Is there any interspecific competition between dwarf crocodiles (Osteolaemus tetraspis) and Nile monitors (Varanus niloticus ornatus) in the swamps of central Africa? A study from south-eastern Nigeria

Luiselli, Luca; Akani, Godfrey C.; Capizzi, Dario

doi:10.1017/s0952836999001132

Cited by 18 publications

(31 citation statements)

References 2 publications

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“…The choristoderes are more likely to have competed for resources with a range of other freshwater animals including predatory fish, turtles, juvenile crocodiles and aquatic lizards, as well as other small choristoderes. Nonetheless, a recent study in central Africa (Luiselli et al, 1999) examined the ecological relationship between the small extant crocodile Osteolaemus and a similarsized potential competitor, the predatory lizard Varanus. The two reptiles could co-exist as long as prey was abundant, and this is likely to have been the case for the choristoderes in relation to other small aquatic predators.…”

Section: Choristoderes Within Freshwater Assemblagesmentioning

confidence: 99%

Choristoderes and the freshwater assemblages of Laurasia

Matsumoto¹,

Evans²

2010

J. iber. geol.

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Choristoderes are freshwater aquatic diapsid reptiles of uncertain phylogenetic position. Although the lineage probably diverged from other diapsids in the Permo-Triassic, choristoderes apparently never reached Gondwana. Within Laurasia, however, they have been recovered from Japan, China, Mongolia, Trans-Baikal Russia, Central Asia, Western Europe, and North America, reaching extreme northern latitudes. Setting aside controversial Triassic records, their known temporal range currently extends from the Middle Jurassic (Britain, Kyrgyzstan) to the Miocene (Czech Republic). However, although small choristoderes are known to span the entirety of this period, the larger, more derived neochoristoderes are recorded only from the Early Cretaceous through to the earliest Eocene. The gavial-like neochoristodere Champsosaurus is the most familiar taxon, characterised by large size, a long rostrum and flared temporal fenestrae, but research over the last three decades has revealed many new genera and exposed an unexpected diversity in terms of body size (small to relatively large), neck length (long v. short) and skull morphology (longirostrine v. brevirostrine, open v. closed lower temporal fenestrae). Typically choristoderes occur as part of a mesic assemblage that includes fish, lizards, mammals, turtles, frogs, salamanders, small dinosaurs and, usually, crocodiles. At maturity, Jurassic choristoderes were generally smaller than co-occuring crocodiles and were relatively unspecialized postcranially. The Early Cretaceous of Asia saw a dramatic diversification of choristoderes, including the appearance of much larger neochoristoderes. Perhaps significantly, the relevant Asian horizons (e.g. Yixian Formation, China; Okurodani and Kuwajima formations, Japan) yield no crocodiles. In Late Cretaceous and Paleogene horizons however, across Euramerica, large gavial-like neochoristoderes came to share freshwater ecosystems with a diversity of crocodiles, the neochoristoderes apparently occupying a specialist (gavial-like) piscivorous niche as long as it was available and resources were adequate.

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Section: Choristoderes Within Freshwater Assemblagesmentioning

confidence: 99%

Choristoderes and the freshwater assemblages of Laurasia

Matsumoto¹,

Evans²

2010

J. iber. geol.

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“…The sister taxon of V. niloticus once considered the same species, the ornate monitor ( V. ornatus ), has been found to eat a large number of crabs throughout both juvenile and adult stages (Luiselli et al. ). Due to these limited data, the utility of the teeth must therefore be speculated upon through analogy with both congenerics and other durophagous taxa.…”

Section: Discussionmentioning

confidence: 99%

“…Although Losos & Greene (1988) found snails to be the most important food item in certain individuals, grasshoppers, beetles and slugs were also very important (in addition to a range of other invertebrates, small vertebrates, and vertebrate eggs found). The sister taxon of V. niloticus once considered the same species, the ornate monitor (V. ornatus), has been found to eat a large number of crabs throughout both juvenile and adult stages (Luiselli et al 1999). Due to these limited data, the utility of the teeth must therefore be speculated upon through analogy with both congenerics and other durophagous taxa.…”

Section: Functional Explanationsmentioning

confidence: 99%

Illustrating ontogenetic change in the dentition of theNile monitor lizard,Varanus niloticus: a case study in the application of geometric morphometric methods for the quantification of shape–size heterodonty

D’Amore

2015

Journal of Anatomy

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Many recent attempts have been made to quantify heterodonty in non-mammalian vertebrates, but the majority of these are limited to Euclidian measurements. One taxon frequently investigated is Varanus niloticus, the Nile monitor. Juveniles possess elongate, pointed teeth (caniniform) along the entirety of the dental arcade, whereas adults develop large, bulbous distal teeth (molariform). The purpose of this study was to present a geometric morphometric method to quantify V. niloticus heterodonty through ontogeny that may be applied to other non-mammalian taxa. Data were collected from the entire tooth row of 19 dry skull specimens. A semilandmark analysis was conducted on the outline of the photographed teeth, and size and shape were derived. Width was also measured with calipers. From these measures, sample ranges and allometric functions were created using multivariate statistical analyses for each tooth position separately, as well as overall measures of heterodonty for each specimen based on morphological disparity. The results confirm and expand upon previous studies, showing measurable shape-size heterodonty in the species with significant differences at each tooth position. Tooth size increases with body size at most positions, and the allometric coefficient increases at more distal positions. Width shows a dramatic increase at the distal positions with ontogeny, often displaying pronounced positive allometry. Dental shape varied in two noticeable ways, with the first composing the vast majority of shape variance: (i) caniniformy vs. molariformy and (ii) mesially leaning, 'rounded' apices vs. distally leaning, 'pointed' apices. The latter was twice as influential in the mandible, a consequence of host bone shape. Mesial teeth show no significant shape change with growth, whereas distal teeth change significantly due primarily to an increase in molariformy. Overall, heterodonty increases with body size concerning both tooth size and shape, but shape heterodonty changes in the mandible are much less pronounced. Although it is unclear to what degree V. niloticus specializes in hard prey items (durophagy), previous studies of varanid feeding behavior, along with research on analogous durophagous vertebrates, indicate a division of labor along the tooth row in adults, due to a possible transition to at least a partial durophagous niche. The geometric morphometric method proposed here, although not without its own limitations, may be ideal for use with a number of dental morphotypes in the future.

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“…Varanus niloticus and V. ornatus are closely related (Böhme, 2003) and used to be considered different subspecies (e.g. Luiselli, Akani & Capizzi, 1999). Because they are morphologically similar, individuals of both species are grouped in the analysis.…”

Section: Methodsmentioning

confidence: 99%

Prey capture in lizards: differences in jaw-neck-forelimb coordination

Montuelle

Herrel

Libourel

et al. 2012

Biological Journal of the Linnean Society

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Although prey capture is thought to be based on the coordinated movements of the jaw and locomotor apparatus (i.e. the vertebral column and the limbs), jaw–neck–forelimb coordination has never been compared among related species. The kinematics of jaw, neck, and forelimb movements were recorded in lizards that use jaw prehension: Gerrhosaurus major, Tupinambis merianae, Varanus niloticus, and Varanus ornatus. These species provide a comparative framework to discuss the influence of morphological differences and ecological convergence on the jaw–neck–forelimb coordination patterns. Jaw–neck–forelimb coordination was quantified by determining whether maximum neck elevation and maximum forelimb flexion are synchronized with either the start of jaw opening or maximum gape. Significant differences in the jaw–neck–forelimb coordination pattern among species were observed, with maximum neck elevation being synchronized with the start of jaw opening in varanids, whereas in T. merianae and G. major, it is achieved closer to maximum gape. Differences in locomotor–feeding integration are suggested to be related to dietary specializations, and as such may play a role in feeding adaptation. The jaw–neck–forelimb coordination pattern used by varanids may indeed be advantageous to prepare a quick strike triggered from further away, providing a critical advantage when feeding on evasive prey. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 607–622.

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Is there any interspecific competition between dwarf crocodiles (Osteolaemus tetraspis) and Nile monitors (Varanus niloticus ornatus) in the swamps of central Africa? A study from south-eastern Nigeria

Cited by 18 publications

References 2 publications

Choristoderes and the freshwater assemblages of Laurasia

Choristoderes and the freshwater assemblages of Laurasia

Illustrating ontogenetic change in the dentition of theNile monitor lizard,Varanus niloticus: a case study in the application of geometric morphometric methods for the quantification of shape–size heterodonty

Prey capture in lizards: differences in jaw-neck-forelimb coordination

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