SVP 2018: New Mammalodon relative with marine worm bores

Shipps, Peredo and Pyenson 2018 report
on a Late Oligocene mammalodontid, the first from the Northern Hemisphere. “The skull and teeth of this specimen bear boreholes from bone-eating Osedax worms, providing valuable information on the taphonomy of the specimen. Critically, this specimen preserves intact ear bones and several teeth.”

Osedax is marine worm.
According to Wikipedia, “The worms bore into the bones of whale carcasses to reach enclosed lipids, on which they rely for sustenance.”

Figue 1. Mammalodon nests within the clade Anthracobune basal to desmostylians and mysticetes.

Figue 1. Mammalodon nests within the clade Anthracobune basal to desmostylians and mysticetes.

Mammalodon (Fig. 1) is indeed in the lineage of mysticete whales, but several nodes distant (Fig. 2) in the large reptile tree. It is related to Janjucetus and Anthracobune, basal to desmostylians, not far from hippos. Desmostylians are also found along the Pacific rim, so this appearance of an ancestor in Washington state is expected. All are mesonychids, not ungulates.

Figure 2. Subset of the LRT focusing on mysticetes, including Sitsqwayk, and their predecessors.

Figure 2. Subset of the LRT focusing on mysticetes, including Sitsqwayk, and their predecessors.

References
Shipps BK, Peredo CM and Pyenson ND 2018. An unexpected Northerner with burrowed bones: a new mammalodontid (Mysticeti) from the Pacific Northwest with Osedax bores provides insight into Oligocene marine taphonomy and mysticete evolution. SVP abstracts.

wiki/Osedax
wiki/Janjucetus
wiki/Mammalodon
wiki/Anthracobune

 

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Cornwallius: not a desmostylian, an ancestor to desmostylians

These taxa
are part of the a recent review of mysticete (baleen whale) ancestors you can read about here, here and here.

Cornwallius sookensis (originally Desmostylus sookensis, Hay 1923, Cornwall 1922; Beatty 2006a, b; Early Oligocene, 25 mya; Fig. 1) was originally and traditionally considered a desmostylian (Fig. 3). Here it nests with Cambaytherium (Fig. 2), both basal to anthracobunids like Janjucetus. These taxa have a narrow skull and a deep jugal beneath the squamosal. The nares are anterior, rather than dorsal in location.

Figure 1. Adult Cornwallius look more like desmostylians. Juveniles look more like anthracobunids. Both are descendant taxa.

Figure 1. Adult Cornwallius look more like desmostylians. Juveniles look more like anthracobunids. Both are descendant taxa.

Note the resemblance
(lack of a downturned snout) on the juvenile to Cambaytherium (above). Apparently, neotony produces a straights-snout anthracobunid. Otherwise it evolves to the tusky, droop-snout, desmostylian grade.

Figure 2. Cambaytherium with a an alternate rostrum reversing taphonomic shifts.

Figure 2. Cambaytherium with a an alternate rostrum reversing apparent taphonomic shifts.

Beatty 2006
produced the following cladogram (Fig. 3) in which desmostylians are derived from the Moeritherium/Elephas clade. In the large reptile tree (LRT, 1163 taxa) cambaytheres and desmostylians arise from mesonychids and hippos.

Figure 2. From Beatty 2006b, a phylogeny of desmostylians derived from moeritherium, an aquatic relative of elephants and sirenians (manatees). Actually desmostylians arise from cambaytheres and anthracobunids, arising from hippos and mesonychids. 

Figure 3. From Beatty 2006b, a phylogeny of desmostylians derived from moeritherium, an aquatic relative of elephants and sirenians (manatees). Actually desmostylians arise from cambaytheres and anthracobunids, arising from hippos and mesonychids.

References
Beatty, BL 2006a. Rediscovered specimens of Cornwallius (Mammalia, Desmostylia) from Vancouver Island, British Columbia, Canada. Vertebrate Palaeontology. 1(1):1–6.
Beatty, BL 2006b. Specimens of Cornwallius sookensis (Desmostylia, Mammalia) from Unalaska Island, Alaska. Journal of Vertebrate Paleontology. 26(3):785–87.
Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST, Thewissen JGM 2014. Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PLoS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMID 25295875.
Cornwall IE 1922. Notes on the Sooke Formation, Vancouver Island, B.C. Canadian Field Naturalist. 36:121–23.
Hay OP 1923. Characteristics of sundry fossil vertebrates. Pan-American Geologist. 39:101–120.
Kumar K 1991. Anthracobune aijiensis nov. sp. (Mammalia: Proboscidea) from the Subathu Formation, Eocene from NW Himalaya, India”. Geobios. 24 (2): 221–39. doi:10.1016/s0016-6995(91)80010-w. OCLC 4656806310.
Rose, KD et al. (8 other authors) 2014. Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nature Communications. 5 (5570). doi:10.1038/ncomms6570.

wiki/Cambaytherium
wiki/Cornwallius

Harpagolestes uintensis is a mesonychid. Harpagolestes macrocephalus is not.

Welcome to the wonderful world of convergence!
Harpagolestes uintensis (Fig. 2) and H. macrocephalus (Fig. 1) look similar enough to be considered similar, but they are not congeneric in the LRT. One of them needs a new generic name.

Of the several heresies
recovered by the large reptile tree (LRT, 1120 taxa) the latest is the separation of some former mesonychids (Fig. 1, Andrewsarchus, Sinonyx, Hapalodectes) from current and traditional mesonychids (Fig. 2, Mesonyx and Harpagolestes uintensis). The clade of former mesonychids now nests as giant tenrecs. This clade produced odontocete whales and transitional taxa. The latter group of true mesonychids gave rise to mysticete (baleen) whales and the following transitional taxa: hippos, anthrobunids and desmostylians.

Figure 1. Harpagolestes macrocephalus compared to sisters Sinonyx and Andrewsarchus to scale.

Figure 1. Harpagolestes macrocephalus compared to sisters Sinonyx and Andrewsarchus to scale.

Today the addition of Harpagolestes macrocephalus
(Fig. 1) to the LRT nests it not congenerically with Harpagolestes uintensis (Fig. 2), but between Andrewsarchus and Sinonyx. So the two are not congeneric.

Figure 1. Andrewsarchus, Sinonyx, Mesonyx and Harpagolestes to scale for direct comparison of these two tenrecs with these two mesonychids.

Figure 1. Andrewsarchus, Sinonyx, Mesonyx and Harpagolestes to scale for direct comparison of these two tenrecs with these two mesonychids.

We’ve seen convergence many times
in the LRT. This is just one more example of convergence that has been traditionally overlooked.

Deleting nine tenrecs
on either side of Sinonyx + Andrewsarchus + H. macrocephalus changes nothing in the LRT. The above taxa still nest with odontocetes far from mesonychids through mysticetes, though some loss of resolution occurs in the mammal subset of the LRT.

Deleting hippos and anthracobunids
from the mesonychid clade changes nothing.

References
O’Leary MA and Rose KD 1995. Postcranial skeleton of the early Eocene mesonychid Pachyaena (Mammalia: Mesonychia). Journal of Vertebrate Paleontology 15(2):401-430.

Related mammals that nest at the bases of several hoofed clades

The value
of the large reptile tree (LRT, 1013 taxa) and the reconstructions gathered together at ReptileEvolution.com lie in their ability to put faces on names (Figs, 1) sometimes to scale (Fig. 2) to help one recognize patterns that may have gone unrecognized while just looking at names and scores.

These are the mammals that nest with one another
as sisters after deletion of more derived taxa in each of their several clades (listed at right, Fig. 1). Thus they, more or less, represent the basal radiation of hoofed mammals prior to each clade radiation. And to no one’s surprise, they look like each other, despite wide variations in size.

Frankly,
I’m reexamining the traits of these taxa because the LRT had trouble resolving them. There were mistakes in there. Now, after some score corrections, the resolution is complete again, but some Bootstrap scores have risen to just above 50. Not great, but better than below 50. Remember, I don’t have access to these specimens and sometimes work from published drawings.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids. The differences are harder to see than in derived taxa in each clade (column at right). See figure 2 for skeletons to scale.

Some of these basal taxa
gave rise to baleen whales. Others were ancestral to giraffes, elephants, horses and everything in between. None of these taxa are nearly so famous or interesting to the general public, but it is from these generalized (plesiomorphic) taxa that the few and subtle evolutionary changes that are key to each clade first make an appearance.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale. Note the presence of phylogenetic miniaturization at the base of the Artiodactyla. Consider this scenario: mesonychids radiated widely, including to create larger and smaller taxa. The larger homalotheres did not radiate greatly, as far as we know. On the other hand, the smaller taxa radiated to become a long list of extinct and exact hoofed taxa. And, of course, the mesonychid clade radiated to include today’s hippos and baleen whales. 

Sometimes a ‘show and tell’ drives a point home
better than just a ‘tell’. Even so, these are not the precise individuals in the direct lineage of known derived taxa, but the close relatives of those perhaps eternally unknown and hypothetical individuals. The suite of traits that lump and separate these taxa can be gleaned from the present MacClade file, continually added to and updated, and available here., which is where you can also see the cladogram from which the above taxa were pulled.

 

Fleshing out Andrewsarchus, the giant tenrec

All we know of Andrewsarchus
is its skull — without a mandible. A few days ago the dentary of a sister taxon, Sinonyx, was added to the skull of Andrewsarchus ((Osborn 1924; middle Eocene, 45 mya; AMNH 20135; 83cm skull length; also see Fig. 1) just to see if it would fit.

Before that…
everyone forever has always fleshed out Andrewsarchus like a giant bear/dog, moving the eyeballs to the top and giving it a bear/dog nose. Image googling Andrewsarchus will give you an idea what a widespread and accepted tradition that has been. I even followed that tradition back in 1989 in the book Giants, which you can see here as subset 1 of a larger pdf of the entire book.

Unfortunately,
Andrewsarchus does not nest with bears, dogs or mesonychids. It nests with tenrecs and Rhynchocyon (Fig. 2.), one type of elephant shrew. (The other type of elephant shrew is unrelated, as we learned here, Fig. 2). Tenrecs have a long flexible nose.

So, here, without further adieu
is a first shot at adding tenrec soft tissue to the skull of Andrewsarchus (Fig. 1). Is it close to being correct? I hope so, given the present evidence.

Figure 1. Andrewsarchus restored as giant tenrec alongside, Canis, the wolf to scale. Note the small and low-set eyes on Andrewsarchus. The mandible comes from Sinonyx. Note the natural tilt of the canid skull permitting binocular vision. Andrewsarchus had low-set eyes, rather un-canid-like. We have to give up the bear-dog restoration of Andrewsarchus.

Figure 1. Andrewsarchus restored as giant tenrec alongside, Canis, the wolf to scale. Note the small and low-set eyes on Andrewsarchus. The mandible comes from Sinonyx. Note the natural tilt of the canid skull permitting binocular vision. Andrewsarchus had low-set eyes, rather un-canid-like. We have to give up the bear-dog restoration of Andrewsarchus.

Now, just imagine the post-crania…
and the best clue we have is the living tenrec, Rhynchocyon (Fig. 2) with long legs, robust torso and short tail, only ten times bigger.

Figure 6. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Figure 3. Rhynchocyon (above) and Macroscelides (below) the other type of elephant shrew compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Maybe it’s time to 
give up the bear-dog restoration for Andrewsarchus and give it the giant  tenrec restoration it deserves based on phylogenetic bracketing and phylogenetic analysis.

Figure 3. The skull of Andrewsarchus mated to the body of Leptictis to make a chimaera.

Figure 3. The skull of Andrewsarchus mated to the body of Leptictis to make a chimaera.

References
Osborn HF 1924. Andrewsarchus, giant mesonychid of Mongolia. American Museum Noviattes 146: 1-5.

Better data on Ocepeia: a basal mesonychid from 60 mya

And, in keeping with several recent posts…
Ocepeia is also a baleen whale (mysticete) ancestor (with legs) appearing shortly after the big asteroid impact.

Earlier we looked at a cat-sized herbivore, Ocepeia daouiensis (Gheerbrant et al 2001, 2014; Paleocene, 60 mya; 9 cm skull length; Fig. 1) as a hippo ancestor. And given the data then available (Fig. 1, left) it did look like a hippo ancestor. But, there was less resolution at that node. So, a search for better data recovered a set of CT scans (Fig. 1, right) which cast a new light on Ocepeia, which now nests basal to mesonychids, derived from a sister to Phenacodus. At that node, Ocepeia continues to be a sister to a coeval but unknown hippo ancestor.

Figure 1. Ocepeia: before and after. The original reconstruction is here compared to a tracing of CT scan, duplicated left to right.

Figure 1. Ocepeia: before and after. The original reconstruction is here compared to a tracing of CT scan, duplicated left to right. Ocepeia now nests at the base of the Mesonychidae, close to the origin of hippos, desmostylians and baleen whales.

The pneumatized skull
contains many air spaces. The larger skulls have larger canines and so are considered male. The jugal deepens below the orbit, hiding the posterior molars in lateral view. The premaxilla is transverse. The upper canine rubs against the lower large incsior creating a facet, as in hippos and Harpagolestes.

Ocepeia was found with aquatic taxa
and was probably amphibious. Mesonychids became land hippos. Hippos gave rise to anthracobunids, desmostylians, thick-tailed desmostylians and finally baleen whales.

The name Ocepeia derives from
the initials of Office Chérifien des Phosphates (O.C.P.), the national Moroccan phosphate mining company. In a similar fashion, the name of the basal reptile Eledeceeon, comes from the Livingston Development Corporation.

References
Gheerbrant E, Sudre J, Iarochene M, Moumni A 2001. First ascertained African “Condylarth” mammals (primitive ungulates: cf. Bulbulodentata and cf. Phenacodonta) from the earliest Ypresian of the Ouled Abdoun Basin, Morocco. Journal of Vertebrate Paleontology. 21 (1): 107–118.
Gheerbrant E, Amaghzaz M, Bouya B and Goussard F and Letenneur C 2014. Ocepeia (Middle Paleocene of Morocco): The Oldest Skull of an Afrotherian Mammal. PLoS ONE. 9 (2): e89739. doi:10.1371/journal.pone.0089739.

wiki/Mesonyx
wiki/Harpagolestes
wiki/Ocepeia

Adding Pakicetus and Indohyus to the LRT

Pakicetus inachus (Gingerich & Russell 1981; middle Eocene; Figs. 1, 2) was originally hailed as “one of the oldest whales known anywhere.” Despite its lack of fins and flukes, Pakicetus was considered a whale based largely on the large posterior process of the periodic (near the ear region) and the thick, dense auditory bulla characteristic of all cetaceans. These traits indicate a underwater hearing and habitat even though Pakicetus had slender running legs and no flukes (Fig. 1). The resemblance of Pakicetus to Tenrec is striking — and remember some tenrecs, like Limnogale (Fig. 4), retained a long tail and are aquatic with webbed feet.

Figure 1. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Figure 1. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes. Mysteceti (baleen whales) had a separate origin in Desmostylia.

The case for a tenrec ancestry for Odontoceti continues
Indohyus major (Fig. 1; Rao 1971, Thewissen et al. 2007; Eocene, 48 mya; 1m in length) was considered an artiodactyl, but nests in the large reptile tree (LRT with Leptictidium (Fig. 1) between tenrecs and odontocete whales. So the case for Leptictidium as a whale ancestor is strengthened with the addition of its sister Indohyus. The case for a traditional artiodactyl ancestor for whales is much diminished.

As we learned earlier, mysticete (baleen) whales are derived from desmostylians like Paleoparadoxia and Behemotops.

Figure 2. Skulls of transitional taxa between tenrecs and Odontoceti (toothed whales). These include Tenrec, Lepticitidium, Pakicetus, Rhodhocetus and Orcinus.

Figure 2. Skulls of transitional taxa between tenrecs and Odontoceti (toothed whales). These include Tenrec, Lepticitidium, Pakicetus, Rhodhocetus and Orcinus. The gradual accumulation of traits should be readily visible to the casual observer here.

One of the major problems with the artiodactyl-whale hypothesis
is this: artiodactyls are herbivores. Odontocetes are carnivores. Tenrecs eat a wide variety of animals.

Mystecete whales have no teeth, and did not evolve from carnivores. Although hippos, mesonychids and desmostylians all have big teeth, all are herbivores. Their largest teeth function more like tusks.

Figure 3. Indohyus skeletal elements nest between tenrecs and whales.

Figure 3. Indohyus skeletal elements nest between tenrecs and whales. While a sister to Leptictidium, the lines are more nearly equal in length here. We don’t know if Indohyus had claws or hooves. Leptictidium had long claws.

The mystery tenrec, Limnogale
No Limnogale skeletons are known to tenrec experts I contacted and little else is known of this extant, nocturnal, aquatic and long-tailed tenrec from Madagascar. It may hold a key place in the origin of whales. It appears to be plesiomorphic enough to do so, but it sure would be great to someday see a skeleton. The ears and eyes are small, the whiskers are bushy. Some tenrecs echolocate, but this taxon has been so little studied that I don’t know if it is an echolocator.

Figure 4. The rare and rarely studied web-footed tenrec Limnogale mergulus, which has a long tail, is nocturnal and aquatic.

Figure 4. Is this the true ancestor of odontocete whales? The rare and rarely studied web-footed tenrec Limnogale mergulus, which has a long tail, is nocturnal and aquatic. Both images copyright PJ Stephenson and used with permission.

Thewissen et al. 2007 report,
Indohyus shares a similar auditory bulla with cetaceans, not present in artiodactyls. “Other significant derived similarities between Indohyus and cetaceans include the anteroposterior arrangement of incisors in the jaw, and the high crowns in the posterior premolars.”

Well, those traits,
as you can see (Fig. 2) are also found in Tenrec and its sisters, but Thewissen et al. did not test tenrecs and any of the sisters recovered in the LRT, other than Andrewsarchus and Sinonyx. Indohyus had thick bones (osteosclerosis) which provided ballast for underwater activities. That it nests with Leptictidium (Figs. 1, 2) adds credence to the aquatic hypothesis advanced earlier here.

Figure 5. Subset of the LRT, higher placental mammals with a focus on whales (yellow) and their ancestral clades, the Tenrecidae and Mesonychidae. Both are a fair distance from artiodactyls.

Figure 5. Subset of the LRT, higher placental mammals with a focus on whales (yellow) and their ancestral clades, the Tenrecidae and Mesonychidae. Both are a fair distance from artiodactyls. Note the displacement of Janjucetus. Now it looks like it probably had legs. We’ll look at Behemotops soon.

Traditional paleontology
holds that “Mysticeti split from Odontoceti (toothed whales) 34 million years ago during the Eocene” and whales moved to the sea 50 mya (Rose 2001) having descended from hooved mammals. The present hypothesis (Fig. 5) holds that indeed Mysticeti were derived from hooved mesonychids/hippos/desmostylians. However, Odontoceti, the toothed carnivorous/piscivorous whales arise from clawed tenrecs, like Leptictidium (Figs, 1, 2). The hands and feet of the protowhale Artiocetus (Fig. 6) are well known and at least several of its unguals are claws — though much reduced and somewhat transformed due to their much reduced use on land and unknown extent of the webbing. At least one tenrec had webbed feet, Limnogale (Fig. 4). I know of no artiodactyls with webbed feet.

6. Artiocetus manus and pes had claw-like unguals, not hooves.

6. Artiocetus manus and pes had reduced claw-like unguals, not hooves. And Limnogale shows some tenrecs had webbed feet.

India/Pakistan and Madagascar
where odontocetes started and tenrecs now survive, were one continuous island that split apart some 88 million years ago… so there is no geographical barrier to the present hypothesis of tenrec and odontocete relations. But it does indicate the antiquity of the tenrec – odontocete split and relationship.

Australia and the Pacific rim
where mysticetes started and desmostylians were found is a much, much wider area. We find Desmostylia like Paleoparadoxia and Behemotops have only been found along the Pacific rim (Japan > Russia > Aleutian Islands > Pacific coast of North America  south to Baja California. A desmostylian sister, Anthracobune, is found in Eocene (40 mya) Pakistan. Janjucetus is found in younger 25 mya strata in Australia. A hippo and mesonychid sister, Ocepeia, dates to the Paleocene (60 mya) in Morocco, which is even further from Australia. So, the origin of the Mysticeti, appears to be somewhere along the Pacific rim.  More details tomorrow.

References
Gingerich PD and Russell DE 1981. Pakicetus inachus, A New Archaeocete (Mammalia, Cetacea) from the Early-Middle Eocene Kuldana Formation of Kohat (Pakistan). Contributions from the Museum of Paleontology, The Museum of Michigan. 25 (11): 235–246.
Rao AR 1971. New mammals from Murree (Kalakot Zone) of the Himalayan foot hills near Kalakot, Jammu and Kashmir state, India. Journal of the Geological Society of India. 12 (2): 124–34.
Thewissen JGM, Williams EM, Roe LJ and Hussain ST 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature 413:277-281.
Rose KD 2001. The Ancestry of Whales. Science. 293 (5538): 2216–2217. PDF
Thewissen JGM, Cooper LN, Clementz MT, Bajpai S and Tiwari BN 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature 450:1190-1195.

wiki/Indohyus
wiki/Pakicetus