Comparative Anatomy & Evolution: Integumentary System

Vertebrate Comparative Anatomy & Evolution (Part I) - Integumentary System

• Nails, Claws, Hooves: These structures are composed primarily of compressed stratum corneum cells, reinforced with dense keratin deposits. Different parts include the nail, matrix cells, subunguis, and unguis.
• Nails: Composed of a compressed layer of stratum corneum cells. Hardness comes from keratin deposits. Key parts include the body (painted portion), free border (tip), nail bed (rests on stratum spinosum), and the eponychium (cuticle). The hyponychium is the quick, stratum corneum of the nail covering the hidden border, also known as the hangnail area. Growth originates from the nail matrix below the hidden border; the lunula (semi-circle at the base) is visible.
• Foot and Hoof Anatomy: Hoofs are complex, featuring layers of the hoof wall (from bone, dermis, and epidermis). Key parts include the hoof wall, toe callous, quarters, bars, heel buttress, frog, central sulcus, and heel bulbs. The hoof's structure functions to protect the bone and tissues within the foot.
• Horns and Antlers: Horns are permanent, bony structures, often unbranched (e.g., pronghorn), or small, ossified knobs covered by the integument (e.g., giraffe). Antlers are branched structures that are shed and regrown annually (e.g., elk, moose).
• Other Types of Horns: Pronghorn horns' bony core remains unbranched, while their sheath branches. Giraffe horns are small ossified knobs coated by the integument. Rhinoceros horns consist of compacted keratinized fibers without an inner bony core.
• Baleen from a Whale: Baleen whales use baleen plates in their mouths to filter feed. These plates are crucial for filtering small organisms from water.
• Dermal and Epidermal Derivatives: Beaver tails, Glyptodon shells, and turtle shells are examples of epidermal and dermal derivatives. Dermal bones appear as plates of bone that strengthen the skin and sometimes form protective structures.
• Teeth: Teeth are dermal armor variations, from placoid scales. Primarily dentin, surrounded by enamel. Diverse among vertebrates, differing in distribution, permanence (some continually replacing teeth, others developing sets). Whales use baleen for filtering, while other toothed vertebrates have numerous and widely distributed teeth in the oral cavity and pharynx.
• Tooth Structure and Development: Teeth are structured with enamel, dentin, cementum, and pulp cavity. Odontoblasts produce dentin. Ameloblasts produce enamel. Other components including gums, periodontal ligament, and root canals aid the teeth functionality.
• Tooth Attachment Types: Thecodont teeth are held within bony sockets, like those of mammals. Acrodont teeth have their bases fused to the upper jaw, acro meaning ‘top’, characteristic of the lizards. Placodont teeth are fused directly to the upper jaw's surface, in the form of plates, rather than sockets; this is often seen in many reptiles.
• Tooth Morphology: Bunodont teeth, like those of omnivores, are low-crowned. Hypsodont teeth have tall crowns, frequently seen in herbivores. Lophodont teeth have ridges or "lophs"—these species are mostly herbivorous. Selenodont teeth have curved "seleniform" ridges, common in browsing herbivores. Mammals demonstrate heterodont dentition with diverse tooth shapes (incisors, canines, premolars, molars) for diverse functions (cutting, tearing, grinding).

This quiz explores the integumentary system of vertebrates, including the anatomy of nails, claws, and hooves. Learn about key components such as the nail matrix, subunguis, and hoof structure. Enhance your understanding of how these features contribute to vertebrate biology and evolution.