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Animal Database
Protocetidae
Maiacetus
Maiacetus skeleton
Scientific Classification
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Cetacea
Family †Protocetidae

The protocetids form a diverse and heterogeneous group of cetaceans known from Asia, Europe, Africa, and North America.

Description[]

There were many genera, and some of these are very well known (e.g., Rodhocetus). Known protocetids had large fore- and hindlimbs that could support the body on land, and it is likely that they lived amphibiously: in the sea and on land. It is unclear at present whether protocetids had flukes (the horizontal tail fin of modern cetaceans). However, what is clear is that they are adapted even further to an aquatic life-style. In Rodhocetus, for example, the sacrum – a bone that in land-mammals is a fusion of five vertebrae that connects the pelvis with the rest of the vertebral column – was divided into loose vertebrae. However, the pelvis was still connected to one of the sacral vertebrae. Furthermore, the nasal openings are now halfway up the snout; a first step towards the telescoped condition in modern whales. Their supposed amphibious nature is supported by the discovery of a pregnant Maiacetus, in which the fossilised fetus was positioned for a head-first delivery, suggesting that Maiacetus gave birth on land. The ungulate ancestry of these early whales is still underlined by characteristics like the presence of hoofs at the ends of toes in Rodhocetus.

Genus Aegyptocetus[]

Aegyptocetus is an extinct genus of protocetid archaeocete whale known from Egypt.

Description[]

Aegyptocetus is known from the articulated holotype MSNTUP I-15459, an almost complete cranium, lower jaws (with teeth) and a partial postcranial skeleton (cervical and thoracic vertebrae and ribs). The specimen was recovered when marbleized limestone was imported commercially to Italy. It was collected in the Khashm el-Raqaba limestone quarry (28.5°N 31.8°E, paleocoordinates 22.9°N 27.2°E) from the Gebel Hof Formation on the northern flank of Wadi Tarfa in the Eastern Desert of Egypt, dating to the late Mokattamian age of the middle Eocene, about 41 to 40 million years ago. Its cause of death may have been an attack by a large shark as pattern of shark tooth marks preserved on the ribs.

Genus Babiacetus[]

Babiacetus is an extinct genus of early cetacean that lived during the late Lutetian middle Eocene of India (48.6 to 40.4 million years ago). It was named after its type locality, the Harudi Formation in the Babia Hills (23.5°N 68.8°E: paleocoordinates 5.9°N 61.8°E), Kutch District, Gujarat, India.

Description[]

Babiacetus is one of the larger protocetids. Its hydrodynamic skull and pointed, anteroposteriorly (front-back) oriented incisors are typical of archaeocetes. A densly ossified auditory bulla and large mandibular canal indicate it was adapted for hearing in water. Babiacetus differs from pakicetids and ambulocetids (more primitive families) by the large mandibular foramen and a medially concave ascending ramus; distinct from remingtonocetids and basilosauroids (more derived families) by the single-cusped trigonid and talonid on the lower molars. Its long synostotic (fused) mandibular symphysis, which reaches as far back as P2, distinguishes it from Pappocetus and Georgiacetus (other protocetids). Its auditory bulla is more narrow than Rodhocetus'. Babiacetus lacks the prominent molar protocone present in Indocetus. The anterior premolars are large.

Genus Georgiacetus[]

Georgiacetus is an extinct genus of ancient whale known from the Eocene period of the United States. Fossils are known from Georgia, Alabama, and Mississippi and protocetid fossils from the right time frame. but not yet confirmed as Georgiacetus, have been found in Texas (Kellogg 1936) and South Carolina (Albright 1996).

Georgiacetus is an extinct protocetid (early whale) which lived about 40 million years ago and hunted the rich, Suwannee Current powered coastal sea which once covered the Southeastern United States. This was during the earliest Bartonian Stage of the Eocene Epoch (40.5 to 37.2 million years ago). Current research puts Georgiacetus as the link between the protocetids and modern whales,[2] making the Georgia whale a scientifically important ancestor to all modern whales. An articulated and completed cast of the find is currently on display at the Georgia Southern University Museum in Statesboro, Georgia; Georgia Southern University also houses the actual 1983 Georgiacetus fossils and has the animal’s fossilized hip bones on display.

Discovery[]

Georgiacetus was discovered in 1983 during the construction of the nuclear power plant Plant Vogtle in Burke County, Georgia (in the Lutetian Blue Bluff Formation, 33.1°N 81.8°W, paleocoordinates 33.7°N 70.3°W). The find consisted of three individuals all identified as belonging to the same species; two of the individuals were represented by isolated bones recovered separately which included a few vertebrae, ribs and tooth crowns. The main find was discovered during the cutting of a drainage channel at a depth of about 30 ft (9.1 m) below the surface. It was a 75%-80% complete individual consisting of more than 60 bones and teeth; including a well preserved skull and mandible. Fortunately, Georgia Power halted construction activities in the area and assisted in the recovery effort. The main mass was collected from an area about 3.3 m (11 ft) square, they were not articulated. There was evidence of light scavenging with scratches on one rib but only ten shark’s teeth were recovered with the find. There was no duplication of fossilized bones in the main mass so a single individual was represented. This was an adult animal with fully erupted and well worn molars. There was no apparent cause of death. The main mass of bones were first reviewed in the field (1983) by geologist E. A. Shapiro of the Georgia Geologic Survey (which was "abolished" in 2004). On Shapiro’s recommendation Georgia Southern University was called in and Richard Petkewich and Gale Bishop led the effort to recover the specimen.

Description[]

Cranium and dentition[]

Dr. Richard Hulbert, also with Georgia Southern University at that time, led the research team which described the find as a new genus and species in 1998. The skull is more than 30 in (760 mm) long, 12 in (300 mm) wide and about 24 in (610 mm) deep, fleshed out it would have been decidedly larger.

The structure of its inner ear bones confirms Georgiacetus as belonging with the whales; throughout their long history all whales and their terrestrial ancestors have possessed an identifiable and unique inner ear bone structure.

It’s hard to know the total length of the animal as no legs or tail vertebrae were found, but researchers estimate a length of at 10 to 20 ft (3.0 to 6.1 m) considering the head would have been nearly three feet long for a living animal. Georgiacetus was equipped as an active predator capable of taking and processing large prey. There was a prominent crest at the top rear of the skull which would have anchored powerful jaw muscles. The front teeth were curved, banana shaped (though in life most of the banana shape would have been deep in the jaw with just the tip exposed) and peg-like. These teeth were adapted to seize and hold struggling prey; moving back in the jaws there were deeply rooted triangular edged teeth for shearing, and further back were sharp molars for crushing. Large fish, birds or turtles could have been caught and processed into manageable chunks.

The tooth and skull arrangement shows a clear, direct relationship between the Basilosauridae family and Georgiacetus. Basilosaurids possessed teeth and a skull remarkably similar in function and structure, both have nostrils (blowholes) located halfway back on the snout, just in front of the eyes. The basilosaurid tooth arrangement appears as a more efficient and specialized version of the Georgiacetus arrangement. Georgiacetus predated the basilosaurids by nearly three million years; the Georgia Whale was very likely the source of the basilosaurids. In their turn, the basilosaurids led to modern whales.

Postcranium[]

Uhen 2008 described new Georgiacetus material from Alabama and Mississippi. These finds included several tail vertebrae, teeth, and a partial mandible. The most important find was a single end-of-tail vertebra, one which would have occupied the very end of the vertebral column. This end-of-tail vertebra possessed two distinct, muscle supporting flanges. It did not show that simplified, compressed end-of-tail arrangement seen in both modern whales and Basilosaurus. It did not show any fluke supporting adaptations. This single vertebra showed that Georgiacetus apparently lacked a fluke and likely swam with its hind legs.

Georgiacetus had a tail and lacked the fluke present in slightly younger fossils. It probably swam using its hindlimbs by wiggling its hips and moving its trunk up and down, a locomotor behaviour abandoned by modern whales. Whales evolved in South Asia, and it was previously thought that the fluke helped early whales spread across Earth from there, so Georgiacetus' presence in America and its legs and tail contradicts this hypothesis.

Uhen 2008 also established the clade Pelagiceti to show the relationship between Georgiacetus, the basilosaurids and modern whales. This clade begins just after Georgiacetus, includes the basilosaurids, baleen and toothed whales. This shows that Georgiacetus led to the basilosaurids, which in turn led to modern whales. The right and left hip bones of Georgiacetus were recovered though no hind leg or tail material was preserved. The hip bones were relatively large and showed well developed sockets were the legs had attached indicating that Georgiacetus had well developed hind legs actively used in some manner and since the hip bones were so much larger than those known from Basilosaurus, and Basilosaurus was a dramatically larger animal than Georgiacetus, it was cautiously assumed that the hind legs of Georgiacetus were much larger, as related to body-size, than the tiny hind legs of Basilosaurus. Yet the hip bones were not fused to the spine, (neither are those of Basilosaurus) which suggests that the Georgia whale probably could not support its own weight out of the water.

Paleoenvironment[]

Global sea levels were about 130 ft (40 m) higher than modern levels when these whales lived. The fossils were discovered 93 mi (150 km) inland from the modern coastline. The invertebrate fossils recovered along with the main mass of bones showed that the whale died well off-shore in a shallow, open water environment approximately 30 mi (48 km) from the coastline (today Georgia's fall line). These invertebrate fossils also allowed accurate dating of the remains.

Dispersal into North America[]

Georgiacetus was held as the earliest North American whale until Geisler, Sanders & Luo 2005 published a paper on Carolinacetus, a slightly older, more primitive whale than Georgiacetus, based on a partial skull, mandible, several teeth, ribs and vertebra. An important find in itself, one of the interesting questions the authors asked was how did whales get to North America?

Whales emerged about 52 million years ago in the Tethys Ocean (between present-day India and Asia). It was a warm, fertile shallow sea very much like the one which covered southeastern United States 40 million years ago when whales (Georgiacetus & Carolinacetus) were already present in America. There are two schools of thought on how they got there: one involves a direct, deep water Atlantic crossing, the other involves a polar route northwards up the European coastline, across to Greenland, and southward along the North American coastline. This polar route would not have been a cold water trip as the climate was much warmer then and Greenland was very likely green. Both routes would require long deepwater crossings. Also, as sea levels were much higher at that time, the journey would be longer than it is today. Whichever route taken, the fact that the journey occurred shows that by the time Carolinacetus and Georgiacetus lived, whales (which did not yet possess flukes) were already capable of extended deep water activity.

Genus Natchitochia[]

Natchitochia is an extinct protocetid early whale known from the Middle Eocene (Bartonian, 40.4 to 37.2 million years ago) Cook Mountain Formation in Natchitoches Parish, Louisiana (31.7°N 93.1°W, paleocoordinates 32.6°N 84.5°W).

Natchitochia is known from three incomplete ribs and thirteen vertebrae of which four are thoracics, five lumbars, one sacral, two caudals, and one of indeterminable position. Natchitochia is significantly larger than most other early protocetids, except Eocetus and Pappocetus. The vertebrae of Natchitochia are smaller than those of Eocetus and lack (1) elongated lumbar centra and (2) the ventral keel seen the vertebrae of Pappocetus. The ribs are smaller than those of Pappocetus.

The fragmentary specimen was collected in 1943 during a ground water survey and then sent to the United States National Museum where Remington Kellogg identified it as a new genus of archaeocete but never formally described it. Uhen 1998 finally described and named the genus and the species; the genus for the type locality and the species honors discoverer Paul H. Jones.

Genus Pappocetus[]

Pappocetus is an extinct protocetid cetacean known from the Eocene of Nigeria and Togo.

Pappocetus differs from all other known protocetid genera by the step-like notch on the ventral margin of the mandible below M2 and M3; from Indocetus and Rodhocetus by the deciduous double-rooted P1; from Protocetus and Babiacetus by the presence of accessory cuspules; and from Babiacetus by the unfused symphysis terminating just before P3. Its molar morphology is similar to Georgiacetus and its estimated body size to that of Eocetus.

Genus Makaracetus[]

Makaracetus is an extinct protocetid early whale the remains of which were found in 2004 in Lutetian layers of the Domanda Formation in the Sulaiman Range of Balochistan, Pakistan.

Makaracetus is unique among archaeocetes in its feeding adaptations; its proboscis and the hypertrophied facial muscles. The genus was adequately named after Makara, a Hindu mythological animal, half-mammal (often an elephant), half-fish, and cetus, Latin for "whale". The species name, bidens, is Latin for "two-teeth", in reference to the retention of only two incisors in each premaxilla. Makaracetus' unique features even lead Gingerich et al. 2005 to propose a new classification of Protocidae based on the degree of their aquatic adaptation; with Makarcetus alone in the subfamily Makaracetinae.

A combination of cranial features indicate that Makaracetus had a short, muscular proboscis similar to a tapir. There are broad and shallow narial grooves on the dorsal side of the premaxilla extending the nasal vestibule to the anterior end of the rostrum. These grooves are paralleled on the ventral side by extraordinary lateral fossae, stretching from the anterior maxilla and over the premaxilla. The rostrum is angled downwards, like in a dugong, and has a reduced number of incisors. Enlarged foramina in front of the orbits indicate that the rostrum had a rich blood supply.

No living mammal displays this combination of characteristics. The expanded nasal is present in tapirs, but they are not aquatic animals. The morphology of sirenian rostra is similar, but sirenians are herbivorous whereas Makaracetus' dentition clearly indicate that it was carnivorous. Walrus cranial morphology is different, but they are aquatic and use specialized buccal and facial muscles to feed on mollusks, fossils of which are abundant in the Domanda Formation, and they probably provide the best ecological model among living mammals. More complete fossils must be recovered before Makaracetus can be adequately described.

Genus Artiocetus[]

Artiocetus is an extinct genus of early whales belonging to the family Protocetidae. It was a close relative to Rodhocetus and its tarsals indicate it resembled an artiodactyl.

Description[]

Artiocetus clavis existed in the early Lutetian age (47 million years ago) and is one of the oldest known protocetid archaeocetes. Though the whale may have been primarily aquatic, the discovery of ankle bones lends to the idea that this fossil may have been a transition between sea-based and land-based mammals. While whales eventually returned to the sea, the anthracotheres, ancestors of the hippopotamus, are thought to have descended from an ancestor shared with the whale.

Like Rodhocetus, artiocetus had limbs comparable to Ambulocetus but larger fore and hind feet, which were probably webbed. They could probably move on land, but rather clumsily like a modern seal.

Protocetidae were the first group of whales to develop tail flukes, which suggests they were quick, agile predators. Though Protocetidae as a family possessed tail flukes, it has been suggested that Artiocetus did not. Thewissen et al. states that "Artiocetus had a long tail and thus probably lacked a tail fluke".

Genus Crenatocetus[]

Crenatocetus (from Latin: crena, "notch", and cetus, "whale") is an extinct genus of protocetid early whale that lived along the Atlantic Coastal Plain of the United States during the Lutetian in the late middle Eocene. The species is named in honour of paleontologist Clayton E. Ray, former curator at the National Museum of Natural History.

McLeod & Barnes 2008 estimated the skull to be 75 cm (30 in) long, which makes Crenatocetus a mid-sized protocetid. Georgiacetus (from Georgia) is an older and more primitive close relative, while Pappocetus (from Nigeria) is a younger and more derived relative.

Genus Gaviacetus[]

Gaviacetus (from Latin Gavia, "loon" and cetus, "whale") extinct archaeocete whale that lived approximately 45 million years ago. Gaviacetus was named for its characteristic narrow rostrum and the fast pursuit predation suggested by its unfused sacral vertebrae.

Description[]

The skull of Gaviacetus is characteristic of protocetids, but the rostrum is extremely narrow anterior to P3, suggesting some kind of trophic specialization. The well-preserved auditory bulla in Gingerich, Arif & Clyde 1995's specimen is dense like in other archaeocetes, is equipped with a prominent sigmoid process, but has 3-5 contacts with the rest of the cranium.

Preserved alveoli (tooth sockets) show that Gaviacetus had double- and tripple-rooted cheek teeth, but some controversy remains regarding the number of molars. Based on other cranial characters, Gingerich, Arif & Clyde 1995 concluded that Gaviacetus is a protocetid (more primitive archeocetes with a third upper molar) and therefore assumed the presence of M3 though no traces thereof are preserved in their specimen. In opposition to this, Bajpai & Thewissen 1998, who's specimen is also lacking the essential maxillar part, thought the cranium above the very small M2 to be to narrow for the presence of M3, hence indicating Gaviacetus is a basilosaurid (a more derived archaeocetes lacking a third upper molar). Uhen 2009 argued against this assignment until more solid evidences have been found.

The preserved sacral vertebra was not fused with its posterior neighbour, indicating that Gaviacetus was a tail-powered swimmer like Protocetus, better adapted to pursuit predation than Rodhocetus. The preserved transverse process of the sacral vertebra is distally expanded, suggesting a synchondrosal joint between the vertebral column and pelvis.

Genus Maiacetus[]

Maiacetus ("mother whale") is a genus of early middle Eocene (ca. 47.5 mya) cetacean from Pakistan.

Palaeobiology[]

The genus contains a single species Maiacetus inuus, first described in 2009 on the basis of two specimens, including a specimen which has been interpreted as a pregnant female and its fetus. This represents the first description of a fetal skeleton of an archaeocete. The position of the fetus (head-first) suggests that these whales gave birth on land. Whales generally give birth tail first, while all land mammals give birth head first. That the Maiacetus should give birth on land is not so implausible because this whale is semiaquatic or amphibious. Maiacetus represents the transition of land mammals back to the oceans where these animals were living on the land-sea interface and going back and forth.

However, J. G. M. Thewissen, discoverer of Ambulocetus, has questioned these conclusions, suggesting that the smaller skeleton could be a partially digested meal. Even if the small skeleton is a fetus, Thewissen writes that it may not have been preserved in its normal in-vivo position.

This species is medium-sized with a skeleton 2.6 metres (8.5 ft) in length and an estimated weight of 280 to 390 kilograms (620 to 860 lb).

Genus Qaisracetus[]

Qaisracetus is an extinct protocetid early whale known from the Eocene (Lutetian, 48.6 to 40.4 million years ago) of Baluchistan, Pakistan.

Description[]

Qaisracetus is known from a dozen specimens, all found in or near the type locality. Among them are several well-preserved elements, including a well-preserved skull, partial skulls and braincases, several vertebrae including an almost complete sacrum, a left innominate, ribs, and partial limb elements. Qaisracetus is smaller than Pappocetus and Babiacetus but larger than Indocetus. Qaisracetus arifi is almost as complete as Rodhocetus kasranii, the most complete articulated skeleton of a protocetid, and they were similar in size: the latter had an estimated body weight of 620 kg (1,400 lb), compared to 590 kg (1,300 lb) for the former.

Qaisracetus has a generalized protocetid skull with the external nares located relatively anteriorly (above C1) and a relatively broad frontal shield. The rostrum is more narrow in Qaisracetus than in Takracetus. The four sacral vertebrae are only partially fused: the first two are solidly fused, the third is locked in place by rib-like processes (a pleurapophyseal synchondrosis), while the fourth has a caudal (tail-like) morphology including two ventral chevron processes. The fusion between S1 and S2 distinguished Qaisracetus from other protocetids such as Protocetus, Rodhocetus, Gaviacetus, Natchitochia, and Georgiacetus. Qaisracetus' vertebrae are not dense and thick like in Eocetus. In contrast to Qaisracetus, Rodhocetus has a sacrum where non of the vertebrae have fused centra, which is derived to be a protocetid, but Rodhocetus is primitive in retaining pleurapophyseal connections between all sacral vertebrae. The sacral morphology of Rodhocetus and Qaisracetus indicate protocetids represent a wide range of specializations, although which is ancestral to later whales is unclear.

Genus Rodhocetus[]

Rodhocetus is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea.

Description[]

Rodhocetus (from the mid-Eocene) was named from the flank of the Rodho ‘bald’ part of the Zinda Pir anticlinorium on the east side of the Sulaiman Range in Pakistan. The first species to be discovered (Rodhocetus kasrani) exhibited such features as a large pelvis fused to the vertebrae, hind legs, and differentiated teeth. Of a recently discovered species (Rodhocetus balochistanensis), the ankle bones were recovered, further strengthening the already well-founded link to artiodactyls, and weakening the link to mesonychids.

Rodhocetus balochistanensis is in fact believed to demonstrate a direct evolutionary link to artiodactyls (modern examples of which include hippopotamuses, now believed to be the closest cousin species of the cetaceans). The structure of the ankle bones of this species, the trochlea, is double-spooled. This trait is only known in artiodactyls, as all other mammalian orders have a single-spooled trochlea. This matches studies of the genetic relations between whales and other animals. Previous fossil-based hypotheses that whales were directly descended from mesonychids have been largely overturned.

The ear bones of Rodhocetus are already very whale-like, though the swimming style is very different. Rodhocetus is more obviously aquatic than earlier known species (e.g. Ambulocetus) and had large, paddling hind feet to propel it through the water. It also had a strong tail which may have helped to act as a rudder. Many[who?] suggest that Rodhocetus may have swum like a modern otter, but through a principal components analysis done in 2003, Philip Gingerich demonstrated that its limb proportions were closer to that of the Russian desman.

Fossils[]

The first fossils of this species were found in Balochistan Province, Pakistan in 2001 by Philip Gingerich. Dating from about 47 million years ago, they are one of a series of recent discoveries, including the pakicetids, which have thrown considerable light on the previously mysterious evolutionary origin of whales.

Genus Takracetus[]

Takracetus was a primitive cetacean that lived approximately 45 million years ago. The type specimen (GSP-UM 3041) is a partial skull though the literature mentions a second more complete specimen.

Genera[]

Family Protocetidae

Aegyptocetus
 A. tarfa

Georgiacetinae

Babiacetus
 B. indicus
 B. mishrai
Carolinacetus
Eocetus
Georgiacetus
 G. vogtlensis
Natchitochia
 N. jonesi
Pappocetus
 P. lugardi

Makaracetinae

Makaracetus
 M. bidens

Protocetinae

Artiocetus
 A. clavis
Crenatocetus
 C. rayi
Gaviacetus
 G. razai
 G. sahnii
Indocetus
Maiacetus
 M. inuus
Protocetus
 P. atavus
Qaisracetus
 Q. arifi
Rodhocetus
 R. kasrani
 R. balochistanensis
Takracetus
 T. simus

Gallery[]

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