Ankylorhiza

Last updated

Ankylorhiza
Temporal range: Oligocene
~29–23.5  Ma
Ankylorhiza tiedemani holotype 1.jpg
Holotype rostrum (snout) of A. tiedemani from below and above; originally assigned to " Squalodon " tiedemani
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Parvorder: Odontoceti
Genus: Ankylorhiza
Boessenecker et al., 2020
Species:
A. tiedemani
Binomial name
Ankylorhiza tiedemani
(Allen, 1887)
Synonyms

Ankylorhiza (meaning "fused roots"; in reference to the type of dentition seen in early toothed whales) is an extinct genus of toothed whale that lived in what is now the United States during the Oligocene epoch, between 29 and 23.5 million years ago. The type and only known species is A. tiedemani, though two fossil skeletons may represent an additional, second species within the genus. Ankylorhiza was about 4.8 meters (16 ft) long, with a long, robust skull bearing conical teeth that were angled forwards at the tip of the snout.

Contents

Ankylorhiza is the largest known Oligocene toothed whale and is one of the most completely known early members of this group, with characteristics intermediate between basal and derived cetaceans. The taxon would have had powerful jaw musculature and probably fed on large prey by seizing it and puncturing it with its robust teeth. The animal likely occupied a fast-swimming predator niche similar to that of living orcas.

Discovery and naming

The holotype of Ankylorhiza (cataloged under specimen number AMNH 10445) consists of a partial snout fossil discovered in the Ashley Formation of South Carolina, United States. The layers the bones were found in date to the Oligocene epoch of the Paleogene period, between 29 and 23.5 million years ago. [1] In 1887, zoologist Joel Asaph Allen attributed AMNH 10445 to the extinct river dolphin Squalodonnow considered a wastebasket taxon—as a new species he named Squalodontiedemani. [1] [2] The specific name tiedemani is in honor of I. B. Tiedeman, who discovered the fossils and donated them to the American Museum of Natural History, where they're currently stored. [2]

In a 2020 publication, paleontologist Robert Boessenecker and colleagues found the fossil snout to represent the same taxon as CCNHM 103, a nearly complete skeleton of large toothed whale found in the same formation; and CCNHM 220, a partial skull with associated vertebrae. They referred all of these fossils to the newly named and described dolphin genus Ankylorhiza, which "S." tiedemani was synonymized with A. tiedemani as the only species. The generic name Ankylorhiza is Ancient Greek for "fused roots", alluding to the type of dentition exhibited by stem Odontoceti. [1]

Description

Life restoration of A. tiedemani Ankylorhiza tiedemani life reconstruction by PaleoGeek.png
Life restoration of A. tiedemani

Ankylorhiza had a 97.2-centimeter (38.3 in) long skull that measured 42.5 centimeters (16.7 in) at its widest point, and a total body length of around 4.8 meters (16 ft), making it the largest known toothed whale from the Oligocene epoch. In the early Miocene, greater lengths were attained by physeteroids (the ancestral group including modern sperm whales) within this group of whales. [1]

Ankylorhiza's skull was relatively elongated, and had the largest temporal fossae (shallow depressions on the sides of the skull) of any known toothed whale; they composed 24% of the skull's total length and 36% of its width at the rear. Each side of Ankylorhiza's upper jaw bore 13 teeth; three incisors, one canine, and nine postcanines. Between the first canine and the fifth postcanine tooth, the maxilla (main upper jaw bone) became thicker and formed bony supports divided by deep furrows between each tooth, which would have helped the animal's dentition precisely interlock when it closed its jaws. Ankylorhiza's sharp-tipped teeth had carinae (cutting edges) on both edges that bore occasional serrations, and its tooth enamel was adorned with lengthwise ridges. The lower incisors in the upper jaw were tusk-like and angled forwards. [1]

The morphology of Ankylorhiza's forelimbs was between that of basal (early-diverging or "primitive") and living cetaceans. Ankylorhiza's humerus (upper arm bone) had an enlarged head and flattened attachment sites for the ulna and radius (lower arm bones), as well as a shaft that was short relative to those of basilosaurids, but still longer than in extant toothed whales. In comparison to modern toothed whales, the hands and fingers were much longer. In the spinal column, the vertebrae (backbones) at the base of the tail formed a more rigid structure than in earlier cetaceans, while the lumbar region–consisting of vertebrae between the rib cage and pelvis—was very flexible. The height and width of the vertebral centra (bodies of the vertebrae) increase in height from the back of the chest to the basal part of the tail, with the second caudal (tail) vertebra being the tallest and broadest, indicating this region of the body experienced the most undulation when the animal was swimming. [1]

Classification

Ankylorhiza was a member of the toothed whale parvorder Odontoceti. [1] This group contains all cetaceans that feed with teeth, including dolphins, porpoises, beaked whales, sperm whales and others; baleen whales (Mysticeti), in contrast, filter-feed using baleen plates in their mouths. [3] In 2020, Boessenecker and colleagues phylogenetically placed A. tiedemani as a basal odontocete that split off between the xenorophids and squalodontids, in a position between the more basal family Basilosauridae and modern toothed whales. Along with Microcetus , Ankylorhiza is one of the most completely known early toothed whales. Boessenecker and colleagues found A. tiedemani to form a clade with specimens CCNHM 1075 and ChM PV2764, two undescribed Oligocene toothed whale skeletons found in Charleston, both of which may turn out to represent another species within the genus Ankylorhiza. [1] The following cladogram is adapted from the results of Boessenecker and colleagues' analysis in 2020. [1]

Holotype snout fossil of A. tiedemani in side view (1), and a fragment of the mandibular ramus in various views (2-3) Ankylorhiza tiedemani holotype 2.jpg
Holotype snout fossil of A. tiedemani in side view (1), and a fragment of the mandibular ramus in various views (2-3)
Cetacea

Georgiacetus vogtlensis

Basilosauridae

Mysticeti

Odontoceti

Ashleycetus planicapitus

Archaeodelphis patrius

Mirocetus riabinini

Xenorophidae

Patriocetus kazakhstanicus

ChM PV 2761

ChM PV 5852

Agorophius pygmaeus

Ankylorhiza tiedemani

Otekaikea spp.

Waipatia maerewhenua

Squalodon calvertensis

Prosqualodon davidis

Phoberodon arctirostris

Notocetus vanbenedeni

Xiphiacetus bossi

Zarhachis flagellator

Physeteroidea

Platanista gangetica

Ziphiidae

Inioidea

Delphinoidea

Paleobiology

Reconstruction Ankylorhiza.jpg
Reconstruction

The jaws were shorter and more well-built than those of earlier toothed whales, indicating an overall stronger snout. The deep and enlarged temporal fossae at the back of the skull would have served to anchor large, powerful jaw muscles; which together with the thick dental cementum indicates Ankylorhiza employed a high bite force for feeding on large prey. This may also explain why the upper jaw became so thick towards the front of the snout for additional reinforcement. Known skull remains of Ankylorhiza often show severe breakage of the postcanine teeth, possibly caused during impacts with solid bone when the animal was feeding. Ankylorhiza's conical teeth with lengthwise ridges suggest they were adapted for seizing and piercing into prey animals. [1] The unique forward-pointing incisors of Ankylorhiza were potentially used for intraspecific combat, though Boessenecker and colleagues note that use for ramming, a method used by living orcas to injure whales, [4] may be more likely. [1]

Paleoecology

The jaw, tooth, and vertebral anatomy of Ankylorhiza, as well as its large body size all indicate that it was a fast-swimming predator, and probably occupied an ecological niche similar to that of modern orcas, thus making it the earliest known large macrophagous toothed whale. After the genus became extinct around the beginning of the early Miocene epoch, its niche was probably reoccupied successively by Squalodon, macroraptorial sperm whales, and extant orcas. [1]

Related Research Articles

<span class="mw-page-title-main">Toothed whale</span> Parvorder of cetaceans

The toothed whales are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. 73 species of toothed whales are described. They are one of two living groups of cetaceans, the other being the baleen whales (Mysticeti), which have baleen instead of teeth. The two groups are thought to have diverged around 34 million years ago (mya).

<span class="mw-page-title-main">Megalodon</span> Extinct giant shark species from 23 to 3.6 million years ago

Otodus megalodon, commonly known as the megalodon, is an extinct species of giant mackerel shark that lived approximately 23 to 3.6 million years ago (Mya), from the Early Miocene to the Pliocene epochs. O. megalodon was formerly thought to be a member of the family Lamnidae and a close relative of the great white shark, but has been reclassified into the extinct family Otodontidae, which diverged from the great white shark during the Early Cretaceous.

<span class="mw-page-title-main">Evolution of cetaceans</span>

The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya. Cetaceans are thought to have evolved during the Eocene, the second epoch of the present-extending Cenozoic Era. Molecular and morphological analyses suggest Cetacea share a relatively recent closest common ancestor with hippopotami and that they are sister groups. Being mammals, they surface to breathe air; they have 5 finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors. Research conducted in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.

<i>Ambulocetus</i> Genus of extinct mammals of the order Cetacea

Ambulocetus is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene (Lutetian). It contains one species, Ambulocetus natans, known solely from a near-complete skeleton. Ambulocetus is among the best-studied of Eocene cetaceans, and serves as an instrumental find in the study of cetacean evolution and their transition from land to sea, as it was the first cetacean discovered to preserve a suite of adaptations consistent with an amphibious lifestyle. Ambulocetus is classified in the group Archaeoceti—the ancient forerunners of modern cetaceans whose members span the transition from land to sea—and in the family Ambulocetidae, which includes Himalayacetus and Gandakasia.

<i>Squalodon</i> Extinct genus of mammals

Squalodon is an extinct genus of whales of the Oligocene and Miocene epochs, belonging to the family Squalodontidae. Named by Jean-Pierre Sylvestre de Grateloup in 1840, it was originally believed to be an iguanodontid dinosaur but has since been reclassified. The name Squalodon comes from Squalus, a genus of shark. As a result, its name means "shark tooth". Its closest modern relative is the South Asian river dolphin.

<i>Janjucetus</i> Extinct genus of mammals

Janjucetus is an extinct genus of cetacean, and a basal baleen whale (Mysticeti), from the Late Oligocene around 25 million years ago (mya) off south-east Australia, containing one species J. hunderi. Unlike modern mysticetes, it possessed large teeth for gripping and shredding prey, and lacked baleen, and so was likely to have been a predator that captured large single prey animals rather than filter feeding. However, its teeth may have interlocked, much like those of the modern-day filter-feeding crabeater seal, which would have allowed some filter-feeding behaviour. Its hunting behaviour was probably similar to the modern-day leopard seal, probably eating large fish. Like baleen whales, Janjucetus could not echolocate; however, it did have unusually large eyes, and so probably had an acute sense of vision. The only specimen was found on the Jan Juc beach, where the remains of the extinct whales Mammalodon, Prosqualodon and Waipatia have also been discovered.

Mammalodon is an extinct genus of archaic baleen whale belonging to the family Mammalodontidae.

<i>Zygophyseter</i> Extinct genus of mammals

Zygophyseter varolai is an extinct sperm whale that lived during the Tortonian age of the Late Miocene 11.2 to 7.6 million years ago. It is known from a single specimen from the Pietra Leccese Formation in Italy. It was a member of a stem group of fossil macroraptorial sperm whales also including Brygmophyseter, Acrophyseter, and Livyatan. It probably grew to be around 6.5 to 7 meters in length and shared some characteristics with other raptorials, such as large teeth with tooth enamel that were functional in both the upper and lower jaws which the modern sperm whale lacks. It also had a beak, the ability to echolocate prey, and could have probably swum faster than the modern-day sperm whale which can reach 4 kilometers per hour (2.5 mph). These were probably used in the capture of large prey, such as large fish, seals, and whales. In fact, its common name, the killer sperm whale, refers to its feeding habits that would have had a resemblance to the modern-day killer whale.

<i>Aetiocetus</i> Extinct genus of mammals

Aetiocetus is a genus of extinct basal mysticete, or baleen whale that lived 33.9 to 23.03 million years ago, in the Oligocene in the North Pacific ocean, around Japan, Mexico, and Oregon, U.S. It was first described by Douglas Emlong in 1966 and currently contains known four species, A. cotylalveus, A. polydentatus, A. tomitai, and A. weltoni. These whales are remarkable for their retention of teeth and presence of nutrient foramina, indicating that they possessed baleen. Thus, Aetiocetus represents the transition from teeth to baleen in Oligocene mysticetes. Baleen is a highly derived character, or synapomorphy, of mysticetes, and is a keratinous structure that grows from the palate, or roof of the mouth, of the whale. The presence of baleen is inferred from the fossil record in the skull of Aetiocetus. Aetiocetus is known from both sides of the Pacific Ocean: it was first documented in Oregon, United States, but it is also known from Japan and Mexico. The genus is currently constrained to the Northern hemisphere and has little value in biostratigraphic studies of the Oligocene due to its limited occurrences across the Pacific.

<i>Brygmophyseter</i> Extinct genus of toothed whale (fossil)

Brygmophyseter, known as the biting sperm whale, is an extinct genus of toothed whale in the sperm whale family with one species, B. shigensis. When it was first described in 1994, the species was placed in the genus Scaldicetus based on tooth morphology, but this was later revised in 1995. In 2006, it was classified into the genus Naganocetus, which is considered to be a junior synonym. The only known specimen, a nearly complete skeleton, was dated to be around 16–15 million years old. Brygmophyseter is thought to have been 6.5–7 meters (21–23 ft) long, and it probably had 11 or 12 teeth in the upper and lower jaws. Brygmophyseter is part of a group of macroraptorial sperm whales which tended to be apex predators using their large teeth to catch struggling prey such as whales. It had a spermaceti organ which was probably used for biosonar like in the modern sperm whale. The whale has made an appearance on The History Channel's TV series Jurassic Fight Club.

<i>Livyatan</i> Extinct genus of sperm whale from the Miocene epoch

Livyatan is an extinct genus of macroraptorial sperm whale containing one known species: L. melvillei. The genus name was inspired by the biblical sea monster Leviathan, and the species name by Herman Melville, the author of the famous novel Moby-Dick about a white bull sperm whale. It is mainly known from the Pisco Formation of Peru during the Tortonian stage of the Miocene epoch, about 9.9–8.9 million years ago (mya); however, finds of isolated teeth from other locations such as Chile, Argentina, United States (California), South Africa and Australia imply that either it or a close relative survived into the Pliocene, around 5 mya, and may have had a global presence. It was a member of a group of macroraptorial sperm whales and was probably an apex predator, preying on whales, seals and so forth. Characteristically of raptorial sperm whales, Livyatan had functional, enamel-coated teeth on the upper and lower jaws, as well as several features suitable for hunting large prey.

<i>Acrophyseter</i> Extinct genus of mammals

Acrophyseter is a genus of extinct sperm whales that lived in the Late Miocene off the coast of Peru comprising two species: A. deinodon and A. robustus. It is part of a group of macroraptorial sperm whales which all shared several features for the purpose of hunting large prey, such as deeply-rooted and thick teeth. Acrophyseter measured 4–4.5 metres (13–15 ft), making it the smallest raptorial sperm whale. Because of its short pointed snout, and its strong curved front teeth, it probably fed on the large marine vertebrates of its time, such as seals and other whales.

<i>Orcinus citoniensis</i> Extinct species of killer whale

Orcinus citoniensis is an extinct species of killer whale identified in the Late Pliocene of Italy and the Early Pleistocene of England. It was smaller than the modern killer whale, 4 m (13 ft) versus 7 to 10 m, and had around 8 more teeth in its jaw. It may have resembled the modern killer whale in appearance, and could represent a transitional species between the modern killer whale and other dolphins. O. citoniensis could have hunted fish and squid in pods, and coexisted with other large predators of the time such as the orcinine Hemisyntrachelus and the extinct shark Otodus megalodon.

<i>Karenites</i> Genus of therapsids from the Late Permian of Russia

Karenites is an extinct genus of therocephalian therapsids from the Late Permian of Russia. The only species is Karenites ornamentatus, named in 1995. Several fossil specimens are known from the town of Kotelnich in Kirov Oblast.

<span class="mw-page-title-main">Squalodontidae</span> Extinct family of mammals

Squalodontidae or the shark-toothed dolphins is an extinct family of large toothed whales who had long narrow jaws. Squalodontids are known from all continents except Antarctica, from the Oligocene to the Neogene, but they had a maximal diversity and global distribution during the Late Oligocene and Early to Middle Miocene.

<i>Albicetus</i> Extinct genus of mammals

Albicetus is a genus of stem-sperm whales that lived during the Miocene Epoch, around 15 million years ago, and was discovered in Santa Barbara, California in 1909. It was categorized for decades as belonging to a group of extinct walruses erroneously thought to be sperm whales. It was named Albicetus, meaning "white whale", is a reference to the leviathan in Herman Melville's classic 1851 novel Moby-Dick.

<i>Coronodon</i> Extinct genus of whales

Coronodon is a genus of toothed (transitional) baleen whales from the Early Oligocene Ashley and Chandler Bridge formations of South Carolina. The genus contains three species: the type species C. havensteini, and additional species C. newtonorum and C. planifrons.

<i>Abdalodon</i> Extinct genus of cynodonts

Abdalodon is an extinct genus of late Permian cynodonts, known by its only species A. diastematicus.Abdalodon together with the genus Charassognathus, form the clade Charassognathidae. This clade represents the earliest known cynodonts, and is the first known radiation of Permian cynodonts.

<span class="mw-page-title-main">Macroraptorial sperm whale</span> Predatory family of extinct whales

Macroraptorial sperm whales were highly predatory whales of the sperm whale superfamily (Physeteroidea) of the Miocene epoch that hunted large marine mammals, including other whales, using their large teeth. They consist of five genera: Acrophyseter, Albicetus, Brygmophyseter, Livyatan, and Zygophyseter. All species are known by at least a skull, and are informally grouped without a family designation. They were all likely the apex predator of their habitats, comparable to the modern day killer whale, and achieved great lengths, with one species–Livyatan–measuring about 13.5–17.5 m (44–57 ft).

Nihohae is an extinct genus of waipatiid dolphin that was native to the waters surrounding New Zealand during the Oligocene. It possessed long, tusk-like teeth unlike those of any extant cetacean, which were likely used like the “saw” of a sawfish to stun and injure prey. The genus contains a single species, N. matakoi, known from a partial skull and skeleton.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 Boessenecker, Robert W.; Churchill, Morgan; Buchholtz, Emily A.; Beatty, Brian L.; Geisler, Jonathan H. (2020). "Convergent Evolution of Swimming Adaptations in Modern Whales Revealed by a Large Macrophagous Dolphin from the Oligocene of South Carolina". Current Biology. 30 (16): 3267–3273.e2. doi: 10.1016/j.cub.2020.06.012 . ISSN   0960-9822. PMID   32649912. S2CID   220435400.
  2. 1 2 Allen, J. A. (1887). "Note on squalodont remains from Charleston, S.C.". Bulletin of the American Museum of Natural History. 2: 35–41. hdl:2246/1611.
  3. Hooker, Sascha K. (2009-01-01), "Toothed Whales, Overview", in Perrin, William F.; Würsig, Bernd; Thewissen, J. G. M. (eds.), Encyclopedia of Marine Mammals (Second Edition), London: Academic Press, pp. 1173–1179, ISBN   978-0-12-373553-9 , retrieved 2020-07-30
  4. Ferguson, Steven H.; Higdon, Jeff W.; Westdal, Kristin H. (2012-01-30). "Prey items and predation behavior of killer whales (Orcinus orca) in Nunavut, Canada based on Inuit hunter interviews". Aquatic Biosystems. 8 (1): 3. doi: 10.1186/2046-9063-8-3 . ISSN   2046-9063. PMC   3310332 . PMID   22520955.