Module 11 Flashcards
South America as an island
Describe how the isolation of South America during the late Cretaceous and early Eocene periods contributed to the evolution of unique mammalian lineages, such as the Xenarthra and Afrotheria.
- K-T Boundary 65 mya (extinction event)
- Between ~75 to 52 mya South America was an island
- Coinciding development of two major clades (Xenarthra in South America and Afrotheria in Africa)
Trace the origins of distinct mammalian orders in South America, including ground sloths and notoungulates, and identify the factors that influenced their evolution, such as climate, geography, and available ecological niches.
*** Not much talk on the climate part??
Analyze the ecological roles of extinct groups like Litopterna and Notoungulata, comparing them with modern herbivores in terms of feeding strategies, habitat use, and evolutionary significance.
** Don’t forget to compare in more depth
Explain examples of convergent evolution in South American mammalian species, such as the similarities between extinct notohippids and modern horses, despite their unrelatedness.
The notohippids (Notoungulata; Toxodontia) looked very much like horses (Order Perissodactyla), but were unrelated.
Already in the late Eocene they had very high crowned cheek teeth with a cementum sheath, features not seen in true horses for another 25 million years, demonstrating convergent evolution with equids.
Explain how and when South America behaved as an island.
Between the late Cretaceous Period (~75 mya) and the early Eocene Epoch (~52 mya), Antarctica lost its connection to Australia, but maintained its connection to South America.
During the same period of time, South America lost its connection to North America.
By the late Eocene (~35 mya) South America and Australia also became separated, isolating both continents.
Does the name Eremotherium mean anything to you?
Biggest giant ground sloth
- herbivorous
- knuckle walker
- bends trees by weighing them down to eat the leaves
- southern North America, Central America, and northern South America
Who is SHE?
Megalonychid (‘giant claw’)
- Giant two-toed sloth
- Ground sloths first appeared in the early Oligocene, about 35 mya in Southern Argentina (Patagonia)
What is the reason ground sloths were knuckle walkers?
As this animal adapted from a tree dweller to being ground-based, its limbs still showed a relationship to its ancestors.
Typically ground sloths walked on the sides of their hind feet and the backs of their forefeet.
What is a Toxodon? What is an example of convergent evolution with the Toxodon?
Toxodon (meaning “bow tooth” in reference to the curvature of the teeth) is an extinct genus of large ungulate native to South America from the Pliocene to the end of the Late Pleistocene.
Toxodon, an extinct South American notoungulate, and rhinos share some physical similarities, particularly their robust build and herbivorous diet. However, they are not closely related and belong to different evolutionary lineages. Toxodons were large, hoofed mammals with short legs and a hippo-like face, resembling a short rhinoceros. Rhinos, on the other hand, are odd-toed ungulates belonging to the Perissodactyla order, which also includes horses and tapirs.
Avilla & Mothé (2021) hypothesized that some extinct South American mammals (Xenungulata/Notoungulata) may actually belong to the Afrotheria lineage, suggesting an Africa-S. America migration route before continental breakup (~100 mya).
Why is this finding significant for biogeography?
How does this research challenge previous ideas?
Welker et al. (2015) found S. American ungulates (Notoungulata/Litopterna) are Perissodactyls (related to horses, rhinos) using ancient protein sequencing (collagen) from fossils, suggesting a North America-S. America route (e.g., via land bridges).
How do the two papers disagree on the evolutionary ties of S. American ungulates?
Could both hypotheses be partly true?
It implies Afrotherians migrated to South America before the continents fully separated, expanding their known ancient range.
It suggests that Afrotheria were not restricted to Africa and may have diversified in South America before extinction.
Avilla & Mothé (2021) link them to Afrotheria, while Welker et al. (2015) link them to Perissodactyls.
It is possible that both hypotheses are true. Some groups (e.g., Xenungulata) might be Afrotherians, while others (Notoungulata) are Perissodactyls—more research needed!
Notoungulates can be divided into what two groups (according to Cifelli’s 1993)?
Cifelli’s (1993) analysis of notoungulate relationships suggests that they can be divided into two main groups:
Taxodontia and Typotheria, plus two basal notoungulate families.
Define Mixotoxodon and Homlodotherium.
Mixotoxodon is an extinct genus of notoungulate of the family Toxodontidae inhabiting South America, Central America and parts of southern North America during the Pleistocene epoch, from 1,800,000—12,000 years ago.
Homalodotherium is an extinct genus of South American native ungulates in the order Notoungulata. Fossils of Homalodotherium have been found in the Middle Miocene Santa Cruz Formation of Argentina and the Río Frías Formation of Chile.
Who were the Interatheriids?
Notoungulata, Typotheria
Interatheriidae is an extinct family of notoungulate mammals from South America. Interatheriids are known from the Middle Eocene to the Early Pleistocene. These animals were principally small-sized, occupying a habitat like hares, marmots and viscachas. The majority were very small, like rodents.
Let’s talk about Mesotheriidae.
Mesotheriidae is an extinct family of notoungulate mammals known from the Oligocene through the Pleistocene of South America. Mesotheriids were small to medium-sized herbivorous mammals adapted for digging.
Convergent evolution with rodents:
- Teeth: Both had high-crowned (hypsodont) teeth for grinding tough plants.
- Incisors: Some mesotheriids had ever-growing incisors (like rodents), but with enamel on both sides.
- Skulls: Robust jaws with strong chewing muscles and a diastema gap (toothless space).
- Lifestyle: Some were burrowers (clawed limbs) or grazers, filling similar niches.
These similarities are likely due to similar environments and ecological pressures.
Let’s talk about Mesotheriidae.
What species are they convergent with?
Mesotheriidae (“Middle Beasts”) is an extinct family of notoungulate mammals known from the Oligocene through the Pleistocene of South America. Mesotheriids were small to medium-sized herbivorous mammals adapted for digging, convergent with modern rodents.
Top Convergent Traits: Mesotheriids vs. Rodents
- Teeth: Both had high-crowned (hypsodont) teeth for grinding tough plants.
- Incisors: Some mesotheriids had ever-growing incisors (like rodents), but with enamel on both sides.
- Skulls: Robust jaws with strong chewing muscles and a diastema gap (toothless space).
- Lifestyle: Some were burrowers (clawed limbs) or grazers, filling similar niches.
Both groups were shaped by environmental factors and availabilities in the niche.
Is the Archaeohyracidae a true hyrax?
No, Archaeohyracidae is not a hyrax. Archaeohyracidae is an extinct family of notoungulate mammals known from South America, while hyraxes are a living group of mammals related to elephants.
Instead, Archaeohyracidae is convergent with the modern hyraxes.
Similar Traits Between Archaeohyracidae & Hyraxes
- Size & Build: Small, stocky bodies (~rabbit-sized) with short limbs.
- Dentition:
Bilophodont molars (two transverse ridges) for folivorous (leaf-eating) diets.
Reduced canines and similar tooth wear patterns. - Skull Shape: Short snouts and robust skulls adapted for chewing tough vegetation.
- Digit Structure: Plantigrade feet (walked on soles) with hoof-like nails (hyraxes) or claw-like digits (some archaeohyracids).
- Ecological Niche: Both were rock-dwelling or scampering herbivores in rugged habitats.
Key Difference:
Hyraxes have tusk-like incisors, while archaeohyracids had more rodent-like incisors.
Why It’s Cool: They evolved alike despite hyraxes being afrotherians (close to elephants) and archaeohyracids being notoungulates (possibly related to horses/rhinos)! 🌿🐾
Okay wait, so who are the Litopterns?
Order Litopterna
Sister order to Notoungulata
Litopterns (all extinct) are the second most diverse group of South American ungulates, also decended from the Condylarthra but not part of Perissodactyla or Artiodactyla.
They include forms similar to antelopes, horses, and camels, all with relatively low-crowned cheek teeth.
- Likely hindgut fermenters
- Likely preyed upon by Smilodon
