Category: Other Creatures

A world without the Blue whale: Battle for the throne of the largest animal in Earth’s history.

In one of last year’s articles, I was able to compile data to provide the size parameters for the largest animal in Earth’s history, the blue whale (Balaenoptera musculus). While the blue whale’s ranking amongst megafauna is well-recognized across the scientific community,  there’s next to no definitive ranking for the second-largest, third, or even fourth largest. Well it may or may not come to surprise you that each of these are likely to be an extant whale species rather than a dinosaur!

The size-rivals

Outside of large whales, the other largest taxa of Earth’s history are the sauropods.  For generations, these two groups have been interlocked in mortal combat in size comparison discussions, yet directly comparing their metrics can be problematic. The chief reason being the issues in precisely reconstructing taxa known only from fragmentary material. Mass estimates for sauropods are notably sensitive to differences in reference taxa, scaling formulas, measurement accuracy, etc. (1). As methodologies improved, sauropod mass estimates generally get downsized. One example is the dethroned Patagotitan, which was once estimated to weigh 70 tonnes, but current figures place it at 50-57 tonnes (1,2,3) Even relatively complete specimens aren’t immune, as the 26-meter subadult of Dreadnoughtus went down from its initial estimate of 59-tonnnes  to 31-45 tonnes (2,3,4).

The existing figures for the masses of larger whales are also called estimates, but that can be misleading as 90-94% of a whale’s mass is directly measured in piecemeal weighings. The remaining portion is a conservative estimate of the body fluids lost the flensing process, which has been verified in experiments comparing whole weighing to piecemeal weighing (5). Unlike sauropod estimates, the calculated mass for whales leaves very little room for overestimation and are in fact more prone to the opposite as solid tissue, in addition to body fluids, can be lost in the flensing process.

Another problem is that sauropod mass estimates only provide a look at individuals. If my previous post on blue whales is anything to go by, size distributions across a population or species is a very important factor to account for. Unfortunately, that data isn’t available to us. We’re not entirely sure whether these mature individuals were small , average, or exceptional within their species. Since comparing sauropods to whale species isn’t exactly apples-to-apples, some allowance must be made.

 When looking at the largest dinosaurs,  Argentinosaurus huinculensis is considered the heaviest species by mass that’s known from decent material (3,6). The holotype is positioned to be around 70 tonnes while another specimen within its genus is calculated to have been slightly larger at 80 tonnes (7). Maraapunisaurus fragillimus may also be a good contender, but it’s known only from a giant vertebrae that is completely gone now. Like Argentinosaurus, M.fragillimus’ total length is estimated at around 35m, certainly surpassing even the largest blue whale in length. It’s thought to have weighed anywhere from 80-120 tonnes, though other recent estimates position it as low as 70 tonnes (3,7).

It seems that the most reliable mass estimates for sauropods top out at 80 tonnes, though if I stick too close to this, my article may become outdated by a new titanosaur, diplodocid, or mamenchisaurid that’s incrementally larger than Argentinosaurus. Due to the more restricted data present on sauropod masses, I will set the parameters for the ”largest sauropod” at  60-80 tonnes for the adult average with 100 tonnes as the maximum.  I don’t want anyone saying I’m not giving them a fair shot.

Argentinosaurus (2)

Regardless of the leeway modern sauropod mass estimates are given, it remained scientific consensus that the blue whale outsizes these giants by a wide margin. Although several taxa are estimated to exceed the blue whale’s maximum length, many fall short in overall volume and mass. However, I rarely see discussions that settle on who has second place. Does that go to a sauropod, or another whale? I will present every species of whale that can be confidently estimated to outsize the largest sauropods.

The Overlooked Rorqual

Lets start off with the fin whale (Balaenoptera physalus). Fin whales are the type species for the genus Balaenoptera and are the second largest species of whale by length. Fin whales are very interesting creatures, but are often left ignored or overlooked due to being outsized by their more popular cousins. On a related note, I should warn those wishing to research this species to be careful. Older literature as recent as the early 20th century would often ignore Linneaus’ designations and assign fin whales to B.musculus while blue whales were referred to as ”B.sibbaldii” (8,9).

Like the blue whale, we have the 2 subspecies respective to the Northern Hemisphere (B.p.physalus) and the Southern Hemisphere (B.p.quoyi). Currently, there is debate on whether the North Pacific and North Atlantic populations should be elevated to separate subspecies (10,11). There is also a proposed pygmy subspecies that has yet to be rigorously validated; nonetheless, the designation is officially recognized (12).  For this  review, I will simply be focusing on the size parameters for the 2 major subspecies.

Like other rorquals, the southern subspecies is the largest of the fin whales. At birth, Antarctic fin whale calves are about 6-6.5 meters in length and grow to a length of 12 meters by 6 to 7 months of age (13). During the earlier years of commercial whaling, Antarctic fin whales were estimated to reach sexual maturity at 10-11 years of age, at lengths of 19.9 meters and 19.2 meters for females and males, respectively (14,15,16). As exploitation continued, fin whales began reaching maturity at younger ages of about 6-8 years old (16,17,18,19).  It’s suspected this may be due to density-dependent changes in their environment. With depleted populations, individual fin whales have improved food availability, enabling them to grow at a faster rate. Fin whales physically mature at an age of 20-30 years (20,21). In the Antarctic, males cease growth at an average of 21 meters and females cease at an average of 22-22.9 meters (13,14,20,22).

As for the northern subspecies, very similar figures exist for the size at birth. Across the North Pacific and North Atlantic, the estimated length of sexual maturity ranges from around 17-18 meters for males and 18-19 meters for females (20,23,24,25). Research has shown a similar decline in age at sexual maturity as observed in the southern subspecies. However, no change in length was observed (25,26). On average, male northern fin whales enter physical maturity at 18.9 meters and females at 20.1 meters (24).

Fin whale life history

In the Northern Hemisphere, most individuals don’t grow much longer than 22-23 meters.  The longest reports in the whaling record I could find was a 24.4-meter male taken in the North Atlantic in 1905 and a 24.7-meter female taken off the Pacific between 1919-1926 (8,27). However, due to issues with unstandardized measuring methods, rounding, or deliberate exaggeration, these records may potentially be inaccurate. However, Clapham makes the note that the fin whale catch records containing the 24.7-meter fin whale show signs of accurate measuring. Furthermore, there’s a mounted skeleton of a 24-meter male fin whale skeleton in Shanghai (28). When taking into consideration the sexual dimorphism of baleen whales, we can confidently claim a max length of >24 meters.  Therefore, I consider 24.7 meters as the maximum length for females to be a reliable figure.

In the Antarctic, fin whales typically don’t exceed 24 meters. The largest female recorded by Mackintosh and Wheeler was 24.53 meters; while their text states that their largest male was 22.40 meters, both their tables and their appendix presents one male that was 23.60 meters (13).  It was the only male to surpass 23 meters. The largest fin whale ever directly measured by a scientist was a 25.9-meter female (29) The largest I could find from whaling reports in the Southern Hemisphere was 27.3 meters for females and about 26.8 meters for males (30,31). Given that the average mature lengths for male fin whales is 2 meters greater in the Antarctic than in the north, the maximum length for male Antarctic fin whales shouldn’t be any less than 24 meters.

As for the whaling data, the 26.8m male was caught during the 1931/1932 whaling season. Aside from issues stemming from minimum-size restrictions enforced in later years, most of the unreliability for length statistics were less apparent by the 1930s. However, I am  distracted by how in most years, the maximum lengths for males do not exceed 24-25 meters and most females very rarely exceed 26 meters. I am inclined to think this 26.8m male was either inaccurately measured or a female that was incorrectly identified.

Interestingly, the disparity between the whaling record and scientific record is about 1 meter for females. This can go either way as the difference can be owed to either sampling or measuring error. I think the 1934/35 whaling season provides a good idea of of  the maximum lengths for both sexes: 25 meters for males and  26.8 meters for females (32). I think by this period, measurements for fin whales appeared more reliable as the largest reported individuals don’t often surpass 25.9-meters for females or 25-meters for males. This 25m/27m maximum for Antarctic fin whales conforms with general expert opinion (32).

SubspeciesLength at sexual maturity (meters)Length at physical maturity (meters)Maximum length (meters)
Northern18.6 (females)
17.7 (males)		20.1 (females)
18.9 (males)		24.7 (females)
24 (males)
Antarctic19.9 (females)
19.2 (males)		22.3 (females)
21 (males)		27 (females)
25 (males)

I will be approximating the masses by the same method outlined in my previous article on the blue whale  but with some changes. Lockyer noted that her measuring of the seasonal fattening in the Antarctic was constrained by the lack of individuals present later in the feeding season (22). I’ve recently came across data acquired from the Japan’s scientific whaling expeditions in the Antarctic (18). In accordance with food availability enabling faster growth, whales were heavier at equal lengths than they were during the commercial whaling period. They also included specimens further into March, when whales are at their peak weight. The old data from commercial whaling estimates that fin whales can weigh up to 6.51 times their skeletal weight (22). Despite the JARPA weight data only presenting the length-wise averages for the individual components, I was able to reasonably approximate that by March, the body weight/bone weight ratio increases to around 8. The fattest individuals had a ratio of 8.8. With the new ratio of 5.65 for the lean weight, Antarctic fin whales appear to gain about 42% of their lean weight over the feeding period.

Along with these modifications for Antarctic fin whales, I will be using a different approach to the weight of northern fin whales. Studies have shown that they have unique tissue compositions and may not be directly comparable to their southern counterparts (34). The alternative regression I’m using is compiled from the weights of 40 northern fin whales cited in literature (5,34,35)

SubspeciesMass at sexual maturity
(metric tons)		Mass at physical maturity
(metric tons)		Maximum Mass
(metric tons)
Northern 41.7 (females)
36.3 (males)		51.8 (females)
43.6 (males)		92 (females)
85 (males)
Antarctic46-65 (females)
42-60 (males)		59-83 (females)
52-73 (males)		85-120
(females)
74-105
(males)

It doesn’t seem that the northern fin whales will beat out the largest sauropod species except maybe with maximum mass. The Antarctic subspecies is much closer, and clearly has the edge in maximum mass. Historically, the lean nature of fin whales have been overstated, with older regressions suggesting that a 25-meter fin whale would weigh 70 tonnes (33). This is likely the consequence of having no data of either properly fattened or longer individuals for a long time. The data here clearly shows that a 25-meter fin whale’s mass would overlap with that of a blue whale’s at said length, which ranges from 86-128 tonnes. 

Evidently, fattened fin whales will at least surpass the blue whale’s lean weight at an  equivalent lengths. A maximum weight beyond 100 tonnes for a fin whale appears entirely feasible. However, the fin whale is not the 2nd heaviest extant whale after the blue whale, that title belongs to two other species.

The Corpulent Balaenids

If there are a group of extant animals that do not create as much noise as they should in discussion of megafauna, it’s the Balaenidae family. This group includes the three species of right whales (Eubalaena. spp) and the bowhead whale (Balaena mysticetus). These whales don’t grow as long as the fin whale, but their girths can approach or exceed 70% of their body lengths (37). At equal lengths, no whale can challenge their weight.

 There are three species in the Eubalaena genus, but I personally think the standards for treating them as separate species rather than subspecies like in other baleen whales is mostly a convention. There were originally 2 species for the Northern (E.glacialis) and Southern Hemispheres (E.australis), but molecular studies revealed that the North Pacific population is closer related to the southern species than the North Atlantic population, warranting their own designation (E.japonica)(38). These whales were hunted for centuries and depleted by the 19th century. Of these three, only the southern species has made a significant recovery towards ‘Least Concern’ status.

The life history of North Atlantic right whales (NARW) has been the most rigorously examined. Newborns are estimated to be around 4-4.5 meters in length at the time of birth (39,40). Like rorquals, they rapidly grow within less than a year to 9.9 meters. NARWs are estimated to reach sexual maturity at around 8-9 years of age, corresponding to a length of 12 meters for males and 13 meters for females (40). When scaling these lengths at 90% of their physically-mature length, male NARWs cease growth at about 13.3 meters and females at 14.4 meters. This occurs as they approach 30 years of age. These parameters, however, may have changed for many individuals as a recent study found that entanglement has been stunting the sizes of NARW’s (41). The energetic costs incurred from dragging the nets impairs these whales’ growth, which in turn limits their calving rate. Nets pose a monumental threat towards their population recovery. Unlike other baleen whales, their southern counterparts (SRW) don’t seem to outsize them as the females appear to mature at the same size (42).

The one physical difference that truly distinguishes any of the right whales from each other is that the North Pacific right whale (NPRW) is much larger. Observations suggest newborns are larger in this species, but that’s difficult to discern as the rate of growth at this stage of life is rather rapid (37,43). Weaning is estimated to be at around 11 meters based on an 10.75-meter male that still had both milk and zooplankton in its stomach; individuals over 11 meters had no milk at all. Since no sexually mature individuals below 14 meters for either sex has been observed, males and females appear to enter sexual maturity at 14-15 meters (37,43,44). It’s estimated that both sexes physically mature at a range of 16-17 meters (37). This appears realistic given the frequency of adults of this length being caught or sighted.

Right whale life history

Maximum sizes are challenging to discern for the smaller two species. By the time scientists and whalers provided standard measurements, right whales were already seriously depleted and was lacking in older individuals. The largest NARW measured by a scientist was 16.5-meter female and the largest I could find in the 20th century whaling record was 18 meters. However, this could have been the length along the curve (45,46). Visual estimates from scientists in North Atlantic tagging expeditions indicate individuals possibly between 17-18 meters(47).  When the Soviets illegally harvested SRWs, the largest measured 16.6 meters and 16.4 meters for females and males, respectively (48). The standard measuring technique was very common in the 1950s-1970s, so these are likely accurate figures. Given that males can exceed 16 meters, 17-18 meters for the maximum of female right whales in the North Atlantic and Southern Hemisphere appears likely. Since the size trends for SRW’s and NARW’s are so similar, they will be compiled together.

As for the North Pacific species, older whaling reports and visual sightings from Klumov suggest lengths exceeding 20 meters (43,46). Soviet catch records  from their illegal harvests suggest a maximum of 18 meters and 19.8 meters for males and females, respectively (44). Given the inaccuracies from visual estimations and older whaling data, I think the more recent catch records are the best source.

SpeciesLength at Sexual Maturity (meters)Length at Physical Maturity (meters)Maximum Length (meters)
North Atlantic/ Southern Hemisphere13
(females)
12
(males)		14.4
(females)
13.3
(males)		*17-18
(females)
16.4
(males)
North Pacific**15
(females)
**14.5
(males)		**17
(females)
**16
(males)		19.8
(females)
18
(males)
*Approximate length based on maximum for males in Southern Hemisphere **Estimated range by Klumov (1962) and Omura (1969) with accounting for sexual dimorphism

Approximating weight is pretty straightforward as the three right whale species are nearly identical in morphology. A 2019 study by Fortune et. al combines North Pacific and North Atlantic weight data to improve on existing weight regressions, however there’s one minor issue (40).  Some of the weight data provided was originally published in Klumov’s 1962 report and cited again by Omura in 1969 (37,43). Since only Omura’s report was available in English for decades, few in the anglosphere directly cite Klumov. I consulted the currently-available English translation for Klumov’s report and I learned that major components were unmeasured for 3 whales. While no adjustments were directly made to the figures, Klumov expressed in the text that 10-11 tonnes should be added to these whales (43). These adjustments were neither made nor acknowledged in Omura’s publishing of this data, and were thus not adjusted in Fortune’s 2019 study.  Therefore, I’ve carefully measured what was missing from each whale and made conservative estimates for the missing parts based on weights from individuals of the same-length. 

This regression is probably the best I have for a species. The data had a very tight correlation and it covered a wide portion of the adult length range, up to 17.4 meters.  Some allowance should be made for each of the values in the chart as the data clearly shows major differences between individuals of similar length. I have not rigorously calculated it, but to give an idea, I generally see a gap as large as 10-20 tonnes between individuals in the 16-17 meter range.

SpeciesMass at sexual maturity
(metric tons)		Mass at physical maturity (metric tons)Maximum Mass
(metric tons)
North Atlantic/Southern Hemisphere34 (females)
27 (males)		47 (females)
37 (males)		87(females)
71 (males)
North Pacific54 (females)
48 (males)
79 (female)
66 (males)		127 (females)
95 (males)

 The heaviest flensed weight measured for NPRWs was 106.5 tonnes from a 17.4-meter female; the intact weight would have been 114 tonnes (43). Unlike the rest of Klumov’s sample, this individual was carefully weighed by scientific personnel and every piece of it was accounted for. It’s the only direct weighing of any animal other than a blue whale that exceeds 100 tonnes. My regression predicts a mass of 85 tonnes for a whale of this length. It seems that weight can vary on the order of 20-30%, which agrees with weight range of 65-100 tonnes for 16-17m right whales that Klumov described (43). While accounting for this, it seems that a fattened right whale of over 19 meters could approach 150 tonnes. That’s about 3 times the weight of a blue whale at 20-meters! It’s clear from the weighings and this regression that we can confidently position NPRWs above any reliable sauropod estimate.  

Now it’s time for the bowhead, a whale that will lead you down a few weird rabbit holes the more and more you learn about it. These whales are superlative by almost every convention: they have the largest skulls in the world that take up 1/3 of their body length, the thickest blubber, and the longest baleen that grows over 4 meters long  in large individuals (49). They are also the only baleen whales that are residents of Arctic and subarctic waters. That’s just the tip of the iceberg!

The bowhead whale’s growth is quite unique from other baleen whales. Newborns are around 4 meters in length and rapidly grow after 12 months to  8-8.5 meters(49,50). As yearlings, bowheads are known as ‘ingutuqs’ by the Inuit hunters. Their increased girth and tissue were so different from other bowhead classes, hunters were convinced they comprised their own species (49,51). Unlike their relatives, bowheads cease growth for roughly four years. All the growth during these years is dedicated towards increasing the size of the head and baleen towards their adult proportions, which likely improves feeding efficiency (51).  These juveniles are a lot leaner and are dubbed  the ‘‘qairilik’’. By age 5, bowheads resume growth, but don’t reach sexual maturity until their mid-twenties (49,50,52). Females sexually mature at about 13-13.5 meters and males at 12.5-13.0 meters (49,50,52,53). Physical maturity is estimated to set in between 40-50 years of age at averages of 16 meters for males and 17 meters for females (49,52). Bowheads have amazing longevity, with several confirmed individuals that lived over 100 years, and one estimated at potentially 211 (49).

Bowhead whale life history (1)

As for the maximum length, the largest length ever reported was 21.3-meters from Yankee whalers and claims from Inuit hunters reported specimens measuring 22-24 meters (54,55). This sounds very similar to the alleged maximums for NPRWs. It should be noted that within aerial surveys, less than ~1% of  bowheads have been detected to exceed 17 meters amongst 1800 photographs (49). Therefore, bowhead whales rarely approach 18 meters. Within modern fisheries data, the largest was a 17.37-meter male along with three records of females ranging from 19-19.5 m (49). The largest length recorded by subsistence whaling data was a 19.8 m specimen taken in between 1988-1992 (56). The sex is not stated, but the lack of records for males over 18 meters strongly suggest that this was a female.

SexLength at Sexual Maturity (meters)Length at Physical Maturity
(meters)		Maximum Length
(meters)
Females13-13.51719.8
Males12.5-131617.37

Weight estimations for bowhead whales are a bit of an issue as very little weight data exists. Some data was collected for regressions, but predictions from length alone aren’t that great due to the low sample size and small body sizes  of the weighed individuals (49,55).  A regression that incorporated both length and girth was far more reliable. Testing this formula against independently-acquired volume measurements validated that it can accurately predict weights of large bowheads (49). I can use this better mass regression if I combine it with another formula that predicts the girth of a bowhead from its body length. To provide an upper-bound value for each mass,  I will also be using the max-girth mean of 68% of the body length (49).

SexMass at sexual maturity (metric tons)Mass at physical maturity (metric tons)Maximum Mass (metric tons)
Females31-4270-90120-142
Males28-3857-7575-96

As you might have been able to assume, the length-weight correlation for bowheads is very similar to the values presented for right whales, which was acknowledged by the authors (49).  Another way a bowhead’s weight can be approximated is through its oil yield, as oil tends to compose a consistent fraction of a bowhead’s total weight (55). An oil yield of at least 230 barrels would predict a total weight of 100 tonnes for a bowhead. Yields exceeding 275 barrels were well-recorded and would correspond to 120 tonnes. The largest yields ever recorded were of 327 and 375 barrels; as far as I have read, the latter is the largest oil yield ever reported for a single whale. The body masses calculated from these yields would be about 144 and 164 tonnes. These approximations bolster my earlier claim that the largest right whales could approach 150 metric tons.

Final Ranking?

So in the end, it looks like at least three extant species of whales outsizes the sauropods:

  • Antarctic fin whales with average adult weights of 50-80 tonnes and a max weight of 120 tonnes 
  • North Pacific right whales and bowhead whales, with adult masses ranging from 60-90 tonnes and maximum weights potentially approaching or exceeding 150 tonnes.

Argentinosaurus (3)

Is that all? Well yes. The next largest whale is the sperm whale, where females only range from 10-20 tonnes, but males average 35-55 tonnes and max out at 80. A bull sperm whale would certainly be comparable to some of the larger sauropods. However, when taking into account its own average weight and the species-average being brought down by the females, I can’t reasonably rank it above the Argentinosaurus. So I guess that’s all we’re done now… NOPE!

Triassic Giants!

Whales and sauropods have been recognized as the largest creatures in Earth’s history for generations, however ichthyosaurs have recently been making the scene over the past 2 decades. The fact they were the last group to be recognized for their size is ironic as the large Triassic ichthyosaurs were the first creatures of such size to exist on earth. Among these was a deep-bodied ichthyosaur that was estimated to reach up to 15 meters in length, Shonisaurus popularis of the Shastasaurid family (58). It was kind of the Brachiosaurus of its day, long touted a the largest, but has been dethroned by at least 2-3 other ichthyosaurs that were larger.

In 2004, a 21-meter ichthyosaur known as Shonisaurus sikanniensis was discovered (58). Even larger specimens were observed in the area, but no size estimates have been provided, even 18 years later (58). It is still the largest ichthyosaur that we know from good material. For some years, it was reassigned to the Shastasaurus genus, but has since switched back to Shonisaurus (59,60). Its designation under Shastasaurus created a lot of confusion for me in both conversation and research as this reassignment back to Shonisaurus wasn’t convincing t0 either the general audience or experts. Therefore, I will continue ro just refer to this species as just S.sikanniensis.  

In addition to this, jaw fragments recovered from the United Kingdom revealed even larger individuals (61). The Lilstock specimen was estimated to be 25% larger than S.sikanniensis (26m) and the Aust Cliff ichthyosaur was estimated to be over 30% larger than the Lilstock specimen (>30m). However, due to their fragmentary nature, there are wide margins of error, as scaling from Besanosaurus resulted in a length of 22 meters for the Lilstock ichthyosaur. It’s even more shaky considering that the referenced total length for S.sikanniensis is an estimate itself. Still, regardless of the lack of precision, these animals were no doubt huge. They’re even suggested by many to be the most convincing contenders for dethroning the blue whale as the largest animal. 

 Now I bet those of you out of the loop are begging to see the mass estimates for these majesties. Unfortunately, that’s been a dry well for a very long time as only length estimates were focused on due to the trouble it takes to reconstruct ichthyosaurs.  It was only recently that volumetric studies on recent reconstructions have allowed us to approximate S.sikanniensis’ and  S.popularis’ weights at 80 tonnes and 20 tonnes at the lengths of 21 meters and 13.5 meters, respectively (62,63). However for S.sikanniensis, this mass is faulty. The volumetric model used to approximate this weight was constructed purely from S.popularis (63). In its description, the holotype of S.sikanniensis was described to have a slender body plan, and not deep-bodied like S.popularis. The max depth of its rib cage was only 1.90 meters. Therefore, this estimate is not reliable. 

 Despite many depictions portraying S.sikanniensis as a bulky animal, like a scaled-up S.popularis, it appears to have actually been leaner than a rorqual of equal length.  I’m no expert myself on reconstructing extinct taxa, but I have seen paleoartists who claimed to have paid close attention to Nicholl’s and Manabe’s description give it a  more slender body plan. When sticking to my strengths, I managed to comb through the literature on osteological studies on rorquals and have compiled about 12 specimens to get a rib length/total length regression.

Total length (meters)Max rib length (centimeters)Species
11.28129.5Sei (64)
12.30141.0Bryde’s (65)
13.70157.3Bryde’s (66)
14.70177.2Bryde’s (67)
15.30209.0Sei (68)
17.35*210.0Fin (69)
18.60231.0Pygmy Blue (70)
19.50220.9Fin (9)
20.50255.5**Pygmy Blue (71)
22.87241.0Blue (70)
25.00***287.0****Blue (72)
26.50315.0Blue (73)
*Length of reconstruction, without intervertebral tissue, the length was 14.6m

**Reported length for rib was ”10 feet”, I assumed to be the chord, not straight length. Used chord-straight length ratio from other studies on blue whales to arrive at this estimate, which
fitted the regression much better

***Estimated length for a fossil from a bizygomatic width regression for extant Balaenoptera. There were two other estimates of 22m and 23m from 2 other BZW-TL regressions, but the 25m estimate provided the closest expect rib length.

****Longest rib preserved. Used 60cm scale bar to approximate total length. Given its size, it was likely the 5-7th rib, which is sufficient enough for this regression.

Despite being a mixture of multiple species, the regression appears to have a tight, linear  correlation of 11.162x + 12.011 ( R^2=0.9446). According to this formula, a rib-cage depth of 190cm is expected for a rorqual of 15.95 meters. Given that the figures in the 2004 paper shows that the ribs from S.sikanniensis aren’t any more widely arched than a rorqual’s, I figure their rib cages can be fairly compared. The JARPA II expedition collected the dorso-ventral heights from Antarctic fin whales, which had a ~250cm average for individuals 19 meters in total length (18). My regression approximates a rib cage depth of 220cm for a 19-meter fin whale, which means that dorso-ventral height appears to be 14% greater than the rib depth.

Given that most of these whales had a fattened body condition, I don’t think  this type of ratio would risk shrink-wrapping S.sikanniensis. This is also falls in line with most skeletals I see for ichthyosaurs, which don’t extend soft-tissue outlines far beyond the silhouette of the skeleton. Assuming the flesh and blubber of S.sikanniensis covers the body as it does in a fat fin whale,  2.2-meters would be the estimated D-V height for S.sikanniensis. Going further, I can even use my ”whale-rib” regression to try estimating the weight for the  S.sikanniensis holotype, Lilstock, and Aust Cliff specimens.

Shonisaurus sikkanniensis (1)

 It’s reasonable, at this current time, to assume that these fragmentary specimens would have a similar body plan to S.sikanniensis as this species was the reference for approximating their lengths. Furthermore, the only other ichthyosaurs that are estimated to exceed 17m, like Cymbospondylus youngroum, are also quite slender (61). My process will be calculating the rib depth of the shastasaurid of a given length by scaling linearly from the shastasaurid holotype. This  means that for a 22m shastasaurid, I will multiply 190cm by 22/21 for a rib depth of 199cm. I will then use my maximum rib-length regression to find the corresponding length of a rorqual, which is 16.75-meters. Afterwards, I will use Dr. Mikhalev’s weight regressions to find the weight of this rorqual and multiply it by the length difference (74). So this weight will be multiplied by 1.31 (22/16.75).  I’m using Mikhalev’s regressions  because they’re among the most optimized ones I could find for large rorqual species at a given length. They also can provide a decent prediction for seasonal fattening as the regression for Antarctic fin whales appears to correspond to my values for the fattened state.

To put things in simpler terms, I’m basically taking a whale, a creature we can reliably estimate the weight for, and manipulating its girth and length to match that of a shastasaurid. It’s not precise, but in lieu of a more rigorous method by experts or even knowledgeable amateurs, this is the best that I can do with the skill and knowledge at my disposal. Lengths of 22m and 26m will be tested for the Lilstock specimen  and Aust Cliff specimens will be estimated at 30.8m and 36.4m. The latter two are based on a 40% scaling of the range for the Lilstock specimen.

Shastasaurid length (meters)Mass-scaling from Sei whale (tonnes)Mass- scaling from fin whale (tonnes)
21 2634
223139
264964
30.878105
36.4126170

These results are pretty much what I expected given S.sikanniensis’ dimensions. While no published source quoted masses for most of these sizes, I have read of others casually estimating a mass of around 30-tonnes for the holotype based on trying to scale up from smaller, more complete shasatsaurids like S.pacificus or Guanlingsaurus liangae.

More interestingly, Molina-Perez and Larramendi did publish a 60-tonne estimate for a 26-meter ”unnamed Shastasaurid”, which was likely the Lilstock specimen (7). Assuming they used a very valid method to approximate this mass, I feel feel pretty good about the range I’ve estimated. Besides that, it appears that the Lilstock specimen isn’t usurping any of the species I’ve covered, including Argentinosaurus. It would be, however, very comparable to the other larger  sauropods or a bull sperm whale.

The Aust Cliffe specimen is interesting as at nearly 31-meters, its mass is only that of a 25-meter blue whale. Even at a length of a whopping 36.4 meters, it still doesn’t quite exceed the maximum mass for a blue whale, though it does get very close.  Nonetheless, it firmly exceeds every other animal. And if it’s length is on the lower end, it might get overtaken by the balaenids and the largest fin whales in mass. Keep in mind, however, these estimates are actually stacking off of several layers of other estimates, even down to S.sikanniensis’ total length. If it turns that revisions to 17-19m for the total length of the holotype are correct, the downstream effect on these size estimates would be pretty amplified.

The Final Ranking

On one last note. I am revising my figure for the largest blue whale to be more conservative. Given the uncertainty of whaling records of blue whales exceeding the largest whale measured by a scientist (29.9m/ 98 feet), I consulted some extra resources to help me arrive to a reliable maximum length. I have come to the conclusion that a whale of 31.1-meters/102-feet can be considered a fair estimate for the maximum length. I came to this conclusion from three means.

  1. If a recorded length 33-meters was actually taken along the whale’s curves, the true length would be approximately 31.3 meters as  curve-lengths are about 6% greater than the standard measurement (75).
  2.  During the 1930s to 1940s, measuring issues like rounding did not disappear, but were still markedly less common than in earlier years(76). Accordingly, there was a notable change in the lengths of the largest blue whales.  Between 1918-1930, blue whales up to 115 feet were recorded. Those exceeding 110-feet were most certainly inaccurate. From 1931-1949, the largest reported blue whales never exceeded 102 feet.
  3. I was informed that a normal distribution for a large sample of carefully measured mature blue whale cows predicts a ~1/16,000 probability of one or more exceeding 100-feet. This left a 99.3% chance of 1 or more exceeding 100-ft amongst the >77,000 taken by whalers, but a 45% chance of any exceeding 102-ft. (T.Branch, personal communication, May 23rd,2022).

Together, the second and third points really make a strong case for my 31.1-meter figure. I still entertain a possible maximum around 32-33 meters, as normal distributions don’t always perfectly predict the behavior of real populations. For example, in a population of 7-billion humans, individuals the height of Yao Ming or greater shouldn’t exist within a normal distribution. At 7’6”, he’s 7.3 standard deviations away from the mean height of adult males. The equivalent distance for a female Antarctic blue whale would be 34.8m/114 ft (T.Branch, personal communication, May 23rd,2022) . Nonetheless,  there’s currently not enough reliable data to conservatively support a maximum size greater than 31.1-meters. 

How much would this whale weigh? Lockyer’s regression from 1981 predicts  lean/fat weights of 144-215 tonnes (22). While no piecemeal weight was recorded for a whale of that length, I do have exciting information pertaining to what I covered in the bowhead section!

Apparently I was wrong in my previous article, 305 barrels is not the heaviest yield to come from a blue whale. In fact, a yield of 354 barrels was recorded for a 101-foot whale caught on March 21st, 1931 (77). According to the International Whaling Statistics, this whale was pregnant. When taking both this and the date of capture into consideration, this whale was most certainly in a fattened condition. Oil yield averages out to 24% of the flensed weight for a blue whale in the fattened condition according to Lockyer (22). The largest percentage in her dataset was ~28%, which was the case for a pregnant female. When dividing the reported weight of 56,640 tonnes of oil by these percentages, we get an intact mass range of 216-252 tonnes. If we assume oil yield can range up to 30%, then the lowest estimate would still be 202 tonnes! Given the pregnant status and length of the whale in mind, I think 200-216 tonnes is the most realistic range for this whale.

So at equal lengths of about 30.8 meters, a blue whale would weigh nearly twice as much a shastasaurid with S.sikanniensis‘ body plan. Even though my shastasaurid estimates are ballpark and using a not so perfect methodology, I still think they provide realistic weights for a marine tetrapod that has less girth than rorqual of equal length.

Argentinosaurus (7)

So here’s what the current ranking appears to be when ranking by mass

  1. Antarctic blue whale 
  2. 36.4-meter Shastasaurid
  3. Tie between North Pacific right whale and bowhead whale
  4. Antarctic fin whale
  5. 30.8m Shastasaurid
  6. Argentinosaurus
  7. & onward-Some of the other sauropods, Lilstock specimen, and bull sperm whale.

And now I’ve covered everything I wanted to get through. I hope you guys liked this. The writing and source gathering took a few months, but really, this article is a culmination of 2 years of work. Hopefully, any attention this article gets will influence a bigger push for more reliable mass estimates for Shastasaurids and maybe some photogrammetry data for blue whales in the Antarctic.

Acknowledgements

I would like to thank Dr. Trevor Branch for his contribution to this article. His expertise and shared interest in blue whales has been excellent resource for my own research.

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