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Sorting Branches on the Tree of Life August 07 2020, 0 Comments

Studies of the diversity of life are a pillar of life science at elementary level. In the past, Montessori classrooms used charts that show Linnaean classification – Kingdom, Phylum, Class, etc. Those charts are no longer very useful except in studies of the history of science. Instead, children need an introduction to the Tree of Life, which they can get via a branching diagram aka family tree, evolutionary tree, phylogenetic diagram, or phylogeny. If you need a Tree of Life diagram, you can download one for free at my website.

In early childhood, children sort pictures under labels, beginning with living vs. nonliving, animal vs. plant, and invertebrate vs. vertebrate, for example. Later, they sort pictures under more categories such as classes of vertebrates or phyla of invertebrates. The activity in my new material, Sorting Branches on the Tree of Life, will look somewhat familiar to children, but it has enough differences to make it challenging and interesting.

As Montessori classrooms adapt to the changing world of academic knowledge, one of the first things will be to help children learn the main branches on the Tree of Life. They need an introduction to the Tree of Life to get an overview, and then they are ready to start studying the main branches. Note that I use the terms “clade,” “lineage,” and “branch” to mean more or less the same thing – an ancestor and all of its descendants.

A challenge of Tree of Life classification is that the big branches have little branches, and the branches are not ranked (aren’t a phylum, class, etc). One simply has to know that the vertebrates are a branch of the chordates, for example. It really isn’t as hard as it sounds. Sorting Branches on the Tree of Life will help children and adults learn the main branches as they sort photos of organisms under a set of heading labels. When children have completed the diagrams, they will be able to see that the organisms belong to a number of clades. They will also be more prepared to use phylogenies (branching diagrams) that show the main branches. Older ones may even want to try their hand at drawing a phylogeny based on a diagram they have completed.  

Sorting Branches on the Tree of Life covers the vertebrates and the plants. It has a series of lessons, each of which builds on the last to help children learn the clades (branches, lineages). The lessons use images of extant animals (with one exception) and plants, but they tie into some of the history of the clades as well. One really can’t teach about the diversity of life without giving information about the origin of the branches of life.

I’ll start with descriptions of the lessons for the vertebrates in this article and leave the plants for another day. The first lesson shows the earliest branching of the vertebrates, which produced the jawless fish and the vertebrates with jaws. The latter clade, called the gnathostomes, has two branches, the cartilaginous fishes and the bony vertebrates. I have called the second branch the bony vertebrates instead of the bony fishes because it holds more than just fish. It is actually our branch as well.

The bony vertebrates have two branches, the ray-finned fish and the lobe-fins. The latter includes the coelacanth and the lungfish, as well as the tetrapods, the animals with four limbs. I used a picture of a lion to represent the tetrapods so that children could see that ALL the tetrapods belong to that lineage, not just the amphibian-like, first ones to evolve.

The second lesson shows the branches of the tetrapods, and its diagram shows that birds are a branch of the reptiles.

Reptiles, birds, mammals, and eutherian mammals each have another lesson with a diagram. The reptile and mammal lessons come after children have had the tetrapod lesson. The reptile lesson shows that this branch of life divides into the lepidosaurs (“scaly lizards”) and the archosaurs (“ruling lizards”). For the latter, the branches are the crocodilians (crocodiles, alligators, and relatives) and the dinosaurs. The pictures under the dinosaur label are a non-avian dinosaur and an avian dinosaur – a chicken. Yes, the birds are really dinosaurs, and they should be placed under the archosaur label.

Don’t panic at the idea of birds being a branch of the reptiles. We can still teach about those two branches of life separately. The traditional reptile lessons usually give the characteristics of the squamate reptiles – lizards and snakes – or of turtles, which are a world of their own, a sister branch to the archosaurs. Lessons can emphasize the traits that birds and crocodilians share. Studies of birds can note their reptile-like traits such as scaly skin on their legs.  

The mammal diagram shows the first two branches as the monotremes and the therians. This omits a lot of mammal history, but the point of these lessons is not the whole history of the organisms. It is about the branches of the currently living ones. The therians are the marsupials and the eutherian mammals, aka placental animals. When you have finished the lesson on the eutherian mammals, children can go back through and make a list of their own branches of life.

I produced this material this spring, and children in a Montessori classroom got to see a prototype just before the schools closed because of the pandemic. The teacher reported that they were very interested in the material, partly because it doesn’t look like all their other materials. By elementary age, children are ready for variety and challenge. Sorting Branches on the Tree of Life supplies both.

I am happy to answer questions you may have about this material. I supply it as a digital download, a file that you can print for yourself. See https://big-picture-science.myshopify.com/collections/biology/products/sorting-branches-on-the-tree-of-life-vertebrates-and-plants.

An imaginary look at the animal kingdom nesting boxes January 14 2020, 2 Comments

In my last post, I took readers on an imaginary tour of nesting boxes for the plant kingdom. These materials are traditionally called Chinese boxes, but I prefer to use “nesting boxes.” Children explore the structure and major lineages of a kingdom of life with this material. Nesting boxes work well for showing the lineages of the animal kingdom provided the content reflects current knowledge.

Here’s an imaginary tour of nesting boxes for the animal kingdom as it is defined today. I believe firmly that we should be giving children terms that they will see in their further studies, not terms that are historical and that do not appear in modern textbooks.

To start our tour, picture a large red box labeled “Animal Kingdom.” We remove the lid, and inside there is a small box that is labeled “Phylum Porifera, the sponges.” This group was once called the Parazoa, but this term has fallen out of favor, and I recommend these animals be called the sponges. Once thought to be several separate lineages, they are now placed on one lineage, Porifera (“the pore-bearers”).

Along with the little Porifera box, there is a much larger box that takes up most of the animal kingdom box. It is labeled “Eumetazoa, the true animals.” We lift the lid, and inside there are two small boxes labeled “Phylum Ctenophora, the comb jellies” and “Phylum Cnidaria, the stingers.” A large box labeled “Bilateria” takes up most of the remaining space, and it holds the animals with bilateral symmetry.

Cnidarians include the sea anemones, corals, and jellyfish. The comb jellies include sea gooseberries and sea walnuts. These two phyla were previously placed in a single phylum. That phylum, Coelenterata, is obsolete and should not appear in current animal kingdom classification studies. Our small red boxes are labeled “Phylum Cnidaria, the stingers,” and “Phylum Ctenophora, the comb-bearers,” and “Coelenterata” is not here at all.

The big box labeled “Bilateria, animals with bilateral symmetry” contains two boxes, which are labeled Protostomes (“mouth first”) and Deuterostomes (“mouth second”). These names reflect a difference in the development of the fertilized egg in these two lineages. The deuterostome box takes up about 1/3 of the space. We look inside it, and we find two boxes, one labeled “Phylum Echinodermata, the spiny skins,” and the other “Phylum Chordata, the corded ones.” The echinoderm box has the sea urchins, sea stars, and sea cucumbers inside. The chordate box has its three subphyla inside, the lancelets, the tunicates, and the vertebrates. Note that chordates are not the same as vertebrates! I’ve seen them mistakenly equated in Montessori materials. (If you find the term “non-chordate” in your materials, it would be best to change it to “invertebrate.”)

The protostome box has two boxes inside, one labeled “Spiralia” or “Lophotrochozoa” and one labeled “Ecdysozoa.” The Spiralia box has the rotifers, the flatworms, the mollusks, and the annelids (segmented worms). This box also has the name Lophotrochozoa although some biologists use this cumbersome term for only a part of the Spiralia. The term Spiralia could change so check again in a few years to see the current story. The Spiralia are named for the pattern of cells in the early embryos of most species.

“Lophotrochozoa” is still used for the Spiralia lineage in many college textbooks, but this could to change by the time elementary children reach college age. I have adopted “Spiralia” because of biologists’ support for it, and it is easier to spell and say. My book, Kingdoms of Life Connected, still has “Lophotrochozoa” because when I reprinted it last year, the term “Spiralia” was not yet shown in Wikipedia (usually a good source for the latest phylogeny). I hope biologists have settled on the name by the time I print the book again.

The ecdysozoa are the molting animals. They shed their whole outer covering at once. This is the most successful animal lineage in terms of numbers of species and numbers of individuals. The Phylum Arthropoda, the jointed feet, and the Phylum Nematoda, the roundworms, are the two main phyla in this box. Tardigrades and velvet worms could also go here if space allows and if you want to get that level of detail.

If any of your animal kingdom materials include “protozoa,” please remove them and study them with the eukaryotic supergroups (protists). They do not belong in the animal kingdom. If your nesting boxes for animals have protozoa, the best time to change this was about 40 years ago. The second best time is now.

I’ve presented a basic look at the animal kingdom here. If you would like further information on the animal kingdom or the lineages I gave in this article, please see my book, Kingdoms of Life Connected. https://big-picture-science.myshopify.com/collections/biology/products/kingdoms-of-life-connected-second-edition (printed) and https://big-picture-science.myshopify.com/collections/biology/products/kingdoms-of-life-connected-ebook-1 (pdf).

If you want to evaluate an animal kingdom chart, look for the groupings I gave for the nesting boxes. The nematodes should be grouped with the arthropods. The echinoderms should be grouped with the chordates. This is because biologists group organisms according to their shared ancestors, not just how they look. The chart from InPrint for Children places related phyla next to each other. See https://big-picture-science.myshopify.com/collections/biology/products/animal-kingdom-chart.

My photo card set for the animal kingdom - https://big-picture-science.myshopify.com/collections/biology/products/zoology-photo-cards-set-1-major-phyla-of-the-animal-kingdom – gives you high quality images of representative animals across the kingdom. They could be used in or alongside a nesting box material.

Happy explorations of the animal kingdom,

Priscilla

 

PS. I am putting my reply here to two comments below. I'm sorry I don't have pictures of this imaginary material for you, Gail. I, too, am a visual learner. I think Cindy's idea of referring to the animal kingdom diagram from my Tree of Life chart might help. Yes, the lids on the boxes would be like a node on the evolutionary tree (phylogeny). The reason that there isn't a box for the Radiata is that they don't seem to share a common ancestor other than the one for all animals. If they did share a more recent ancestor, they might still be in Coelenterata. They have a similar organization, although the ctenophores are described as biradially symmetrical. They have a combination of radial and bilateral symmetry. The cnidarians are genuinely radially symmetrical. These two phyla came from separate experiments by early animal life. This is different than the the two phyla shown in the Ecdysozoa. They shared a common ancestor - at least there evidence for this in their genomes. 

Thank you for sending your questions and comments. Please feel free to ask further questions.  


Moving past zoology and botany April 30 2019, 0 Comments

Normally, I write about elementary or secondary education in my blog. In this one, I’m addressing an issue that starts in early childhood, and it affects the way children view the living world in their later studies.

Traditionally, Montessori life science (biology) was divided into zoology and botany. The divide began when young children sorted pictures into animals vs. plants. This exercise fit well with the two kingdom approach to classifying the living world. I certainly hope that Montessori teachers no longer use two kingdoms. Biologists began moving away from two kingdoms in the mid-1800s, although it took a hundred years and major advances in biochemistry and microscopy to complete the break. We can give children a more useful overview of the living world than simply animals and plants.

It is time to quit thinking of life science as zoology or botany, or structuring our teaching albums (manuals) this way. When we offer only two categories for living things, children miss much of the living world. While young children are not ready for lots of details, they can sort pictures of living things into three categories, the third being “Other living things.” This tells them that there are organisms that are neither plants nor animals, and it keeps the door open for further learning. Mushrooms, lichens, and kelp are examples of macroscopic organisms that fit under the “Other” heading.

I started my work to bring current science concepts and content to teachers over 20 years ago. My first conference workshop was about the Five Kingdom classification. I spent nearly a decade helping teachers move from two kingdoms to five kingdoms. Then I had to switch gears again as expanding knowledge (via DNA and RNA) of the relationships between living things led to new concepts of classification, principally the Tree of Life and phylogenetics. My book, Kingdoms of Life Connected: A Teacher’s Guide to the Tree of Life, has learning activities and resources for exploring all the branches of life and viruses, too.

The microscopic living world is more abstract and harder to observe than plants and animals, but that does not mean that children shouldn’t know about it. They can learn that microorganisms help plants grow, recycle nutrients, and make foods like yogurt and cheese possible. The disease-causing microorganisms are the ones that we experience most directly, and these get the most attention, but children need to understand the vital importance of microorganisms to all ecosystems.

The book, Tiny Creatures, by Nicola Davies and Emily Sutton (2014) is a valuable resource for introducing young children to the microscopic world. These authors have a second book (2017), Many: The Diversity of Life on Earth, which supports a more inclusive view of life. The Invisible ABCs by Rodney P. Anderson (2006) sounds like it would be for early childhood, but it looks better for beginning elementary. This publication from the American Society for Microbiology has accurate information and good images of the organisms. Its breezy style makes this abstract world more interesting.

Moving past botany and zoology also means considering more than biological classification. It means thinking about the ecosystems, environments, and interactions of life, the structures of life, and the evolutionary history of organisms. Elementary children will have a better idea of the importance of microorganisms after they read Ocean Sunlight: How Tiny Plants Feed the Seas by Molly Bang and Penny Chisholm (2012). This book uses the term “plants” for the ocean’s protists that perform photosynthesis, even though many are not on the green algae-plant lineage. More importantly, it shows children the microbial underpinnings of the ocean ecosystem.  

In elementary life science studies, there will be times to focus on the animals or the plants, but children will have a better perspective if they start with an introduction to the whole Tree of Life and learn to use this conceptual framework. As children develop their abstract thinking, they are likely to be interested in exploring all the branches of life. They will need good tools, such as magnifiers and microscopes, to help them observe the protists and prokaryotes. They also need appropriate search terms for finding resources they can read and understand.

I hope you and your children enjoy studying the greater living world.

Priscilla