A homologous structure is an example of an organ or bone that appears in different animals, showing a descent from a common ancestor. In other words, it’s when very different animals have bones that appear very similar in form or function and seem to be related
Bats, humans and tigers all share the similar structure of the long bone, connected to two thin bones which are connected to carpals (cluster of small bones) followed by fingers or digits. Even if these limbs are used for completely different purposes such as flying, driving, eating, walking, they come from the same organism. They come from the same prokaryotic microorganism around 3.8 billion years ago.
A vestigial structure is an anatomical feature that no longer seems to have a purpose in the current form of an organism of the given species. Tigers do not have any vestigial structures. Humans have vestigial structures, such as a tail bone, that indicate a relationship to other animals, such as the tiger that still has a tail.
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. In other words, it is a fossil that shows the transition that has taken place in a life form from its previous to current state.
The extinct Panthera zdanskyi was a jaguar-sized tiger that lived in what is now northwestern China more than 2 million years ago. Shown here, an artist's reconstruction of the tiger.
Scientists have discovered a new skull and jaw from an extinct jaguar-sized tiger in northwestern China dating back 2.16 million to 2.55 million years, predating other known tiger fossils by up to a half-million years. This represents the oldest complete skull hitherto found of a pantherine cat — the lineage that includes tigers and all other living big cats. The scientific name for this newfound species is Panthera zdanskyi. The researchers suggest this extinct cat was a sister species to the modern tiger. Their analysis argues that the tiger lineage developed features of its skull and upper teeth early on, while its lower jaw and teeth evolved at a different rate.
Other remains of tigers come from China and they are dated at more than 2 million years old. These early fossil remains indicate that the tiger was much smaller then than it is today. However, it is strongly believed that the tiger is related to the Saber Tooth from about 35 million years ago. They evolved into some subspecies about 25 million years ago and that is where the tiger fits in. The tiger (Panthera tigris) is one of the largest living cats, a giant predator native to Asia reaching up to 13 feet (4 meters) in length, including its tail, and weighing up to 660 pounds (300 kilograms).
It is believed that modern tigers all stem from the Miacid, an ancient carnivore that lived over 62 million years ago. Even though Miacids lived so long ago, the similarities between them and the modern tigers are uncanny. The four legs, patterned fur, and tail are all similarities between the two creatures.
Embryology is the study of the development of embryos from fertilization until they become fetuses, or the point at which you can distinguish the species. Comparative embryology is the comparison of embryo development across species.
Comparative embryology supports the theory of evolution because scientists have found that the embryos of many different species show similarities, which proves they share a common origin. For example, in humans the embryo passes through a stage in which it has a gill structure similar to that of fish.