Lecture 2.6: Evidence for Evolution

Fossils Examples Genetics Refs

Unit 2: Transmission Genetics

Lecture 2.6: Evidence for Evolution

John D. Nagy

BIO 181: General Biology for Majors, Scottsdale Community College

2020 Revision

John Nagy Lec 2.6: Evidence for Evolution 1/36


Outline

1 Some interesting fossilsSynapomorphiesBody planVestigesTimeline

2 ExamplesMammalsAviansTetrapods

3 Molecular Genetic Evidence

4 Literature cited


Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline

What kind of creature is this?



Indohyus

“Indohyus was an animal similar in size to a cat but quite differentfrom a cat in shape. It had a long snout and a long tail and longslender limbs. At the end of each limb, there were four or five toesthat ended in hoof, similar to that of a deer” [11, pg. 274].

The ear bones have a “thickened wall. . . called the involucrum [which]is present in all cetaceans, fossil and recent. The involucrum is notpresent in other mammals, except for one: Indohyus” [11, pg. 275].



Ventral (underneath) view of dog cranium

The ear bones Thewissen et al. [11] refer to are auditorybullae.

So Indohyus is a racoon-shaped mammal with hooves like adeer and ear bones like a whale.






Ambulocetus

Ambulocetus was “roughly the size of a large male sea lion”[11, pg. 279].

“Toes are terminated by a short phalanx carrying a convexhoof” [12, pg. 211].

“The [auditory] bulla has a thick and massive involucrumon its medial side” [9, pg. 726].

‘[T]the lower jaw and the auditory bulla have a bonycontact unlike any other cetacean” [9, pg. 726].



Ambulocetus

“In hunting behavior, Ambulocetus may have been similar to amodern crocodile, and, externally, Ambulocetus may havelooked like a crocodile” [11, pg. 279]



Ventral view of. . . what is that?

Where are the auditory (tympanic) bullae?



Ventral view of bottlenose dolphin (Tursiops truncatus)

The auditory bullae have fallen off. They are not attached tothe skull.



Cetaceans have weird, unique ears

Cetacean auditory bullae areunique because they are

are very thick on one side;they have an involucrum(red arrows);

not attached or poorlyattached to the skull.

(A) and (B): Fossil baleen whales;(C): Fin whale; (D): Rightwhale; (E) and (F): Fossil toothedwhales.



Summary of observations so far

Shared traits collect species naturally into groups:

Indohyus and Ambulocetus all had hooves, like the rest ofthe Artiodactyla (group including hoofed mammals withan even number of toes).

Indohyus, Ambulocetus and the rest of the Cetacea(whales, dolphins and porpoises) had thick auditory bullaewith in an involucrum.

Definition: Synapomorphy

Shared, derived characters like these group organisms intonatural catagories. They are called synapomorphies.



Another interesting fossil—Basilosaur

These species “have a nasal opening that has shifted back fartoward the eyes to form a blowhole and have flippers forforelimbs, a fluke at the end of the tail” [11, pg. 283-4].



Look at the front limbs—Hand or flipper?



Compare to modern northern right whale



Body plans for different functions are the same



What is this?



Basilosaurs—whales with feet

“The hind limbs of basilosaurids retain. . . the femur, [patella], tibia, fibula,tarsals, metatarsals, and phalanges. However, [they] are greatly reduced insize and the pelvis is not attached to the vertebral column, making the hindlimbs unsuitable to support the body weight of these whales” [11, pg. 284](Image from [2]).



Modern whales have hind limb bones, but no legs

Definition: Vestigial trait

A body part that is imperfectly formed and unable to functionproperly is called vestigial.






It’s one of these

Pantropical spotted dolphin (Stenella attenuata) mother and baby.

What happened to the hind limbs in the embryo?

Note that in the Cargegie State 17 embryo, hind limb buds areregressing. Hind limbs are vestigial.



In addition to gills and hind limbs, embryonic dolphins developwhiskers like a cat’s. These are all examples of vestigial traits.Image from [11, pg. 273].



Lay the fossils out in time

Lay the species out in chronological order based on the earliestknown fossils of each type. When we do, we see the followingpatterns:

All are connected by a synapomorphic trait: involucrumson their auditory bullae.

They appear to be a single lineage changing through time:

The hind limbs are becoming detached from the spine andreduced (vestigial).The auditory bullae are becoming more detached from theskull.They are becoming more aquatic.



Transitional fossils

If this hypothesis of change through time were true, we shouldfind transitional fossils. And we do.

Pakicetus: Hooves, involucrum, other cetacean characteristics [1].

Maiacetus: Involucrum, other cetacean characteristics, stronglyattached auditory bullae, attached pelvis [3].

Rodhocetus: Cetacean characteristics, attached pelvis (probably) [4].

Peregocetus: Cetacean characteristics, attached pelvis [7].

Georgiacetus: Cetacean characteristics, detached pelvis [5].



A more accurate view:

Indohyus did not becomePakicetus, etc.

Rather, ancestries back tocommon ancestors, asdepicted by the chart.

This phylogeny representsevolutionary relationships.Each connection is a node.

Nodes represent ancestors.

Therefore, at least 17species are represented: the9 named + 8 nodes.

Groups are defined bysynapomorphies (red).

Example: Indohyus ismore closely related tobaleen whales (Mysticetes)that to hippos.


Fossils Examples Genetics Refs Mammals Avians Tetrapods

These patterns are common: Mammals

Fossils show transition of reptilesto mammals:

Bottom: Early synapsidscalled pelycosaurs havereptile (laid eggs, jaw attachedto back of skull), somemammal-like, characteristics.

Middle: Later synapsids,called cynodonts, are moremammal-like (maybe hair, andmilk) but retain some reptiliancharacteristics (laid eggs).

Top: Even later synapsidsbecome modern mammals(have hair and feed young withmilk, jaw attachmentunderneath skull).



Another transitional fossil

This is a fossil dinosaur called Microraptor [8].

Long, bony tail and teeth, unlike birds.

Feathers over its body, with long feathers for gliding on arms and legs.

Chemical traces in the fossil suggest black, slightly irridescent featherslike modern black birds.



These patterns are common: Birds

Birds came from dinosaurs.

Many dinosarus with feathershave been discovered, includingVelociraptor of Jurassic Parkand Jurassic World fame.

Feathers are synapomorphic inone group of dinosaurs.

All creatures defined byfeathers, including birds, arenested within the dinosaurgroup; therefore, dinosaurs bydefinition never wentextinct.

Unrelated traits—patterns ofbone articulations in the digits,for example—aresynapomorphic in precisely thesame group.



These patterns are common: Tetrapods

Tetrapods (4-legged creatures)came from fish

Early lobe-finned fish(Eusthenopteron): bones in finsimilar to tetrapod pattern beforeany vertebrates existed onland.

Tiktaalik (middle) is a nearlyperfect transition between fish andamphibians—it possesses keycharacteristics of both.

First true amphibians arise about10 million years later (Tulerpeton).

Note: When did this occurrelative to when whales arose?



Two hypotheses

If modern cetaceans arose from hoofed mammals like the fossils suggest,then genes of whales and dolphins should be more like those of hoofedmammals than any other mammal type.

Genetically, either cetaceans would be a sister group of hoofedmammals (A), or

they would be, genetically, hoofed mammals themselves (B).



Comparing species genetically

This is a DNA sequence alignment from GNAT3 gene inhumans, mice, cows, hippos and a variety of cetaceans [6].



Evidence: Whales are genetically hoofed mammals

Evidence from genetic and morpho-logical comparisons [10].

Most analyses place cetaceansalongside hippos genetically.

Genetically, hippos (hoofedmammals) are more like whalesand dolphins than they are likeother hoofed mammals.

This analysis [10] corroboratesmany other studies.

This corroborates fossil evidence:Indohyus and Ambulocetus clusterwith whales and dolphins.

Another group—Mesonychus, anextinct group of hoofedcarnivores—may or may notcluster with cetaceans.



How did these changes occur?



References I

Philip D. Gingerich, Donald E. Russell, and S. M. Ibrahim Shah.

Origin of whales in epicontinential remnand seas: New evidence from the early Eocene ofPakistan.Science, 220:403–406, 1983.

Philip D. Gingerich, B. Holly Smith, and Elwyn L. Simons.

Hind limbs of Eocene Basilosaurus: Evidence of feet in whales.Science, 249:154–157, 1990.

Philip D. Gingerich, Munir ul Haq, Winghart von Koenigswald, William J. Sanders,

B. Holly Smith, and Iyad S. Zalmout.New protocetid whale from the middle Eocene of Pakistan: Birth on land, precocialdevelopment, and sexual dimorphism.PLoS ONE, 4:e4366, 2009.

Philip D. Gingerich, Munir ul Haq, Iyad S. Zalmout, Intizar Hussain Khan, and M. Sadiq

Malkani.Origin of whales from early artiodactyls: Hands and feet of Eocene Protocetidae fromPakistan.Science, 293:2239–2242, 2001.

Richard C. Hulbert, Richard M. Petkewich, Gale A. Bishop, David Bukry, and David P.

Aleshire.A new middle eocene protocetid whale (Mammalia: Cetacea: Archaeoceti) andassociated biota from Georgia.J. Paleont., 72(5):907–927, 1998.



References II

Takushi Kishida, J. G. M. Thewissen, Takashi Hayakawa, Hiroo Imai, and Kiyokazu

Agata.Aquatic adaptation and the evolution of smell and taste in whales.Zool. Lett., 1:9, 2015.

Olivier Lambert, Giovanni Bianucci, Rodolfo Salas-Gismondi, Claudio Di Celma, Etienne

Steurbaut, Mario Urbina, and Christian de Muizon.An amphibious whale from the middle Eocene of Peru reveals early South Pacificdispersal of quadrupedal cetaceans.Curr. Biol., 29:1352–1359, 2019.

Quanguo Li, Ke-Qin Gao, Qingjin Meng, Julia A. Clark, Matthew D. Shawkey, Liliana

D’Alba, Rui Pei, Mick Ellison, Mark A. Norrell, and Jakob Vinther.Reconstruction of Microraptor and the evolution of iridescent plumage.Science, 335:1215–1219, 2012.

Sirpa Nummela, J. G. M. Thewissen, Sunil Bajpai, Taseer Hussain, and Kishor Kumar.

Sound transmission in archaic and modern whales: Anatomical adaptations forunderwater hearing.Anat. Record, 290:716–733, 2007.

Michelle Spaulding, Maureen A. O’Leary, and John Gatesy.

Relationships of Cetacea (Artiodactyla) among mammals: Increased taxon samplingalters interpretations of key fossils and character evolution.PLoS ONE, 4(9):e7062, 2009.



References III

J. G. M. Thewissen, Lisa Noelle Cooper, John C. George, and Sunil Bajpai.

From land to water: The origin of whales, dolphins, and porpoises.Evo. Edu. Outreach, 2:272–288, 2009.

J. G. M. Thewissen, S. T. Hussain, and M. Arif.

Fossil evidence for the origin of aquatic locomotion in Archaeocete whales.Science, 263:210–212, 1994.


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Lecture 2.6: Evidence for Evolution