Biology Darwinius Masillae Paper
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Introduction: Darwinius masillae
On May 19, 2009, a team led by paleontologist Jørn Hurum of the Natural History Museum in Oslo Norway announced a significant new fossil discovery to the world. Nicknamed “Ida” after Hurum’s daughter, the team argued that the fossil was a type specimen, the individual fossil used to describe a species new to science (also called a holotype). The team named the new species Darwinius masillae, because the discovery was made in the 200th anniversary year of Charles Darwin’s birth.
Ida was not a typical fossil discovery. The specimen had actually been discovered by a private collector much earlier, in 1983, near Messel Germany. Her remains had been split into two separate slabs, which remained separate until 2000. The collector kept the main part (known as “Slab A”), while the second part (“Slab B”) was sold to the Wyoming Dinosaur Center in the United States. The two slabs are shown here:
The parts of skeleton B that are outside of the dashed lines were fabricated so the fossil would look complete when it was displayed. This is normal for fossil casts (replicas) but is not normally done with real fossils unless they are relatively worthless. In spite of the Plate B fabrication, Ida is a remarkable and very important fossil for two reasons: how complete the specimen is and the fossil’s antiquity. With 95% of the skeleton, she represents one of the most complete fossils of her age ever found. Better preservation of a more complete fossil always gives scientists more information– so this is really important. Ida’s remains are so well preserved because of the way she became fossilized (her taphonomy). She was found near an ancient volcanic lake called a maar that was formed by an explosion when hot magma underneath the earth’s surface came in contact with a water table. The lake had no rivers feeding into it, so it had very little oxygen, which you may remember from our Explorations reading is a condition that creates exceptional preservation potential for fossils. She is so well preserved that her last meal (fruit) was preserved and fossilized in her gut. How old is Ida? She comes from the Eocene epoch (55-34 mya) and is dated to 47 million years old, meaning she existed early in primate evolution. Her fossil was dated by taking a core sample from the volcanic rocks in the Messel pit that formed the lake.
Ida is small, with her tail she measures about 23 inches (58 centimeters) long and her body is only 9 inches long and as you can see, her legs are longer than her arms, suggesting that leaping was a normal mode of locomotion for her. This hypothesis is based on analogy (comparison with the skeletal structures of living species). Likewise, comparison to living primates’ dentition supports the evidence from her stomach contents and suggests she was a frugivore. Her large eye orbits probably indicate a nocturnal life style. Scientists assigned her sex as female based on the fact that she had no baculum, the male penile bone found in primates (though not in humans), and other skeletal features. Several other important traits are also very clear: Ida has five digits on her hands and feet, long fingers and toes and nails instead of claws on all of her digits. Importantly, she has fully opposable thumbs and toes on her hands and feet. She also had unerupted molars pushing out her baby teeth, so she was a juvenile, perhaps about 9 months of age. Finally, her cause of death is unknown, but it is clear she has a broken wrist. One possible scenario is that her broken wrist prevented her from climbing in trees and being closer to the ground may have caused her to be exposed to gasses from the lake, which could have caused her to lose consciousness and drown.
Ida’s Taxonomic Significance
Where does Ida belong in the early primate family tree? How does her discovery change our understanding of this period in evolutionary history? The discovery of Darwinius masillae has had important significance for our understanding of early primate evolution. In addition to analogy (comparison to living species), the fossil record is also interpreted using comparison to the existing fossil record. The first thing to do with a fossil discovery like Ida is to determine which living taxa she is affiliated with. Many of her characteristics support that Ida is a primate (her limb structure, skull features, dentition, grasping hands, opposable digits) and there is no scientific debate on this point.
Once her general placement in primates is secure, the next question is which living primates does she resembles most closely. Ida is missing several key characteristics that are found among living lemurs and lorises. For example, Ida lacks a dental comb and doesn’t have a grooming claw on her hands and feet– both of these are traits found in living lemur species, as you learned in the last module. She also has a shorter snout than living lemurs and a tarsus (an ankle bone– the bone that tarsiers get their name from) that appears more like haplorhines than lemurs or lorises. Along with her highly opposable thumbs (again, more associated with living monkeys), these traits have led some to interpret Ida as a potential ancestor for the living haplorhines. Ida’s discoverers argued that her fossil may represent a transition from more primitive strepsirrhine ancestors to the haplorhine lineage (Franzen et al 2009). Once a fossil discovery is published and interpreted by its discoverers, their claims are evaluated and responded to by scholars with relevant expertise. It is quite normal for discussion and debate to occur around taxonomic assignment of a new species, especially when a new species is monotypic (there is only a single specimen that assignment is based on).
In a 2009 article coauthored with Hurum, Franzen et al argue that the ancient primate group adapiforms that many scholars identify as likely ancestral to living strepsirrhines, should instead be seen as a transitional group between haplorhines and strepsirrhines (Franzen et al 2009). Stony Brook University scholar Eric Seiffert and colleagues disagree with these interpretations,arguing that Franzen and his colleagues analyzed too few traits in their paper. Seffert and colleagues examined 360 morphological traits across 117 species of extant and extinct primates, and argue that Ida is more closely related to living lemurs and lorises, but should be put on a side branch, along with another recently discovered 37 mya primate, Afradapis (Seiffert et al 2009). According to Seiffert’s analysis, the similarities between Ida and living haplorhines are not because they are ancestral to them, but rather due to convergent evolution, where organisms not closely related evolve similar characteristics due to occupying similar environmental niches. This is a phylogenetic tree representing Seiffert’s interpretation:
Another critical assessment of Franzen et al was offered by Williams et al (2010), who also assert that Darwinius is better seen as basal (meaning a group that gave rise to a later lineage) to strepsirrhines and not haplorhines, as the discoverers claimed. Darwinius’ discoverer Jørn Hurum has said he is open to the possibility that Ida is on the strepsirrhine side of our primate family, but like so many taxonomic debates this one may never actually get resolved. Additional evidence is critical but given the ancient time frame, this evidence will be not be easy to come by and new discoveries, precious as they are, will no doubt complicate the picture further even as our understanding of the evolutionary past improves. Evolution is complicated and a better sample of fossils usually leads us in that direction!
Darwinius. (n.d.). In Wikipedia. Retrieved March 27, 2020. https://en.wikipedia.org/wiki/Darwinius (Links to an external site.)
Franzen, J. L.; Gingerich, P. D.; Habersetzer, J.; Hurum, J. H.; Von Koenigswald, W.; Smith, B. H. (2009). J., Hawks (ed.). Complete primate skeleton from the Middle Eocene of Messel in Germany: morphology and paleobiology (Links to an external site.). PLoS ONE. 4 (5): e5723.
Schons, Mary. 2011. Who Was Ida? October 24. National Geographic. https://www.nationalgeographic.org/article/who-was-ida/ (Links to an external site.)
Seiffert, Erik R.; Jonathan M. G. Perry; Elwyn L. Simons; Doug M. Boyer (22 October 2009). “Convergent evolution of anthropoid-like adaptations in Eocene adapiform primates”. Nature. Nature Publishing Group. 461 (7267): 1118–1121. Bibcode (Links to an external site.):2009Natur.461.1118S. doi (Links to an external site.):10.1038/nature08429. PMID (Links to an external site.) 19847263.
Williams, Blythe A., Richard F. Kay, E. Christopher Kirk, and Callum F. Ross. 2010. Darwinius masillae Is a European Middle Eocene stem Strepsirrhine—a reply to Franzen et al. Journal of Human Evolution 59: 567–573.
As you learned in your Explorations reading this week, fossils are historically the most important line of evidence about our distant past, but they can be extremely difficult to find. Important fossil discoveries like Ida still make headlines in magazines and newspapers for good reason. As the fossil record grows, so too does our understanding of the past and important new discoveries can rewrite our understanding of the evolutionary past.
For this assignment, you are to find an important fossil discovery that paleontologists or paleoanthropologists have made after the year 2000. Your fossil must be a hominin. Hominins are defined as species regarded as human, directly ancestral to humans, or very closely related to humans. Generally speaking, hominins are bipedal(walk on two legs). You can think of the story of Darwinius massilae above as a model for your assignment, though note that Darwiniius is not a hominin. I was also trying to illustrate some important concepts for this module, so you do not need to be quite as thorough as I was.
Start by googling important fossil discoveries and find one you think is interesting and important. Remember, your fossil must be a hominin and it must have been discovered since the year 2000. After you have chosen a fossil discovery, cover the following in a minimum of 800 words:
The fossil’s scientific name and popular name (if it has one)
A short account of the discovery (when, where, by whom, etc)
A description of the fossil remains, including the techniques used to date it
A photo of the fossil specimen(s)
A description of the important traits the fossil shows and their relationship to the fossil record and living species
An assessment of the impact of the discovery on our knowledge of evolution (including discussion and debate about the fossil’s taxonomic place)
An image of a phylogeny/family tree showing where (at least some) scholars have placed your fossil discovery
A list of your sources (not included in the word total)
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