Vertebrate Paleontology

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• Forelimb converted to wing - fused hand bones support flight feathers
• Rigid shoulder joint with fused clavicles (furcula)
• Keeled sternum to support huge breast (=flight) muscles
• Trunk vertebrae and pelvis fused into solid but light structure
• Tail bones fused - support tail feathers
• Some fused leg bones
• Teeth lost - keratin beak
• Entire body adapted for flight
• Trunk solidified and neck elongated
• Forelimbs reduced to flight feather supports
• Keeled sternum for attachment of pectoralis (downstroke) and supracoracoideus (upstroke) muscles (similar to pterosaurs)
• Supracoracoideus tendon runs through triosseal (3-bone) canal in coracoid, scapula and furcula.

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• Includes air sacs that allow lungs to operate more efficiently than in mammals, also act as air conditioning - dissipate excess heat from high metabolism animals. Air sacs also lighten body and bones.
• Some dinosaur bones may have air sacs, suggesting a flow through respiratory system.

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• intricate structures - provide effective flight surface and excellent insulation with lightweight materials.
• Bird bones hollow to reduce weight, but have internal struts to enhance their strength. Some have air passages connected to lungs.

• Archaeopteryx="ancient wing"
• a Jurassic bird
• Bird features:
• -wing and body feathered
• -Possible streptostyle movable quadrate)
• Furculum (also in some dinosaurs)
• Reptile features:
• -Dinosaur-like (theropod-like) skeleton
• -toothed jaws; long lizard-like tail
• Clawed forelimbs
• -No sternal keel, strong muscles for sustained flight.
• Anatomy:
• -Quadrate appears flexible as in later birds (parallel to lizards)
• -long tail (no pygostyle)
• Interdental plates on medial side of jaw as in some dinosaurs and basal archosaurs

• Mammals
• -Share endothermy, 4-chamber heart, large brains
• -clearnly convergence
• Basal Diapsids
• -Traditional view, previously no good specific candidates for close bird relatives identified
• Dromeosaurid Dinosaurs
• -Similarities that appear to be synapomorphies

• Archaeopteryx compared to a theropod dinosaur (above) and a modern bird (below)
• Basically a small theropod dinosaur with feathers!
• Most bird specilizations came later.

first discovered skeleton of Archaeopteryx lacked feathers and was misidentified as Compsognathus

• Thecodonts (basal archosaurs) - similarities between birds and theropods represent convergence.
• Primitive crocodiles - birds share features of jaw and ear with early crocodiles, but could be convergence - otherwise very different.
• Birds share more similarities with theropods than other reptiles, so some paleontologists consider them ancestors.

• Alan Feduccia and others argue birds and theropods do not share special close relationship.
• Each=three fingers; theropods=1-2-3, birds=2-3-4 NON HOMOLOGOUS reduction pattern!
• Strongly suggests convergence rather than common ancestry.
• Conclusion=based on homology arguments although those with too much invested in birds=dinosaurs idea refuse to accept it.

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• Evidence against homology, Coelophysis lower left forelimb showing reduced fourth and fifth fingers (ventrolateral view; arrows). b)Transient appearance of fifth digit condensations as chick limb develops. Finger IV (forms first, as in all tetrapods) labeled. Digit V condensation shown my arrowhead. (Burke and Feduccia, 1997.)

• Advocates of dinosaur-bird connection argue that frameshift occurred, only in the case of coelophysis.
• Timing of ossification of repeating elements controlled by Hox genes - no necessary linkage between cartilage precursors and bone.

• Protoavis
• Phesant-sized animal (late Triassic of west Texas), bird-like theropod - or earliest bird? Sankar Chatterjee (Texas Tech University) argues for bird, but few convinced.
• A bird this early casts doubt on theropod origin of birds.
• Fragmentary remains may come from >one species.

A Chinese farmer created this forgery, sold it on the black market. Front half=bird skeleton, back half=slab and counter-slab of a theropod dinosaur. Intent= to show a close link between dinosaurs and birds (and make more money).

• Flight origin from the ground upward?
• Gliding from treetops downward?
• Catching insects?
• Insulation?
• Archaeopteryx claws well-adapted for tree climbing - easier at first to glide out of a tree than take off from the ground (GRAVITY!!).

• Marine soarers and aerial predators
• -High aspect ratio, low wing loading
• -Albatrosses, gulls, swallows, falcons, kites
• Diving birds
• -High aspect ratio, high wing loading
• -Penguins, auks, gannets, some ducks and grebes
• Thermal soarers
• -Low aspect ratio, low wing loading
• -Eagles, hawks, vultures, storkes, herons, large owls
• Poor flyers
• -Low aspect ratio, high wing loading
• -Turkeys, grouse, peacocks, pheasants, cormorants

• Ostrom: could not or hardly fly - because no keeled sternum or triosseal canal.
• Rayner: good flyer - well-formed wings and flight feathers, even with no strong upstroke.
• Could probably fly well at high speed but poorly at low speed, so takeoff and landing would have been biggest problems.
• May have climbed trees and glided away for escape (typical of gliders) then developed flapping flight to extend that ability.

• Earliest Cretaceous Birds
• Rahonavis - Madagascar=bird based on reversed hallux and ulnar feather papillae. It retains all primitive features of Archaeopteryx.
• Jeholornis of China retains most primitive features but has begun specilization of hand that would continue in later birds. Seeds preserved in stomach area clearly indicate diet.

• confuciusornis sanctus
• Earliest toothless (beaked) bird, from early Cretaceous of China, still has clawed hands.

• Earliest birds lacking teeth
• first with pygostyle (8-9 fused caudal vertebrae) and synsacrum (7 fused sacral vertebrae)
• Slight keel on sternum
• Considered earliest memebers of the Pygostylia
• Beautiful preservation from Liaoning Province, China
• Lack of teeth, claws on fingers, pygostyle, and tail of long feathers.  Males with much longer tails than females.

• "egg stealers"
• Upper Cretaceous of Mongolia
• Short snouts, toothless jaws
• Large fenestrae in mandible
• Deep, strong lower jaws
• Crest of sponge-like bone on tip of snout
• Fused clavicles (as in birds)
• Evidence of brooding their eggs
• alternately aberrant flightless birds or coelurosaurs (related to ornithomimosaurs).

• The puzzle of Monoykus
• Late Cretaceous of Mongolia
• Either a flightless bird or bizarre theropod.
• Radically reduced, specialized forelimbs hide most of the evidence.

• Basal group of new clade: Ornithothoraces
• -Short trunk fewer than 13 thoracic vertebrae
• -Strut-like coracoid with triosseal foramen
• Major group of Cretaceous birds (40+ species)
• Fossils found nearly worldwide
• Sparrow-sized to 1-meter wingspan
• Mid-grade of birds with a mix of modern and primitive characters.

• sinornis
• Early Cretaceous of China, had keeled sternum and perching feet but retained teeth and small wing claws.
• Smallest of the Enantiornites, from China

• Iberomesornis
• A small Enantiornithes from Spain
• Eight free caudal vertebrae and a plate-like pygostyle
• Specialized for perching with a reversed hallux
• Retains claws on wings

• Hesperornis - flightless marine bird
• Late Cretaceous, Niobrara Chalk

• Large flightless foot-probelled diving birds
• Retained teeth for eating fish
• Wings reduced from lack of use
• Pointed anterior process of the quadrate and other features in common with modern birds
• Hesperornis found in Niobrara Chalk from Kansas to South Dakota
• Found just before Archaeopteryx and hailed as a missing link ( a bird with teeth)

• Gull-sized flying bird also from Niobrara Chalk
• Relatively large head and long bill and strong recurved teeth for catching fish
• Probably dove for fish like modern terns, pelicans and boobies
• Deeply keeled sternum to support large flight muscles
• Tail more reduced than in Hesperornis

• Icthyornis - a flying marine bird
• Late Cretaceous of North America, still has teeth but otherwise like modern birds. Marine birds well known because of good chance of preservation. Other Cretaceous birds known from fewer/ more fragmentary fossils.

• Pointed orbital process of the quadrate
• Shortened back
• Pelvic elements run nearly parallel as pubis rotates fully posteriorly
• First seen in Hesperornis and Ichthyornis

• Loss of teeth
• Pneumatic foramen in humerus

• Neornithes radiated in Tertiary after competing birds died out at the end of Cretaceous.
• Neornithes lineage back to early Cretaceous (based on disputed fragmentary remains), and molecular clocks supported early Cretaceous diversification.
• Proponents of Tertiary radiation claim that molecular clocks sped up after big extinction or are miscalibrated.
• Polarornis is the most convincing neornith, from latest Cretaceous of Antarctia.
• Wings not found but feet suggest food-propelled diver ?=a loon.
• Controversy not ended, truth may be in the middle: that neornith radiation begain in late Cretaceous.

• Paleognathae
• -Large vomer attached to pterygoid
• -Joint between pterygoid and braincase
• -Flightless ratites and tinamous
• Neognathae
• -Vomers reduced or lost
• -Joint between palatine and pterygoid
• -Most modern birds

• =old palate Birds
• Tinamous - small flightless birds from South America
• Ratites - flightless birds with no keel on sternum
• -Ostriches of Africa
• -Emus and Cassowaries of Australia
• -Kiwis of New Zealand
• Rheas of South America
• Extinct Elephantbirds of Madagascar
• Extinct Moas of New Zealand (up to 3 meters tall)

• Paleognathus Birds
• Extinct moas of new Zealand
• Flightless ground-dwelling birds, reduced wings and a distinct palate, some giant, mostly on southern continents.

• Previous controversy: Paleognaths=monophyletic or= polyphyletic derivatives (degerates) of various Neognaths.
• now considered monophyletic from palate synapomorphy and DNA>
• No early fossil record allows ongoing debate over how long ago they diverged and whether it predated Gondwana breakup.
• DNA evidence suggests older (Gondwana) origin even though a fossil group (Lithornithiformes, which were flyers) found in N. America/Europe.

• Most modern birds (9,000 species)
• Neognathous palate with considerable flexibility.
• Ankle axis shifted from astragalus - calcaneum (prior to fusion of bones of tibiotarsus)
• New ankle structures-synapomorphy for the Neognathae, unclear when it first developed.

• A distinct group among neognaths
• -Anseriformes - ducks, geese, swans (waterfowl)
• -Galliformes - turkeys, grouse, chickens, quails, pheasants (land fowl)
• -Gastornithiformes - giant flightless carnifores from the early Cenozoic of North America/Europe
• Based on similarities in skull bones, supported by DNA relationships
• Some workers still dispute this grouping.

• Giant flightless birds of he cenozoic
• While large flightless birds of today are mainly plant eaters, several lines in the early Cenozoic became giant and predatory.

• Diverse Neognaths
• left - Presbirnis, an early Cenozoic duck
• middle - Diatryma
• right - swimming penguins
• bottom - Teratornis, and extinct giant vulture
• These are all considered part of the "waterbird assemblage"

• Diatryma of North America is traditionally considered a carnivore, but some have argued for herbivory becasue it lacks a hooked bill like other carnivores.
• Phorusrhacos of South America and elsewhere was definitely a carnivore (mostly in the absence of mammalian carnivores). It survived until the isthmus of Panama developed.

• the Hoatzin
• Small south american ground bird ?=related to doves
• Juveniles have claws on two wing fingers for climbing back to nests.
• Probably atavism (accidental genetic return to former feature) rather than persistent primitive trait.
• The hoatzin also odd - uses crop as a fermentation vat similar to the rumen of cows!

• Rich fossil bird deposits in Eocene lake sediments of Germany.
• Parrot (Psittacopes) shows all the modern bird characters.
• 13/24 bird orders represented at Messel.

Variation in beaks among finches on various islands led Darwin to believe that they evolved from a common ancestor that colonized the islands.