Arnason et al. 1993 and Messenger and McGuire 1998
studied ‘whale’ phylogeny using molecules (DNA) rather than traits.
First, Arnason et al. 1993 reported,
“The sequence of the mitochondrial control region was determined in all 10 extant
species commonly assigned to the suborder Mysticeti (baleen or whalebone whales)
and to two odontocete (toothed whale) species (the sperm and the pygmy sperm
Prediction: The molecules should be different in these unrelated clades.
The difference between the control regions of the mysticetes and those of the
sperm whales is very large.“
As predicted. They are unrelated.
“Because the mitochondrial control regions of the delphinids and the mysticetes
had shown unexpectedly large similarity, we investigated the sequence of this region in all extant mysticete species, in order to determine interspecific differences.”
Whenever dolphins and mysticetes show more similarity than dolphins and sperm whales. Arnason et al. should have considered that an error in methods.
Arnason et al. reported:
“The central domain of the mitochondrial control region was used by Saccone et
al. (1991) to construct a phylogenetic tree including man, common chimpanzee, pygmy
chimpanzee, dolphin, cow, rabbit, mouse, and rat.
This is the epitome of cherry-picking taxa. Eight taxa. And it is a deep time study with questionable results. No results should ever be trusted. Rather find out for yourself by testing traits nd include fossil taxa with results that are easy to validate by examining each trait.
“The dating of the separation between the cow and the dolphin, ~27 MYBP, is, however, at variance with mtDNA comparisons between the fin whale and the cow (Arnason et al. 199 la), which placed their separation at x55 MYBP.However, the figure = 55 MYBP may not represent the dating of the artiodactyl/cetacean separation, which may have occurred later, provided that the cetaceans evolved from an artiodactyl lineage other than that represented by the cow.”
Can we all agree that the cow is a poor and unlikely outgroup taxon for any whale? After testing 1900 taxa tenrecs are close to the pakicetid ancestors of odontocetes. Hippos? Yes, for mysticetes. Strange that whale experts still hold on to the artiodactyl myth. That’s as bad as hoping someday to find a pre-dinosaur close to pterosaurs. Some things will never happen.
“The large values between the sperm whale and the remaining cetaceans, except
the pygmy sperm whale, are greater than that between the cow and the same cetacean
Don’t be surprised by any deep time results in molecular phylogeny. Anything can happen.
“The tree shows that the primary separation among the mysticetes is between the two balaenids (the bowhead and the northern right whale) and the remaining species.
This matches the LRT (Fig. 1) and pre-cladistic studies. Granted, sometimes molecules match traits, but not often enough. Too many times molecules lead scientists astray… and too many times scientists follow those results without a critical eye.
“In the latter group the pygmy right whale has a separate position. The analysis revealed a close relationship between the gray whale (family Eschrichtiidae) sequence and those of the rorquals (family Balaenopteridae ). We suggested that the pygmy right whale should be removed from the family Balaenidae, sensu latu.”
Five years later, Messenger and McGuire 1998 reported,
“Following the publication of several DNA sequence data and molecular clock papers
that suggested sperm whales were more closely related to baleen whales than to other odontocetes. Our morphological data set strongly supports the traditional view of odontocete monophyly.”
Messenger and McGuire did not test tenrecs or any non-whales other than artiodactyls.
Bennett and Lehmann 2009 nested
the taxon ‘balaenopterid’ with ‘Delphinium‘ and “Hippopotamus” a long way from Echinops, the hedgehog, which they considered a tenrec relative. Echinops is not a tenrec in the LRT. So tenrecs have not yet been tested with odontocetes in mtDNA studies.
It might help to remember the following:
- Tenrecs and odontocetes have a full arcade of sharp teeth. Artiodactyls and mysticetes have a large to complete diastema.
- Tenrecs and odontocetes are predators. Artiodactyls are herbivores while mysticetes eat plankton (floating masses of tiny animals).
- Basal odontocetes (archaeocetes) have a long, straight, pointed snout, as do tenrecs. Basal mysticetes (like the gray whale) have a maxilla ventral rim that is concave. as in desmostylians.
- Tenrecs and odontocetes use echolocation. Artiodactyls and mysticetes do not.
- Tenrecs and odontocetes have five fingers. Artiodactys and mysticetes have four.
- Tenrecs, archaeoctes and hippos all have a double-pulley ankle (astragalus)
- Tenrecs and land whales like Maiacetus had long slender toes without hooves and plantigrade feet without underlying pads. Hippos have digitigrade hooves with underlying pads. Mysticetes with legs have not been found, but desmostylians with hooves and feet flattened for paddling have been found.
- Male whales, hippos and tenrecs have undescended testicles.
- Female odontocetes and tenrecs have a cloaca.
- whales and artiodactyls have a subdivided stomach. No data yet for tenrecs. Hippo stomachs are subdivided functionally, but not anatomically according to one report. According to another report, a hippo’s stomach consists of three distinct chambers
- whales and artiodactyls have non-lobed lungs. No data yet for tenrecs.
- larynx/voice box, similar in whales and hippos. No data yet for tenrecs, but echolocation in common for some.
Messenger and McGuire 1998 reported,
“Recent phylogenetic analyses of cetacean relationships based on DNA sequence data
have challenged the traditional view that baleen whales (Mysticeti) and toothed whales (Odontoceti) are each monophyletic, arguing instead that baleen whales are the sister group of the odontocete family Physeteridae (sperm whales).”
“We reach four primary conclusions: (1) Our morphological data set strongly supports the traditional view of odontocete monophyly; (2) the unrooted molecular and morphological trees are very similar, and most of the conflict results from alternative rooting positions; (3) the rooting position of the molecular tree is sensitive to choice of artiodactyl outgroup taxa and the treatment of two small but ambiguously aligned regions of the 12S and 16S sequences, whereas the morphological root is strongly supported; and (4) combined analyses of the morphological and molecular data provide a well-supported phylogenetic estimate cons istent with that based on the morphological data alone (and the traditional view of toothed-whale monophyly) but with increased bootstrap support at nearly every node of the tree.”
In a morphological analysis Messenger and McGuire 1998 reported
they used a cow, camel, a mouse deer, a peccary and “Archaeoceti” for outgroup taxa. This is called cherry-picking. You should let your wide gamut phylogenetic analysis tell you which taxa are the most proximal outgroup for any ingroup. And avoid suprageneric taxa. Mistakes due to taxon exclusion published by Messenger and McGuire include baleen whales were the first clade to branch off followed by sperm whales. In accord with the LRT, dolphins are derived from larger ancestors.
In Messenger and McGuire a combined analysis of morphology + modified DNA
recovered a broadly similar tree that lacked pertinent taxa.
Finding that whales are diphyletic
was first considered by Van Valen 1968. The LRT (Fig. 1) recovered a tree topology in which toothed whales (Odontoceti) were derived from tenrecs and baleen whales (Mysticeti) were derived from desmostylians and more distantly, hippos, among living sisters. Thus the mysticete-odontocete split would have to have occurred in the Cretaceous or earlier, 100+mya, when the last common ancestor was a tree shrew.
Arnason U, Gulberg A and Widegren B 1993. Cetacean Mitochondrial DNA Control Region: Sequences of All Extant Baleen Whales and Two Sperm Whale Species. Molecular Biological Evolution 10(5):960-970.
Bennett NC and Lehmann T 2009. The new framework for understanding placental mammal evolution. BioEssays 31:853–864, DOI 10.1002/bies.200900053
Messenger SL and McGuire JA 1998. Morphology, Molecules, and the Phylogenetics of Cetaceans. Systematic Biology 47(1):90-124.
Van Valen L 1968. Monophyly or diphyly in the origin of whales. Evolution. 22 (1):37–41.
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