iguanodon

• The first potential evidence of herding behavior was the 1878 discovery of 31 Iguanodon dinosaurs which were then thought to have perished together in Bernissart, Belgium, after they fell into a deep, flooded sinkhole and drowned.
  بلجيكا بعد أن سقطوا في شق أرضي عميق ومغمور بالماء.