Module 13 Flashcards
Perissodactyla
Describe the defining characteristics of Perissodactyla and distinguish them from other ungulate groups.
- Odd-toed ungulates: Primarily bear weight on the central (3rd) digit, with mesaxonic limb structure.
- Digit reduction: Most species have reduced or lost lateral digits (e.g., horses have one toe, rhinos three).
- Unguligrade posture: Walk on tips of toes protected by hooves.
- Simple stomachs: Hindgut fermenters (unlike ruminants), relying on cecum/colon for cellulose digestion.
- Dentition: Lophodont or selenodont molars for grinding tough vegetation; often lack upper incisors.
Understand limb anatomy specialization in Perissodactyls, including adaptations related to mesaxonic limb structure, calcaneum modifications, and phalangeal arrangements in relation to locomotion.
Mesaxonic limb structure:
- Weight is borne primarily on the central (third) digit, which is enlarged and robust.
- Reduction/loss of lateral digits (e.g., horses retain only a single toe).
Calcaneum modifications:
- The calcaneus (heel bone) is elongated, improving leverage for fast, efficient locomotion (e.g., cursorial adaptations in horses).
- Articulates with the fibula in some species, stabilizing the ankle during movement.
Phalangeal arrangements:
- Reduced number of phalanges in lateral digits (e.g., modern horses have only one digit with three phalanges).
- Elongated distal phalanges form hooves, enhancing durability and speed on hard ground.
Locomotor adaptations:
- Unguligrade posture (walking on tips of toes) improves stride length and energy efficiency.
- Limb bones (e.g., metapodials) are elongated for cursorial (running) lifestyles in open habitats.
Compare the digestive adaptations of Perissodactyls to other herbivorous mammals, particularly in relation to hindgut fermentation.
Hindgut fermentation is when fermentation occurs in the caecum and colon.
Trace the evolutionary history of horses (Equine), from Eohippus (Hyracotherium) to modern Equus, and explain the morphological changes associated with this transition.
- Grew over time
Eohippus (Hyracotherium) (~56–45 Ma)
Change: Small, forest-dwelling, 4-toed forelimbs, browsing teeth.
Mesohippus (~40–30 Ma)
Change: Larger, 3-toed, longer limbs, transitional teeth.
Merychippus (~20–10 Ma)
Change: Hypsodont teeth for grazing, central toe dominant.
Pliohippus (~10–5 Ma)
Change: First single-toed horse, fully grazing-adapted.
Equus (~4 Ma–present)
Change: Modern monodactyl hooves, fast cursorial locomotion.
Trend: Toe reduction, limb elongation, tooth crown height increase, size increase.
Discuss extinct Perissodactyl groups, including Brontotheriidae and Chalicotheriidae, and explore their ecological roles and evolutionary relationships.
Brontotheriidae (“Thunder Beasts”)
Time & Habitat: Eocene to early Oligocene (~56–34 Ma), North America and Asia.
Morphology: Large, rhino-like bodies with paired bony nasal horns (not true horns).
Ecological Role: Bulk browsers in open woodlands, likely outcompeted by climate shifts and artiodactyls.
Evolution: Early perissodactyl offshoots, related to tapirs/horses but with no living descendants.
Chalicotheriidae (“Clawed Perissodactyls”)
Time & Habitat: Eocene to Pleistocene (~40–1 Ma), global distribution.
Morphology: Unique among perissodactyls—long forelimbs, clawed feet (knuckle-walkers), and gorilla-like posture.
Ecological Role: Specialized folivores, possibly hanging branches to feed (convergent with ground sloths).
Evolution: Part of the Ancylopoda clade, closely related to modern tapirs and rhinos despite bizarre anatomy.
Key Evolutionary Insight: These groups show the diversity of perissodactyls before artiodactyl dominance, with adaptations (horns, claws) reflecting niche experimentation.
Their extinctions highlight vulnerability to climate change and competition.
Examine the conservation history and status of Equus ferus ferus (Tarpan) and Equus ferus przwalskii (Przewalski’s horse), including efforts to reintroduce these species into the wild.
The Tarpan (Equus ferus ferus), Europe’s wild horse, went extinct in the late 19th century due to hunting and habitat loss, though “back-breeding” projects have attempted to recreate its phenotype. Przewalski’s horse (Equus ferus przewalskii), the last truly wild horse, was nearly extinct by the 1960s but has been successfully reintroduced to Mongolia and China through captive breeding and protected reserves, with populations now considered “Endangered” but stable.
Discuss the diversity of Rhinocerotidae and Tapiridae, including both extinct and extant rhinoceros species, and their adaptations to different ecological niches.
Rhinocerotidae (Rhinos)
Extant: 5 species (e.g., white rhino = grazer, Javan rhino = browser).
Extinct: Giant Elasmotherium (Eurasia, single horn), woolly rhino (Coelodonta, Arctic-adapted).
Adaptations: Hypsodont teeth (grazers) vs. brachydont (browsers), horns (keratin/nasal bone), size for defense.
Tapiridae (Tapirs)
Extant: 4 species (tropical forest dwellers, short trunks for browsing).
Extinct: Tapirus augustus (giant Pleistocene tapir), Heptodon (Eocene, hornless rhino-like).
Adaptations: Prehensile snouts, brachydont teeth, nocturnal/secretive lifestyles.
Ecological Roles: Rhinos = megaherbivores in open/savanna habitats; tapirs = seed dispersers in forests. Both show niche conservatism (limited post-Oligocene diversification).
Understand the role of convergent evolution, using examples such as chalicotheres and giant ground sloths; and Indricotherium (now Paraceratherium) and sauropod dinosaurs (high-browsing megaherbivores).
Tetraclaenodon puercensis
an extinct genus of small, primitive ungulate mammal of the herbivorous family Phenacodontidae
- early-stage perissodactyl
Phenadocus
Phenacodus is an extinct genus of mammals from the late Paleocene through middle Eocene, about 55 million years ago. It is one of the earliest and most primitive of the ungulates, typifying the family Phenacodontidae and the order Perissodactyla
Meniscotherium
Meniscotherium is an extinct genus of dog-sized mammal which lived 54–38 million years ago. It was a herbivore and had hooves.
A 2014 cladistic analysis places it within stem perissodactyls
Family: Phenacodontidae
Summarize the broad evolutionary history of Perissodactyla.
Broad Evolutionary History
Origins: Emerged ~56 Ma (early Eocene) from condylarth ancestors.
Diversity peak: Dominated mid-Cenozoic (e.g., giant Indricotherium, early horses like Hyracotherium).
Decline: Outcompeted by Artiodactyla post-Oligocene, possibly due to less efficient digestion.
Extant groups: Only 3 families survive—Equidae (horses), Rhinocerotidae (rhinos), and Tapiridae (tapirs).
Siberian Unicorn
Wooly Rhino
