Gavialis Research Articles

Convergence and functional evolution of longirostry in crocodylomorphs

AbstractDuring the Mesozoic, Crocodylomorpha had a much higher taxonomic and morphological diversity than today. Members of one particularly successful clade, Thalattosuchia, are well‐known for being longirostrine: having long, slender snouts. It has generally been assumed that Thalattosuchia owed their success in part to the evolution of longirostry, leading to a feeding ecology similar to that of the living Indian gharial, Gavialis. Here, we compare form and function of the skulls of the thalattosuchian Pelagosaurus and Gavialis using digital reconstructions of the skull musculoskeletal anatomy and finite element models to show that they had different jaw muscle arrangements and biomechanical behaviour. Additionally, the relevance of feeding‐related mandibular traits linked to longirostry in the radiation of crocodylomorph clades was investigated by conducting an evolutionary rates analysis under the variable rates model. We find that, even though Pelagosaurus and Gavialis share similar patterns of stress distribution in their skulls, the former had lower mechanical resistance. This suggests that compared to Gavialis, Pelagosaurus was unable to process large, mechanically less tractable prey, instead operating as a specialized piscivore that fed on softer and smaller prey. Secondly, innovation of feeding strategies was achieved by rate acceleration of functional characters of the mandible, a key mechanism for the diversification of certain clades like thalattosuchians and eusuchians. Different rates of functional evolution suggest divergent diversification dynamics between teleosaurids and metriorhynchids in the Jurassic.

A field observation of the critically endangered Indian Gharial, Gavialis gangeticus (Gemlin 1789), in the Lower Ganga Canal, Narora, Uttar Pradesh, India

A field observation of the critically endangered Indian Gharial, Gavialis gangeticus (Gemlin 1789), in the Lower Ganga Canal, Narora, Uttar Pradesh, India

New Miocene Caribbean gavialoids and patterns of longirostry in crocodylians

Gavialoidea is a clade of slender- and long-snouted crocodylomorphs with a single living species, the Indian gharial Gavialis gangeticus. Because elongated snouts (longirostry) have evolved independently in several crocodylomorph clades, this head shape has been interpreted as an ecological adaptation. How this condition affected patterns of diversification and how longirostrine-associated cranial features changed through adaptive radiations remain poorly understood. Two new small gryposuchine gavialoids, Dadagavialis gunai gen. et sp. nov. (early Miocene, Panama) and Aktiogavialis caribesi sp. nov. (late Miocene, Venezuela), evidence remarkable Miocene diversification of longirostrine forms in the Neotropics and support transmarine biogeographical relations between northern South America, the Caribbean, and southernmost North America before the Isthmus of Panama was fully established. By integrating phylogenetics and geometric morphometrics, we focus on this gavialoid diversity to investigate patterns of longirostry across the crown group of crocodylomorphs (Crocodylia). Analyses revealed that the snout shape of gavialoids has occupied a small, distinct and almost invariable morphospace since the Cretaceous, in contrast with the morphologically labile snout shape of other crocodylians (crocodyloids and alligatoroids). Our results suggest iterative environmental shift occupations throughout gavialoid evolution without major changes in snout proportions, but involving conspicuous rearrangements of the circumorbital bones. The longirostrine gavialoid morphotype is a distinct adaptation for seizing small prey and typically includes short and wide premaxillae and enlarged ‘caniniform’ teeth only at the tip of the snout. In longirostrine crocodyloids (Tomistoma, Crocodylus intermedius), the conservation of powerful bites and ‘caniniforms’ closer to the jaw joints allowed them to exploit a wider range of prey sizes, which could explain their snout shape plasticity. Therefore, the Mio–Pliocene extirpation of gryposuchine gavialoids from the Caribbean by the arrival of Crocodylus is quite unlikely. The last gryposuchine survived throughout the Pliocene in the south-eastern Pacific, where Crocodylus has never been documented.http://zoobank.org/urn:lsid:zoobank.org:pub:34CDBC8B-98E1-4770-8FC3-A77D3DBF4057

Counting crocodiles from the sky: monitoring the critically endangered gharial (Gavialis gangeticus) population with an unmanned aerial vehicle (UAV)

Technology is rapidly changing the methods used in the field of wildlife monitoring. Unmanned aerial vehicles (UAV) are an example of a new technology that allows biologists to take to the air to monitor wildlife. A fixed-wing UAV was used to monitor the critically endangered gharial population along 46 km of the Babai River in Bardia National Park, Nepal. The UAV was flown at an altitude of 80 m along 12 pre-designed missions and, with a search effort of 2.72 h of flight time, acquired a total of 11 799 images covering an effective surface area of 8.2 km2 of riverbank habitat. The images taken from the UAV could differentiate between gharial and muggers. A total count of 33 gharials and 31 muggers with observed density (per square kilometre) of 4.64 and 4.0 for gharial and mugger, respectively. Comparison of count data between one-time UAV and multiple conventional visual encounter rate surveys’ data showed no significant difference in the mean. Basking season and turbidity were important factors for monitoring crocodiles along the riverbank habitat. Efficacy of monitoring crocodiles by UAV at the given altitude can be replicated in high-priority areas with lower operating cost and acquisition of high-resolution data.

Differential response to disturbance factors for the population of sympatric crocodilians (Gavialis gangeticus and Crocodylus palustris) in Katarniaghat Wildlife Sanctuary, India

Abstract Katarniaghat Wildlife Sanctuary along the Indo‐Nepal border in India harbours a well‐known breeding gharial (Gavialis gangeticus) population in its global distribution range together with a substantial population of breeding muggers (Crocodylus palustris). However, no systematic information on size and structure is available for either of the species' populations in the protected area. This study was undertaken in winter and the ensuing summer of 2010–2011 to estimate the relative population density and structure of the two crocodilian species and to examine the effect of various disturbance factors, with the main focus on the effects of tourism and illegal fishing on the behavioural attributes of the two species. Five daytime surveys were conducted from December 2010 to April 2011. Relative density based on encounter rate (number per 20 km) was highest for gharial juveniles followed by gharial adults and gharial sub‐adults in all the five surveys. Muggers, on the other hand, showed the opposite trend, with the lowest encounter rate being for juveniles, followed by sub‐adults and adults. The encounter rate of both species declined with increase in the mean ambient temperature from December to April. The river habitat was divided into 2 km segments and disturbance factors were recorded at intervals of 100 m on both river banks. Wariness was taken as an indicator of response to disturbance caused by human beings and was measured from mechanized boats used for tourism and non‐mechanized boats used for illegal fishing. Segments with sandbars, in spite of moderate to high disturbance rate, were preferred for basking by both species. In conclusion, with suitable habitat for basking, gharials and muggers were observed to tolerate moderate levels of disturbance. Wariness resulting from disturbances from the non‐mechanized boats was higher than that from the mechanized boats. Gharials tend to avoid humans, possibly with age/size acquired experience and knowledge, whereas muggers become more tolerant to human presence with increased age/size. Despite many disturbance factors, the crocodilian population in Katarniaghat Wildlife Sanctuary is doing relatively well compared with populations in other habitats in India. With the involvement of local stakeholders and strict implementation of forest laws, the habitat can be further improved and a healthy gharial population can be ensured.

Crocodylian nuclear factor kappa B.

We deduced the amino acid (aa) sequence of the nuclear factor kappa B (NFκB) protein from genomic data for the American alligator (Alligator mississippiensis), the estuarine crocodile (Crocodylus porosus), and the Indian gharial (Gavialis gangeticus). A 105kDa protein, NFκB1 exhibits complex post-translational processing, multiple mechanisms of activation, and acts as precursor for a p50, a Rel homology transcription factor which influences the expression of key genes for developmental processes, apoptosis, and immune function. The aa sequences of the crocodylian proteins share very high identity with each other (97.2±0.7%), birds (81.0±1.1%, n=6), mammals (75.3±1.6%, n=4), reptiles (80.3±5.1%, n=2), and less identity with fish (55.5±5.5%, n=4) and one amphibian (66.1±0.8%). The crocodylian protein has a well-conserved Rel homology domain, a nuclear localization signal, and a glycine-rich region which facilitates proteasome-mediated generation of p50. The Rel homology domain contains sequences responsible for dimerization, DNA-binding, and nuclear translocation. In addition, seven ankyrin repeats were located, which putatively allow for inhibition of transcriptional regulation by mediating interaction with Inhibitor kappa B. Other features include a death domain, and conserved serine residues, near the C-terminal end, which act as potential phosphorylation sites for activation of the proteolytic generation of p50. Western blot analysis showed both the 105kDa precursor and the 50kDa mature NFκB were expressed in the alligator liver. Nuclear factor κB exhibited diffuse cytoplasmic distribution in alligator hepatocytes, and almost no cytoplasmic localization in infected animals. In addition, nuclear NFκB exhibited specific binding to the consensus NFκB promoter element.

Conservation and Population Recovery of Gharials (Gavialis gangeticus) in Nepal

Abstract: The remnant populations of Gharials, Gavialis gangeticus, are now confined to the large, deep rivers of northern India and Nepal. In lowland Nepal, the populations are restricted to a few stretches of the Narayani–Rapti and Karnali–Babai river systems. Periodic censuses of the wild populations have been made over the past 12 yr. Here, we present population trends of Gharials in the Narayani, Rapti, and Babai rivers based on these surveys. The results indicate that the combined numbers of adults and subadults have been gradually increasing since 2005, but the numbers of adults are low and female biased, with very few males recorded from all study sites. In 1978, Nepal established a captive breeding center in Chitwan National Park, from which captive-bred animals have been periodically released 4–7 yr after hatching, at which time the animals are about 1.5 m total length. The detection of hatchlings and subadult classes that are smaller than these released animals in the rivers indicates that ther...

Assessment of trophic ecomorphology in non-alligatoroid crocodylians and its adaptive and taxonomic implications.

Although the establishment of trophic ecomorphology in living crocodylians can contribute to estimating feeding habits of extinct large aquatic reptiles, assessment of ecomorphological traits other than the snout shape has scarcely been conducted in crocodylians. Here, I tested the validity of the proposed trophic ecomorphological traits in crocodylians by examining the correlation between those traits and the snout shape (an established trophic ecomorphology), using 10 non-alligatoroid crocodylian species with a wide range of snout shape. I then compared the ontogenetic scaling of trophic ecomorphology to discuss its adaptive and taxonomic significance. The results demonstrated that degree of heterodonty, tooth spacing, size of supratemporal fenestra (STF), ventral extension of pterygoid flange and length of lower jaw symphysis are significantly correlated with snout shape by both non-phylogenetic and phylogenetic regression analyses. Gavialis gangeticus falls outside of 95% prediction intervals for the relationships of some traits and the snout shape, suggesting that piscivorous specialization involves the deviation from the typical transformation axis of skull characters. The comparative snout shape ontogeny revealed a universal trend of snout widening through growth in the sampled crocodylians, implying the existence of a shared size-dependent biomechanical constraint in non-alligatoroid crocodylians. Growth patterns of other traits indicated that G.gangeticus shows atypical trends for degree of heterodonty, size of STF, and symphysis length, whereas the same trends are shared for tooth spacing and ventral extension of pterygoid flange among non-alligatoroid crocodylians. These suggest that some characters are ontogenetically labile in response to prey preference shifts through growth, but other characters are in keeping with the conserved biomechanics among non-alligatoroid crocodylians. Some important taxonomic characters such as the occlusal pattern are likely correlated with ontogeny and trophic ecomorphology rather than are constrained by phylogenetic relationships, and careful reassessment of such characters might be necessary for better reconstructing the morphological phylogeny of crocodylians.

Two Different Complement C3 Genes in Crocodilians

Crocodilians exhibit powerful antibacterial activities in their tissues and blood. The activities have been partially attributed to the presence of a potent serum complement system of proteins that acts in a nonspecific manner to kill bacteria. Complement activation involves activation of complement C3, a component with broad immune and regulatory function. We searched the crocodilian genomes (Alligator mississippiensis, Crocodylus porosus, and Gavialis gangeticus) for complement C3, and found two genes that code for isoforms with quite different sequences. Birds and mammals express only a single isoform of the complement C3 protein. Some snakes were shown to have two C3 genes; however, these encode proteins with very similar amino acid sequences. To date, only fishes were reported to express complement C3 isoforms with diversity similar to that of the crocodilian forms. Phylogenetic analysis suggests the gene duplication leading to the two crocodilian paralogs probably occurred within the order Crocodyli...

A new crocodile displaying extreme constriction of the mandible, from the late Oligocene of Riversleigh, Australia

ABSTRACTA new fossil crocodile, Ultrastenos willisi, is described from a cranium and postcranial materials collected from the Riversleigh World Heritage Area, northwestern Queensland, Australia. The mandible displays pronounced anterior constriction, approaching that seen in the extant gharial, Gavialis gangeticus, and false gharial, Tomistoma schlegelii. As such, U. willisi potentially filled the ecomorphological niche associated with longirostry that has been previously unaccounted for in Riversleigh's Oligo–Miocene crocodile fauna. The pronounced constriction and features of the posterior cranium further distinguish U. willisi from all other known crocodiles, including the only reported Australian Oligo–Miocene longirostral crocodile, Harpacochampsa camfieldensis, from Bullock Creek in the Northern Territory. Ultrastenos willisi is recognized as a new genus and species assigned to subfamily Mekosuchinae on the basis of phylogenetic analysis.http://zoobank.org/urn:lsid:zoobank.org:pub:7C6DC891-BD9C-4F84-AF7D-409A4A8C720DSUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Stein, M., S. J. Hand, and M. Archer. 2016. A new crocodile displaying extreme constriction of the mandible, from the late Oligocene of Riversleigh, Australia. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1179041.

A New 13 Million Year Old Gavialoid Crocodylian from Proto-Amazonian Mega-Wetlands Reveals Parallel Evolutionary Trends in Skull Shape Linked to Longirostry.

Gavialoid crocodylians are the archetypal longirostrine archosaurs and, as such, understanding their patterns of evolution is fundamental to recognizing cranial rearrangements and reconstructing adaptive pathways associated with elongation of the rostrum (longirostry). The living Indian gharial Gavialis gangeticus is the sole survivor of the group, thus providing unique evidence on the distinctive biology of its fossil kin. Yet phylogenetic relationships and evolutionary ecology spanning ~70 million-years of longirostrine crocodylian diversification remain unclear. Analysis of cranial anatomy of a new proto-Amazonian gavialoid, Gryposuchus pachakamue sp. nov., from the Miocene lakes and swamps of the Pebas Mega-Wetland System reveals that acquisition of both widely separated and protruding eyes (telescoped orbits) and riverine ecology within South American and Indian gavialoids is the result of parallel evolution. Phylogenetic and morphometric analyses show that, in association with longirostry, circumorbital bone configuration can evolve rapidly for coping with trends in environmental conditions and may reflect shifts in feeding strategy. Our results support a long-term radiation of the South American forms, with taxa occupying either extreme of the gavialoid morphospace showing preferences for coastal marine versus fluvial environments. The early biogeographic history of South American gavialoids was strongly linked to the northward drainage system connecting proto-Amazonian wetlands to the Caribbean region.

Population, Basking and Hatching Success of Gavialis gangeticus in Narayani River, Chitwan National Park, Nepal

This study was carried out to investigate the habitats and abundance of the Gharials in Narayani river of Chitwan National Park from 2012 to 2013. A total of 38 Gharials including 3 hatchlings, 8 juveniles, 12 sub-adults and 15 adults were recorded during the study period. Only one breeding male was observed reflecting the critical condition for the breeding in the wild within Chitwan National Park. The abundance of the gharial was restricted in 2 areas, namely Khoria muhan and Velaunji due to suitability of the habitat conditions and minimum human disturbances. The Basking activities in relation to depth showed that > 80 % of the Gharials selected sandy banks. Among the 2 populations, the gharials in Khoria muhan preferred shallow to moderate depth of water because of presence of braided channels in the area. In contrast, the Gharials in Velaunji select deep water course of the main channel. The park management must adopt conservation measures such as ban of fishing and regular monitoring of habitats and population to maintain long term conservation of gharials in Narayani river.J. Nat. Hist. Mus. Vol. 27, 2013: 1-11

Neuroanatomy of Gryposuchus neogaeus (Crocodylia, Gavialoidea): a first integral description of the braincase and endocranial morphological variation in extinct and extant gavialoids

ABSTRACTMorphological studies of the braincase and cranial endocast of fossil crocodylians, especially gavialids, are scarce. Here, we present a detailed description of the neuroanatomy of Gryposuchus neogaeus from the Miocene of Argentina, based on CT scans. The cranial endocast is sub-horizontal and the angle formed between the mid-brain and the hind-brain is poorly marked. When compared with Gavialis gangeticus, the mid-brain of G. neogaeus is relatively shorter, although the distribution of cranial nerves is similar. In the floor of the endocranial cavity, posterior to the dorsum sellae, there is a median foramen that leads into a canal that runs anteroventrally through the basisphenoid to penetrate the posterior wall of the pituitary fossa (open foramen for the basilar artery?). The same structure is present in G. gangeticus, but is absent in other living crocodylians, suggesting a potential synapomorphy of Gavialoidea. The pneumaticity of the skull roof and the lateral branches of the pharyngotympanic system in G. neogaeus are markedly reduced when compared with the extant species. Comparisons with the living Gavialis indicate that the pattern of braincase morphology of Gavialidae was present in the Miocene; however, the internal morphology, including brain shape, pneumaticity of the skull roof and basicranium, is different in the two species. This work is the first step to understand the variation of the neuroanatomy in this group of archosaurs and its palaeobiological implication.

A Simple PCR-RAPD is Method to Identification of Indian Crocodiles

We describe the development of PCR-RAPD method to detection of Indian crocodiles. According to CITES (Convention on International Trade in Endangered Species) of Wild Fauna and Flora and 1972 Indian Wildlife Protection Act, for conservation of crocodile species listed subject to illegal trade for three Indian crocodile species were selected for simple, rapid and reliable molecular method for identification of crocodile-based crime exhibits like bones, skin, etc. DNAbased identification of species using PCR-RAPD technique for an identification of all the three Indian crocodile species, Crocodylus porosus, Crocodylus palustris and Gavialis gangeticus is presented here. A 780 bp segment of cytochrome b gene was amplified using novel primer followed by RAPD method it has produced Indian crocodile species-specific pattern for identifying three Indian crocodile species separately, which fulfills the prerequisite for its forensic application, this technique will show useful in recognition of all three Indian crocodile species genetic identification assay for enforcement use and strengthen conservation efforts.

How the local community views wildlife conservation: a case of Hastinapur Wildlife Sanctuary, Uttar Pradesh, India

A study was conducted to assess the local community’s attitudes towards wildlife conservation in Hastinapur Wildlife Sanctuary (HWS), Uttar Pradesh, India. It is the largest sanctuary in the state and under the highest anthropogenic pressure. People engage in fishing, livestock grazing, fuel wood/fodder collection, cash cropping of cucurbits in the sandy river banks for sustenance and commercial extraction of sand and grass for construction. These activities threaten the survival of threatened species like Swamp Deer Rucervus duvaucelii, Gangetic Dolphin Platanista gangetica, Smooth-coated Otter Lutrogale perspicillata and Gharial Gavialis gangeticus. Interviews were conducted with heads of randomly selected families and ‘yes/no’ opinions were taken. Questions included direct statements on biodiversity status and relationship with the Sanctuary resources. Data was classified in percent values and it was found that there is no difference in people’s perception on increase, decrease or stability of biodiversity. Further, a majority of people find life around a protected area disadvantageous, or with dismal advantages. Building on this premise the study suggests that a better share in development and alternative livelihood options for the local community of HWS can decrease their dependence on natural resources and improve conservation as a favourable option in the present perceptions of the people.

Some Helminth Parasites of Gharial from Chitwan National Park, Nepal

A study on helminth parasites on captive gharial (Gavialis gangeticus) was conducted during July-December 2012 at Gharial Breeding Centre, Kasara, Chitwan National Park to isolate, identify and find out their prevalence. Dead gharial hatchlings were collected directly from the centre in fresh and frozen conditions. Out of 85 samples examined, 40 samples 47.06% as prevalence rate of helminth parasites. During the study three helminth parasites were first reported from the gharials of Nepal; Pentastomid (Sebekia sp.), Capillarioids and Ascaridoids. The dead hatchlings were found to be infected with Pentastomid (41.17%), Ascaridoids (7.05%), Capillarioids (1.17%), Proctocaecum gairhei (3.52%) and Exotidendrium sp. (36.47%). In the month of December helminth parasites showed highest prevalence; Sebekia sp. (100%) and Proctocaecum gairhei (75%) and Exotidendrium sp. (100%) and the lowest prevalence in the month of July; Sebekia sp. (4%), Capillarioids (4%) and Exotidendrium sp. (8%).DOI: http://dx.doi.org/njst.v15i2.12111Nepal Journal of Science and Technology Vol. 15, No.2 (2014) 37-40

Conservation of the Indian Gharial Gavialis gangeticus: successes and failures

The Gharial Gavialis gangeticus, a long‐snouted crocodilian endemic to the Indian subcontinent, is Critically Endangered and has teetered on the brink of extinction for the past several decades. From historical populations of perhaps 10 000 animals, Gharials numbered in the hundreds by 1974. Project Crocodile – an Indian government initiative – became a poster boy for crocodile conservation. Based almost entirely around a head‐starting programme, the effectiveness of Project Crocodile was called into question when populations crashed again in the late 1990s. In the 21st century, with the support of the international zoo community and the International Union for Conservation of Nature/Species Survival Commission's Crocodile Specialist Group, Madras Crocodile Bank Trust began to address the shortcomings of Gharial conservation up to that point, to ensure that future plans for the species would succeed.

Hematology and serum biochemistry of captive gharial (Gavialis gangeticus) in India

Aim: To study the hematological and serum biochemical parameters of the critically endangered gharial (Gavialis gangeticus). Materials and Methods: Blood samples for hemato-biochemical analyses were collected from the ventral median coccygeal vein of six juvenile and six sub adult gharials of Dewari Gharial Rearing Centre of National Chambal Sanctuary, Madhya Pradesh, India. Hematological examination was performed manually. Differential leukocyte count was performed on the blood smears stained with Giemsa’s stain. The analysis of serum was conducted by eppendorf ECOM-F 6124 semi auto biochemical analyzer using standard ERBA biochemical reagent kits. Results: Peripheral blood cells of gharial showed erythrocytes with an oval outline and centrally located prominent round to oval nucleus. Erythrocyte count in sub adult gharials was significantly greater than juveniles. Whereas erythrocyte mean corpuscular volume and erythrocyte size in juveniles was significantly larger than sub adults. The average most abundant leukocyte type in gharial was lymphocytes (53%), followed by heterophils (27%), eosinophils (10%), monocytes (7%) and basophils (3%). Aspartate aminotransferase, alkaline phosphatase, blood urea nitrogen, triglycerides and albumin concentrations in sub adult gharials were significantly higher than juveniles. No significant differences were determined in other hemato-biochemical parameters between juvenile and sub adult gharials under study. Conclusion: A preliminary database on hematology and blood biochemistry of gharial was established. The data will be useful in routine health evaluations, especially in relation to determining potential effects associated with factors such as pollution and infectious diseases.

An expanded combined evidence approach to the Gavialis problem using geometric morphometric data from crocodylian braincases and Eustachian systems.

The phylogenetic position of the Indian gharial (Gavialis gangeticus) is disputed - morphological characters place Gavialis as the sister to all other extant crocodylians, whereas molecular and combined analyses find Gavialis and the false gharial (Tomistoma schlegelii) to be sister taxa. Geometric morphometric techniques have only begun to be applied to this issue, but most of these studies have focused on the exterior of the skull. The braincase has provided useful phylogenetic information for basal crurotarsans, but has not been explored for the crown group. The Eustachian system is thought to vary phylogenetically in Crocodylia, but has not been analytically tested. To determine if gross morphology of the crocodylian braincase proves informative to the relationships of Gavialis and Tomistoma, we used two- and three-dimensional geometric morphometric approaches. Internal braincase images were obtained using high-resolution computerized tomography scans. A principal components analysis identified that the first component axis was primarily associated with size and did not show groupings that divide the specimens by phylogenetic affinity. Sliding semi-landmarks and a relative warp analysis indicate that a unique Eustachian morphology separates Gavialis from other extant members of Crocodylia. Ontogenetic expansion of the braincase results in a more dorsoventrally elongate median Eustachian canal. Changes in the shape of the Eustachian system do provide phylogenetic distinctions between major crocodylian clades. Each morphometric dataset, consisting of continuous morphological characters, was added independently to a combined cladistic analysis of discrete morphological and molecular characters. The braincase data alone produced a clade that included crocodylids and Gavialis, whereas the Eustachian data resulted in Gavialis being considered a basally divergent lineage. When each morphometric dataset was used in a combined analysis with discrete morphological and molecular characters, it generated a tree that matched the topology of the molecular phylogeny of Crocodylia.

English

The Corbett Tiger Reserve (CTR), a very highly rated protected area in the State of Uttarakhand, India, is home to the third largest breeding population of adult gharial globally. It contributes 20% to the estimated global population of 200 - 250 adults of the taxon and it is also the only known population of the taxon which lives predominantly in a lake-like environment. CTR was surveyed for gharial in 2008 which was the first systematic survey with regard to the taxon since 1974 and the meta-population here was found distributed amongst six sub-populations in the Sarpduli, Dhikala, Kalagarh, Sonanadi, Palain and Adnala Ranges of the Reserve. This paper documents a multi-method approach for the estimation of gharial at Dhikala (Dhikala Range) namely: at the confluence of the Ramganga River with the Kalagarh Reservoir. It details the use of trail cameras combined with boat surveys along the shoreline and stationary counts for estimating the adult population of gharial at Dhikala, the site of the largest sub-population of gharial in CTR. Using this multi-method approach to count basking animals, we estimated the adult population in the area to consist of 32 adults (inclusive of seven adult males) based on the maximum ± minimum (MM) method. We also considered the unknown proportion of adults that may have gone undetected during these surveys by subjecting the data to a Double Sampling analysis. The results are indicative that we were able to sample 88.9% of the adult gharial population at Dhikala using this Multi-Method Approach. Based on our three population estimates (n= 29, 32 and 36) we averaged the adult population at Dhikala as 32.3 ± 1.69 adults (Mean ± SE) with an encounter rate of 4.01 ± 0.33 adults km⁻¹ over 8.06 km of shoreline. Further, comparing population estimates between 2008 and 2013 based on the maximum ± minimum (MM) method, we estimated that the number of adults in Dhikala increased by 77.8% between 2008 and 2013. This increase in adult gharial numbers detected in the study area between 2008 and 2013 is primarily a result of: (1) Improved survey techniques which detected more number of animals in the area due to the cumulative effects of population growth from sub-adults to adults, in-migration and the possibility of some animals being missed during the 2008 surveys; (2) improved knowledge and familiarity with the study area; (3) effective protection measures already in place in CTR particularly in Corbett National Park (CNP), which has allowed the adult population to increase naturally without any disturbances. The ability of this multi-method approach in detecting these changes in numbers is important for monitoring the taxon and studying population trends within CNP. Key words: Gharial, Gavialis gangeticus, Corbett Tiger Reserve, Corbett National Park (CNP), trail cameras.