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Home : Naracoorte Caves National Park : Wonambi Fossil Centre : Reconstructing Animals from Fossils : How do we know what the skeletons were like?

How do we know what the skeletons were like?

 

Bones are often found jumbled together

An intact skeleton is rarely found in the caves.

Faced with a pile of bones, palaeontologists must decide from which type of animal each bone came.

Was it a mammal, a reptile or a bird?

Cleaning and sorting bones

Parts of a skeleton that preserve well, such as jaws, teeth, vertebrae and limbs, are most useful. They possess characteristics unique to an animal group and its way of life.

Animals which look and behave in similar ways generally have similar skeletons.

Sorting fossil bones into groups of similar size and form enables palaeontologists to gather the pieces necessary to reconstruct the skeletons.

 

Sorting and Identifying the Bones

Teeth, jaws and vertebrae have features which allow them to be sorted into different classes of land-based animals: mammals, birds, reptiles and amphibians.

Teeth

Mammals such as the Thylacine have four different types of teeth, and a single jaw bone.

Only mammals have teeth with roots, and their jaws contain different types of teeth: incisors, canines, premolars and molars.

Reptile teeth have no roots and the teeth are all similar in shape, although they may differ in size.

Jaw Structure

Reptiles, such as the Goanna, have similar-shaped teeth and a lower jaw made up of several bones

Mammals have only a single bone in the lower jaw, whereas reptiles, birds and amphibians have several bones.

The Goanna has six bones in its lower jaw (dentary, splenial, coronoid, angular, surangular and articular).

 

Vetebrae

The vertebrae of reptiles, such as the Goanna, fit together with ball and socket joints, which provide flexibility for the spine. The socket of each vertebra faces forwards, and the ball points backwards

The vertebrae of mammals differ from those of other vertebrates. Mammals have flat disks between each vertebra.

Reptiles and amphibians have vertebrae connected by a 'ball and socket' joint.

 

 

  

 

Identifying Reptile Bones

Reptile vertebrae

Reptiles can be identified by their vertebrae, teeth and skulls.

Vertebrae

Reptiles have a 'ball & socket'-like articulation between their vertebrae (bones of the spine).

Reptile jaw showing articular bone

The cranial (skull) side of a vertebra is concave, whereas its caudal (tail) side is convex.

The processes (projections) on snake vertebrae differ from those of lizards.

Reptile jaws with peg-like teeth

Lower Jaw

The lower jaw of a reptile consists of several bones.

The 'articular bone' at the back of the jaw bone articulates (ie hinges) with the quadrate bone on the side of the skull. 

Teeth

Reptile jaws have peg-like teeth all of the same type, with neither roots nor complex crowns.

This is related to their feeding; reptiles simply bite and swallow, they do not chew their food.

In the image on the right are the fossil jaw bones of three different lizards found at Naracoorte:

a. Goanna or Lace Monitor Varanus varius

b. Shingleback Lizard Tiliqua rugosa

c. Eastern Bearded Dragon Pogona barbata

Identifying Bird Bones

Limb bones and vertebrae are used to identify birds, because their beaks are rarely preserved and they lack teeth.

Limb bones

Limb bones of the Emu Dromaius novaehollandiae

Bird bones are relatively hollow and light with extensive air spaces which reduce their weight for flight.

Even though the bones are thin-walled they have to be strong to resist the stresses involved in flight, and they are often preserved as fossils.

Vertebrae

Neck vertebrae of a bird, showing the saddle shaped articulations

Bird vertebrae are easily identified as their articulations (the joints between them) are 'saddle shaped'.

Each vertebra interlocks with adjacent vertebrae to provide the rigid support necessary for flight.

 

 

 

 

Most of Australia's native mammals are marsupials, eg kangaroos and Koalas.

Marsupials give birth to tiny young, which then mature in the mother's pouch. Placental animals, such as rodents and bats or introduced species like dogs and sheep, give birth to young which are sufficiently mature that they can survive in the outside world with care from the mother.

Features of their teeth and jaws distinguish marsupials from placental mammals.

Numbers and types of teeth

Most marsupials have a maximum of three premolar and four molar teeth, whereas placental mammals generally have a maximum of four premolar and three molar teeth. In addition the crowns of marsupial teeth have a distinctive form different from that of placental mammals.

Placental mammals, like the dog, have different numbers of molar and premolar teeth than do marsupial mammals, such as the Tasmanian Devil

Marsupial mammals have a shelf to which the jaw muscles attach

Jaw shape

Placental mammals have no shelf on the jaw bone

The lower jaw of marsupials has a pronounced angular process (often called the marsupial shelf) which is an area where the jaw muscles are attached.

Mammals do not have such a shelf on their lower jaw bones.