Separate returns to water for whales and hippos? No.

From the Springer et al. 2021 abstract:
“The macroevolutionary transition from terra firma to obligatory inhabitance of the marine hydrosphere has occurred twice in the history of Mammalia: Cetacea and Sirenia.”

No. Cetacea is diphyletic (Figs. 1, 2) in the large reptile tree (LRT, 1823+ taxa) with separate origins for tenrecs + archaeocetes + odontocetes apart from hippos + desmostylians + mysticetetes.

Figure 3. the Merycoidodon cladogram includes hippos, whales and a number of extinct taxa.

Figure 2. The nesting of Eocene Andrewsiphius basal to extant tenrecs between leptictids and pakicetids.

“In the case of Cetacea (whales, dolphins, and porpoises), molecular phylogenies provide unambiguous evidence that fully aquatic cetaceans and semiaquatic hippopotamids (hippos) are each other’s closest living relatives.”

No. As noted many times earlier, molecular phylogenies too often deliver false positives. Use traits. We cannot trust DNA results in deep time studies… and most fossils are excluded.

“These results, together with histological differences in the integument and prior analyses of oxygen isotopes from stem hippopotamids (“anthracotheres”), support the hypothesis that aquatic skin adaptations evolved independently in hippos and cetaceans.”

If so, the authors are “Pulling a Larry Martin” by ignoring taxa, ignoring traits and pinning all their hopes on unreliable genes and skin isotopes.

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References
Springer MS et al. (10 co-authors) 2021. Genomicand anatomical comparisons of skin support independent adaptation to life in water by cetaceans and hippos. Current Biology https://doi.org/10.1016/j.cub.2021.02.057

Interested in whale carpals?

Gavazzi et al. 2020 bring us their views
on whale and pre-whale carpal elements. They used the invalidated artiodactyls, pig (Sus) and  (Diacodexis) as outgroup taxa. The latter is incompletely known, slender and appears to be not far from the more completely known Cainotherium.

By contrast
here  (Figs. 1–3, 5, 7, 8) competing whale and pre-whale carpal elements are presented along with tree shrew (Ptilocercus) carpals (Fig. 4) as an example of the plesiomorphic condition in placentals.

Bottom line:
Due to taxon exclusion, actual evolutionary patterns were overlooked by Gavazzi et al., but that didn’t matter much. About the same story can be told with the wrong outgroup taxa. Carpals don’t change much across these members of the placental clade.

Figure 1. Odontocete flipper and ancestral taxa manus. Homologous wrist elements are colored the same. Green is the pisiform, missing in the dolphin, Tursips.  Ambulocetus image from Gavazzi et al. 2020 and repaired here. Dorudon image from Cooper et al. 2007 and repaired here.

From the Gavazzi et al. 2020 abstract:
“During the land-to-water transition in the Eocene epoch, the cetacean skeleton underwent modifications to accommodate life in the seas. These changes are well-documented in the fossil record. The forelimb transformed from a weight-bearing limb with mobile joints to a flipper with an immobile carpus.”

Unfortunately Gavazzi et al. still consider ‘Cetacea’ a monophyletic clade. That hypothesis of interrelationships became invalid in 2017 with a blogpost here and an online paper here.

Figure 2. The manus of Eubaelana, an extant right whale (bottom) compared to two desmostylians. Note the similarities between the two unrelated clades. Missing parts are restored based on phylogenetic bracketing.

Mammal carpal homologs:

1. Distal carpal 1 = Trapezium – red
2. Distal carpal 2 = Trapezoid – cyan
3. Distal carpal 3 = Capitum – lavender
4. Distal carpal 4+5 = Hamatum – yellow green
5. Radiale = Scaphoideum – pink
6. Intermedium = Lunatum – yellow
7. Ulnare = Triquetrum – pale orange
8. Centrale = Centrale – indigo
9. Pisiform = Pisiform – green

Figure 3. Hippos manus. Pisiform in green.

Continuing from the Gavazzi et al. 2020 abstract:
“We used micro-CT imaging to assess evolutionary changes in carpal size, orientation, and articulation within Eocene cetacean taxa associated with the transition from a terrestrial to amphibious niche. We compared Ambulocetus natans (Fig. 1), a well-preserved amphibious archaeocete, with other archaeocetes, and with Eocene terrestrial artiodactyls, the sister group to Cetacea.”

Figure 4. Ptilocercus is a tree shrew closer to the plesiomorphic wrist condition. Compare to taxa in figures 1 and 2.

Figure 5. X-ray of Tursiops flipper showing no trace of a pisiform. But look at digit 5. Compare to figure 4.

Eocene terrestrial artiodactyls are not the sister group to Cetacea, which is not a monophyletic clade in the LRT. Adding overlooked taxa resolves this issue.

“A cylindrical carpus in terrestrial taxa evolved into a mediolaterally flattened, cambered carpus in the semi-aquatic and fully aquatic cetaceans.

Gavazzi et al. chose the wrong terrestrial taxa.  Tenrec carpals (Figs. 1, 7) are not as cylindrical as those of pigs and their ancestors, though the pisiform does orient itself ventroposteriorly. All flippers are flattened with a lateral pisiform, which turns out to be a reversal back to the tree shrew orientation (Fig. 4).

“Specifically, the pisiform bone shifted from a ventral [= posterior, Fig. 3] orientation in terrestrial taxa to a lateral orientation, in plane with the carpus, within semi-aquatic and fully aquatic taxa.”

A ventroposterior pisiform is also found in Tenrec (Fig. 1)  and Hippopotamus (Fig. 3) among the actual ancestors of odontocetes and mysticetes respectively.

“Flattening of the carpus, including lateral rotation of the pisiform, likely relates to functional shifts from weight-bearing terrestrial locomotion to aquatic locomotion. This laterally projecting pisiform morphology is retained in all extant cetaceans.”

Gavazzi et al. used the wrong outgroup taxa. In both Tenrec and Hippopotamus the carpus is less cylindrical than in the artiodactyls, Sus and Diacodexis.

By the way, the pisiform is absent in the dolphin Tursiops (Figs. 1, 5), but look at the lateral orientation of digit 5 in comparison to the lateral orientation of the pisiform in the plesiomorphic wrist of Ptilocercus (Fig. 4). One wonders if Gavazzi et al. mistook digit 5 in Tursiops for a pisiform, given their statement.

“Our results suggest this shift, along with other modifications to the carpus, predominantly occurred during the middle Eocene and facilitated an obligatorily aquatic lifestyle in late Eocene cetaceans.”

Without the real ancestors, the Gavazzi et al. paper and its conclusions would be a waste of time, except that carpals are largely interchangeable in quadrupedal placentals. So their conclusions remain largely valid. Thirteen years ago Cooper et al. 2007 also looked at whale carpals and compared them to predecessor taxa (see below).

Figure 6. Ambulocetus carpals from Gavazzi et al. (left) here restored to their original positions and colored.

Try to always restore scattered elements
to their original positions. Don’t leave the work half done. Colors help to make this process easier and aid in making confident comparisons between taxa.

Figure 7. Manus and wrist of the extant tenrec Hemicentetes (from Digimorph.org and used with permission). Colors added. Compare to related taxa in figures 1 and 6. Pisiform in bright green.

The traditionally overlooked overall resemblance of tenrecs
to Indohyus (Fig. 8) and later odontocete ancestors (Fig. 8) extends to the manus and carpus.

Whale workers who refereed the manuscript
‘The Triple Origin of Whales‘ declined to allow it to be published. In that light, one wonders why whale workers prefer to cherry-pick pigs and pig ancestors rather than adding valid taxa to their cladograms. Keeping their blinders on is a continuing problem in paleontology, which is why this blogpost exists. For those readers hoping someday to make discoveries in this field of science, beware. Many professors will attempt to suppress your work to  keep the discoveries for themselves.

Figure 8. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Figure 9. Taxa in the lineage of right whales include Desmostylus, Caperea and Eubalaena. The tiny bit of jugal posterior to the orbit (in cyan) is found in all baleen whales tested so far. The frontals over the eyes are just roofing the eyeballs in Desmostylus, much wider in Caperea and much, much longer in Eubalaena.

Cooper et al. 2007
dissected extant whale flippers and compared them to Ambulocetus (Fig. 1) and Dorudon (Fig. 1) without correcting for disarticulation problems in fossils. Cooper et al. report, “Most odontocetes also reduce the number of phalangeal elements in digit V, while mysticetes typically retain the plesiomorphic condition of three phalanges.” Perhaps Cooper et al. did not notice there are four phalanges on digit five in Eubaelana (Fig. 2). The unguals are tiny.

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References
Cooper LN, Berta A, Dawson SD and Reidenberg JS 2007. Evolution of hyperphalangy and digit reduction in the cetacean manus. The Anatomical Record Special Issue: Anatomical Adaptations of Aquatic Mammals 290(6): https://doi.org/10.1002/ar.20532
Gavazzi LM, Cooper LN, Fish FE, Hussain ST and Thewissen JGM 2020. Carpal Morphology and Function in the Earliest Cetaceans. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2020.1833019

https://www.researchgate.net/publication/328388746_The_triple_origin_of_whales

SVP abstracts 7: Coombs follows the traditional whale origin myth

Coombs 2020 studied whale skulls
using a traditional, but recently invalidated phylogeny. She did not understand the diphyly of the former clade ‘Cetacea’.

From the Coombs abstract:
“The extant clades of whales, Odontoceti (toothed whales) and Mysticeti (baleen whales), diverged ~39 Ma.”

According to the large reptile tree (LRT, 1749+ taxa) that divergence occurred way back when whale ancestors were still tree shrews. A tiny taxon, Anagale (Fig. 1; Late Cretaceous, 75-71mya) is near their last common ancestor.

Figure 1. We are very fortunate to have several of these basal placental taxa still living with us, as chronologically long-lived taxa. Starting with the extant Didelphis at the base of the Theria, phylogenetic miniaturization gave us the smaller Monodelphis domestics and the even smaller M. sores and M. kunsi, which gave rise to the larger Nandinia at the base of the Carnivora, Tupaia, at the base of the expanded Glires, Ptilocercus at the base of the expanded Archonta, and the Condylarthra, aka the rest of the mammals.

Continuing from the Coombs abstract:
“Odontocetes evolved high-frequency echolocation and cranial asymmetry, while mysticetes evolved larger masses and filter feeding.”

Actually odontocete ancestors, represented by extant tenrecs, developed echolocation and cranial asymmetry, by the Paleocene 65mya.

Mysticete ancestors did not develop filter feeding until the Oligocene, 34-23mya at the earliest. Mystacodon (Fig. 2; 36mya) was considered the earliest baleen whale, but this toothy whale nests with the odontocete clade.

FIgure 2. This toothy whale with a tiny pelvis is Mystcodon, originally promoted as the earliest known mysticete (baleen whale).

Continuing from the Coombs abstract:
“Despite an excellent fossil record and unique morphology, there has been little quantitative study of shape evolution spanning cetacean diversity.”

Before making that statement, Coombs should add taxa to start with a valid phylogeny, lacking at present. Ancestors to both whale clades (Fig. 3) have been traditionally overlooked due to taxon exclusion.

“To quantify morphological disparity and evolutionary rate in cranial shape and to identify ecological correlates of shape variation across Cetacea, I gathered 3D scans of specimens representing 84 living (72 odontocetes, 12 mysticetes) and 72 Eocene to Pliocene fossil (45 odontocetes, 17 mysticetes, 10 archaeocetes) cetaceans. I then digitized 123 landmarks and 64 curves on these scans and conducted high-dimensional geometric morphometric and macroevolutionary analyses within a phylogenetic framework.”

The Coombs phylogenetic framework is fatally flawed due to taxon exclusion. Adding pertinent taxa will solve this problem.

Figure 3. Subset of the LRT focusing on the odontocetes and their ancestors.

Continuing from the Coombs abstract:
“The largest component of cranial variation (PC1 = 39.9%) reflects a posterior shift in the nares and separates odontocete and mysticete modes of cranial telescoping. Rostrum length is the major component of variation on PC2 (20.7%) with dolicocephalic [having a long skull] (e.g., Pontoporia blainvillei) and brachycephalic [having a short skull] (e.g., Kogia sima) crania representing the extremes.”

Figure 4. The oreodont-mesonychid-hippo-desmoystlian-mysticete clade subset of the LRT

Continuing from the Coombs abstract:
“Cranial asymmetry in archaeocetes is high in the rostrum, squamosal, jugal, and orbit, possibly reflecting preservational deformation. In odontocetes, it is highest in the naso-facial region. Mysticetes show levels of asymmetry similar to terrestrial artiodactyls.”

In other words: essentially no asymmetry. Why? Because mysticetes and odontocetes had different ancestors. Artiodactyls had nothing to do with whales ever since the LRT pulled hippos out of the artiodactyls and into the mesonychids (Fig. 4).

Figure 5. Taxa in the lineage of right whales include Desmostylus, Caperea and Eubalaena. The tiny bit of jugal posterior to the orbit (in cyan) is found in all baleen whales tested so far. The frontals over the eyes are just roofing the eyeballs in Desmostylus, much wider in Caperea and much, much longer in Eubalaena.

Continuing from the Coombs abstract:
“Significant rate shifts in asymmetry are observed in the stem odontocetes Xenorophidae (∼30 Ma), Physeteroidea (∼27 Ma), Squalodelphinidae (~27 Ma), and Monodontidae (~7 Ma). Rapid evolution of both cranial shape and asymmetry in cetaceans occurred in the Middle-Late Oligocene and peaks in the Middle Late Miocene, largely due to subclade-specific diversification of rostrum and facial morphology.”

Coombs’ results, no matter how carefully measured, are incomplete because they are not recovered within a valid phylogenetic context. Add pertinent taxa to resolve this issue.

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References
Coombs E 2020. Cranial morphology in whales: A study spanning the evolutionary history and diversity of the Cetacean skull. SVP abstracts 2020.

Coombs et al. 2020 re-study odontocete skull asymmetry

Coombs et al. 2020 described odontocete (toothed whale) skull asymmetry
but did not trace it back to its origins in tenrecs (Fig. 1), as we did here two years ago. Without a valid phylogenetic context, the answers they sought evaded the Coombs team.

Nine years ago
whale skull asymmetry was studied by Fahlke et al. 2011, likewise without including tenrecs.

Figure 2. Hemicentetes an extant echolocating tenrec, also has a twisted skull, like its descendants, the odontocete whales.

From the Coombs et al. abstract:
“Unlike most mammals, toothed whale (Odontoceti) skulls lack symmetry in the nasal and facial (nasofacial) region. This asymmetry is hypothesised to relate to echolocation, which may have evolved in the earliest diverging odontocetes.”

Earlier. See figure 1.

“Early cetaceans (whales, dolphins, and porpoises) such as archaeocetes, namely the protocetids and basilosaurids, have asymmetric rostra, but it is unclear when nasofacial asymmetry evolved during the transition from archaeocetes to modern whales.”

Earlier. See figure 1.

“Early ancestors of living whales had little cranial asymmetry and likely were not able to echolocate.”

Incorrect conclusion. Add taxa. See figure 1. And see Gould 1965, who described echolocation in tenrecs.

Figure 2. Odontoceti (toothed whale) origin and evolution from tree shrews to killer whales. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Illustrations like these
(Fig 2) can be extremely helpful for ‘seeing’ evolution take place in a series of micro-evolutionary events. Typical of evolution, several lineages go extinct, while one or a few continue to the present day. Here we are lucky enough to have a few flesh and blood tenrecs at the genesis and several odontocetes to compare. This would make a great PhD project.

Coombs et al. 2020
are still not aware that the traditional clade ‘Cetacea’ is no longer valid because odontocete ‘whales’ arise apart from mysticete ‘whales’ in the large reptile tree. Click the links in this paragraph and in the citations below to get more backstory.

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References
Coombs EJ, Clavel J, Park T, Churchill M and Goswami A 2020. BMC Biology 18:86 https://doi.org/10.1186/s12915-020-00805-4
Fahlke JM,  Gingerich PD, Welsh RC and Wood AR. 2011. Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water. PNAS 108 (35) 14545-14548; https://doi.org/10.1073/pnas.1108927108
Gould E 1965. Evidence for Echolocation in the Tenrecidae of Madagascar
Proceedings of the American Philosophical Society 109 (6): 352-360. online here.

https://www.researchgate.net/publication/328388746_The_triple_origin_of_whales

 

Livyatan (originally Leviathan) enters the LRT

Lambert et al. 2010 made a ‘big splash’
when they introduced a giant ‘raptorial’ odontocete, Leviathan melvillei (Fig. 1). Distinct from a similarly-sized sperm whale (Physeter), Leviathan has a shorter rostrum and retained giant teeth on the maxilla. It also had a preoccupied name, so it was later renamed Livyatan.

Figure 1. Livyatan diagram from Lambert et al. 2010 and colored here.

Size:
The skull of Livyatan was fifty percent larger skull than the largest sauropterygians, similar in size to the skull of the largest ichthyosaurs, 3/4 the length of the skull of the largest odontocete, Physeter, but with much larger teeth.

Phylogeny
In the large reptile tree (LRT, 1666+ taxa), Livyatan is transitional between several extinct archaeocetes and all extant odontocetes of which Physeter and Tursiops  are the most primitive. The dolphin smile famously worn by Tursiops had its genesis in Livyatan (Fig.1) and was lost in long-jawed Physeter.

One question:
The lateral extent of the premaxilla in the Lambert et al. diagram (Fig. 1) is different in dorsal, lateral and palatal views.

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References
Lambert O et al. (6 co-authors) 2010. The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature 466:105–108.

wiki/Livyatan (Leviathan)
wiki/Physeter

SVP 2018: Tooth loss in mysticete whales x5 abstracts

Five SVP abstracts
fumble with the issue of tooth loss preceding the origin of mysticete whales under the invalid assumption that the traditional clade Cetacea is monophyletic. It is not. Whales had two or three (right whales make it three) separate origins, as we learned earlier here.

ABSTRACT 1
Ekdale and Deméré 2018
continue beating a dead horse trying to figure out how Aetiocetus evolved into the clade Mysticeti (Figs. 1-4). In the large reptile tree (LRT, 1038 taxa) mysticetes evolved from desmostylians (Fig. 2-4) while being tested against all prior candidate taxa. Odontocetes evolved from tenrecs, pakicetids and archaeocetids (Fig. 1). Ekdale and Deméré 2018 mistakenly (through taxon exclusion) consider the toothed Aetiocetus a member of the traditional ‘toothed mysticetes’ that they mistakenly think “plays a central role in the debate.”

Figure 4. Subset of the LRT focusing on the odontocetes and their ancestors.

The authors conclude:
“These results provide critical evidence that the lateral palatal foramina in A. weltoni are
homologous with lateral nutrient foramina in extant mysticetes. As such, the lateral nutrient
foramina in A. weltoni provide strong support for the hypothesis that aetiocetids possessed both teeth and some form of baleen.” Unfortunately the authors saw what they wanted to see. They never tested tenrecs or desmostylians and so failed to recover the correct phylogenetic framework upon which their work could proceed. Maybe a similar CT scan will find similar nerve and blood vessel patterns in desmostyians. Only testing will reveal what the cladogram indicates.

Figure 2. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

ABSTRACT 2
Gatesy et al. 2018 reassess “phylogenetic studies presented over the past dozen years that have variously reconstructed this complex evolutionary sequence. Early work proposed a step-wise transformation in which toothed mysticetes transitioned via ‘intermediate’ forms with both teeth and baleen to toothless filter feeders. Later studies presented alternative scenarios featuring filtration with teeth instead of baleen, loss of a functional dentition before the evolution of baleen, pure suction feeding, and/or convergent evolution of several key mysticete features. We reanalyzed published cladistic matrices in the context of extensive new molecular data, assessed character support for alternative relationships, and mapped six features related to filter feeding in Mysticeti: presence/absence of 1) teeth, 2) baleen, 3) lateral nutrient foramina on the palate (possible osteological correlates of baleen), 4) a broad rostrum, 5) laterally bowed mandibles, and 6) an unsutured mandibular symphysis.”

All for naught.
They could have and should have run a wide gamut phylogenetic analysis like the LRT which separates the ancestors of odontocetes from the ancestors of mysticetes by a wide phylogenetic distance of intervening taxa (Figs. 1, 2). The ancestors of mysticetes are not to be found among the ancestors of odontocetes. This has been online for two years now.

ABSTRACT 3
Geisler, Beatty and Boessnecker 2018
discuss, to no avail, new specimens of Coronodon havensteini, which they say is the most basal mysticete (in the absence of desmostylians and kin) and the LRT nests at the base of the odontocetes and aetiocetes. Surprisingly, the authors report, “these specimens support the hypothesis that Coronodon engaged in macrophagy and filter feeding, and underscores the challenges for reconstructing the behaviors of extinct species based on the limited sample provided by the fossil record.” No they have evidence for macrophagy and they have contrived a scenario for filter feeding. 

Figure 3. Taxa in the lineage of the right whale (Eubalaena) include the pygmy right whale (Caperea) and the desmostylian, Desmostylus. You don’t have to look for tooth loss in desmostylians. They already have that trait and so many more.

ABSTRACT 4
Lanzetti, Berta and Ekdale 2018
looked at fetal mysticetes and reported, “We present new evidence on the ontogeny of the minke whale, which develops a dense tissue dorsal to the rostral canal where the tooth buds are either already absent or clearly undergoing resorption. The identity of this tissue should be confirmed by histological analysis, but it may be the first sign of baleen development, as posited by previous studies of these species. Overall, the GM analyses show that the fossils occupy a different morphospace than modern species, possibly indicating that they had specific feeding adaptations not shared by modern mysticetes.”
Clearly they are not looking at desmostylians, which loose most of their teeth in adults.

Figure 41. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

ABSTRACT 5
Peredo 2018
thinks tooth loss precedes the origin of baleen in mysticetes by considering an Early Oligocene specimen from Oregon. In his thinking Peredo, like the authors above, is barking up the wrong tree when he reports, “Although living baleen whales are born without teeth, paleontological and embryological evidence demonstrate that they evolved from toothed ancestors that lacked baleen entirely.” However his specimen might be a desmostylian in the lineage of mysticetes when he reports, “This new material includes a transitional fossil mysticete that lacks both teeth and baleen entirely, demonstrating that tooth loss precedes the origin of baleen in mysticetes.”

A toothy Oregon taxon, Salishicetus, was described by Peredo and Pyenson 2018, who nested it basal to other aetiocetids. They reported, “The description of Salishicetus resolves phylogenetic relationships among aetiocetids, which provides a basis for reconstructing ancestral feeding morphology along the stem leading to crown Mysticeti.”

References
Ekdale EG and Deméré TA 2018. Tooth-to-baleen transition in mysticetes: New CT evidence of vascular structures on the palate of Aetiocetus weltoni (Mysticeti, Cetacea). SVP abstract.
Gatesy et al. (4 co-authors) 2018. Contrasting interpretations of the teeth to baleen transition in mysticete cetaceans. SVP abstract.
Geisler J, Beatty BL and Boessenecker RW 2018. New specimens of Coronodon havensteini provide insights into the transition from raptorial to filter feeding in whales. SVP abstract.
Lanzetti A, Berta A and Ekdale EG 2018. Looking at fossils in a new light: teeth to baleen transition in relation to the ontogeny and phylogeny of baleen whales. SVP abstract.
Peredo CM 2018. From teeth to baleen: Tooth loss precedes the origin of baleen in whales. SVP abstracts.
Peredo CM and Pyenson ND 2018. Salishicetus meadi, a new aetiocetid from the late Oligocene of Washington State and implications for feeding transitions in early mysticete evolution. Royal Society Open Science 5: 172336. http://dx.doi.org/10.1098/rsos.172336

Coronodon: another wannabe mysticete ancestor

Geisler et al. 2017
presented Coronodon as a recent addition to the panoply of toothed whales said to be ancestral to mysticetes. Taxon exclusion is once again the problem. The real ancestors of mysticetes (Fig. 3) are mesonychids, hippos, anthracobunids and desmostylians, as we learned earlier. These taxa were not tested by Geisler et al. 2017.

Figure 1. Coronodon, was originally considered a toothed mysticete, but only in the absence of desmostylians, the real ancestors of mysticetes. This taxon lies at the base of Odontoceti and Aetioceti in the LRT.

Coronodon havensteini (Geisler et al., 2017; early Oligocene, 30 mya) was originally and is traditionally considered a mysticete whale, basal to baleen whales like Balaenoptera. With more tested taxa here it nests basal to odontocete whales like Aetiocetus and Physeter. The archaeocete teeth were considered the first stage in filter-feeding. Here they are relics from an archaeocete ancestry. Descendants in both branches (aetiocetes, odontocetes) both have simple peg teeth.

Figure 2. The nesting of Eocene Andrewsiphius basal to extant tenrecs between leptictids and pakicetids.

The LRT ancestors to mysticetes
are shown below:

Figure 3. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale. Key post-crania is missing here, but the skulls tell the tale.

References
Geisler JH; Boessenecker RW; Brown M; Beatty BL 2017. The origin of filter feeding in whales. Current Biology. 27 (13): 2036–2042.e2. doi:10.1016/j.cub.2017.06.003

wiki/Aetiocetus
wiki/Coronodon

Sitsqwayk: Not a transitional (toothed/baleen) whale

Sitsqwayk cornishorum (Peredo and Uhen 2016, Fig. 1) was originally considered a transitional whale linking toothy aetiotheres to toothless mysticetes (but only in the absence of desmostylians).

Figure 1. Sitsqwayk reconstruction over the ghosted image of Cetotherium. 456 cm represents the ‘total body length’ according to Peredo and Uhen 2016. Seems too short. The largely restored rostrum is shorter here to match the mandible.

Taxon exclusion issues
Here testing a wider gamut of mysticete ancestor candidates, Sitsqwayk nests between Cetotherium and two other cetotheres,  Yamatocetus and Tokarahia. Sitsqwayk has a short rostrum, a convex posterior mandible and a relatively large scapula. The total length was reported as 456 cm, which would make it proportionately much shorter than Cetotherium (ghosted Fig. 1), based on a common scapula size.

Figure 2. Subset of the LRT focusing on mysticetes, including Sitsqwayk, and their mesonychid and desmostylian predecessors. Note that hippos are not artiodactyls, contra tradition.

The term chaeomysticeti (see citation below)
refers to the ‘toothless’ mysticetes. Such a clade is only possible if aetiocetes and Mammalodon are considered mysticetes, but they are not in the large reptile tree (LRT, 1201 taxa) where all mysticetes are toothless and they arise from desmostylians. Mammalodon has teeth, but it is basal to desmostylians, which progressively loose their teeth as they transition to baleen.

Going one step further…
current evidence (i.e. the LRT) indicates that mysticetes should be divided between right whales and all other mysticetes, both with desmostylian ancestors with legs.

It only takes the deletion of a few taxa
to nest odontocetes with mysticetes, or to nest mysticetes with odontocetes in the LRT, due to massive convergence in living whales… as you might expect. That’s why taxon exclusion can be such a problem in phylogenetic analysis. (Keyword: ‘taxon exclusion‘ for dozens of examples of this in this blog).

References
Peredo CM and Uhen MD 2016. A new basal chaeomysticete (Mammalia: Cetacea) from the Late Oligocene Pysht Formation of Washington, USA. Papers in Palaeontology. 2 (4): 533–554.

wiki/Cetotherium
wiki/Sitsqwayk

Monodon: THE weirdest skull of all mammals

Today two blogposts are published
because they relate strongly to one another. Here is the post on torsioned tenrec/odontocete skulls.

Figure 1. Distinct from most narwhals, this skull also has right tusk emerging from the canine position. And yes, that’s the maxilla covering most of the skull, even above the orbit! I added an eyeball here to help locate the orbit. The mesethmoid is the red bone that divides the naris (blow hole).

The narwhal (genus Monodon, Fig. 1)
is famous for having one giant spiral tooth sticking out ahead of its skull. Monodon also has one of the most bizarre skulls of all mammals and departs from that of all tetrapods, partly due to the root of the tooth and partly due to the migration of the nares to the back of the skull. Except for its tips, the jugal is missing. The maxilla, lacks teeth (if you don’t count the tusk) and rather than extending below the orbit, extends over the forehead, following the naris on its migration to the back of the skull. The bulbous portion of the skull, the cranium is made of parietals in most mammals, but the parietals are greatly reduced, nearly absent in Monodon.

Figure 2. The beluga, Delphinapterus, is closely related to, though less derived than the narwhal, Monodon. More teeth of a regular shape were present in the jaws. Those two yellow arrows indicate a misalignment of the centerline of the top of the occiput vs. the bottom. Compare to figure 3. The mesethmoid is the red bone in the blow hole. This skull is also bent left, as in the narwhal.

The sister taxon of the narwhal
is the beluga (genus: Delphinapterus). It helps one understand the narwhal a bit better. At least the beluga has a few traditional teeth. These two taxa nest together in the large reptile tree (LRT, 1087 taxa, Fig. 4).

Figure 3. Chonecetus has a more primitive skull with nares closer to the snout tip and no maxilla above the orbit. Not a transitional taxon to baleen whales, which have another separate origin. This drawing lacks any indication of torsion, perhaps because the back half was separated from the front half and the artist ‘repaired’ the twist.

Less derived and more primitive
is Chonecetus (Fig. 3), which has nares closer to the snout tip, and more teeth, and more cranium. This taxon and its sister, Aetiocetus, have been traditionally considered transitional from toothed whales to baleen whales, like Balaenoptera, but baleen whales have an entirely separate ancestry derived from desmostylians, like Desmostylus.

Figure 4. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

A recent paper on Monodon tusks (Nweeia et al. 2012)
found “the narwhal tusks are the expression of canine teeth and that vestigial teeth have no apparent functional characteristics and are following a pattern consistent with evolutionary obsolescence.” (See Figs. 5, 6).

Figure 5. Image from Nweeia et al. 2012 showing the unerupted right tusk and the root of the left tusk in the male narwhal along with two unerupted tusks in the female. Note the angle of the posterior skull relative to the anterior midline.

In dorsal or ventral view
it is clear that the the tusk (left) side of the skull is longer than the right side due to angling the posterior skull relative to the rostrum.

Figure 6. CT scans of a female narwhal (Monodon) showing soft tissues and unerupted teeth. Note the angle of the posterior skull relative to the anterior. The left side, the tusk side, is shorter than the right side in figure 5, so the label ‘ventral’ is an error here. This is a dorsal view of the female skull in figure 5. Always test scale bars and labels.

I wonder about the bending of the skull
toward the left in these two whales. Could asymmetry have anything to do with stereo auditory senses? Asymmetry is also found in owl skulls, another taxon that depends strongly on acute hearing for locating prey.

Figure 7. Fetal narwhal skull, here colorized from Nweenia et al. 2012. The jugal disappears in adults. The asymmetry is already apparent here.

Figure 8. Common bottle nose dolphin skull (genus: Tursiops) also displays a bit of asymmetry in dorsal view. Note the yellow arrows on the parietal showing the wee bit of torsion here. 

Update:
With 1187 taxa and 231 traits full resolution was recovered in the LRT after running PAUP FOR 16 minutes and 15 seconds. The single best tree has 16,329 steps.

References
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.’
Nweeia MT et al. (9 co-authors) 2012. Vestigial tooth anatomy and tusk nomenclature for Monodon monoceros. The Anatomical Record 295:1006–1016.
Pallas PS 1766. Miscellanea Zoologica.

wiki/Narwhal
wiki/Beluga_whale

Mystacodon: See how far they’ll go to ‘find’ a mysticete ancestor

According to Wikipedia
“Mystacodon (Lambert et al. 2017) is a genus of toothed mysticete from the Late Eocene Yumaque Formation of Peru. It is the earliest known member of the Mysticeti, and the second confirmed Eocene mysticete.” Here (Fig. 1) you can compare it to the smaller and more primitive (because it has a bigger pelvis) Maiacetus, to scale. Mystacodon is no mysticete. It’s what a tenrec/odontocete becomes when it gets good at swimming, but not as good as Zeuglodon, which has an even smaller pelvis. We looked at the origin of mysticetes among desmostylians earlier here, here and here. It was first reported here, last October, perhaps too late for the manuscript submission publishing schedule. Even so, whale experts have omitted, overlooked or ignored desmostylians in their quest for mysticete ancestors, and this is what happens.

This is what happens with taxon exclusion.
You get a ‘by default’ nesting, like nesting turtles and Vancleavea with archosaurs or Tetraceratops with therapsids. It also reminds me of when David Hone and Sterling Nesbitt bent over backward to find a mandibular fenestra and an antorbital fossa on pterosaurs in a desperate attempt to prove an invalid hypothesis.

FIgure 1. My, what big teeth you have! This toothy whale with a tiny pelvis is Mystcodon, originally promoted as the earliest known mysticete (baleen whale). Note the size and placement of the teeth matching Maiacetus.

And the whale authors got all the publicity they wanted
in this Guardian article with illustrations. Here is a quote from the article:

“Fossil hunters say they have unearthed a missing link in the evolution of baleen whales after digging up the remains of a creature thought to have lived more than 36 million years ago.

The whales, known as mysticeti, sport a bristling collection of sieve-like plates known as baleen that they use to filter water for food. Species include the enormous blue whale, the gray whale and the humpback whale.

But while baleen whales are known to have shared a common ancestor with toothed whales, which are the other major group of modern whales, the path by which the creatures emerged has been somewhat hazily understood. Now researchers say they have discovered the oldest known cousin of modern baleen whales, offering unprecedented insights into their evolution.

“This [split in the family tree] has been dated to about 38 or 39m years ago,” said Olivier Lambert, co-author of the research from the Royal Belgian Institute of Natural Sciences. “The whale we discovered here has been dated to 36.4 [million years ago], so it is only two to three million years younger than this presumed origin.”

From Nature.com:
“This is the fossil that we’ve been waiting for,” says Nick Pyenson, a palaeontologist at the Smithsonian National Museum of Natural History in Washington DC. 

“To determine where M. selenensis fit in the whale family tree, the researchers compared characteristics such as the shape of its skull and pelvic bone to those of other fossil whales. The creature’s flat snout resembles that of modern baleen whales. But its pelvic bone fit more with ancestral whales, complete with areas where the leg bones would typically slot in, says Lambert. “So, we think that this animal still had tiny legs protruding from the body.”

“Lambert and his colleagues think that M. selenensis might have sucked up its prey from the ocean floor. This wasn’t unusual, however, because baleen-whale ancestors around that time sported a wide variety of dental and feeding mechanisms. “There’s big toothed things, there’s little toothed things and there’s toothless things, all at once,” says Uhen. But by around 23 million years ago, all the whales in this group had baleen, and “all these toothy things go away”, he says.”

Mystacodon has a wide flat triangular rostrum…
so does Physeter, the sperm whale (Fig. 3).

Figure 3. Physeter (sperm whale) skull. Note the low, flat, triangular toothless rostrum.

Workers:
Examine all possible candidates. Don’t exclude relevant taxa. Mystacodon sheds no light on the origin of baleen whales—but it does shed light on the origin of odontocetes.

References
Lambert, O. et al. (seven co-authors) 2017. Earliest Mysticete from the Late Eocene of Peru Sheds New Light on the Origin of Baleen Whales. Current Biology 27:1535–1541.e2 doi:10.1016/j.cub.2017.04.026.