PHP как из массива вытащить ключи по типу string и из этих данных создать новый массив

<?php
 $geolocationOfAnimals = array (
  "Eurasia" => array(
      "Himalayan" => "Bear",
      "Red" => "Wolf"
  ),
  "Africa" => array(
      "Elephan" => "African",
      "4" => "giraffe"
  ),
  "North America" => array(
      "5" => "Coyote",
      "6" => "Puma"
  ),
    "South Americ" => array (
        "7" => "Lama",
        "8" => "Jaguar"
    ),
    "Australia" => array(
        "Tasmanian" => "Devil",
        "10" => "Kangaroo"
    ),
    "Antarctica" => array(
        "11" => "Seals",
        "12" => "Penguins"
    )
);
foreach ($geolocationOfAnimals as $key => $element)
{
    foreach ($element as $key => $element)
    {
        if (!is_numeric($key)) {
            $assoc[] = $element;
        }
    }
}

Пример

Итог:

array(4) {
  [0]=>
  string(4) "Bear"
  [1]=>
  string(4) "Wolf"
  [2]=>
  string(7) "African"
  [3]=>
  string(5) "Devil"
}