Size comparison of a modern blue whale (Balaenoptera musculus) and the extinct Perucetus colossus, known from a fossil discovered in Peru.
Image by Cullen Townsend (https://www.cullentownsenddesign.com/)
Scientists may have got it wrong when they thought they had the fossilised remains of the heaviest thing that ever lived, in the form of a 39 million-year-old fossil whale from the Peruvian Middle Eocene, which they called Perucetus colossus.
But, before creationists get over-excited, thinking it's the 30 million years they got wrong, they need to read on; it isn't the age they got wrong, but the estimated mass.
A new analysis by palaeontologist at the University of California Davis has put Perucetus colossus back into the same range as modern whales and lighter than the blue whale, which retains its position as the largest and heaviest organism ever to exist on Earth, dwarfing even the largest dinosaurs.
How they went about it is the subject of an open access paper in PeerJ and a news release from UC Davis:
A 30-million-year-old fossil whale may not be the heaviest animal of all time after all, according to a new analysis by paleontologists at UC Davis and the Smithsonian Institution. The new analysis puts Perucetus colossus back in the same weight range as modern whales and smaller than the largest blue whales ever recorded. The work is published Feb. 29 in PeerJ.
A fossil skeleton of Perucetus was discovered in Peru and described in a paper in Nature last year. The animal lived about 39 million years ago and belonged to an extinct group of early whales called the basilosaurids.
Perucetus’ bones are unusually dense. Mammal bones usually have a solid exterior and are spongy or hollow in the center. Some animals have more of the center filled in with solid bone, making them dense and heavy. In aquatic animals, heavy bones can offset buoyancy from body fat and blubber, allowing the animal to maintain neutral buoyancy in water or – in the case of the hippopotamus – to walk on river beds.
The fossil whale bones have both extensive in-filling and extra growth of bone on the outside as well, a condition called pachyostosis also seen in some modern aquatic mammals, such as manatees.
Based on a series of assumptions, the original authors (Giovanni Bianucci at the University of Pisa, Italy and colleagues) estimated a body mass for Perucetus of 180 metric tons (ranging from 85 to 340 metric tons). This would make Perucetus as heavy as, or heavier than the biggest blue whales known, even though it is considerably shorter at 17 meters long compared to a blue whale at about 30 meters.
How to weigh a whale?
Professor Ryosuke Motani, a paleobiologist at the UC Davis Department of Earth and Planetary Sciences, said that these estimates would make Perucetus impossibly dense.
Motani and Nick Pyenson at the Smithsonian Institute National Museum of Natural History reexamined the assumptions used to make those estimates.It would have been a job for the whale to stay at the surface, or even to leave the sea bottom--it would have required continuous swimming against the gravity to do anything in the water.
Professor Ryosuke Motani, lead author
Palaeobiologist
Department of Earth and Planetary Sciences
University of California Davis.
The first problem is that Bianucci et al used the fossil bones to estimate the weight of the skeleton, then extrapolated to the weight of the entire animal, assuming that the skeletal and non-skeletal mass would scale at the same rate with increasing body size. But measurements of other animals show this is not the case, Motani and Pyenson argue.
The original estimates also overestimated how much overall body mass increases as a result of pachyostosis. But evidence from manatees shows that their bodies are relatively light relative to their skeletal mass.
Motani and Pyenson estimate that the 17-meter long Perucetus weighed in at 60 to 70 tons, considerably less than the known weights of blue whales. A Perucetus that grew to 20 meters could weigh over 110 tons, still well short of the largest blue whales at 270 tons.
Paleontologists have not yet uncovered a skull or teeth of Perucetus, so it is hard to tell what it ate. Sustaining a huge body takes a lot of food. Bianucci et al suggested that Perucetus might have browsed on coastal fish and shellfish, or scavenged carcases, as some sharks do. The new slimmed-down size estimate puts Perucetus in a similar range to sperm whales (80 tons, 20 meters long), which hunt large prey such as giant squid.The new weight allows the whale to come to the surface and stay there while breathing and recovering from a dive, like most whales do.
Professor Ryosuke Motani
AbstractCreationists should note that this paper doesn't question the age of the fossil, only the calculation of its mass, but it is the 39 million-year aga of the fossils that should worry creationists. So, how was this age of the Peruvian Middle Eocene sedimentary rocks in which the whale fossil was found calculated?
Extremes in organismal size have broad interest in ecology and evolution because organismal size dictates many traits of an organism’s biology. There is particular fascination with identifying upper size extremes in the largest vertebrates, given the challenges and difficulties of measuring extant and extinct candidates for the largest animal of all time, such as whales, terrestrial non-avian dinosaurs, and extinct marine reptiles. The discovery of Perucetus colossus, a giant basilosaurid whale from the Eocene of Peru, challenged many assumptions about organismal extremes based on reconstructions of its body weight that exceeded reported values for blue whales (Balaenoptera musculus). Here we present an examination of a series of factors and methodological approaches to assess reconstructing body weight in Perucetus, including: data sources from large extant cetaceans; fitting published body mass estimates to body outlines; testing the assumption of isometry between skeletal and body masses, even with extrapolation; examining the role of pachyostosis in body mass reconstructions; addressing method-dependent error rates; and comparing Perucetus with known physiological and ecological limits for living whales, and Eocene oceanic productivity. We conclude that Perucetus did not exceed the body mass of today’s blue whales. Depending on assumptions and methods, we estimate that Perucetus weighed 60–70 tons assuming a length 17 m. We calculated larger estimates potentially as much as 98–114 tons at 20 m in length, which is far less than the direct records of blue whale weights, or the 270 ton estimates that we calculated for body weights of the largest blue whales measured by length.
Introduction
Extremely large organisms, especially those belonging to vertebrates, readily capture public interest. However, these organisms are equally valuable to biologists because organismal extremes can be informative about fundamental ecological and evolutionary processes (Goldbogen, Pyenson & Madsen, 2023). Whales (or cetaceans) are particularly good examples of this dual phenomenon: living cetaceans, such as blue whales (Balaenoptera musculus) are perennial objects of popular fascination as the largest vertebrates ever; equally, studies on blue whale physiology, behavioral and feeding ecology have important implications for understanding broader trends among cetaceans and other mammals (Abrahms et al., 2019; Goldbogen et al., 2019.1a, 2019.2b). Recent improvements in animal-borne technology, including tags and aerial photogrammetry, have dramatically increased the precision for measuring the body sizes of living cetaceans in the field (Christiansen et al., 2019.3; Bierlich et al., 2022). These improvements in data collection facilitate further studies in the macroecology of these extremely large organisms: in many cases, body size informs energetics, and models of the ecological impact that these top consumers have on ocean ecosystem health (Savoca et al., 2021).
Despite the improved precision for measuring body size in living cetaceans, there remain challenges for validating and disseminating basic information about the body size of these taxa. In both popular and scientific literature, the specific body size values for superlative taxa are often cited as approximations or they are unspecific about their precision or origin. At closer inspection, the actual data for many of these superlative or champion size values are surprisingly difficult to find, vet, and evaluate.
Recently, Bianucci et al. (2023.1) reported a new basilosaurid whale, Perucetus colossus, based on a partial skeleton collected in Eocene rocks from southern Peru. Based on the associated skeletal material (i.e., thoracic and lumbar vertebrae in association with four ribs and an incomplete pelvis), Bianucci et al. (2023.1) suggested it was the heaviest whale ever, possibly reaching 17 to 20 m in length and 85 to 340 tons in total weight, rivaling or exceeding the mass of the largest blue whales. They based their estimates on a new method, in which they first estimated the total skeletal mass of Perucetus through extrapolation from the skeletal material and then used the value to secondarily extrapolate its body mass, assuming skeletal to body mass ratios based on extant cetaceans and sirenians. A simple ratio mandates an isometric relationship between body and skeletal masses, and they justified this step by testing for isometry using a phylogenetically controlled regression. They argued that the productivity in Eocene oceans was sufficiently high to support a marine predator weighing as much as 340 tons, a proposal with as profound implications for vertebrate morphology as for marine ecology.
The logic behind such a high body mass estimation may appear consistent within its own framework. However, their method involves questionable assumptions that suggest their body mass estimates are not reasonable when viewed from different perspectives. For example, a simple allometric relationship between whale length and mass suggests that the largest mass estimates for Perucetus cannot fit the body of a 20-m bauplan. A 17 to 20-m whale is much smaller than a 30-m whale (Figs. 1A and 1B vs. 1C and 1D), so for it to be as heavy as the latter, it would need to be 3.375 (=1.53) times denser or 1.83 times fatter in body diameter, or various combinations of increases in these two values. Yet, the whole-body density of vertebrates is known to fit in a narrow range of 0.75 to about 1.2 (Larramendi, Paul & Hsu, 2021.1), with the highest values found only in land turtles with heavy bone armor, whereas a whale can only be so much fatter than the blue whale. Therefore, it is extremely difficult for a 20 m whale to rival a 30 m individual in body mass.
The body mass of fossil vertebrates is never directly measurable, so paleontologists have struggled to quantitatively estimate this value for over a century (Gregory, 1905). Today, there are many methods available, which are roughly group into regression-based and volumetric approaches (Hurlburt, 1999; Smith, 2002; Brassey, 2016; Campione & Evans, 2020; Motani, 2023.2). We note that all of these methods have challenges: for example, the best body mass estimates for terrestrial non-avian dinosaurs are derived from a cross-examination of the results from both classes of approaches (Sellers et al., 2012; Campione & Evans, 2020). The published mass estimates of Perucetus colossus have yet to be validated in this regard. The purpose of this article is to cross-examine the published body mass estimates of Perucetus using data and methods informed by different perspectives. Specifically, we test the following hypotheses, which were assumed to be true by Bianucci et al. (2023.1): (1) the published body mass estimates of Perucetus fit the body outline as reconstructed in the same article; (2) the assumption of isometry between skeletal and body masses is valid even with extrapolation; (3) pachyostosis in Perucetus did not lead to overestimated body mass; (4) error rate is low in the body mass estimation method used; (5) skeletal to body mass ratio is well-established and stable within Cetacea; and (6) a large body mass of 340 tons was ecologically feasible given Eocene oceanic productivity.
Figure 1: Comparisons of body size between Perucetus colossus and Balaenoptera musculus based on Paleomass models with superelliptical exponent of 2.0.
(A) Perucetus with a fork length of 17 m, based on the lateral view only and thus overestimating the true volume. (B) Same with a fork length of 20 m. (C) B. musculus with a fork length of 30 m, based on both the lateral and ventral views, approximating the true volume. (D) B. musculus with a fork length of 30 m, based on the lateral view only and thus overestimating the true volume. (D) Overestimates the volume of (C). Scalebars are 30 m.
Motani R, Pyenson ND. 2024.
Downsizing a heavyweight: factors and methods that revise weight estimates of the giant fossil whale Perucetus colossus.
PeerJ 12:e16978 https://doi.org/10.7717/peerj.16978
Copyright: © 2024 The authors.
Published by PeerJ, Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
How was the age of the Middle Eocene epoch in Peru estimated? The age of the Middle Eocene epoch in Peru, like in many geological contexts, is estimated through a combination of methods including radiometric dating, biostratigraphy, and correlation with other well-dated geological formations around the world.To dispute the 39 million year age of this whale fossil, creationists need to either, provide evidence of massive contamination by isotopes of potassium (K) or argon (Ar) of the rock in which the fossil was found, or provide evidence that the half-life of 40K was so much shorter 10,000 years ago that it would make 10,000 years look like 39 million years, without making the formation of atoms impossible 10,000 years ago when life was allegedly created.
Radiometric dating involves the use of radioactive isotopes to determine the age of rocks. For the Middle Eocene epoch in Peru, scientists might use radiometric dating techniques such as uranium-lead dating, potassium-argon dating, or argon-argon dating on volcanic rocks or mineral deposits within sedimentary rocks to establish absolute ages.
Biostratigraphy involves the study of the fossil content within rock layers. By examining the types of fossils present and comparing them to known fossil assemblages from other locations with well-dated ages, scientists can infer the relative age of the rock layers.
Correlation with other well-dated geological formations is another important method. If a certain rock layer in Peru contains similar fossils or geological features to layers found in other regions with well-established ages, scientists can use this correlation to estimate the age of the Peruvian rocks.
Additionally, other dating methods such as paleomagnetism and stratigraphic analysis may also be employed to further refine the age estimates of geological formations in Peru, including those from the Middle Eocene epoch.
Tell me more about potassium-argon and argon-argon dating.
Potassium-argon (K-Ar) dating and argon-argon (Ar-Ar) dating are both methods used to determine the age of rocks and minerals, particularly volcanic rocks. These techniques are based on the decay of radioactive isotopes of potassium to argon.Both K-Ar and Ar-Ar dating are valuable tools in geological and archaeological research for determining the ages of rocks and minerals, understanding the timing of geological events, and reconstructing the Earth's history. These methods have been instrumental in dating volcanic eruptions, determining the ages of fossils, and establishing the geological timescale.
- Potassium-Argon (K-Ar) Dating:
- In this method, the radioactive isotope potassium-40 (40K) decays into the stable isotope argon-40 (40Ar) with a half-life of approximately 1.25 billion years.
- Potassium is a common element in many minerals, particularly in feldspars and micas, which are commonly found in volcanic rocks.
- When volcanic rocks solidify, they trap some of the naturally occurring 40K. Over time, this radioactive isotope decays into 40Ar.
- By measuring the ratio of 40K to 40Ar in a sample, and knowing the half-life of 40K, scientists can calculate the age of the rock.
- Argon-Argon (Ar-Ar) Dating:
- Ar-Ar dating is a refinement of the K-Ar dating method and is often used to date very old rocks and minerals, or to improve the precision of age determinations.
- In Ar-Ar dating, the sample is irradiated with neutrons in a nuclear reactor to convert a portion of the stable isotope potassium-39 (39K) into the radioactive isotope argon-39 (39Ar).
- This method allows for the direct measurement of both the parent isotope (39K) and the daughter isotope (40Ar), as well as their ratios.
- By measuring the isotopic ratios of (39Ar and 40Ar, along with the ratio of 39K to 40K, scientists can calculate the age of the sample with greater precision than traditional K-Ar dating.
How do they allow for possible contamination?
Contamination is a concern in potassium-argon (K-Ar) and argon-argon (Ar-Ar) dating because it can affect the accuracy of the age determination. Contamination can occur through various processes, including the incorporation of foreign materials into the sample, the loss or gain of argon during sample preparation or handling, and the presence of inherited or secondary minerals. Here are some ways contamination can be addressed or minimized in these dating methods:Despite these precautions, it's important to recognize that complete elimination of contamination is often not possible. Therefore, scientists must exercise caution and interpret the results of K-Ar and Ar-Ar dating within the context of the specific geological setting and the potential sources of contamination.
- Sample Selection: Careful selection of samples is crucial. Scientists typically choose rocks or minerals that are least likely to have been affected by contamination. This often involves visually inspecting the sample for signs of alteration or contamination, as well as conducting preliminary analyses to assess the sample's integrity.
- Sample Preparation: Proper sample preparation techniques are essential to minimize contamination. This may involve crushing the sample to a fine powder to ensure homogeneity and removing any visible impurities. Additionally, samples may be chemically treated to remove secondary minerals or other contaminants.
- Analytical Techniques: Sophisticated analytical techniques are employed to measure isotopic ratios with high precision and accuracy. Mass spectrometry is commonly used in both K-Ar and Ar-Ar dating to measure the abundance of argon isotopes. Isotopic ratios are determined with great care to ensure that any contamination is identified and accounted for in the age calculations.
- Blank Corrections: Blank corrections are applied to account for any contamination introduced during sample preparation or analysis. This involves measuring the background levels of argon isotopes in laboratory equipment and subtracting these values from the measurements obtained from the sample.
- Replicate Analyses and Quality Control: Multiple analyses of the same sample, as well as analyses of standard reference materials with known ages, are often conducted to assess the reliability and reproducibility of the results. Quality control procedures are implemented to identify and correct any sources of error or contamination.
And then they would still have the uranium-lead (U-Pb) dating of volcanic zircons - about the most accurate and reliable geochronological technique - to refute.
Unless a creationist can do that, they are stuck with trying to explain how a whale could have been fossilised almost 39 million years before Earth was created.
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