Module 1 Flashcards
Background: Cladistics, Geological Time, Fossil Record
Why is Carl Linnaeus and his contributions to science relevant to mammal ecology?
Carl Linnaeus published Systema Naturae, which served as the basis for the phylogenic categorization of animals. This is extremely important for understanding mammal life history, as it was deduced by observing similarities in the fossil record.
How do we categorize mammals today, in terms of taxonomy?
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Then..
Order; Family; Genus; Species
Ex) Carnivora, Felidae, Panthera, Panthera pardus
* Genus and Species should always be italicized
There are additional ranks and sub ranks but this is the simplified version.
Note that taxonomic identification/categorization is dynamic. There is ongoing research or new findings in the fossil record that may redefine these categorizations at any time.
We can make inferences of the evolutionary processes that acted on animal ancestors to form those we know today by forming different taxonomic groups.
Define paraphyletic, polyphyletic, and monophyletic.
A paraphyletic group includes the common ancestor and some, but not all, of the ancestor’s descendants.
A polyphyletic group does not include common ancestor of the group
A monophyletic group includes the common ancestor and all descendants of that ancestor
Why are monophyletic groups the most valuable for mammal lineage analysis?
Polyphyletic, and sometimes paraphyletic, groups can represent traits formed through converging evolution. Meaning the traits were not evolved from a common ancestor, but rather coincidentally due to similar environmental conditions or selective pressures.
When we are trying to determine mammal lineage, it is important to look at traits which are sourced from prior species. In other words, monophyletic groups best represent the process of speciation.
However, it is important to note that polyphyletic or paraphyletic groups may be formed when evidence suggests relation but lacks sufficient evidence to be certain of this claim.
Primates are commonly differentiated into what two groups? What characteristics are these categories based on?
Haplorhini (dry noses): apes, humans, gorillas
Have shorter rostrums and a plate separating orbits from temporal fossa
Strepsirhini (wet noses): lemurs
Have relatively long rostrum and posses postorbital bars. Do not have a plate separating orbits from temporal fossa.
Define the following terms:
homologous organs, homologs, synapomorphy
Homologous traits are derived from a common ancestor while, homoplastic traits are derived from convergent evolution
Homologous organs: organs from different organisms that have similar structures but different functions. They are the result of divergent evolution, which is when species with a common ancestor develop similar structures to adapt to different environments.
Homologs: biological features that are descended from a common ancestor. They can be chromosomes, genes, or other features.
Synapomorphy: a characteristic present in an ancestral species and shared exclusively (in more or less modified form) by its evolutionary descendants; or possession by two or more organisms of a characteristic inherited exclusively from their common ancestor
How can we use atomic analyses and isotopes to understand more about the life history of a fossil?
Many elements, such as carbon, decay over extremely long periods of time. This radioactive decay occurs of the neurons, thus producing isotopes. For example, Carbon-14 degrades to isotopes C-13 then C-12 over time. After 5730 years, a fossil will have half the C-14 that was present at time of death; this is the Half-life of Carbon-14.
Living organisms will reflect isotopic ratios based on how carbon was originally acquired in the ecosystem (atmosphere, lake, etc.) and incorporated into the tissues of the organisms. This can reflect the trophic level of the organism and helps us to determine what the diet and ecological role of the specimen likely was.
We are able to use these processes because the living material of the bones are gone. All that remains is the mineral deposits, or “rock”. It is extremely rare to find fossilized soft tissues. These are called “sub-fossils”.
Summarize the geological history of our planet in regards to mammal evolution using the following terms:
Precambrian, cool, warm, Phanerozoic, Palaeozoic, mesozoic, triassic, jurassic, cretaceous, cenozoic, Palaeocene
The planet goes through constant warming and cooling cycles that are not uniform in nature (average global temperatures ranging from 12°C to 22°C). These cool and warm periods were key factors in the evolution of life on the planet.
We can divide the Earth’s geological history into two Eons: Precambrian and Phanerozoic.
The Precambrian eon occurs 4600-545 million years ago (mya) and was characterized by the earliest fossil record of life then, later, shelled animals.
To kick off the Phanerozoic eon we have the beginning go the Paleozoic era (specifically the Cambrian period) at ~545 mya. During the Cambrian period the first fish are established. After about 40 million years pass (505 mya) the first land plants evolve. Consequentially, the Ordovician period is characterized by the most oxygen on Earth that animals have ever experienced (true to this day). Animals with poor lungs were able to survive in these conditions. However, there was a major reverse of global warming with the rapid uptake of atmospheric carbon. Throughout the Paleozoic era, animals continue to evolve and the Earth continues to cool. At 408 mya the first amphibians walk the Earth and 360 mya reptiles. By 286 mya (the Permian period), it is very cold and Pangea forms.
By the start of the Mesozoic era, the Triassic period, global temperatures have risen again to average highs. This is important because at this time, 245 mya, the first mammals and the first dinosaurs evolve into existence. These high temperatures remain until the end of the jurassic period (208-144 mya), when we see the first birds. By the end of the Cretaceous period, the Earth enters another “warm” cycle and, 66 mya, a major asteroid event (which was deduced from uranium deposits on earth from that time) results in the extinction of the dinosaurs.
This marks the beginning go the Cenozoic era and the Palaeocene epoch. It was in this new environment, in the absence of the dinosaurs, that mammals were able to establish themselves to predominately on the planet. This would take place throughout the Cenozoic era until present day (Holocene). Note that we are nearing the end of a cool cycle.
When did true mammals first appear? What did these mammals look like?
in the Triassic period, 245 million years ago
“Juramaia is an extinct genus of very basal eutherian (placental) mammal from the Late Jurassic period. It is a shrew-like mammal with a body length of approx. 70-100 mm”
This means the origin of placental mammals (Eutheria) may be as long ago as 160 mya!!
How does the formation of Pangea and her breaking into the continents relate to mammal evolution and ecology?
Prior to Pangea breaking, everything that would later become a mammal was together. The breaking of Pangea and the creation of the continents lead to the speciation of mammals and the evolution of the lineages we know today.
For example, at 40 mya most marsupials were out-competed by placental mammals except in isolated locations like Australia.
Summarize our current understandings of basic mammal phylogeny.
When summarizing our current understandings of basic mammal phylogeny, we begin with synapsid reptiles. These were reptiles that possessed the features that would soon evolve into those characteristic of mammals. From the synapsids, the therapsids evolved. These are reptile-like mammals which serve as the basis for the evolution of the mammals we know today. From this same lineage, but much later in time, evolved the Prototherids (Platypuses).
At the end of the Cretaceous period, both monotremes (egg-laying mammals) and marsupials evolve. Both of these would later be mostly out-competed by placental mammals (Eutheria), which arrive on the scene around the Palaeocene. The evolutionary success of the placental mammals, along with continental drift, results in a great variety in placental mammals.
