For an introduction to the geology, stratigraphy, archaeocetes, and toothed mysticetes of mid-Cenozoic Zealandia, see part 1 here.
For part 3, on the fossil toothed whales - Odontoceti - from New Zealand, click here (coming next Monday!)
Life restoration of a New Zealand eomysticetid by the kiwi artist Chris Gaskin: this was originally supposed to be the Earthquakes eomysticetid, now Waharoa, but we used it instead for the "Island cliff" eomysticetid Tokarahia. Copyright Chris Gaskin/Otago Geology Museum; from Boessenecker and Fordyce (2015c).
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Two professors and accidental paleocetologists: Professor William Benham (left, 1860-1950), ca. 1907, and Professor Brian Marples (right, 1907-1997), ca. 1967. These two gentlemen were responsible for studying the bulk of early discoveries of fossil whales. Marples work tended to be more careful, though he had the benefit of working during a more scholarly connected era and a greater pool of knowledge. Benham named Mauicetus parki and Marples named "Mauicetus" lophocephalus (now Tokarahia lophocephalus). Ewan Fordyce met Marples on several occasions and loved the guy.
The discovery of Mauicetus parki - the first early mysticete from New Zealand
In 1937, Professor William B. Benham of the Department of Zoology at the University of Otago published a short paper naming the new cetacean Lophocephalus parki, based on a broken braincase from an unknown locality, but most likely the Milburn Limestone at the Milburn Lime Quarry just about 40 km southwest of Dunedin (and, for anyone flying in to the country, quite close to the airport). Professor Benham noted that the skull was clearly not from a "squalodont" - which, as you may have guessed from part 1, and will be expanded upon in part 2, most heterodont cetaceans from the Oligocene and early Miocene were identified as "squalodonts" - but did not initially consider it to be a baleen whale. Based on the sagittal crest and narrow occipital shield, he considered Lophocephalus (ridged head, after the tall muscle attachment crests) to be an archaeocete whale. Another specimen, which he thought was from Lophocephalus, included a partial mandible and some blocks of limestone with associated teeth - Benham assumed these were from the same species, writing "I think I am justified in associating these teeth with those from Waimate, and attributing them to Lophocephalus parki."
The unassuming fragmentary braincase of Lophocephalus parki, from Benham (1937).
Benham's (1937) initial interpretation of Lophocephalus parki as an enormous archaeocete. Correspondence with Remington Kellogg would pointed out that the frontoparietal suture is present in the fragment, meaning that the skull is considerably more telescoped than Benham thought, and that it represented a mysticete.
Some of the specimens that Benham (1937) initially referred to Lophocephalus parki - a completely reasonable action given that he thought it was an archaeocete. Later it would become obvious that these were in fact odontocete specimens, now considered Squalodon or something similar.
This conclusion, however, was fleeting. Benham wrote a followup paper five years later in 1942 that precipitated from letters he had received from Remington Kellogg of the Smithsonian Institution in 1940. Kellogg pointed out that the braincase was much more complete than had been assumed by Benham, who had missed the frontal-parietal suture, though clearly present in his published photographs. Kellogg wrote that the skull was rather similar to Aglaocetus moreni, redescribed and illustrated by Kellogg in 1934. Further, Benham (1942) wrote that "after distribution of reprints of that article, my attention was drawn by a zoologist in America to the devastating fact - which I confess I had overlooked - that this generic name [meaning the genus name Lophocephalus] had been bestowed already on three animals of widely different groups, viz., on a Gregnarine, on a beetle, and on a fish! Hence, it is necessary to substitute another name for this extinct whale." Benham recognized that the specimen was in fact a baleen whale, and named it Mauicetus parki. Benham (1942) was forced to essentially re-publish a basic description of the fossil owing to the fact that, at the time, it was typical for descriptions to essentially consist of a long list of comparisons, his mistaken identity in 1937 sadly resulting in some anatomical misinterpretations that made the original study practically useless in most regards. In the 1942 redescription, Benham makes extensive comparisons with Aglaocetus moreni, and concludes that, thanks to Kellogg's correspondence, Mauicetus parki is indeed a "cetothere".
Ewan Fordyce and colleagues would go on to find many more Mauicetus-like fossils, including some fragmentary specimens reported by Hiroto Ichishima in his (unpublished) doctoral thesis. One specimen, collected not by Ewan but by F.M. Climo and colleagues in 1971, ZMT 67, is a large, 2.5 meter long partial skull with some postcrania that represents either a species of Mauicetus or a closely related genus. This specimen is earliest Miocene in age and from the very top of the Otekaike Limestone. In 2004 or so, Ewan and field assistants excavated a partial skull of a juvenile Mauicetus parki from Haugh's Quarry in the Hakataramea Valley of South Canterbury. He presented this in his 2005 presentation at the Society of Vertebrate Paleontology meeting in Mesa (Phoenix) Arizona, my first SVP - ten of us undergraduate students from Montana State University had carpooled down from Bozeman on a group road trip, taking turns napping and driving, in a 14 hour trek. I had been interested in fossil marine mammals, and just finished my first field season of permitted field work - and eagerly attended the marine mammal session on the morning of the second day. I saw a talk by Phil Gingerich on the giant archaeocete Basilosaurus isis from Egypt, a talk by Larry Barnes on kentriodontid dolphins from Calvert Cliffs, a talk from Mark Uhen on xenorophid dolphins from Onslow Beach, North Carolina (published three years later as Albertocetus), and a talk by Ewan Fordyce on a mysticete skull from New Zealand. I was shocked as Ewan described how he would excavate these specimens from the soft, sandy limestone with a chain saw. The entire excavation - which would have taken a crew of 3-4 pick/chisel-armed graduate students 3-4 days to excavate - took Ewan only about 2-3 hours! This material is still not yet published, unfortunately, but my doctoral labmate Felix Marx is continuing Ewan's research on Mauicetus. All I can say about Mauicetus parki is that it has an acutely triangular occipital shield, and earbones and mandibles that are similar to but slightly more primitive-looking than those in American "cetotheres" like Diorocetus and Parietobalaena. One of the key features I can mention is that Mauicetus has one critical earbone feature that is shared with modern baleen whales, to the exclusion of toothed mysticetes and eomysticetids: the posterior process of the two earbones (periotic and bulla) are fused into a long, cylindrical process. Near the base of this structure, the elliptical foramen in the bulla is also closed up. Mauicetus is the oldest known mysticete with these features.
The holotype skull of "Mauicetus" lophocephalus, from Marples (1956): on the right, the skull is shown as it was discovered and excavated in the Kokoamu Greensand. On the left is the skull as it was prepared, prior to being lost sometime in the 1960s or 1970s. At first glance, the skull of Mauicetus parki looks rather similar...
The holotype atlas and axis vertebrae of "Mauicetus" lophocephalus (left) and "Mauicetus" waitakiensis (right), from Marples (1956).
More Mauicetus, of Marples: Mauicetus lophocephalus, Mauicetus waitakiensis, and Mauicetus brevicollis
Professor Brian J. Marples of the University of Otago Zoology Department was an accidental paleontologist. He was actually an arachnologist - specializing in the zoology of trap-door spiders in New Zealand. In the 1940s, his work on these spiders brought his nose to the ground in the vicinity of the Waitaki River - and Oligocene rock layers. As a result, he and his students discovered some interesting cetacean and penguin fossils. He published on some of the fossil penguins in 1952, identifying them as Palaeeudyptes antarcticus. These identifications were determined later to be too conservative, and several were named as new species after Marples (by none other than G.G. Simposon) along with the new genus Marplesornis. Marples also found several baleen whale specimens consisting of partial skeletons, which he named in a 1956 paper, all from the Kokoamu Greensand (Duntroonian stage, 27-25 Ma). The most spectacular of these was named Mauicetus lophocephalus - amusingly re-using Benham's original genus name for Mauicetus - based on a partial skull with mandibles, periotic fragment, tympanic bullae, and some neck vertebra. A somewhat more fragmentary specimen consisting of the occipital bone, tympanic bullae, and neck vertebrae was named Mauicetus waitakiensis, and a third specimen consisting of a string of vertebrae was named Mauicetus brevicollis. Mauicetus lophocephalus was unusual in having a relatively primitive looking skull, and three images were produced: a photograph of the specimen in situ as it was discovered, a photograph of the braincase, unfortunately missing most of the rostrum which was apparently destroyed during excavation. The third image is a line drawing, which Fordyce suspected Marples drew while in the field - giving us a near-accurate view of the outline of the complete skull. The skull has a triangular rostrum, very long nasals and a bony naris (blowhole) set far out on the rostrum, large temporal fossae with medially bowed zygomatic arches, and a narrow intertemporal region of the skull with a small, narrow, posteriorly positioned occipital shield and vertex. Another skull resembling this would not be discovered again in New Zealand - or elsewhere on earth - until the 1980s.
The unusually robust sternum of Horopeta umarere. It retains an archaic rod-like structure with expansions at either end, and articular facets for multiple pairs of ribs; eomysticetids, on the other hand, had plate-like, triangular sterna with no obvious deep facets like this, implying only a single lightly attached pair of ribs as seen in the rest of Crown Mysticeti. From Tsai and Fordyce (2015).
Horopeta umarere - the oldest known gulp-feeding mysticete
A large mysticete was excavated from a cliff on the southeast side of Haugh's Quarry in 1988 by Ewan and his preparators Andrew Grebneff and Craig Jones. This specimen has a partial braincase, very well-preserved earbones, partially preserved mandibles, a sternum, and an articulated vertebral column with some ribs. This specimen served as the core specimen in my labmate Cheng-Hsiu Tsai's doctoral thesis, sort of a 'sequel' to Ichishima's 1997 thesis, and was published by Tsai and Fordyce in 2015. They named it Horopeta umarere roughly - translating from Maori to gulper with an unusual sternum . The specimen is from the base of the Duntroonian in the Kokoamu Greensand, dating to around 27-26 Ma. The skull is similar to Mauicetus, as are the earbones - yet they exhibit some features more reminiscent of eomysticetids: there is an open elliptical foramen in the bulla, and the posterior processes are not yet fused. However, the real revelation comes from the mandibles - they are robust, with a D-shaped cross-section, have a large and laterally curving coronoid process and are laterally very strongly bowed - much more strongly bowed than in eomysticetids, and resembling some Miocene "cetotheres" sensu lato ("kelloggitheres") as well as modern balaenopterid whales. This enormous mouth indicates that Horopeta was strongly adapted towards 'gulp feeding' - a more descriptively neutral term for a whale that takes in great mouthfuls of water to filter feed, like the lunge feeding behavior of modern balaenopterids. The sternum is quite robust and rod-like, with attachment points for three ribs - quite different from the plate-like sternum with an attachment for a single pair of ribs in modern mysticetes. Mysticetes tend to only have a single sternal bone - the manubrium, the anteriormost sternal bone, and all of the others, including the posteriormost one, the xiphisternum, are lost. Like other early mysticetes, there doesn't appear to ben articulation for a second sternal body. The robustness of the sternum in Horopeta is quite similar to toothed mysticetes like Llanocetus, Aetiocetus, and Mammalodon, and generally quite different from eomysticetids and modern mysticetes, suggesting a reversal or parallel evolution of a plate-like sternum.
The holotype earbones of Horopeta umarere: it really, really looks like Mauicetus parki, and in many regards, the earbones are a mishmash of archaic features you might expect in an eomysticetid and derived features you would see in a middle Miocene "kelloggithere" like Parietobalaena. From Tsai and Fordyce (2015).
The deeply unusual earbones of Whakakai waipata: the periotic is just massive, generally looking like a hyperinflated eomysticetid periotic. The bulla is nearly indistinguishable from Horopeta and Mauicetus. From Tsai and Fordyce (2016).
Tsai's whales - Whakakai waipati and Toipahautea waitaki
These whales have no common name, and since both were from chapters of Cheng-Hsiu Tsai's thesis, I've always just called them "Tsai's whales". These are two very unusual species, mostly diagnosed from their earbones. They are similar to an unpublished gigantic mysticete from the Kokoamu Greensand that is not yet named, but called the "chocolate whale" - generally resembling a gigantic eomysticetid, though with quite different-looking earbones. We don't yet have a complete skull of one of these things, but I expect study of the "chocolate whale" to reveal an eomysticetid-like morphology. The earbones include a tympanic bulla that is somewhat more like Mauicetus and Horopeta, but unusual periotics that are massively inflated with unfused posterior processes, quite unlike anything else known from the early fossil record of mysticetes. Whahakai waipata (pronounced "fah-caw-kye"; "Wh" in the southern Maori dialect is an "f" sound, see the pronunciation guide in part 1) was named by Tsai and Fordyce (2016) and has a partial braincase, and the top of the skull is a bit flat relative to eomysticetids, and seems to lack a clear sagittal crest - and has an intertemporal constriction that is somewhat shorter than eomysticetids. The periotic, in many regards, looks like an eomysticetid periotic that has been inflated like a balloon - and it's not inconceivable that, with the description and coding of more specimens, these might form a clade with eomysticetids based on some of the earbone features.
Phylogenetic analyses of these whales from Tsai and Fordyce (2018). All analyses I'm aware of, including those conducted using my matrix and Felix Marx's matrix, show these whales as occurring between eomysticetids and Crown Mysticeti - indicating that these are likely to be the whales that crown mysticetes evolved directly from.
Two years later, Tsai and Fordyce (2018) named Toipahautea waitaki based on a slightly more complete specimen that preserves much of the base of the rostrum, parts of the braincase, periotic, bulla, mandible fragments, neck vertebrae, and scapula. Like eomysticetids, the nasal bones are long, the supraorbital process of the frontal is long and bears a large orbit, and the rostrum itself is quite wide - though we don't know how long. The braincase is poorly preserved, but the occipital shield seems to be vertical - resembling right whales - though the shield likely curved anteriorly. Like eomysticetids, the joint for the mandible is very large and shallow. The periotic is somewhat similar to Whakakai, but also shares some similarities with Horopeta.
Mauicetus or mistaken identity? New Zealand Eomysticetidae
In the 1980s and 1990s Ewan Fordyce excavated a number of skulls he recognized were similar to Mauicetus lophocephalus, but was not quite close to naming yet. Sadly, fossils from the Oligocene Chandler Bridge Formation of South Carolina, USA, were discovered and named Eomysticetus by Al Sanders and Larry Barnes in 2002. Ewan quickly realized that this collection of about a half dozen skulls from New Zealand represented eomysticetids, and likely several genera; this family was basically defined by the relatively primitive features outlined above: long nasal bones, long, non-telescoped intertemporal constriction, large temporal fossae, long zygomatic processes, and archaeocete-like earbones. In 2006 Ewan presented these specimens in an oral presentation at the Society of Vertebrate Paleontology meeting in Ottawa, Canada, during a symposium on the Origin of Neoceti - my second SVP meeting. I was wowed by the number of specimens, excellent preservation, and the diversity - they appeared to represent at least 3-4 species. The following year I dug up and prepared a specimen of the much younger baleen whale Herpetocetus from the Purisima Formation in Santa Cruz, California, and presented it at the 2008 SVP in Cleveland, Ohio - after which, Ewan approached me and asked if I was applying to doctoral programs yet. "Not yet! I'm only two months into my master's program!" I exclaimed. "Well, when the time comes, keep New Zealand in mind." I did, and three years later I was accepted into the doctoral program with a scholarship; Sarah and I flew down to Dunedin in March 2012, and I started my work on these specimens. At first there wasn't room to bring out all the skulls for side-by-side comparison, so Ewan encouraged me - in the rare chances we had to chat during my first few months, given that he had around 12 doctoral, master's, and P.G. Dip. Sci. students - to first look at all of the periotics and bullae. Each of the new skulls had at least one periotic and one bulla associated with it. My goal was not only to figure out 1) how many genera and species were present amongst the new specimens, but 2) which might be the same species, or same genus, as the species named by Marples (only Mauicetus lophocephalus and Mauicetus waitakiensis were considered to be eomysticetids; Mauicetus brevicollis is something much closer to Mauicetus parki); 3) determine whether any of these species belonged in the same genus or if they were 'monospecific', and 4) to determine whether any of these were assignable to an existing genus/species from elsewhere (e.g. Eomysticetus, Micromysticetus, Yamatocetus). After a couple of weeks acquainting myself with these specimens and poring over the earbone anatomy of basilosaurid whales and toothed mysticetes, I finally got some clarity and made some predictions about what skulls might be conspecific and which ones were not.
Sadly, one development hampered my research somewhat. Sometime in the late 1950s, and prior to 1962, the Zoology Department moved buildings on Otago campus and the paleontology collections were transferred to the Otago Museum just across Cumberland street from campus. While the earbones, vertebrae, and mandible of Mauicetus lophocephalus were transferred and survive to this day, the skull - embedded in a large block of plaster - was lost, presumably discarded by university maintenance staff during the move. Ewan thought that the skull probably would have looked like a large rock on the floor, and staff may not have spoken to anyone in Zoology with direct knowledge of the specimen. Who knows what other rocks had been earmarked for the rubbish skip (=dumpster for my American readers); the skull is probably sitting in the landfill in Burnside, just south of town.
The evolution of the mysticete skeleton, skull, and tympanic bulla. From Boessenecker and Fordyce (2015c).
In the end, I came to the conclusion that there were six species present in four genera. Neither Mauicetus lophocephalus nor Mauicetus waitakiensis were assignable to Mauicetus, which likely belongs in a completely different (but as yet unnamed) family - and these species were instead identifiable as eomysticetids. The Island Cliff eomysticetid, OU 22235, was the largest single fossil that Ewan had ever excavated, and left in its 500 lb plaster jacket and prepared in relief. The tympanic bulla of this was quite similar to Mauicetus lophocephalus, and this specimen was named Tokarahia kauaeroa (Tokarahia, after Tokarahi - the Maori name for the mesa called "Island Cliff" by white settlers, and kauaroa meaning long jaw) in one of my thesis papers (Boessenecker and Fordyce, 2015c); we transferred Marples' species, with the new combination Tokarahia lophocephalus. One specimen of Tokarahia produced a putative tooth - these mysticetes were initially assumed to be toothless, and this discovery suggested that eomysticetids represented an intermediate stage between the toothed and baleen-bearing aetiocetid toothed mysticetes, and the completely toothless mysticetes of the Miocene and onward. Tokarahia, along with Waharoa (see below), suggest an intermediate stage with vestigial, functionless teeth along with baleen.
The holotype periotic of Tohoraata raekohao and a diagram of the auditory region. From Boessenecker and Fordyce (2015b).
The holotype tympanic bulla of Tohoraata raekohao (left) and Tohoraata waitakiensis (right). From Boessenecker and Fordyce (2015b).
A much more partially preserved specimen consisting of a very big baby (well, juvenile) skull with distinctive earbones, known as the Harvey Farm whale, was named Tohoraata raekohao - tohoraata meaning 'dawn whale' and raekohao meaning 'forehead holes', referring to the distinctive foramina in the frontal bones. The short bullae with triangular outlines matched those of Mauicetus waitakiensis, so we recombined Marple's second eomysticetid as Tohoraata waitakiensis.
The Earthquakes eomysticetid - the holotype skull of Waharoa ruwhenua. From Boessenecker and Fordyce (2015a).
Juvenile eomysticetids - the juvenile paratype skull of Waharoa ruwhenua (left), the perinatal/young juvenile (referred skull, not a paraype) on the upper right, and the holotype perotic of Waharoa. From Boessenecker and Fordyce (2015a).
Were eomysticetids the last toothed mysticetes? Juveniles and adults of Waharoa have three suspicisously tooth socket-looking foramina in their premaxilla, which suspiciously also houses three teeth in most placental mammals (and all toothed mysticetes and archaeocetes). There are additionally similar structures in the tips of the mandibles. Are these alveoli? We cautiously interpreted them as possible alveoli. From Boessenecker and Fordyce (2015a).
Growth changes in Waharoa ruwhenua. On the left are histological samples taken from the ribs of the young juvenile (OU 22075), older juvenile (OU 22163), and the adult holotype (OU 22044); woven bone is present in the juveniles, confirming juvenile status, and there is highly remodeled haversian bone present in the holotype, confirming adult status. This is not as accurate as counting LAGS (lines of arrested growth), but is useful as a general rule of thumb: baby, subadult, or mature adult - in a relative framework. On the right, the earbones of Waharoa change: the tympanic bulla actually grows somewhat, unlike modern mysticetes where they do not grow after birth. In the periotic, the hole for the facial nerve increases in diameter, perhaps corresponding to the increase in length of the palate, jaws, and the tongue - which the facial nerve innervates. From Boessenecker and Fordyce (2015a).
More on growth in Waharoa: the rostrum lengthens considerably during postnatal (e.g. after birth) growth in eomysticetids. Modern balaenopterid whales have long snouts, but they're nearly the same proportion at birth. Eomysticetids have a considerably steeper rate of rostral growth relative to other mysticetes. This strongly suggests that the length of the rostrum is critical in feeding, and the process of acceleration is likely responsible, but to a greater degree than in balaenopterid whales. From Boessenecker and Fordyce (2015a).
Two other genera were uncovered by Fordyce's field work that were completely undetected by Marples' efforts. One of these new taxa consisted of three skulls - the "Earthquakes" eomysticetid, the Haugh's quarry eomysticetid, and the "Springside cleft" juvenile mysticete - a species somewhat more delicately built than Tokarahia or Tohoraata, with smaller earbones and a narrower skull. We named this Waharoa ruwhenua - the species name here is a bit of word play. The fossil locality is called "The Earthquakes", since the way the rocks of the Otekaike Limestone have been exposed and weathered, it looks like a cartoon rift in the ground. Ruwhenua in Maori translates to "shaking land" - the Maori word for an earthquake. Waharoa means 'long mouth', referring to the exceedingly long palate and mandible of the main specimen. Specimens of Waharoa provide some insights into the feeding morphology and growth of eomysticetids, and early mysticetes in general. There are some tooth socket like structures in two of the specimens, suggesting a handful of vestigial peg-like teeth, as potentially preserved in Tokarahia. The palate has a number of palatal foramina, strongly suggesting the presence of baleen. However, these foramina are not present at the very front of the mouth, suggesting a gap in the baleen and perhaps a skim feeding behavior like modern right whales. The growth series of Waharoa ruwhenua includes a perinatal individual likely only a few months old at the very most, a somewhat larger juvenile, and an adult - confirmed through bone histology. The growth series indicates that the rostrum and palate grow rapidly during growth, and that juveniles are born with relatively shorter snouts, with the snout growing much more rapidly than in any modern mysticete. Similarly, one of the various holes in the earbones - the canal for the facial nerve - increases in diameter during growth. The facial nerve innervates the tongue, so it's possible that the nerve increases in diameter to innervate a much larger tongue in later life.
The highly bioeroded skull of the Waihao river eomysticetid - the holotype of Matapanui waihao. Note how the middle section of the right mandible was bioeroded away, but each end stayed in its approximate location; the braincase, and posterior end of the left mandible, were reoriented by currents after considerable bioerosion by bone eating worms (Osedax). From Boessenecker and Fordyce (2017a).
The well-preserved right periotic of Matapanui waihao. The left one was accidentally sawn through with a masonry saw during the excavation. "C'est la vie" Ewan said, when he shared that with me. From Boessenecker and Fordyce (2017a).
The left tympanic bulla of Matapanui waihao, with the posterior process in articulation (held in place with clay). From Boessenecker and Fordyce (2017a).
The last eomysticetid from my thesis was Matapanui waihao - originally named Matapa waihao, but the genus name was preoccupied by a genus of butterflies from Sri Lanka. So, we quickly renamed it Matapanui - translating to "big flat face" in Maori (Boessenecker and Fordyce, 2017c). The species name is after the Waihao river where it was collected (NOT the Waihao greensand!). This species was based off of specimens from the Kokoamu Greensand, and the type specimen is the oldest eomysticetid from New Zealand, dating to the Whaingaroan stage - approximately 28-27 Ma, though only 1-2 million years older than Tokarahia and Tohoraata. Matapanui has a somewhat longer and more 'square' supraorbital process of the frontal that is dorsally quite flat, and a curved rather than pointed apex of the occipital shield. The earbones are quite distinctive, with a proportionally large 'cochlea' (to be specific, the cochlear portion of the periotic). Several specimens were collected in parallel, including a fragmentary specimen from Sisters Creek consisting of a skull fragment, periotic, and partial atlas vertebra, and a partial braincase of a much more mature individual with fragmentary periotic from either the Potikohua Limestone or the Tiropahi Limestone from an underground limestone exposure in Te Tahi Cave on the west coast of the South Island, with poor age control. One of Ewan's students reported the specimen embedded in the side of the cave, and Ewan went spelunking - and wrapped up the braincase in his coat. Based on this fragmentary specimen, Matapanui was likely the largest and most robust of all of the NZ eomysticetids.
A fragmentary juvenile eomysticetid with a distinctive mandible: the end is blocky and curved dorsally, two traits otherwise known only in Yamatocetus from Japan. We proposed that this specimen from the Otekaike Limestone indicated that Yamatocetus had an antitropical distribution in the western Pacific. From Boessenecker and Fordyce (2017b).
The semi-controversial specimen OU 22744 from the "Protula bed" of the uppermost Otekaike Limestone at Hakataramea quarry, which we identified as cf. Waharoa based on the morphology of the atlas vertebra. From Boessenecker and Fordyce (2017b).
Ewan and I reported a couple more eomysticetids in a rather short paper published in 2017. This final paper from my Ph.D. research reported a tentatively identified specimen of Yamatocetus from New Zealand, consisting of a fragmentary braincase associated with distinctive mandibles. The anterior tips of the mandibles were squared, unlike the spear-shaped profile of Tokarahia, Waharoa, and probably Matapanui, and also dorsally curved at their anterior tips - a combination of features only known in the Japanese eomysticetid Yamatocetus canaliculatus. This specimen suggests that Yamatocetus had an antitropical distribution in the western Pacific - e.g. living in both the northern and southern parts of the western Pacific, and likely the only eomysticetid with an antitropical distribution at the genus level. The second specimen was tentatively identified as Waharoa based on the similar morphology of the atlas vertebra, and is a relatively fragmentary postcranial skeleton from near the top of the Otekaike Limestone; we identified the specimen as cf. Waharoa, and owing to its stratigraphic position, it is the only eomysticetid that appears to have dated to the earliest Miocene; indeed, the horizon the specimen is from a horizon dated to 22.8-22.3 Ma, but that has recently been revised (see below). A review paper on the fossil record of New Zealand Eomysticetidae was published by Marcus Richards and I (2024) in the Fossil Vertebrates from Zealandia special volume of the Journal of the Royal Society of New Zealand, wherein we briefly summarize what we know and what the major contributions of the fossil assemblage were, in addition to figuring a couple of recently discovered (and rediscovered) specimens.
Revised Geochronology of latest Oligocene mysticetes from the Otekaike Limestone
A new study by Felix Marx et al. (2024) published in the same special volume of the JRSNZ on fossil vertebrates from Zealandia provides a slate of new Strontium isotope dates for sixteen of the mysticete (and some odontocete) specimens from the Otekaike Limestone. Strontium isotopes have varied naturally in seawater since the Cambrian, with the curve going up and down - and the curve, specifically, being formed by the ratio of Strontium 87 and 86. Both are stable isotopes (e.g. they don't undergo radioactive decay, though 87Sr is radiogenic in origin, decaying from Rubidium 87). Differences in what rocks are weathering out at the earth's surface result in changes to the ratio of 87Sr versus 86Sr, with peaks and valleys through time, but generally since the Cretaceous getting more enriched in 87Sr. In many periods of earth's history, (especially the Cenozoic) the line is steep enough that if you get a new ratio, you can get quite a good date from it - in this study, and thanks to the steepness of the curve during the Oligocene, the error can be as small as +/- 100,000-200,000 years. But, you need relatively robust, unaltered marine invertebrate shells to grind down into a powder and analyzed with an X-ray diffractor. For this study, they used Lentipecten shells - relatively robust scallop shells measuring up to about 1-2 mm in thickness and about 7-9 cm across. At Haugh's quarry, these would sometimes pop out of the limestone free of matrix, and we would unceremoniously throw these at each other like frisbees. Ewan Fordyce had a habit of keeping matrix and associated invertebrates found during the excavation and preparation of fossil cetaceans, and in this case, permitted quite a few specimens to be dated isotopically.
All sampled eomysticetids from the Otekaike Limestone, save one (keep reading) were found to be squarely in the Oligocene, with ages of around 25-24 Ma - slightly younger than originally considered, as some of these were thought to be Duntroonian in age, which is about 27-25 Ma; most of these all seem to be Waitakian (25-23 Ma) instead. As for the specimen that Ewan and I reported that we considered, at the time, to be an earliest Miocene eomysticetid? Marx et al. (2024) think that that specimen is actually some sort of Mauicetus-like mysticete. We were appropriately circumspect about the identification of that specimen as cf. Waharoa, based chiefly on the atlas morphology - but more recently collected Mauicetus-like specimens, including a monolith of a jacket we excavated in 2013, preserve similarly humongous, robust atlases that challenge our identification. Further, if the specimen does turn out to be an eomysticetid, the date on the specimen is somewhat older than we initially thought based on its stratigraphic position relative to the "Protula Bed" in Haugh's quarry, which suggested it was about a meter into the Miocene - instead, the date is 23.08 Ma, just slightly older than the Oligocene-Miocene boundary at 23.03 (though perhaps splitting hairs here, given that the error on this measurement is +/- 0.5 million years).
In sum, this study clarifies that there does seem to be an absence of eomysticetids from the uppermost part of the Otekaike Limestone; the upper ten or 15 meters, generally representing strata immediately at/around the Oligocene-Miocene boundary, appear to only represent Mauicetus-like taxa. There don't appear to be any of the strange mysticetes like "Tsai's whales" - e.g. Horopeta, Whakakai, and Toipahautea - most of these are from the Kokoamu Greensand, or near the base of the Otekaike Limestone. This study also raises the possibility that a couple of the marker beds we've used to identify the base of the Duntroonian might be slightly younger than originally thought, or that the Otekaike Limestone is time-transgressive. Most critically, is that it apparently demonstrates the extinction of the Eomysticetidae just before the Oligocene-Miocene boundary, leading into the Aquitanian baleen whale gap, documented well a few years earlier by Marx et al. (2019).
New Zealand fossil mysticetes and the origin of Crown Mysticeti
One thing is certain - New Zealand boasts, by a very wide margin, the greatest diversity of toothless/baleen-bearing mysticetes in the world during the Oligocene epoch. There are to date approximately six eomysticetids, three of "Tsai's whales" (and at least 1-2 additional unnamed species), Mauicetus parki, the ZMT 67 taxon (either Mauicetus or a closely related genus), a possible balaenoid represented by specimen OU 22224, and likely a couple of others - ballpark, around 12-15 species for the late Oligocene (Chattian stage; e.g. Duntroonian to Waitakian) and earliest Miocene (e.g. ZMT 67 is from the first million years of the early Miocene Aquitanian stage) alone. This sort of diversity is absurd - and, while not all of these species are present at the same horizon, at least half of them are if one takes a look at the Kokoamu Greensand, for example. Further to the point, according to the careful work of Marx et al. (2023), the eomysticetids tend to be lower down stratigraphically and do not temporally overlap with true Mauicetus-type fossils, suggesting some faunal change within the region. In addition to the sheer diversity, New Zealand also boasts the majority of the entire fossil record of Oligocene baleen-bearing mysticetes; there are between fifteen and twenty eomysticetid skulls from Japan, Washington, Oregon, Baja California, South Carolina, and Europe - combined - and at least that many eomysticetid skulls from New Zealand, plus at least that approximate number of whales in the Mauicetus and "Tsai's whales" grade. I would wager that New Zealand boasts something like half or two thirds of the fossil record of Oligocene chaeomysticetes.
A review paper by my PhD colleague and dear friend Cheng-Hsiu Tsai (2023) in the same special volume of the JRSNZ considers this to be likely evidence that crown Mysticeti - the group formed by modern baleen whales and their most recent common ancestor - likely evolved in the southern hemisphere. Tsai points out that whales in the Topiahautea-Whakakai-Horopeta complex (which I've informally called "Tsai's whales" in this blog post) have, so far, really only been found in New Zealand, and further suggests that niche partitioning was likely in effect to permit this unusual degree of diversity. Further to the point, 'toothless' mysticete "assemblages" from the North Pacific and North Atlantic tend to consist of only a single species of eomysticetid: Sitsqwayk and Maiabalaena are both from the Pacific Northwest, but are from different stratigraphic units and not contemporaneous; Yamatocetus is the only 'toothless' mysticete from the Ashiya Group of Japan; and Eomysticetus and Micromysticetus are both found in Charleston, South Carolina, but are found in the Chandler Bridge Formation and underlying Ashley Formation (respectively) and separated in time by about ~4-5 million years. Charleston rivals New Zealand for Oligocene cetacean sampling - and certainly suprasses it in terms of the odontocete assemblage, perhaps three or fourfold (there are between 50 and 80 skulls, versus perhaps one or two dozen from NZ) - but there are only about a half dozen quasi-complete 'toothless' mysticete skulls that have ever been found in Charleston (as opposed to many, many dozens of odontocetes) and they are all eomysticetids (save one, see below).
The skull of Tlaxcallicetus from the Oligocene of Baja California. From Hernandez-Cisneros (2018).
There are a few tantalizing possibilities of "Tsai's whales" being found elsewhere: I strongly suspect that Tlaxcallicetus, named by our Mexican colleague Ehecatl Hernandez-Cisneros a few years ago, may be one of these whales; the periotic is quite strange. There's a fragmentary periotic in a squamosal chunk I acid prepared from the Pysht Formation that looks like Whakakai, and is clearly not an eomysticetid, but it is in bad shape. And lastly, there is a Horopeta-like juvenile braincase I excavated from the ~30 myo Ashley Formation in South Carolina back in 2018 or so, and it remains unstudied. But, these are unconfirmed identifications and I don't put much stock in them for the time being. Even if these are accepted, they barely inflate diversity elsewhere (raising the number to 2 or perhaps 3 baleen-bearing mysticetes) and likely represent diversity 'exported' from the south. Tsai (2023) contrasts these whales, which he terms the Toipahautea-Mauicetus grade, with eomysticetids by highlighting that eomysticetids likely diversified earlier in the Oligocene, having already dispersed to all corners of the globe by the mid Oligocene. On the other hand, "Tsai's whales" and Mauicetus are found only locally, and again, are surprisingly diverse - suggesting that the NZ fossil record is preserving an 'in situ' radiation. He concludes that
One last study requires discussion, and this is analysis of the "baleen whale gap" reported by Marx et al. (2019). This study examined a wide sampling of baleen whale earbones from the Oligocene and early Miocene of New Zealand and Australia, including toothed mysticetes, along with global trends in Oligo-Miocene mysticete diversity. They found that in the more coastal deposits of Australia, the fossil record of mysticetes were dominated by small toothed mysticetes in the Mammalodontidae, which made up about 82% of the fossils altogether; 15% were eomysticetids, and only 3% were non-eomysticetid true mysticetes - e.g. Mauicetus-like species of possible records of "Tsai's whales". In New Zealand, which they considered to represent more pelagic conditions given the near-submergence of Zealandia (see first post) and the remoteness of the Zealandia shelf, the fossil assemblage is instead dominated by baleen-bearing mysticetes with non-eomysticetid mysticetes comprising a staggering 73% of the assemblage, mammalodontids only about 4%, and eomysticetids at 23% of the fauna.
Marx et al. (2019) infer a 'dark age', or as I call it, a baleen whale gap during the first five million years of the Miocene. We know they clearly survived, but baleen whale fossils are astonishingly rare during the Aquitanian stage and earliest Burdigalian, only becoming common again around 17-18 mya. All early Miocene mysticetes known from the Aquitanian are relatively derived species that some of us have informally called "Kelloggitheres" - also slightly less informally referred to as "cetotheres" sensu lato, stem balaenopteroids, or stem thalassotheres. I'll keep using "Kelloggitheres" as the term was devised in an SVP talk years ago by Erich Fitzgerald, in honor of Remington Kellogg, who worked on a ton of these sorts of whales from the Miocene of Maryland/Virginia, California, South America, and Oregon; these are species like the well-known Parietobalaena and Diorocetus from the Calvert Formation of Maryland. Mauicetus parki in particular shares a lot in common with these, differing chiefly in having a somewhat more archaic set of earbones and vertex, and I would argue, is the first "Kelloggithere". One thing I've noticed is that these species are all remarkably similar, and given that aside from the early right whale Morenocetus, virtually all early Miocene mysticetes have "Kelloggithere" affinities, these species are probably extremely oversplit and are in dire need of revision. As a result of this, anatomical diversity - a metric frequently called 'disparity' - tanks during the early Miocene, reflecting the fact that these are all very similar looking whales with very slight variations on a theme.
Marx et al. (2019) correlate the extinction of toothed mysticetes and eomysticetids with a brief but drastic cooling period coinciding with a drop in sea level at the end of the Oligocene, which may have driven faunal collapse in coastal marine settings, leading to the extinction of decidedly shallow marine toothed mysticetes like the mammalodontids. Likewise, there was a crash in global diatom abundance in the earliest Miocene, which may have led to globally reduced biomass of zooplankton. They hypothesized that the whales which seemed to have survived are those from New Zealand with a more pelagic (open ocean) habitus - perhaps explaining their rarity in continental shelf deposits elsewhere for several million years. During this 'dark age', baleen whales were possibly pelagic only and likely to be numerically quite rare - only diversifying once again as climate, primary productivity, and planktonic diversity all increased during the Middle Miocene Climatic Optimum around 15 mya. Curiously, there is a potential early Miocene extinction event recorded in pelagic shark fossils around 18 mya by Elizabeth Sibert and colleagues (2021; covered in an earlier blog post, read it here), and Tsai (2024) suggests that this may be related to the baleen whale 'dark age'. I am tempted to agree, though the baleen whale record tanks several million years prior.
As always, there is more yet to do: all of these jackets in the University of Otago basement contain fossil cetaceans, chiefly from the upper Otekaike Limestone at Hakataramea Quarry (and are therefore about 22-25 Ma), and few have been prepared. Each one potentially represents a future holotype or a referred specimen of an existing species that might shed critical light on the functional anatomy and evolution of the earliest crown mysticetes. From Tsai (2023).
Regardless, we have a lot more to learn - even just from the collections of the University of Otago. Tsai (2024) points out that many of these early mysticetes are known within the Fordyce lab, past and present - but formally, many such specimens are only known as a trail of breadcrumbs in SVP abstracts and mentions in various papers. One such specimen is the "Oligocene right whale", OU 22224 - a mysticete close to the ancestry of Crown Mysticeti. This specimen has a vertical occipital shield and an arched rostrum - resulting in its identification as a possible Oligocene balaenid. If the identification holds, it would be the oldest known crown mysticete, and certainly the oldest member of any modern family. However, it frequently plots out amongst "Tsai's whales" - within the Toipahautea-Mauicetus complex, though in the most recent phylogeny by Tsai and Fordyce (2018), it did plot out as a sister taxon to the Balaenidae. We'll have to await study of the specimen - but aside from this, there are many other unpublished mysticetes known from partial braincases, fragmentary skulls, nearly complete skulls, and most that have been excavated in recent years seem to be Mauicetus-like whales. Recently, for example, the enormous, nearly 3 meter long jacket we nicknamed the "star destroyer" has been prepared and photos shared with me; it looks to be a large whale close to Mauicetus and ZMT 67 in its morphology. There are untold treasures awaiting study in the Otago collection - Fordyce's collecting over the past 40 years will keep us busy for decades.
Three new eomysticetid specimens have either been freshly prepared or were collected entirely after my time at Otago. The first is OU 22473, the periotic of which I had described in 2017 as a specimen of Matapanui waihao. A partial skull (OU 22120) was possibly associated - however, the periotic was separated from the skull after preparation by the late preparator Andrew Grebneff and for a long while it was unclear if the partial skull really belonged. Ewan recalled a white periotic being associated with the block, and this unlabeled specimen seemed to fit the bill - as the only good candidate, we always assumed they were the same specimen. However, short of being able to demonstrate it, we cautiously assigned a new number for the periotic. A while after I left, preparator Sophie White conducted some more preparation of the skull - the skull was in a block of limestone that cracked horizontally right through the rostrum. On one block is the supraorbital process, one mandible, and the base of the rostrum, with the dorsal surface prepped out; on the other block is the ventral surface of the rest of the rostrum. While not prepared completely, the new prepwork showcases the palatal foramina quite beautifully - clearly demonstrating that eomysticetids, when well-preserved, do indeed have an extensive network of vascular channels for the arteries and nerves that feed the baleen. Likewise, it means that if specimens like the holotype skull of Maiabalaena - once championed as evidence that eomysticetids had neither baleen nor teeth - were better preserved, they would likely show something similar. But, you really do need specimens with well-preserved (and well-prepared) palates to make such claims. The other two specimens are more fragmentary. One, OU 22783, is a partial skull with periotic of Tokarahia; it preserves a partial rostrum, posterior mandible, and braincase. The other is the Smite River whale, OU 22028, is another specimen of Matapanui sp., with an even more fragmentary mandible, braincase, and partial periotic. These specimens have been figured and briefly outlined, but I'll have to make it back down to Dunedin sometime to get these specimens written up!
On that note, onto part three - fossil odontocetes from New Zealand, Ewan's true passion.
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