Module 3 Flashcards
Subclass Prototheria Clade (Order) Monotremata
Identify monotreme characteristics. Recognize and describe the key morphological and physiological features that distinguish monotremes (e.g. egg-laying, lack of nipples, presence of a cloaca) from other mammals.
Monotremes exhibit a combination of reptilian and mammalian characteristics.
For example, platypuses have a fur coat adapted to an aquatic lifestyle (that keeps them warm and dry underwater); females lactate, yet lay eggs in underground burrows like reptiles; and males are equipped with venom similar to that of reptiles released from their back claws (spurs); is able to shut eyes and ears when swimming; toothless mouth and rubbery beak like a bird; webbed feet for swimming similar to those of aquatic birds; possess a single opening for anus and ruin-genital system, like birds and reptiles; and possess sophisticated electro-sensory system for underwater foraging. Platypuses also have large forelimbs and backwards facing hindlimb adapted for digging.
Echidnas have elongated snouts adapted for feeding on invertebrates; protective spines; long sticky tongues (common in insectivores); and the limbs adaptations for digging also seen in the platypus (however they do not burrow, only dig for prey, will reside in abandoned burrows dug by other animals); echidnas also possess electroreception in their snouts; and also, like the platypus, lack teeth (instead have hard gums for grinding).
Explain the evolutionary significance of monotremes as one of the earliest-diverging mammalian lineages and their role in understanding mammalian evolution.
Monotremes diverged from the therian mammal lineage ~166 mya and developed a unique suite of characteristics (holoblastic cleavage, placentation, viviparity, testicular descent). However both prototherian and therian mammals share homeothermy and lactation.
“Monotremes are evolutionarily significant because they represent one of the earliest-diverging branches of mammals, providing valuable insight into the transition from reptilian ancestors to modern mammals. Their unique characteristics highlight the evolutionary experimentation that occurred in early mammalian evolution.” (chat)
Identify the extant monotreme species (platypus and echidnas) and describe their geographic distribution, ecological roles, and adaptations to their environments.
Monotremes are the only group of egg-laying (oviparous) mammals indigenous to Australia and New Guinea with two extant families and their species. Ornithorhynchidae, which its only living member is the platypus (Ornithorhynchidae anatinus), and Tachyglossidae (Echidnas; short-beaked and long-beaked).
The platypus is found in eastern Australia and Tasmania, is semi-aquatic, and is known for its distinctive duck-bill, webbed feet, and electroreception abilities used for hunting in water.
Short-beaked echidnas (Tachyglossus aculeates) is found in Australia and New Guinea. This species is adapted to a variety of habitats and feeds primarily on ants and termites.
Long-beaked echidnas (T. Zaglossus spp.) is native to New Guinea. These species have longer snouts and feed primarily on earthworms and other invertebrates. There are three recognized species: the Western Long-Beaked Echidna, Sir David’s Long-Beaked Echidna, and the Eastern Long-Beaked Echidna).
Analyze the unique reproductive strategies of monotremes, including egg-laying, maternal care, and the transition from reptilian to mammalian reproductive traits.
Monotremes have two uteri, one for each ovary and fallopian tube (oviduct). Echidna males actually have double-headed pens as well as double tailed sperm.
Monotremes mothers nest in burrows and lay eggs which hatch underdeveloped young. The offspring attach to their mothers’ fur and lap up milk (also from their mothers’ fur) which is produced by glands and secreted through the skin. This is because monotremes lack nipples.
Summarize the fossil history of monotremes, including the discovery of extinct species, and explain how these findings contribute to our understanding of early mammalian evolution.
There is not much in the fossil record for monotremes unfortunately. However, we do know that we already had platypuses in the crustaceous period.
We have evidence in the fossil record of now-extinct species Steropodon (100 mya), which displayed many of the highly derived features we see in the platypus today (duck-bill, webbed feet, flat beaver-like tail, semiaquatic lifestyle and relevant adaptations in fur).
“Highly derived” means something has come from a source or origin in a significant way, indicating a large degree of development or modification from its original form, often implying a complex or evolved state compared to its ancestors or starting point; in essence, it signifies something that is significantly different from its original source due to multiple layers of development or adaptation.
In other words, has undergone vast evolutionary changes and is, in theory, well adapted to environmental selective pressures of many kinds.
Compare and contrast monotremes with marsupials and placental mammals.
- Epipubic bones– found in monotremes, marsupials, and some fossil mammals– are a pair of bones that extend from the pelvic girdle into the abdominal region of some mammals. Epipubic bones help support the abdominal wall and may protect the pouch of marsupials.
- Monotremes possess reptile-like pectoral girdles resulting in lateral locomotion that has limited range of motion.
Examine the genetic and molecular studies that have provided insights into the evolutionary relationships of monotremes with other mammals and their unique traits.
“Analysis of the first monotreme genome aligned the features specific to the platypus with genetic innovations, discovering that reptile and platypus proteins have been co-opted independently from the same gene families; milk protein genes are conserved despite platypuses laying eggs; and immune gene family expansions are directly related to platypus biology. Expansions of protein, non-protein-coding RNA and microRNA families, as well as repeated elements, are identified. Sequencing of this genome now provides a valuable resource for deep mammalian comparative analyses, as well as for monotreme biology and conservation.” (Warren et al., 2008).
Discuss the conservation status of monotremes, the threats they face (e.g. habitat loss, climate change), and efforts to protect them.
“The platypus’ distribution coincides with many of Australia’s major threatening processes, including highly regulated and disrupted rivers, intensive habitat destruction, and fragmentation, and they were extensively hunted for their fur until the early 20th century. Emerging evidence of local population declines and extinctions identifies that ecological thresholds have been crossed in some populations and, if threats are not addressed, the species will continue to decline.
In 2016, the IUCN Red Listing for the platypus was elevated to “Near Threatened”, but the platypus remains unlisted on threatened species schedules of any Australian state, apart from South Australia, or nationally.” (Bino et al., 2019).
