Lecture on Mammals

Introduction

• Mammals are found in diverse environments: land, sea, air.
• Range from small rodents to large elephants and whales.
• Lecture divided into two parts: Evolution of mammals and major extant orders.

Evolution of Mammals

Origins and Early Evolution

• Started in the Carboniferous period (~310 million years ago).
• Early synapsids like Archaeotheras with unique skull features evolved.
• Synapsids (one skull hole) vs Diapsids (two skull holes leading to reptiles).

Permian Period Developments

• Synapsids thrived during the Permian period.
• Groups like Pelicosaurs (e.g., Dimetrodon) and Therapsids evolved.
• Therapsids included Dinocephalians, Dicynodonts, and Gorgonopsians.
• End-Permian extinction drastically affected these groups.

Triassic Period

• Survivors like Dicynodonts (e.g., Lystrosaurus) spread widely.
• Synapsids evolved towards more mammalian features like being warm-blooded.
• Cynodonts developed mammalian traits like fur, hard palate, and improved jaw musculature.

First True Mammals

• Defined by the jaw joint between denture and squamosal region.
• Developments like lactation and increased brain size appeared.

Jurassic and Cretaceous Periods

• Mammals diversified into various niches but were overshadowed by dinosaurs.
• Examples include Castorocauda (beaver-like) and Repenomamus (predatory).
• Monotremes such as Strepidon appeared in Gondwana.

Major Extant Orders of Mammals

Monotremes

• Lay eggs, possess a cloaca.
• Include platypus and echidnas.

Marsupials

• Notable for pouches (not universal).
• Divided into Ameridelphia and Australidelphia.
• Examples: Opossums (Ameridelphia), kangaroos, koalas (Australidelphia).

Eutherians (Placentals)

• Characterized by live birth supported by a placenta.
• Orders include Atlantogenata (e.g., Xenarthra, Afrotheria), Euarchontoglires (e.g., Primates, Glires), Laurasiatheria (e.g., Carnivores, Bats).

Atlantogenata

• Includes South American and African mammals like armadillos and elephants.

Euarchontoglires

• Contains primates, rodents, and lagomorphs.

Laurasiatheria

• Includes orders like Eulipotyphla (hedgehogs, shrews), Chiroptera (bats), Carnivora (dogs, cats).

Conclusion

• Mammals are a diverse group that evolved from synapsid ancestors.
• Occupy nearly every ecological niche and are integral to the modern world.
• Further exploration of individual families is possible for more in-depth understanding.