Mammalian Origins and Phylogeny12 January 2004

• Announcements for Lecture and Lab

• The amniote phylogeny

• Therapsida and the synapsid skull

• Cynodontia & mammalian grade characteristics

• Archaic Mammals of the Jurassic Period:

Triconodonts, Multituberculates, & Therians

• The rise of endothermy & high reproductive rates

Announcements:12-15 January ‘04

• 12-13 Jan. If we have field trips (most likely, & to be confirmed in lecture) then lab sections meet in Rm 234 Jennings for:

1. Review of Mabry et al. 2003 J. Mammalogy 84:20-25 available on line. See E-Journals on Library home page

2. Prepare for squirrel studies: Concepts and procedures

• 14-15 Jan. If field trips on 12-13 Jan. , then we meet in Rm 145 Brown Hall (computer lab)

1. Analysis of data collected in Museum with Excel

2. Review & discussion of journal papers within project groups

• Taxonomy Take-home due at Examination I

Vertebrate Phylogeny• Fishes (Crossopterygians), Amphibians and Amniotes

(reptiles, birds, & mammals)• So what are amniotes? _________________• First reptiles in the Paleozoic (30 mill. ybp) and the

reptilian radiation of the Mesozoic

• Primitive reptilian skull types (Fig 3-2 & more)   Synapsid skull ‑ temporal opening bounded above by postorbital &

squamosal (below by the jugal & squamosal)

• Subclass Synapsida: Orders Pelycosauria and Therapsida

• Zygomatic arch: a synapomorphy uniting mammals and their ancestors for over 250 million years.

Fig 221, Young 1960, Life of Vertebrates

Origin of mammal-like reptiles

Primitive Reptilian Skull TypesAnapsida

Feldhamer et al ’99, Fig. 4.1

Synapsida

Parapsida Diapsida

squamosalPost orbital

Jugal

Synapsid skull

Mammalian-

reptilian line

Cynodontia: A transitional Suborder of the Triassic & Jurassic Periods

Vertebrate Phylogeny: Traditional & CladisticCriteria for identifying archaic mammalian fossils 1. Secondary Palate & two occipital condyles 2. Heterodonty (I,C,P,M) from homodont ancestors3. Increase in dentary over other bones in the mandible4. Stapes, incus (quadrate) and malleus (articular)-Fig 3-8

5. Masseter muscle & the zygomatic arch 6. Jaw articulation to squamosal‑dentary from? ________7. What about physiological changes?

Outline: IA

First Reptiles

Fig 3-1 Vaughan

Primitive Therapsid Repile

Cynodont Mammal

Fig. 3-4

Fig 4.5 Feldhamer

Archaic Mammals of the Jurassic

Mammalian radiation of the early Jurassic• Tricondodontia (3 cusps in a row) large (750 g),

predaceous mammals of early Triassic

• Monotremata: A living example of Mesozoic mammals

Fossil record is poor, beginning in early Cretaceous

Thought have diverged in Jurassic

• Multituberculata: herbivorous, molars w/ multiple cusps

Highly successful: from Jurassic to Oligocene (100 m yr)

• Zatheria: includes Aegialodon (with tribospenic molar) & ancestor of therian mammals (Eutheria & Metatheria)

Geological Time and the Evolution of Mammals: Pelycosaurs TherapsidsCynodontia: the transitional Infraorder

MammalsFig 4.2, Feldhamer

Triconodontia

Fig 4.9 Feldhamer = Fig. 3-15. Vaughan

Multituberculata

Zatheria Tribosphenic molar & “Therian” grade

Archaic Mammals of the Jurassic & Cretaceous

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Fig 4.8, Feldhamer

Mammals of the Mesozic: the first two-thirds of mammalian evolution

• Rise in early Jurassic and then declined • Early competition with and eventual domination by

(dinosaurs) during Jurassic & Cretaceous • Reduction in body size and development of nocturnality • The rise of endothermy in reptiles, birds & mammals

Energy requirements of embryos and neonates The avian (& dinosaur?) solution ‑ oviparity & large eggs

with parental care after hatching The mammalian solution ‑ viviparity & lactation Evolution of the mammary gland: modified skin glands?