{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Paleo Lab 5 - Worms Arthropods

Paleo Lab 5 - Worms Arthropods - PALEO LABORATORY 5 PAGE 1...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
PALEO LABORATORY # 5, PAGE 1 PALEO LAB # V - WORMS, ICHNOLOGY AND ARTHROPODS A. Phylum Annelida In early classifications, all worm-like organisms were placed within a single phylum, the Vermes. However, subsequent research has shown that many distinct forms may be encased in a worm-like body. Consequently, modern classifications may divide worm-like organisms into as many as fourteen phyla, which is about half of all animal phyla! However, only one phylum (Annelida) has a substantial fossil record. Annelids are characterized by a high degree of segmentation (although some specialized sessile annelids may lose most traces of segmentation). As annelids are usually soft-bodied, they are rare in the fossil record except as trace fossils or where they secrete hard living tubes. Three major classes of annelids are generally recognized; the earthworms (Oligochaeta), bristleworms (Polychaeta) and leeches (Hirudinea). Of these, the polychaetes are the most important fossils. Annelids are primarily differentiated on the basis of "soft" anatomy. Segmentation probably assisted peristaltic burrowing. Successive waves of muscle contraction that passes posteriorly along the body, coupled with elongation and shortening of the body, enables annelids to burrow within the substrate. Polychaetes show advancement over this primitive locomotory type in the addition of parapodia, unjointed fleshy appendages that develop along the lateral body walls. Another paleontologically-significant development within polychaetes is the evolution of hard, jaw-like features termed scolecodonts. These elements range from Ordovician to Holocene and are relatively common in shallow marine facies. However, they have not been used extensively for biostratigraphic zonation, probably due to the taxonomic chaos that makes scolecodonts a rather ill-defined group. Trace fossils of probable annelid origin are common within Phanerozoic (and Proterozoic?) sediments. However, these primarily consist of burrows and trails whose "creators" are virtually impossible to identify. However, some polychaetes secrete sturdy, calcareous living tubes. Two of these polychaetes, Spirorbis and Serpula , are quite abundant as fossils. EXERCISE # 1 - Sketch a specimen of Spirorbis (TSU IP 129) , a calcareous tube secreted by a Lower Permian polychaete. This form typically consists of small, coiled calcareous shells often found attached to shells of other fossils. Spirorbis ranges from the Ordovician to Holocene. EXERCISE # 2 - Sketch a specimen of Serpula (TSU IP 130 - IP 131), colonial polychaete tubes from the Texas Cretaceous. These polychaetes currently form "serpulid reefs" along tropical and subtropical coasts; their biostratigraphic range is from the Silurian to Holocene. EXERCISE # 3 - Observe the scolecodont form genera Protarbellites (TSU IP 133) and Ildraites (TSU IP 132) . What was the function of these structures?
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}