Kent Vliet | University of Florida (original) (raw)

Papers by Kent Vliet

“Morris_CrocodylianHeterochrony_SI.pdf” contains expanded methods (description of landmarks and f... more “Morris_CrocodylianHeterochrony_SI.pdf” contains expanded methods (description of landmarks and functions used in analyses); description of additional analyses with adult & subadult dataset and ecomorph categorization; expanded discussion of phylogenetic history of ontogeny for clades and morphological phylogeny; list of supplementary tables; and supplementary figures.

Scientific Reports, Dec 17, 2019

extant crocodylia are exceptional because they employ almost the full range of quadrupedal footfa... more extant crocodylia are exceptional because they employ almost the full range of quadrupedal footfall patterns ("gaits") used by mammals; including asymmetrical gaits such as galloping and bounding. perhaps this capacity evolved in stem crocodylomorpha, during the triassic when taxa were smaller, terrestrial, and long-legged. However, confusion about which crocodylia use asymmetrical gaits and why persists, impeding reconstructions of locomotor evolution. our experimental gait analysis of locomotor kinematics across 42 individuals from 15 species of Crocodylia obtained 184 data points for a wide velocity range (0.15-4.35 ms −1). our results suggest either that asymmetrical gaits are ancestral for crocodylia and lost in the alligator lineage, or that asymmetrical gaits evolved within crocodylia at the base of the crocodile line. Regardless, we recorded usage of asymmetrical gaits in 7 species of Crocodyloidea (crocodiles); including novel documentation of these behaviours in 5 species (3 critically endangered). Larger crocodylia use relatively less extreme gait kinematics consistent with steeply decreasing athletic ability with size. We found differences between asymmetrical and symmetrical gaits in crocodylia: asymmetrical gaits involved greater size-normalized stride frequencies and smaller duty factors (relative ground contact times), consistent with increased mechanical demands. Remarkably, these gaits did not differ in maximal velocities obtained: whether in Alligatoroidea or Crocodyloidea, trotting or bounding achieved similar velocities, revealing that the alligator lineage is capable of hitherto unappreciated extreme locomotor performance despite a lack of asymmetrical gait usage. Hence asymmetrical gaits have benefits other than velocity capacity that explain their prevalence in crocodyloidea and absence in Alligatoroidea-and their broader evolution. Extant Crocodylia have long been known to use almost all forms of walking and running locomotor modes (e.g., footfall patterns) present in quadrupedal mammals. These gaits include symmetrical (e.g., lateral/diagonal sequence walks; walking and running trots vide 1,2) and asymmetrical (e.g., galloping, bounds and half-bounds) footfall patterns. Nevertheless, the diversity, scaling (body size correlations), and underlying mechanisms of this impressive locomotor repertoire are based only on a few studies of select species from the >23 extant members of Crocodylia. Symmetrical walking gaits have been fairly well studied for Crocodylia, mainly in alligatoroids such as Alligator mississippiensis (also Caiman crocodilus) [ 3-20 and see below]. There have been speculations or anatomical hints of divergent abilities in the "alligator lineage" (Alligatoroidea) vs. "crocodile lineage" (Crocodyloidea) 21-24 , but empirical evidence of any differences in locomotor abilities remains absent. Charig's 25 anecdote of sustained bipedal running in a crocodile (repeated in more recent studies; e.g. 26) is highly specious, never having been reliably documented in that or any subsequent studies. Bounding (synchronized left-right forelimb and hindlimb motions separated by an aerial phase) and galloping (slightly asynchronous left-right motions; essentially a slower version of bounding) gaits have been described for some Crocodylus species, especially C. johnstoni 27,28 , C. porosus 29 and C. niloticus 30,31. It is often misquoted in general media or natural history accounts that C. johnstoni is the only crocodylian known to gallop or bound; some 27 wondered if its bounding ability was "unique" but it is clear that this capacity is more broadly distributed

Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, Jul 13, 2019

The attachments of jaw muscles are typically implicated in the evolution and shape of the dorsote... more The attachments of jaw muscles are typically implicated in the evolution and shape of the dorsotemporal fenestra on the skull roof of amniotes. However, the dorsotemporal fenestrae of many archosaurian reptiles Anatomical Abbreviations: aAU = auricular artery; a,vSO = supraorbital artery and vein; a,vTO = temporoorbital artery and vein; a,vTR = trigeminal artery and vein; aFA = facial artery; aOC = occipital artery; aSO = supraorbital artery; aST = superficial temporal artery; aTO = temporoorbital artery; aTS = superficial temporal artery; ci = carunculate integument; cPO = postorbital communication; ct = cartilago transiliens; DTFen = dorsotemporal fenestra; DTFos = dorsotemporal fossa; EVS =

John Wiley & Sons, Inc. eBooks, Jul 25, 2014

Journal of Morphology, May 11, 2021

The discovery of cryptic biodiversity has blossomed under the advancements of genetic techniques,... more The discovery of cryptic biodiversity has blossomed under the advancements of genetic techniques, but species identification via morphology remains crucial to effective conservation efforts. In this study, we tested the use of continuous cranial shape variation in distinguishing the two living species of Mecistops: the West African slender‐snouted crocodile (M. cataphractus) and the Central African slender‐snouted crocodile (M. leptorhynchus). Using a combination of geometric morphometric characters and ratios of linear measurements, we identified statistically significant variation in cranial bone and overall skull shape of mature individuals that corroborates existing molecular and discrete morphological evidence for two distinct, extant species within Mecistops. Specifically, variation in the shape of the nasal appears particularly diagnostic, while ratios involving metrics of snout length to snout width at the premaxillary notch offer distinguishing features easily measured in the field. Because of the complementary results and applications of the morphometric and cranial ratio analyses, we argue that both methodologies remain relevant to species identification. Moreover, we recommend continued cooperation between geneticists and morphologists in diagnosing species of conservation concern.

Integrative And Comparative Biology

Synopsis Scaling of body shape, gait, limb kinematics, and kinetics can inform about mechanical a... more Synopsis Scaling of body shape, gait, limb kinematics, and kinetics can inform about mechanical and energetic constraints influencing animal locomotion on land. However, our knowledge of terrestrial locomotion among tetrapods is biased toward animals that use parasagittal limb postures (mammals and birds). Whether species that use non-parasagittal limb postures (e.g., crocodylians and lizards) share similar scaling principles remains uncertain, especially toward the larger end of the body size spectrum. Here, we compare new data from large adult American alligators (140–223 kg) with previous data from smaller individuals (0.2–5.6 kg) to evaluate the scaling of gait, limb posture, ground reaction forces, and inertial properties of body segments over a size range spanning three orders of magnitude. Larger alligators walked with higher relative stride frequencies and shorter relative stride lengths at equal dimensionless speeds, suggesting that alligators prioritize stance phase mechan...

Hidrobiológica, 2018

Antecedentes. Los Crocodylia inician su historia de vida al superar la etapa de incubación con la... more Antecedentes. Los Crocodylia inician su historia de vida al superar la etapa de incubación con la eclosión en grupo. La temperatura de incubación es importante para el desarrollo de los embriones y el proceso de eclosión, durante el cual emiten sonidos. Objetivos. Reportar la influencia del tamaño de la nidada sobre la duración y el éxito de eclosión, y describir dicho proceso. Métodos.

The Anatomical Record, 2021

The dorsoventrally flattened skull typifies extant Crocodylia perhaps more than any other anatomi... more The dorsoventrally flattened skull typifies extant Crocodylia perhaps more than any other anatomical feature and is generally considered an adaptation for semi-aquatic feeding. Although the evolutionary origins of caniofacial flattening have been extensively studied, the developmental origins have yet to be explored. To understand how the skull table and platyrostral snout develop, we quantified embryonic development and post-hatching growth (ontogeny) of the crocodylian skull in lateral view using geometric morphometrics. Our dataset (n = 103) includes all but one extant genus and all of the major ecomorphs, including the extremely slender-snouted Gavialis and Tomistoma. Our analysis reveals that the embryonic development of the flattened skull is remarkably similar across ecomorphs, including the presence of a conserved initial embryonic skull shape, similar to prior analysis of dorsal snout shape. Although differences during posthatching ontogeny are recovered among ecomorphs, embryonic patterns are not distinct, revealing an important shift in developmental rate near hatching. In particular, the flattened skull table is achieved by the end of embryonic development with no changes after hatching. Further, the rotation of skull roof and facial bones during development is critical for the stereotypical flatness of the crocodylian skull. Our results suggest selection on hatchling performance and constraints on embryonic skull shape may have been important in this pattern of developmental conservation. The appearance of aspects of cranial flatness among Jurassic stem crocodylians suggests key aspects of these cranial developmental patterns may have been conserved for over 200 million years.

CSV file containing covariate data associated with each specimen (i.e., species, ontogenetic peri... more CSV file containing covariate data associated with each specimen (i.e., species, ontogenetic period, clade, ecomorph shape)

Mecistops and outgroup sequences for nuclear marker CpP2902. See text file "Shirleyetal_Meci... more Mecistops and outgroup sequences for nuclear marker CpP2902. See text file "Shirleyetal_Mecistopssystematics_OTUexplanations.txt" for OTU codes. Refer to Methods text for other relevant details

Accurate species delimitation is a central assumption of biology that, in groups such as the Croc... more Accurate species delimitation is a central assumption of biology that, in groups such as the Crocodylia, is often hindered by highly conserved morphology and frequent introgression. In Africa, crocodilian systematics has been hampered by complex regional biogeography and confounded taxonomic history. We used rigorous molecular and morphological species delimitation methods to test the hypothesis that the slender-snouted croco- dile (Mecistops cataphractus) is composed of multiple species corresponding to the Congolian and Guinean biogeographic zones. Speciation probability was assessed by using 11 mitochondrial and nuclear genes, and cranial mor- phology for over 100 specimens, representing the full geographical extent of the species distribution. Molecular Bayesian and phylogenetic species deli- mitation showed unanimous support for two Mecistops species isolated to the Upper Guinean and Congo (including Lower Guinean) biomes that were supported by 13 cranial characters capable of unambiguously diagnos- ing each species. Fossil-calibrated phylogenetic reconstruction estimated that the species split + 6.5 – 7.5 Ma, which is congruent with intraspecies diver- gence within the sympatric crocodile genus Osteolaemus and the formation of the Cameroon Volcanic Line. Our results underscore the necessity of com- prehensive phylogeographic analyses within currently recognized taxa to detect cryptic species within the Crocodylia. We recommend that the com- munity of crocodilian researchers reconsider the conceptualization of crocodilian species especially in the light of the conservation ramifications for this economically and ecologically important group

ZIP file containing a folder of all images used for landmarking in this analysis. Image names mat... more ZIP file containing a folder of all images used for landmarking in this analysis. Image names match those in the specimen list

Nexus file containing the phylogeny following the molecular topology with branch lengths (after O... more Nexus file containing the phylogeny following the molecular topology with branch lengths (after Oaks, 2016)

Nexus file containing the phylogeny following the morphology topology and character matrix used t... more Nexus file containing the phylogeny following the morphology topology and character matrix used to generate branch lengths (combination go Narvaez et al., 2016 & Brochu, 2010)