Archaeoceti
Encyclopedia
The archaeocetes were once thought to have evolved from the mesonychid
Mesonychid
Mesonychia are an extinct order of medium to large-sized carnivorous mammals that were closely related to artiodactyls and to cetaceans...
s, based on dental characteristics. However, recent studies in molecular genetics and non-dental morphology show that the first whales or the archaeoceti most likely evolved from artiodactyls; genetic evidence indicates that their closest living relatives are the family Hippopotamidae
Hippopotamidae
Hippopotamuses are the members of the family Hippopotamidae. They are the only extant artiodactyls which walk on four toes on each foot.- Characteristics :...
which includes the modern hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
. The ancestors of archaeocetes probably diverged from the other artiodactyls around the time of the Cretaceous–Tertiary extinction event.
Most archeocetes had hind limbs, suggesting that they were fully terrestrial. As the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
epoch progressed, the archaeocetes became less terrestrial and more aquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...
. Before the Eocene epoch came to an end, one group of archaeocetes, the basilosaurid
Basilosauridae
Basilosauridae is family of extinct cetaceans that lived in tropical seas during the late Eocene.-Taxonomy:*Family Basilosauridae** Subfamily Basilosaurinae*** Genus Basilosaurus*** Genus Basiloterus** Subfamily Dorudontinae...
s, gave rise to early modern cetaceans. The archaeocetes suffered a heavy loss of genera during the Eocene-Oligocene extinction event
Eocene-Oligocene extinction event
The transition between the end of the Eocene and the beginning of the Oligocene, called the Grande Coupure in Europe, occurring 33.9 ± 0.1 Ma, is marked by large-scale extinction and floral and faunal turnover .Most of the affected organisms were marine or aquatic in nature...
, but some species survived into the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
. The last archaeocete, which was probably a basilosaurid, became extinct in the Oligocene. They may have become extinct from a combination of competition and climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
.
Taxonomy
- Order CetaceaCetaceaThe order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
- Suborder Archaeoceti
- Family Pakicetidae
- Genus PakicetusPakicetusPakicetus is a genus of extinct terrestrial carnivorous mammal of the family Pakicetidae which was endemic to Pakistan from the Eocene .Pakicetus existed for approximately...
- Genus NalacetusNalacetusNalacetus is an extinct genus of mammal belonging to the family Pakicetidae which were endemic to southern Asia living during the Lutenian stage of the Middle Eocene and existing for approximately ....
- Genus IchthyolestesIchthyolestesIchthyolestes was a genus of mammal belonging to the family Pakicetidae which were endemic to southern Asia living during the Lutenian stage of the Middle Eocene and existing for approximately ....
- Genus Pakicetus
- Family AmbulocetidaeAmbulocetidaeAmbulocetidae is a family of early cetaceans from Pakistan that still were able to walk on land. The genus Ambulocetus, after which the family is named, is by far the most complete and well-known ambulocetid genus due to the discovery by Thewissen et al. of a partially complete specimen of...
- Genus AmbulocetusAmbulocetusAmbulocetus was an early cetacean that could walk as well as swim. It lived during early Eocene some 50-49 million years ago. It is a transitional fossil that shows how whales evolved from land-living mammals. The Ambulocetus fossils were found in Pakistan by anthropologist Johannes Thewissen...
- Genus GandakasiaGandakasiaGandakasia was a genus of ambulocetid from Pakistan, that lived in the Eocene epoch. It probably caught its prey near rivers or streams....
- Genus HimalayacetusHimalayacetusHimalayacetus is an extinct genus of carnivorous aquatic mammal of the family Ambulocetidae from the coastline of the ancient Tethys Ocean during the Eocene, living from 55.8—48.6 mya, existing for approximately ....
- Genus Ambulocetus
- Family RemingtonocetidaeRemingtonocetidaeRemingtonocetidae is a family of early carnivorous freshwater aquatic mammals of the order Cetacea endemic to the coastline of the ancient Tethys Ocean during the Eocene living from 55.8—48.6 mya, existing for approximately ....
- Genus Andrewsiphius
- Genus AttockicetusAttockicetusAttockicetus is an extinct genus of cetacean which existed in Pakistan during the Eocene period. The type species is Attockicetus praecursor....
- Genus DalanistesDalanistesDalanistes is an extinct genus of early carnivorous freshwater aquatic mammals of the family Remingtonocetidae endemic to the coastline of the ancient Tethys Ocean during the Eocene living from 48.6—37.2 mya, existing for approximately .-Taxonomy:...
- Genus KutchicetusKutchicetusKutchicetus is an extinct genus of early carnivorous freshwater whales of the family Remingtonocetidae endemic to the coastline of the ancient Tethys Ocean during the Eocene living from 55.8—40.4 mya, existing for approximately .-Taxonomy:...
- Genus RemingtonocetusRemingtonocetusRemingtonocetus is an extinct genus of early carnivorous freshwater aquatic mammals of the family Remingtonocetidae endemic to the coastline of the ancient Tethys Ocean during the Eocene living from 48.6—37.2 mya, existing for approximately .-Taxonomy:...
- Family ProtocetidaeProtocetidaeThe protocetids form a diverse and heterogeneous group of cetaceans known from Asia, Europe, Africa, and North America. There were many genera, and some of these are very well known . Known protocetids had large fore- and hindlimbs that could support the body on land, and it is likely that they...
- Subfamily Georgiacetinae
- Genus Babiacetus
- Genus Carolinacetus
- Genus Eocetus
- Genus GeorgiacetusGeorgiacetusGeorgiacetus is an extinct genus of ancient whale known from the Eocene period of the United States.At Georgia Southern University there is a Georgiacetus skeleton on display at the campus museum.- References :...
- Genus Natchitochia
- Genus Pappocetus
- Subfamily Makaracetinae
- Genus Makaracetus
- Subfamily Protocetinae
- Genus ArtiocetusArtiocetusArtiocetus clavis is an extinct genus of early whales belonging to the family Protocedidae. Their name arises from a combination of Cetacean and Artiodactyl, as this fossil was the first to show that early whales possessed artiodactyl-like ankles....
- Genus Crenatocetus
- Genus GaviacetusGaviacetusGaviacetus was a primitive cetacean that lived approximately 45 million years ago. Although often represented as having small hind limbs, this is an inference from the general progression of other fossil species towards limb loss; the only postcranial remains found for Gaviacetus itself were a rib...
- Genus Indocetus
- Genus MaiacetusMaiacetusMaiacetus is a genus of early middle Eocene cetacean from Pakistan.-Paleobiology: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...
- Genus ProtocetusProtocetusProtocetus atavus is an extinct species of primitive cetacean from Egypt. It lived during the middle Eocene period 45 million years ago....
- Genus Qaisracetus
- Genus RodhocetusRodhocetusRodhocetus is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea.-Description:...
- Genus TakracetusTakracetusTakracetus was a primitive cetacean that lived approximately 45 million years ago. The type specimen was a partial skull though the literature mentions a second more complete skeleton....
- Genus Artiocetus
- Subfamily Georgiacetinae
- Family BasilosauridaeBasilosauridaeBasilosauridae is family of extinct cetaceans that lived in tropical seas during the late Eocene.-Taxonomy:*Family Basilosauridae** Subfamily Basilosaurinae*** Genus Basilosaurus*** Genus Basiloterus** Subfamily Dorudontinae...
- Subfamily BasilosaurinaeBasilosaurinaeBasilosaurinae is a subfamily of cetaceans archaeocetes containing two genera: Basilosaurus and Basiloterus. Were characterized by elongated distal thoracic vertebrae, lumbar, and proximal sacrococcygeal...
- Genus BasilosaurusBasilosaurusBasilosaurus is a genus of cetacean that lived from in the Late Eocene. Its fossilized remains were first discovered in the southern United States . The American fossils were initially believed to be some sort of reptile, hence the suffix -"saurus", but later found to be a marine mammal...
- Genus Basiloterus
- Genus Basilosaurus
- Subfamily DorudontinaeDorudontinaeDourdontinae are a group of extinct cetaceans that are related to Basilosaurus.- Classification :*Subfamily Dorudontinae** Genus Ancalecetus*** Ancalecetus simonsi** Genus Chrysocetus*** Chrysocetus healyorum...
- Genus AncalecetusAncalecetusAncalecetus is an extinct genus of whale....
- Genus ChrysocetusChrysocetusChrysocetus is an genus of extinct whale....
- Genus CynthiacetusCynthiacetusCynthiacetus is an extinct genus of cetacean archaeocete, belonging to the family Basilosauridae. Lived during the Upper Eocene 38 million years ago. Was found in the southeastern United States, Egypt and Peru. Its skull was similar in size and morphology to Basilosaurus, but unlike it had no...
- Genus DorudonDorudonDorudon was a genus of ancient cetacean that lived alongside Basilosaurus 41 to 33 million years ago, in the Eocene. They were about five meters long and were most likely carnivorous, feeding on small fish and mollusks. Dorudontines lived in warm seas around the world...
- Genus SaghacetusSaghacetusSaghacetus is a extinct genus of cetacean archaeocete, belonging to the family Basilosauridae. Existed during the Upper Eocene in Egypt....
- Genus ZygorhizaZygorhizaZygorhiza kochii is an extinct species of cetacean.Zygorhiza was a smaller, less elongated, 6 m long relative of the famous Basilosaurus. Its bodily proportions were similar to those of modern whales, although, unlike modern species, it had a distinct neck, and flippers which could be moved at...
- Genus Ancalecetus
- Subfamily Kekenodontinae
- Genus Kekenodon
- Genus Phococetus
- Subfamily Stromeriinae
- Genus Stromerius
- Subfamily Basilosaurinae
- Family Pakicetidae
- Suborder Archaeoceti
Phylogeny
CetartiodactylaCetartiodactyla
Cetartiodactyla is the clade in which whales and even-toed ungulates have currently been placed. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. The term Cetartiodactyla reflects the idea that whales evolved within the artiodactyls...
|--Cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
| |--Pakicetidae
| `--+--Ambulocetidae
Ambulocetidae
Ambulocetidae is a family of early cetaceans from Pakistan that still were able to walk on land. The genus Ambulocetus, after which the family is named, is by far the most complete and well-known ambulocetid genus due to the discovery by Thewissen et al. of a partially complete specimen of...
| `--+--Remingtonocetidae
Remingtonocetidae
Remingtonocetidae is a family of early carnivorous freshwater aquatic mammals of the order Cetacea endemic to the coastline of the ancient Tethys Ocean during the Eocene living from 55.8—48.6 mya, existing for approximately ....
| `--Protocetidae
Protocetidae
The protocetids form a diverse and heterogeneous group of cetaceans known from Asia, Europe, Africa, and North America. There were many genera, and some of these are very well known . Known protocetids had large fore- and hindlimbs that could support the body on land, and it is likely that they...
| |--Georgiacetus
Georgiacetus
Georgiacetus is an extinct genus of ancient whale known from the Eocene period of the United States.At Georgia Southern University there is a Georgiacetus skeleton on display at the campus museum.- References :...
| `--Basilosauridae
Basilosauridae
Basilosauridae is family of extinct cetaceans that lived in tropical seas during the late Eocene.-Taxonomy:*Family Basilosauridae** Subfamily Basilosaurinae*** Genus Basilosaurus*** Genus Basiloterus** Subfamily Dorudontinae...
| |--Basilosaurus
Basilosaurus
Basilosaurus is a genus of cetacean that lived from in the Late Eocene. Its fossilized remains were first discovered in the southern United States . The American fossils were initially believed to be some sort of reptile, hence the suffix -"saurus", but later found to be a marine mammal...
| `--+--Dorudon
Dorudon
Dorudon was a genus of ancient cetacean that lived alongside Basilosaurus 41 to 33 million years ago, in the Eocene. They were about five meters long and were most likely carnivorous, feeding on small fish and mollusks. Dorudontines lived in warm seas around the world...
| `--Autoceta
| |--Odontoceti
| | |--Squalodontoidea
| | | |--Squalodontidae
| | | `--Rhabdosteidae
| | `--Physeteroidea
| `--Mysticeti
`--Artiodactyla
See also
- Evolution of cetaceansEvolution of cetaceansThe cetaceans are marine mammal descendants of land mammals. Their terrestrial origins are indicated by:* Their need to breathe air from the surface;* The bones of their fins, which resemble the limbs of land mammals...
- Cetaceans
- MesonychidMesonychidMesonychia are an extinct order of medium to large-sized carnivorous mammals that were closely related to artiodactyls and to cetaceans...
- CetartiodactylaCetartiodactylaCetartiodactyla is the clade in which whales and even-toed ungulates have currently been placed. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. The term Cetartiodactyla reflects the idea that whales evolved within the artiodactyls...