REPTILES & AMPHIBIANS • 31: e21619 • 2024 1 Copyright is held by the authors. Articles in R&A are made available under a Creative Commons Attribution-NonCommercial 4.0 International license. T winning is defined as the development of two embryos in a single egg (Yntema 1970) and has been reported in turtles (Fujiwara 1964; Louro and Pereira 2009), lizards (Speer and Bayless 2000), and snakes (Manimozhi et al. 2006; Dolia 2018), as well as crocodilians. Examples of twinning in crocodilians include Alligator mississippiensis (Ferguson 1985), Caiman latirostris (Larriera and Imhoff 1994), Crocodylus acu- tus (Velasco 2010), C. intermedius (Thorbjarnarson 1989), C. johnstoni (Ferguson 1985), C. niloticus (Blomberg 1979; Ferguson 1985), C. porosus (Hibberd 1996), C. moreletii (Platt et al. 2000), C. siamensis (Platt et al. 2012), C. palustris (Sharma et al. 2020), and Gavialis gangeticus (Acharjyo and Singh 1989). Twinning in reptiles has been observed both in captivity (Acharjyo and Singh 1989; Di Marzio et al. 2023) and in nature (Sharma et al. 2020). However, few reports document twinning in wild reptilian populations, likely attributable to methods of examination, large clutch sizes, and synchronous hatching, especially in communally nesting species (Piovano et al. 2011; Di Marzio et al. 2023). Twins in an egg usually start development at the same time, but can result in hatchlings of equal or unequal sizes, or one developed and one in an embryonic phase (Hirasawa et al. 2019). In crocodiles, twinning occurs as twins, double yolks, or axial bifurcation (Ferguson 1985). One-egg twins are usually undersized compared to normal hatchlings due to the competition for resources inside the egg (Acharjyo and Singh 1989; Platt et al. 2000), which can also compromise post-hatching survival. Causes of twinning are not known but some assumed mechanisms have been reported. Low genetic variation in bottlenecked populations can result in an Twinning in a Wild Breeding Population of Gharials (Gavialis gangeticus) in India Shantanu Ugemuge 1 , Akash Deep Badhawan 2 , Pulkit Gupta 1 , and Gaurav Vashistha 1,3 1 Gharial Conservation Programme, Katerniaghat Wildlife Sanctuary, Uttar Pradesh, India 2 Katerniaghat Wildlife Division, Bahraich, Uttar Pradesh, India 3 Department of Environmental Studies, University of Delhi, Delhi 110007, India (gaurav.vashistha91@gmail.com; https://orcid.org/0000-0002-5553-0725) Figure 1. Twin Gharial (Gavialis gangeticus) hatchlings removed from the egg in which they were found; note their small size and the shared yolk sac. Photograph by Shantanu Ugemuge. Figure 2. A second incidence of twinning in the Gharial (Gavialis gange- ticus), with an undeveloped embryo still attached to the hatchling via the umbilical cord. Photograph by Shantanu Ugemuge. HTTPS://JOURNALS.KU.EDU/REPTILESANDAMPHIBIANS Reptiles & Amphibians ISSN 2332-4961 https://doi.org/10.17161/randa.v31i1.21619 REPTILES & AMPHIBIANS ONSERVATION AND NATURAL HISTORY