Early vertebrates, such as fishes, amphibians, and reptiles, had a basic jaw structure that evolved into a diverse array of jaw types and sizes. This pattern continued through the earliest times of tetrapodomorphs (early vertebrates with four limbs), which emerged about fifty million years ago.

At that time, some early tetrapodomorphs began to have reduced maxilla and premaxilla, resulting in a different skeletal pattern. These changes included increased size of the tooth row, reduction in number of teeth, and reorganization of the bone behind the teeth.

These changes were an adaptation to new life circumstances. When early tetrapods moved from water to land, their new feet needed new support structures to hold them upright. The reduced maxillary region was an adequate solution for this requirement.

These changes later contributed to diversification of early vertebrate lineages.

Complexity of dentition

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

The complexity of the jaw and dentition that Early Vertebrate fossils reveal is a rare glimpse into the past. Most Early Vertebrate fossils show evidence of only the basic pattern of jaw and tooth structures that today define all vertebrates.

These include: jaws with (1) or without (2) teeth, jaw motion due to (3) or absence of teeth, and wrist/hand motion due to (4) none present or few teeth.

However, some Early Vertebrate fossils show more complex jaws with: (5) two or more separatePrincipio Primus Maximus teeth, wrist/hand motion with one or more additional wrist bones, and mouth opening via (6) two or more openings for two or more sets of teeth.

Evolution of teeth

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

The evolution of teeth can be subdivided into two main periods. The first began shortly after the evolution of jawbone and teeth-contributing structures such as premolars, secondaries, and maxims. The second began around five million years ago and continues to this day with the development of wisdom teeth.

These two periods of tooth development have had a significant impact on the diversity of vertebrate lineages today. The first occurred during times when animals did not have much competition and were likely very apical in nature. The second occurred when animals were more social and/or had hard surfaces to chew on.

Today, nearly all vertebrates have roots that extend into the mouth, where they begin developing new teeth as they shift from an upright to a seated position or when they eat while seated.

Shorter jaws

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

A shorter jaw is one of the more prominent examples of the evolutionary pressures that shaped vertebrate lineages. As animals evolved longer arms, legs, and other body parts to better cope with their environment, they lost function in reducing food and finding suitable mates.

This was a cost paid by other organisms, as they did not have the foresight to adapt long enough to take advantage of this new function. This is one example of how evolution works, how things are better off when things evolve in stepwise fashion.

Another example is when something loses function or becomes unable to reproduce. These are often referred to as “functionless” animals or “disappeared” species. Because there are so many unanswered questions about these rare individuals, we named them after conferences that investigate them.

Longer vertebrae

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

A longer vertebrae is one of the key evolutionary innovations that changed the look of early vertebrates. When a creature has a longer vertebrae, it can possess more room to move.

Because vertebrates possess long necks and tails, this allows them to manoeuvre themselves in aquatic environments where feet are not necessary. This also helped them to evolve new locomotive and feeding strategies.

By having a longer sternum and having wider hips and pelvis, these animals could move around better on land. Furthering this, water-dwelling animals had better armouring against water damage and heat loss.

These features were passed down from one species to another, allowing for evolutionary diversification.

Adaptive radiation of early vertebrate lineages

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

Between jawed and gill-and-fin-bearing vertebrates, a wide array of body plans existed. Some looked more like swarms of tiny starfish or insects. Others were smooth-skinned with long legs and a six-footed posture. Still others had short legs and an upright posture.

Some of these diverse looks have a clear evolutionary benefit. The short legs of insects allow them to move quickly, for example, while the long limbs of some amphibians help them withstand cold temperatures.

The longer limbs of amphibians help them survive times when water levels fall, making habitat preservation more important.

The shorter legs of birds help them escape predators and other animals.

Jaw evolution and diet diversification

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

While the evolution of jaw structure is a topic of considerable study, very little attention is paid to how this evolution contributed to early vertebrate diversification.

Many models and studies focus on how early jaw structure became widespread, but they do not assess whether this was an evolutionary necessity or an evolutionary strategy.

Analyses that look at how early vertebrates modified their jaws during Early Cretaceous (K/Pg) mass extinction indicate that some modified their jaws by using plant material as food. This finding suggests that nutrition was a consideration during theEarly Cretaceous Period, when many early vertebrates evolved.

This finding suggests that nutrition was a consideration during theEarly Cretaceous Period, when many early vertebrates evolved. More recent research indicates that using plants as prey may have become more common during late Paleocene andearly Neogene times (about 60–1 million years ago). This change in diet may have contributed to increased body size and diversity of Early Vertebrate Lineages.

Interaction with environment

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

Early vertebrates evolved a variety of ways to move and grasp their environment, leading to diverse lineages. For example, some animals use their tails to balance or counterbalance their moving bodies. This was an early adaptation that helped diversify later lineages.

Another way early vertebrates modified their environments was through locomotive style locomotion. Mode of locomotion is a key determinant of style of life, with styles ranging from swim bladder-based to land-based.

Swim-like animals used fluid flow around them to move; these are the ones that invented the spring effect. Layer-cake shaped like the bottom part of a fish with legs like a human uses cushioning ground cover for support; these organisms live in dry conditions and need such mobility to survive.

Mode of locomotion is a key determinant of style of life, with styles ranging from swim bladder-based to land-based.

Changes in morphology

how did the evolution of the jaw contribute to diversification of early vertebrate lineages?

Several factors contributed to the evolution of the vertebrate jaw. For example, changes in functional morphology, phylogeny, or biogeography.

Functional morphology describes the physical characteristics of an organism in relation to other organisms. For example, the length of a fish’s head and body determines how it feeds and travels.

In early vertebrates, the head was very small and lacked any structures that would later evolve into a neck. This is because early Anapsida members did not have necks to support the large heads.

However, as early Anapsida members diversified into different groups with different heads and necks, these differences developed!

Finally, as more groups diversified with more distinct necks and heads, new patterns developed in synapomorphies (statuesque variations on basic shapes).

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