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Rough Phylogeny of Whales (with Characteristics)
The most marine-adapted of all mammals (or any other living tetrapod) they include the largest living animals (blue whales) yet like sirenians, their ancestors were four-legged mammals that lived on land. Over time (in the early Eocene) they slowly but surely became more adapted to thriving in aquatic ecosysrems, eventually becoming the first undisputed true whales in the mid Eocene- the Archaeocete whales. Around the Late Eocene/ earliest Oligocene, all the Archaeocete whales became extinct and modern whales arose to dominate the whale niches (toothed Odontocetes and toothles Mysticetes). The first true dolphins appeared in the mid Miocene.
Whale Phylogeny 2 Rough Timeline of Whale Evolution
(Majority of these transitional whales found in Pakistan between the 70s- 00s)
Indohyus
-Despite resembling a rabbit (a little larger) had dense bones and a whale-like ear
-Oxygen-18 analysis of bones suggests it was aquatic, while carbon-13 suggests it was terrestrial (teeth suggest it ate land plants)
-Only shown to be a whale ancestor or relative after Dr. Thewissen accidently broke one's fossil, revealing the auditory bulla (ear bones)
Pakicetus
-Found in river deposits dating ~50 MA
-Still very wolf-like
-Dense ear bones, probably starting to hear better underwater
-Small, primitive brain
Ambulocetus (Discovered 1994)
- ~50-47 MA, found nearly complete, seems to have lived in estuarine (or at least fresh and marine) habitats
-Ears still not very specialized yet but front limbs shortening, back limbs and tail more adapted for swimming (likely swam like an otter)
-Likely clumsy on land & water, hypothesized to mostly ambush &/or scavenge prey
Rodhocetus (Discovered shortly after Ambulocetus)
-Greater than 16 feet long, starting to be dolphin-like
-No distinct neck, longer snout
-Pelvic bones still attached to vertebrae so probably could still walk on land
Georgiacetus (found in Georgia, USA, discovered in 1980s)
-Lived ~40 MA
-Likely didn't have a tail flute yet so still undulating up and down + using hind limbs to move
-Estimated 9 feet long or so
-Hip bones large and well developed sockets so still had robust hind limbs
Archaeocete Whales
Dorudon
Pakicetus model Next to Dorudon model
-First whales to really resemble true whales (Starting w/ Dorudon ~40-30 MA, little to no limbs) but still lacked sophisticated ear bones/ echolocation
-Largest one, Basilosaurus, of the late Eocene largest marine predator of the time, measuring 50-60 feet long (& still had vestigial hind limbs, seen in the ones out of the USA)
-Fossil bones (at least vertebrae) of some so common in SE USA (Alabama, Mississippi, Georgia??) that they historically have household uses
-All became extinct by the end of the Eocene
Modern Baleen Whales (Mysticetes)
-Earliest ones were toothed (Late Eocene/ Early Oligocene), but soon all became toothless filter feeders (wielding baleen plates instead by ~23 MA)
-Split from Odontocetes/Archaeocetes by at least ~36 MA
-Have symmetrical skulls, two blowholes, & lower jawbones that are solid but not fused in the middle
-Females are larger than males
-Modern Mysticetes are widespread but generally prefer cold waters at the Poles
Modern whale representative skeletons
Modern Toothed Whales(Odontocetes)
-Originated in at least early Oligocene
-Brain size exploded after echolocation first used
-Skull not symmetrical
-Modern average size ~40 feet long & 77,000 pounds (generally smaller whales besides sperm whales that hunt giant squid in the deep)
Mesonychids
-Hooved Eocene mammals, thought since the mid 1960s to be ancestors to whales due to skull and teeth similarities
-But when proven transitional whales had the pulley-like ankle bones some artiodactyls possessed that Mesonychids didn't, proved whales likely aren't that related to them
-Include the largest known mammal land predator of all time- Andrewsarchus
-All became extinct by the end of the Eocene
Andrewsarchus, the largest Mesonychid
Rough known toothed modern/modern-like whale fossil distribution over time
Etc. Facts
+Earliest cetaceans in Miocene of FL from long beaked dolphins (Pomatodelphis) & small baleen whales (Cetotheriidae)
+Isolated Odontocete fossils are the most common whale fossils in FL (I have found a couple whale ear bones in the Peace river) followed closely by Cetothere whale fossils (one relatively small complete fossil baleen whale found in the Phosphate mines in on display in the Phosphate Museum in Mulberry, Florida)
+Cetotherium whales only ~10-20 feet long around Miocene (became much larger by Pliocene, if not late Miocene)
+The largest item a modern baleen whale can swallow is a grapefruit
Sources:
https://evolution.berkeley.edu/evolibrary/article/evograms_03
https://www.nature.com/news/fossil-of-oldest-known-baleen-whale-relative-unearthed-in-peru-1.21966
http://blogs.cofc.edu/macebrownmuseum/
http://media.timetoast.com/timelines/whale-evolution-timeline-ab06d7b7-51e9-4f88-9928-0e5c145a2c67
25 fossils by Prothero book
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