BSCI392
9-28-07
Reconstructing diets

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Aquatic feeding:

Ancestrally, all animals fed in water - a dense, viscous medium. In some cases, the methods they employed transferred onto land easily. Others could only occur underwater.

Suspension feeding: The filtration of particulate matter or very small prey from the water. This is the topic of an upcoming lecture.

Appendicular feeding: Ancestrally arthropods and their kin captured prey with their limbs and stuffed it into their mouths. Although the tagmosis of arthropod groups and the homology of these limbs differs, all retain this basic pattern in that their paired mouthparts are modified limbs.

Examples:

In a variation of this, nektonic cephalopods grapple onto their prey with their arms (lined with hooks or suckers) then dismember it with their mouths.

The feeding apparatus of the ancestral gnathostome relied on the scissor-like action of the upper and lower jaws to bite and hold prey. However, swimming up to a prey item in the water and taking it into the mouth is difficult because the streamlining of currents around the predator's head tends to sweep prey away from its mouth. Ways around this problem include:

Biting: In some circumstances, creatures get away with using the ancestral scissor-like bite.

Terrestrial feeding

Engulfing of whole prey: In water, this is the most effective method, but in air, suction feeding is impossible. Nevertheless, the first land vertebrates inherited the whole ingestion of small prey from their aquatic ancestors. After the evolution of initial adjustments such as the neck, many vertebrates persisted in simple engulfing of small prey. E.G.: salamander.

Some groups developed special techniques for engulfing whole prey including:

Two major groups evolved the ability to bite pieces off of their food,

Biting - Archosaur-style: Although archosaurs have evolved a wide range of feeding adaptations, their last common ancestor was something like Erythrosuchus, a predator with a uniform row of blade-like serrated teeth, with which it could bite off pieces of its prey, rather than swallowing it whole.

Biting - Synapsid-style:

Synapsids also developed the ability to bite off hunks. In their case, this was accomplished by teeth that were differentiated along the tooth row. Initially, there were large canines for immobilizing prey, and pre- and post-canine teeth for nipping and shearing. These ultimately evolved into the mammalian array of incisors, canines, premolars, and molars.

Ecological specializations: Both synapsids and archosaurs have experimented with a wide range of feeding ecologies, including herbivory and durophagy. Adaptations to herbivory are remarkably similar, despite the phylogenetic differences of the animals. Key adaptations include:

These adaptations are visible in both synapsids:

and archosaurs:

Also evident is the evolution of grinding teeth with self-sharpening surfaces.

In some herbivorous dinosaurs, food was ground with batteries of teeth with little or no enamel on one side. These would self-sharpen with use and fall out and be replaced with new teeth when worn.

In many herbivorous mammals (synapsids), food is ground with teeth containing complexly infolded layers of enamel. With wear, these form complex ridges on the tooth's occlusal surface. Often, these are continuously growing.

Browsing vs grazing: Cenozoic mammals diversified during the same interval in which grasses became common. The processing of grass imposes special demands, mostly because they incorporate large quantities of phytoliths - silicate nodules - in their tissues, making them very abrasive. Mammalian herbivores that became grass specialists evolved special adaptations as grazers, including:

In addition to this comparative evidence, we have direct evidence of diet from patterns of microscopic enamel wear. major types include:

Case studies: What might be the feeding specializations of:

Eurhinosaurus:

Tylosaurus (a mosasaur):

See skull

Propleopus (a kangaroo):

An enigma given that:

See reconstruction

Finally, examination of the victim can reveal the ecology of predators. Consider the fate of Blue Babe, a Pleiostocene steppe bison who met a violent end on the mammoth steppe of Alaska.

Puncture marks in his hide reveal that he was killed by big cats. But by whom? Suspects include:

Evidence takes the form of:

Answer: Blue Babe was done in by lions.