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EVOLUTION
Before diving into the explanation of evolution, it’s good to first get to know taxonomy.
A. TAXONOMY
a. Definition
Classification by giving names. The classification system starts from grouping general characteristics to specific ones.
b. History
Aristotle
Classified living beings into two major groups: animals and plants. Plants were further grouped into herbs, shrubs, and trees. Animals were divided into three groups: land, water, and air.
C. Linnaeus
Known as the father of taxonomy for systematizing taxonomy.
Developed the binomial nomenclature system:
Contains only genus and species. Species describe specific characteristics or where it was found.
Uses Latin, a dead language that no longer evolves.
Easier to use because it contains only two words (previously names could have up to seven words).
Example: Motacilla tragodytes L, 1758 means genus Motacilla, species tragodytes, named by Linnaeus in 1758 and already described.
Names like Motacilla tragodytes (L, 1758) do not explicitly indicate that Linnaeus described the species.
If only the genus is known (species not determined), add "sp" for animals (e.g., Felis sp.) and "spec" for plants (e.g., Magnifera spec.).
If multiple species are suspected but only genus is known, add "spp" (e.g., Felis spp.).
If the organism resembles a known species but is not exactly it, add "cf" (e.g., Magnifera cf. indica).
B. TAXONOMY IN FOSSILS
Many fossil names differ from their original names — is this a problem? It depends on which names are more widely used.
Morphotaxa are taxonomies based only on morphology and are widely used for plants and microfossils, especially pollen (fine to coarse powder made of pollen grains, the male microgametophyte of seed plants producing male gametes). This causes fossil names to differ from plant names. Example: Spinizonacoliptes.
Paleobotany: study of fossil plants, which differ depending on whether leaves, wood, or pollen are studied.
Phytoliths: silica from plants, especially in dry environments, with varying shapes used for naming.
C. EVOLUTION
a. Definition
Changes in inherited characteristics within a population.
b. Development of Evolutionary Theories
Anaximander
The cosmos formed from chaos.
Life arose from dead matter.
Higher organisms evolved from lower (simple to complex).
C. Linnaeus
Creation theory: all creatures created simultaneously by the Creator.
Current forms are the same as at creation.
Cuvier
Catastrophes wiped out all life at the end of each period.
New life appeared different from previous life after each catastrophe.
Buffon
Current life may have arisen from other life forms.
Eugene Darwin
Animals now may have come from stars.
Lamarck
Simple animals first appeared from non-living matter.
Progressed from simple to complex.
Organs frequently used grow and develop perfectly.
Charles Darwin
Current organisms evolved gradually from previous ones.
Struggle for existence requires competitive ability within or between organisms.
Evolution is influenced by three factors:
Genetics
Time
Natural selection: favors those who adapt to geology and climate.
c. Types of Evolution
Macroevolution:
Large scale, over a long time (more than one generation).
Seen in the fossil record.
Microevolution:
Small scale, over a short time.
d. Direction of Evolution
Retrogressive: from complex to simpler forms.
Progressive: from simple to more complex forms.
e. Evolution Pace
Very slow, e.g., brachiopods.
Moderate, e.g., horses.
Very fast, e.g., mammal development from Mesozoic to Cenozoic.
f. Final Result of Evolution
Divergent: one species evolves into many new species (e.g., mammals).
Convergent: similarity between two organs or organisms from different ancestors (e.g., shark and dolphin).
g. Selection
Morphological and physiological changes.
Occurs within a population.
Produces varied offspring.
Inherited genetics.
h. Effects of Evolution
Adaptation
Coevolution-Cooperation (joint evolution)
Speciation
Extinction
i. Evolution Symptoms
Shell growth.
Growth in specific parts (e.g., teeth).
Suture development (e.g., ammonites).
Direction of shell coiling.
Shapes of specific parts.
Back again with me, Kemal, the author of the blog "Catatan Belajarku" (My Learning Notes). So, how’s the spirit, bro? Still excited to talk about fossils? Hehehe. Alright, let’s keep going!
Animals that have a backbone. Vertebrates first appeared during the Ordovician period and still exist today. They initially lived in the ocean as simple, worm-like organisms.
a. Chondrichthyes
Their body structure is made of cartilage. Key features:
b. Osteichthyes
Their body structure is made of true/hard bone. Key features:
c. Myxini (Hagfish)
d. Cephalospidomorphi (Lampreys)
e. Amphibia
f. Reptilia
g. Aves (Birds)
h. Mammalia (Mammals)
In general, vertebrate fossil identification focuses on two morphological aspects: bone morphology and tooth morphology.
a. Bone Morphology
Vertebrate bones are classified into two types: cranial bones and postcranial bones.
Cranial bones refer to the bones in the skull, primarily functioning to protect the brain. These bones are usually flat and plate-like in shape.
Postcranial bones include the supporting bones of the body and limbs. Limb bones are typically round and elongated, while supporting bones show more variation in shape.
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Cranial bone ©️ thepoundlanespaniel.com |
The bones that make up each vertebrate class have distinct characteristics. For example, fish have bones shaped like spines, reptiles tend to have flat bones, and birds have lightweight, hollow bones.
b. Tooth Morphology
Teeth are very important in fossil identification, especially for classifying mammals down to the species level.
In non-mammalian animals, tooth structure tends to be simpler, with little variation in shape. The main difference is usually in tooth size, not form.
In contrast, mammalian teeth are more complex and can be clearly divided into different types:
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Parts of a tooth |
Because mammalian teeth have distinctive shapes that differ from one another, mammal teeth can be represented using a tooth formula. Below is the tooth formula for mammals.
Let’s take the example of a rabbit, which has a tooth formula of 2033/1023. In this formula, the numerator (top number) is 2033, and the denominator (bottom number) is 1023.
The numerator represents the arrangement of teeth in the upper jaw, while the denominator shows the arrangement in the lower jaw. Both numbers represent half of the jaw (either the left or right side) because mammals have bilateral symmetry — meaning the left and right sides are mirror images. So, the upper left and upper right jaws both have 2-0-3-3 teeth, and the lower left and lower right jaws both have 1-0-2-3 teeth.
Since mammals have four types of teeth, the numbers correspond to the order of tooth types: I C P M — Incisors, Canines, Premolars, and Molars.
So, 2033 means the rabbit’s upper jaw (left or right) has:
2 incisors
0 canines
3 premolars
3 molars
And 1023 means the rabbit’s lower jaw (left or right) has:
1 incisor
0 canines
2 premolars
3 molars
This means rabbits don’t have canines, which classifies them as herbivores.
How’s that? Pretty clear, right? Hehe. Below is an example of a tooth arrangement. Try to guess which species it is! (Scroll slowly so the answer doesn’t pop out right away).
Based on observation, this species has a tooth formula of 2123/2123, and the species is a monkey. However, humans also have the same tooth formula.
3. Types of Molars
Tribosphenic: The surface of the molar consists of 3 cusps (points). Found in species like the platypus and marsupials.
Quadrate: The surface of the molar consists of 4 cusps (points). Found in species like porcupines, raccoons, and some primates.
Bunodont: The cusps are rounded with blunt peaks. Found in hominids, bears (Ursidae), and sea lions (Otariidae).
Hypsodont: Teeth with high crowns and enamel that extends well past the gum line. Found in animals like cattle, deer, and horses.
Brachyodont: Teeth with short crowns, just slightly above the gum line, and having at least one root. Found in humans.
Lophodont: Characterized by long, numerous ridges (called lophids) on the tooth surface. Found in elephants, tapirs, and rodents.
Differences between molars of carnivores, herbivores, and omnivores:
Carnivores: Upper and lower molars are large, sharp, and triangular, known as the carnassial type.
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©️ sciencesource.com |
Herbivores: The cusps of the molars are joined together forming grooves, known as the selenodont type.
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©️ museum2.utep.edu |
Omnivores: The cusps of the molar crowns are short and tend to be rounded, known as the bunodont type.
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©️ museum2.utep.edu |
a. Cambrian Period
The first vertebrate fossils, known as ostracoderms, appeared during this time.
b. Early Silurian Period
The first jawed fish evolved.
c. Early Devonian Period
Four major groups of jawed fish emerged:
Acanthodians
Placoderms
Cartilaginous fish (e.g., sharks)
Bony fish (e.g., tuna)
d. Late Devonian Period
These jawed fish began to replace all primitive vertebrates.
e. Late Paleozoic Era
Acanthodians and placoderms went extinct. However, cartilaginous and bony fish continued to evolve and exist today.
f. Carboniferous Period
Amphibians began to evolve, marked by the development of lungs and limbs. Vertebrates diverged into two major groups:
Animals living in cold and humid environments, which developed fur and internal pouches. These later evolved into mammal-like reptiles.
Animals living in hot and dry environments, which lacked fur and pouches. These evolved into reptiles, birds, mammals, and amphibians.
g. Late Paleozoic Era
Mammal-like reptiles became the dominant terrestrial vertebrates.
h. Mesozoic Era
Reptiles reached the peak of their evolutionary development.
i. Triassic Period
Marked the peak of vertebrate diversification and dominance.
j. Late Triassic Period
The first true mammals appeared.
k. Jurassic and Cretaceous Periods
Terrestrial animals dominated, and the first birds began to appear.
l. End of the Mesozoic Era
A mass extinction event occurred, wiping out many dominant reptilian species, including the dinosaurs.
a. Biostratigraphic Purposes
In Indonesia, vertebrate fossils play a significant role in determining the age and depositional environments of terrestrial sediments. This is primarily because much of Indonesia’s geological record—particularly in regions such as Sumatra, Java, and Sulawesi—is dominated by Tertiary and Quaternary strata. During these periods, vertebrates were the dominant fauna, as dinosaurs had already gone extinct by the end of the Cretaceous.
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Biostratigraphy of Java based on index fossils (Puspaningrum, 2016) |
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Biostratigraphy of Sulawesi based on index fossils (Puspaningrum, 2016) |
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Biostratigraphy of Flores based on index fossils (Puspaningrum, 2016) |
After learning about various animal fossils, now it’s time for us to switch topics for a bit—but don’t worry, we’re not straying too far. In this discussion, we’re still dealing with animals, but this time, it’s not about their body parts. So… what part are we talking about then? Curious? Let’s check it out!
Ichnofossils can be defined as sedimentary structures that result from the life activities of animals—or in cooler terms, trace fossils.
a. Burrow: A hole or tunnel dug into soft, unconsolidated substrate.
b. Bioerosion trace fossil / Boring: A hole created in hard, consolidated substrate.
c. Track: An animal footprint formed while walking, usually characterized by a discontinuous trail.
d. Trail: A trace left by an animal moving with its belly in contact with the ground, usually characterized by a continuous, connected path.
e. Coprolite: Fossilized droppings or feces from an organism.
f. Egg/Nest: Fossilized eggs or preserved nests.
a. Same species, different structures
b. Same burrow, different substrates
c. Different tracemakers, identical structures
Similar-looking sedimentary structures can be produced by different species.
a. Definitions
b. Similarity between Ichnofacies and Ichnofabric
c. Difference between Ichnofacies and Ichnofabric
Ichnofacies: Data collection is done qualitatively.
Ichnofossils can be classified based on four main aspects:
a. Taxonomic Classification
For example, Skolithos isp:
Here, Skolithos represents the fossil’s taxonomic genus name, and isp indicates that the species has been identified based on trace fossil characteristics. If the species cannot be clearly identified due to lack of distinctive features, only the genus name is used, followed by the abbreviation igen to indicate it as an ichnogenus.
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Skolithos isp |
b. Preservation Model
Classified by Seilacher based on the position of the trace fossil relative to the sedimentary layer. There are three types of classification:
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©️ researchgate.net |
In the image above, you can see positive (+) and negative (–) signs. The positive (+) sign indicates that the trace fossil is convex (raised), while the negative (–) sign indicates that the trace fossil is concave (depressed) relative to the rock layer.
c. Life Patterns / Ethological Classification
The behavior of an organism can be observed in sedimentary structures and is classified into several types of behavior. Seilacher grouped them as follows:
Cubichnia: Traces formed by an organism when resting, hiding, or positioning itself to ambush prey. Characteristics include:
![]() |
©️ es.ucl.ac.uk |
Repichnia: Traces resulting from the movement of an organism, such as crawling, walking, or running. Characteristics include:
![]() |
©️ es.ucl.ac.uk |
In the image above, there are two examples of Repichnia: Cruziana and Gyrochorte. Cruziana has a concave (–) semirelief shape that reflects the underside of the organism. This contrasts with Gyrochorte, which has a convex (+) semirelief shape reflecting the upper side of the organism.
Domichnia: Traces representing the dwelling or living place of an organism. Characteristics include:
![]() |
©️ es.ucl.ac.uk |
Examples of Domichnia:
Pascichnia: Traces formed by a combination of feeding and moving behavior. Characteristics include:
![]() |
©️ es.ucl.ac.uk |
The image above shows an example of Pascichnia, specifically Helminthopsis, which has a meandering shape.
Fodinichnia: A combination of temporary dwelling and feeding traces. Characteristics include:
![]() |
©️ es.ucl.ac.uk |
Examples of Fodinichnia:
d. Past Environment / Depositional Setting
Trace fossils are grouped into 5 ichnofacies. The formation of these ichnofacies is controlled by salinity, bathymetry, substrate surface, and rock type. The five ichnofacies are:
Scoyenia ichnofacies
Formed in terrestrial or freshwater environments. Examples of genera: Scoyenia, Planolites, and Isopodichnus.
Skolithos ichnofacies
Formed in intertidal zones with sandy substrates and high water fluctuations. Organisms in this environment build deep burrows to:
Cruziana ichnofacies
Formed in shallow marine environments with lower tides and deeper water than Skolithos ichnofacies. Generally, the burrows are vertical or horizontal. Examples of genera: Rusophycus, Cruziana, and Rhizocorallium.
Zoophycos ichnofacies
Formed in bathyal marine zones. Due to the deep water, wave influence is minimal, the water is calm, oxygen levels are relatively low, and the seabed is muddy. Dominated by horizontal burrow forms such as Zoophycos.
Nereites ichnofacies
Formed in abyssal marine zones with clay substrates. Trace fossil abundance is low, but diversity of trace types is high. Examples of genera: Nereites and Scalarituba.
Psilonichus ichnofacies
Formed in non-marine and very shallow environments. Burrows are Y or U shaped, with vertical shafts and horizontal tunnels. An example is Track.
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Ichnofasies (Seilacher 1967) ©️ sepmstrata.org |
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Ichnofasies (Pemberton, 1985) ©️ sepmstrata.org |
e. Burrow Taxonomy
Here, I’m using burrow taxonomy as an example because in our recent paleontology lab, the main focus was on burrows. The parameters used as the basis for naming burrows are as follows:
Orientation relative to bedding planes (Orientation)
There are two types of orientation relative to bedding planes:
Presence or absence of branching (Branching)
Branched: The burrow has branches. Branching is further classified into three types:
Tunnel: horizontal branches
Shaft: vertical branches
Boxwork: combination of tunnel and shaft
General morphology (Shape)
The general shapes vary and include:
Burrow filling (Filling)
The burrow cavity is filled with other minerals. Filling is classified based on the origin of the minerals:
Burrow lining (Burrow lining)
The lining of the burrow is produced by the organism, typically from excreted minerals, and is usually smoother than the surrounding sediment minerals. There are two types:
Note: Filling and burrow lining are often difficult to distinguish clearly.
![]() |
Taxonomi burrow |
The identification steps are as follows:
Check the orientation
In the image, the orientation isn’t directly visible. Let’s hypothesize that the image was taken looking down from above the rock layer. Therefore, we can determine that the trace fossil shape is a positive semirelief with a subhorizontal orientation because it runs parallel to the bedding plane.
Check the branching
The next identification step follows the burrow taxonomy flowchart, which is to identify whether branching exists or not. In the image, there is no branching (unbranched).
Check the shape
Next, we identify the shape. The form is cylindrical because it looks like an elongated tube.
Check the filling
The next step is to identify the type of filling. Since there are no visible septa (partitions) inside the tube, we conclude that the filling is passive filling.
Check the burrow lining
At the final step, we examine the burrow edges to see if there is any burrow lining. Burrow lining can be recognized by a noticeable difference in color between the burrow edge and the burrow itself. It can also be seen in the grain size uniformity (coarse or fine). The image shows that the color and grain size between the burrow edge and the burrow are not uniform, so we conclude that there is burrow lining.
In summary, the information we have gathered is:
Subhorizontal – unbranched – cylindrical – passive filling – lining
When we compare this information with the burrow taxonomy chart, we identify that the fossil is called Palaeophycus.
That’s all from me. Thanks for reading my blog! I appreciate any feedback or suggestions :)
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