II. Appendicular

What are the components of the appendicular skeleton?

The appendicular skeleton consists of the pectoral girdle plus limbs/fins and the pelvic girdle plus limbs/fins.

The anterior limbs of tetrapods are organized: * Brachium – humerus * Antebrachium – radius and ulna * Carpus – carpals * Metacarpus – palm * Digits – phalanges

The posterior limbs of tetrapods are organized: * Femur – femur * Crus – tibia and fibula * Tarus – tarsals * Metatarsus – instep * Digits – phalanges

Which groups lack an appendicular skeleton?
Apodans, snakes and some snake-like lizards do not have appendicular skeletal systems.

Distinguish the structural patterns between shark fins and bony fishes lobe fins.

Modern day shark fins are made up of two bars, the scapulocoracoid and puboischiac and have three enlarged pterygiophores, the metapterygium, mesopterygium. Towards the tip of the tail are the radicals and ceratotrichia. In bony lobed finned fishes the pectoral fin articulates with the scapulocoracoid, clavicle, cleithrum, postcleithrum, supracleithrum, and post temporal.

What were the components of the pectoral girdle in early fishes and how has it changed in tetrapods? Specifically, what is the typical fate of the coracoids and clavicle in the tetrapod girdle?

In early fishes, the pectoral girdle is made up of the cleithrum, clavicle, supracleithrum, and posttemporal. The clavicle is lost in bony fish and in tetrapods it remains. The early tetrapods lose the posttemporal, supracleithrum and post cleithrum. What remain are the paired cleithrum, clavicle and interclavicles. In modern amphibians the dermal bones are lost or reduce to be replaced by the scapuloproacoid that takes position as the dominant girdle element

What is the function of the pelvic girdle? What are the structural components? What changes have occurred in the evolution of the pelvic girdle of anurans, birds, mammals?

The pelvic girdle brace paired appendenages. In tetrapods it is formed by three endochondral bones:

* Illium * Pubis * Ischium

The illium is attached to the vertebral column via the sacral region. There is evidence in the fossil record regarding the evolution of the pelvic girdle.

Dinosaurs pelvic regions can be divided into two main types:

* Saurischians – pelvic girdle with three radiating bones * Ornithischians – hip with pubis and ischium lying parallel and next to each other

What structural modification(s) have taken place in the appendicular skeleton to accommodate the transition from the aquatic to the terrestrial environment?

To transition from water to land required some modifications. The attachment of the pectoral girdle to the skull was lost. This allowed for an increase in movement of the head. The limbs and girdles became larger and reinforced to permit a more terrestrial lifestyle. They were able to hold the weight of the organisms as they moved. The fins were replaced by digits.

Explain how the axial and appendicular skeletal structures participate in locomotion. What limb modifications are associated with cursorality?

The early modes of transportation is to establishing points of pivot. This generally remains constant today. The femurn and the humerus rotate the digits in line with the direction of travel. Cursorial refers to tetrapods that are specialized for running. The modifications include a lengthening of the limb elements, lightening the distal end of the limb to reduce mass, and reducing the number of digits.

Are there structural differences between the pelvises of males and females?

There are very noticable structural changes between the pelvic of a male and that of a female. The birth canal of the female must accomadate the descending head of the fetus, therefore the pelvic region of females are much more wider than males.

What is the main function of fins? What is their general structure? In sharks, what do pectoral fins do?

Fins are used primarily to give the fish increased stability as it glides through the water. In sharks this remains constant. Pectoral fins are used in addition to help navigate the water. It lifts the shark as it swims.

What conditions favored the evolution of the first fins?

There are different types of fins:

* Lobed fins – sarcopteryigians

* Fins rays – elasmobranchs (such as sharks)

Additional features include:

* Ceratotrichia – cartligainous * Lepidotrchia – Ossified or chondrified.

Fins are hypothesized to have evolved from folds along the lateral portion of ancient aquadric animals.

The first fins developed to counterbalance the instability of early fishes that were becoming more and more active. It was designed to limit deflections. The two types of structures that developed were the archipterygial fin and the metapterygial fin. It is hypothesized that the bony exoskeleton moved inward over time to join the girdle structures that were present.

How does the limb orientation of “advanced” tetrapods differ from that of “primitive” tetrapods?

The fossil record shows that there were tetrpods with an increased number of digits than modern day tetrapods. In some vertebrats the major trend has been towards multiple phalanges. In many groups – ungulates – the trend has been toward the reduction in the number of phalanges and loss of fusion of associated carpals and tarsals. The basic tetrapod pattern is pentadactylous which refere to five digits.

What is plantigrade, digitigrade, unguligrade and which groups exhibit this conditions? How variable are the femurs, tibias, and fibulas of tetrapods?

* Plantigrade – flat footed, all bones of manus and or pes are on the ground; amphibians, most reptiles and some mammals.

* Digitgrade – 1st digit is reduced or lost, manus and pes are evelvated, rabbits, rodents and many carivores such as cats.

* Uniguligrade – reduced number of digits, walks on tips or remaining digits, claws become hooves such as is the case with horses.

The hind limbs of tetrapods are very variable. The limbs are responsible for locomotion on land. The bear the weight from the upper body for bipedal vertebrates and are the primary structure for advanced speed in animals such as cats.