relative to the anterior. We propose that lingcod teeth do not migrate in the jaw as they develop; their teeth are fated in size and location, erupting in their functional position.more » « less
-
Abstract Theropod dinosaurs were relatively scarce in the Late Cretaceous ecosystems of southeast Brazil. Instead, hypercarnivorous crocodyliforms known as baurusuchids were abundant and probably occupied the ecological role of apex predators. Baurusuchids exhibited a series of morphological adaptations hypothesized to be associated with this ecological role, but quantitative biomechanical analyses of their morphology have so far been lacking. Here, we employ a biomechanical modelling approach, applying finite element analysis (FEA) to models of the skull and mandibles of a baurusuchid specimen. This allows us to characterize the craniomandibular apparatus of baurusuchids, as well as to compare the functional morphology of the group with that of other archosaurian carnivores, such as theropods and crocodylians. Our results support the ecological role of baurusuchids as specialized apex predators in the continental Late Cretaceous ecosystems of South America. With a relatively weak bite force (~600 N), the predation strategies of baurusuchids likely relied on other morphological specializations, such as ziphodont dentition and strong cervical musculature. Comparative assessments of the stress distribution and magnitude of scaled models of other predators (the theropodAllosaurus fragilisand the living crocodylianAlligator mississippiensis) consistently show different responses to loadings under the same functional scenarios, suggesting distinct predatory behaviors for these animals. The unique selective pressures in the arid to semi‐arid Late Cretaceous ecosystems of southeast Brazil, which were dominated by crocodyliforms, possibly drove the emergence and evolution of the biomechanical features seen in baurusuchids, which are distinct from those previously reported for other predatory taxa.more » « less
-
ABSTRACT Marine mammals have undergone a dramatic series of morphological transformations throughout their evolutionary history that facilitated their ecological transition to life in the water. Pinnipeds are a diverse clade of marine mammals that evolved from terrestrial carnivorans in the Oligocene (∼27 million years ago). However, pinnipeds have secondarily lost the dental innovations emblematic of mammalian and carnivoran feeding, such as a talonid basin or shearing carnassials. Modern pinnipeds do not masticate their prey, but can reduce prey size through chopping behavior. Typically, small prey are swallowed whole. Nevertheless, pinnipeds display a wide breadth of morphology of the post-canine teeth. We investigated the relationship between dental morphology and pinniped feeding by measuring the puncture performance of the cheek-teeth of seven extant pinniped genera. Puncture performance was measured as the maximum force and the maximum energy required to puncture a standardized prey item (Loligo sp.). We report significant differences in the puncture performance values across the seven genera, and identify three distinct categories based on cheek-teeth morphology and puncture performance: effective, ineffective and moderate puncturers. In addition, we measured the overall complexity of the tooth row using two different metrics, orientation patch count rotated (OPCR) and relief index (RFI). Neither metric of complexity predicted puncture performance. Finally, we discuss these results in the broader context of known pinniped feeding strategies and lay the groundwork for subsequent efforts to explore the ecological variation of specific dental morphologies.more » « less
-
Reptile feeding strategies encompass a wide variety of diets and accompanying diversity in methods for subduing prey. One such strategy, the use of venom for prey capture, is found in living reptile clades like helodermatid (beaded) lizards and some groups of snakes, and venom secreting glands are also present in some monitor lizards and iguanians. The fossil record of some of these groups shows strong evidence for venom use, and this feeding strategy also has been hypothesized for a variety of extinct reptiles (e.g., archosauromorphs, anguimorphs, and a sphenodontian). However, evidence of systems for venom delivery in extinct groups and its evolutionary origins has been scarce, especially when based on more than isolated teeth. Here, we describe a potentially venomous new reptile,Microzemiotes sonselaensisgen. et sp. nov., from a partial left dentary recovered from the Sonsela Member of the Chinle Formation (middle Norian, Upper Triassic) of northeastern Arizona, U.S.A. The three dentary teeth have apices that are distally reclined relative to their bases and the tip of the posteriormost tooth curves mesially. The teeth show subthecodont implantation and are interspaced by empty sockets that terminate above the Meckelian canal, which is dorsoventrally expanded posteriorly. Replacement tooth sockets are positioned distolingually to the active teeth as in varanid-like replacement. We identify this new specimen as a diapsid reptile based on its monocuspid teeth that lack carinae and serrations. A more exclusive phylogenetic position within Diapsida is not well supported and remains uncertain. Several features of this new taxon, such as the presence of an intramandibular septum, are shared with some anguimorph squamates; however, these likely evolved independently. The teeth of the new taxon are distinctively marked by external grooves that occur on the entire length of the crown on the labial and lingual sides, as seen in the teeth of living beaded lizards. If these grooves are functionally similar to those of beaded lizards, which use the grooves to deliver venom, this new taxon represents the oldest known reptile where venom-conducting teeth are preserved within a jaw. The teeth of the new species are anatomically distinct from and ~10x smaller than those of the only other known Late Triassic hypothesized venomous reptile,Uatchitodon, supporting venom use across multiple groups of different body size classes. This new species represents the third Late Triassic reptile species to possibly have used envenomation as a feeding (and/or defensive) strategy, adding to the small number of venomous reptiles known from the Mesozoic Era.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1371/journal.pone.0295002
